Analysis of a Rock Mass Overburden Consolidation Grouting Method by Lugeon and Acoustic Tests

Analysis of a Rock Mass Overburden Consolidation Grouting Method by Lugeon and Acoustic Tests | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Analysis of a Rock Mass Overburden Consolidation Grouting Method by Lugeon and Acoustic Tests Jinxi Dou, Xiaolong Yang, Pan Gong, Zhilin Wang, Kexiang Wang, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-2449405/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The Baihetan superhigh arch dam is the largest hydropower station under construction in the world. Columnar jointed basalt (CJB) is widely distributed and densely jointed at the foundation of the Baihetan superhigh arch dam and poses a potential risk to its overall stability. A method of overburden consolidation grouting of the rock mass is proposed that solves the problem of unloading relaxation of CJB due to excavation of the exposed rock mass. The results show the following. 1) The method of nonoverburden grouting cannot achieve the quality inspection standard requirement that at least 90% of the wave velocities be greater than or equal to 4200 m/s, and the overall wave velocity of the rock mass before excavation is greater than that after grouting. 2) After overburden consolidation grouting of the rock mass, which includes controlling grouting pressure and concentration and performing perforation and sequence grouting, the water permeability of the inspection holes is less than 3 Lu, more than 90% of the wave velocities in the rock mass are greater than 4200 m/s, and the integrity of the rock mass is greatly improved. 3) The problems of conventional consolidation grouting technology are solved to protect the thin layer of breccia lava at the foundation of the Baihetan dam. In addition, the problem of unloading relaxation of CJB due to exposure to consolidation grouting is solved in the Baihetan superhigh arch dam project. This application has reference significance for the design and application of consolidation grouting in similar projects. Consolidation grouting Baihetan super-high arch dam Grout take Lugeon test Columnar joints Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 1 Introduction The quality of the foundation rock mass is important for the overall stability of superhigh arch dams. Scholars have conducted many important studies on the causes and treatment of foundation failure in high dams (Dou et al. 2020 ; Fan et al. 2017 ; Fan et al. 2018 ; Shi et al. 2020 ); for example, cement grouting and concrete plug replacement treatment for the class III rock mass of the Ertan arch dam foundation has been studied (Lin et al. 2019 ). In addition, a study was conducted on grouting treatment measures for the structural surfaces of the left and right shoulders of the Xiaowan arch dam and the rock masses in the alteration zone using thrust piers of resistant rock masses, underground cave plugs, concrete replacement, consolidation grouting and groove plugs of the foundation surface (Lin et al. 2015 ). The following principle was proposed for the Xiluodu arch dam: "rock grade as the foundation and safety as the criterion. The weakly weathered rock masses should be reasonably utilized as the foundation rock, and the thrust at the arch end should be divided into elevation sections to determine the degree of utilization" (Fan et al. 2012 ). In recent years, some scholars have explored self-flow controlled grouting technology in the treatment of dam foundations where bedrock is broken and cracks are developed (Fan et al. 2015 ). The integrated construction technique of foundation consolidation grouting is one of the main measures to improve the integrity and deformation resistance of a dam foundation. Dam foundation stability is a critical issue for the overall safety of dams and is especially relevant to the foundation treatment of 300 m class high arch dams. According to the geological and construction conditions, consolidation grouting technology for dam foundations can generally be divided into nonoverburden grouting technology, concrete overburden grouting technology, lead pipe grouting technology and grouting technology derived from a combination of the above three types. In addition, different hydropower projects often adopt different foundation grouting schemes. The dam foundation of Ertan Hydropower Station has good geological conditions; cementation grouting was adopted in a "non-overburden grouting, high-pressure pilot pipe" grouting scheme for the first time in the project there, with high-pressure pilot pipe grouting being employed to target shallow or unqualified rock masses after grouting (Yang et al. 2017 ). Laxiwa Hydropower Station adopted the technique of "grouting without overburden in the first phase and concrete overburden in the second phase" (Zhang et al. 2013 ), and the Jinping first-level hydropower station applied "grouting without overburden, concrete overburden drilling and grouting in the section of a riverbed and slow slope dam" (Zhang et al. 2013 ). In the case of Wudongde Hydropower Station (under construction), the foundation of the riverbed dam is grouted with nonoverburden and concrete conduit grouting. Nonoverburden grouting is mainly applied in cases where the geological conditions are favorable and the foundation rock is not affected by long-term exposure. This approach has the advantages of convenient construction and no interference with concrete construction. The main drawbacks are as follows: it is difficult to improve the grouting pressure, with the effect of surface rock grouting being difficult to guarantee; it is difficult to clear the foundation after grouting; and the ground surface easily forms a series of emergent slurries, resulting in a large amount of slurry waste. Therefore, the application of nonoverburden consolidation grouting technology has limitations. To improve the effect of surface rock grouting, the riverbed dam foundation projects of Xiaowan Hydropower Station (Wang et al. 2011 ) and Xiluodu Hydropower Station (Lin et al. 2016 ) both adopt concrete overburden consolidation grouting and perform warehouse operation preparation and consolidation grouting concurrently during the interval between concrete pouring so that the grouting equipment can be withdrawn for pouring. Overburden grouting usually requires "three in and three out". Overburden concrete consolidation grouting is suitable for many kinds of geological conditions, and its main advantages include improving grouting pressure, guaranteeing grouting quality, reducing surface cascading slurry, and saving pulp materials. Its main disadvantages are that it interferes extensively with concrete construction, is unconducive to concrete maintenance, requires long-term occupation of the concrete pouring bin surface, increases the concrete cracking risk, poses the risk of drilling through cooling water pipes and instrument lines, and causes drilling damage to concrete. Moreover, with overburden concrete consolidation grouting, it is very difficult to clean up the warehouse surface, the amount of concrete drilling work is increased, and the equipment is repeatedly dumped and left idle, which increases the investment. Large blast excavations have significant impacts on the physical, mechanical and hydraulic properties of the rock mass at the excavation boundary. In addition, they can lead to damage and stress redistribution within the rock mass, resulting in shallow rock unloading and increasing the permeability of the rock mass of a dam foundation and dam shoulder (Xia et al. 2020 ). The geological conditions of the dam foundation of Jinshajiang Baihetan Hydropower Station are complex, and the dam foundation is mainly composed of Type І columnar jointed basalt (CJB), which is a special rock mass with undulating and irregular columnar jointed surfaces, irregular and incomplete cutting of column sections (Yan et al. 2011 ), the development of saphenous cracks within the column, and a low deformation modulus. In the dam foundation, misalignment zones develop within the interlayer, the deformation and shear strength are low, and some lithologic sections have dense cleavage zones (Chen et al. 2014 ). Due to the developmental characteristics of the structural surface and the stress state of the rock mass, the horizontal deformation modulus of Type I CJB is significantly larger than the lead deformation modulus. The columnar joints and microcracks in fresh CJB are hard structural surfaces that are closed under the siege state and easily opened and relaxed after lifting the siege state; thus, CJB in the siege state still has a high deformation modulus (Shi et al. 2020 ). The rock mass of an arch dam foundation is required to have sufficient bearing overburden and stability. One of the main engineering geological problems of Jinsha River Baihetan Hydropower Station is that the special rock structure and structural surface development characteristics of Type І columnar joints cannot meet the strict deformation requirements for the foundation of a high arch dam. The objectives of the project there are to increase the deformation resistance of the foundation, improve the shear and seepage resistance of the structural surface, avoid unloading and relaxation of the surface bedrock, reduce the impact of excavation and blasting crack surface opening of the dam foundation, and improve the integrity of the dam foundation. Therefore, it is necessary to consolidate the dam foundation and carry out consolidation grouting. In this study, we analyzed the complex geological conditions and difficulties of consolidation grouting of the Baihetan arch dam, proposed the key technology of "reserving rock mass overburden weight, low-pressure thick slurry closure, overburden concrete consolidation grouting", and proposed special antilifting measures for this technology. According to these special grouting measures, we carried out a large number of grouting inspections and performed data collection. Based on Lugeon tests and the analysis of grout take data and rock mass wave velocity data, we determined the grouting effect of the proposed method. The results are expected to provide a reference for the construction and design of similar projects. 2 Project Overview 2.1 Background of the Baihetan project Baihetan Hydropower Station is located in the lower reaches of the Jinsha River in Ningnan County, Sichuan Province, and Qiaojia County, Yunnan Province. The station controls a basin area of 430,300 km 2 , accounting for 91% of the Jinsha River basin. The main application of the power plant is power generation; it is also used for flood control and shipping and to promote local economic and social development. The total overburden of the reservoir is 20.627 billion m 3 , the regulation overburden is 10.436 billion m 3 , and the flood control overburden is 7.50 billion m 3 . The hub project of Baihetan Hydropower Station mainly consists of river barrage and flood relief energy-dissipation structures, water diversion and power generation systems, and other components, as shown in Fig. 1 . The barrage dam is a concrete double-curved arch dam with a peak height of 834.0 m and a maximum height of 289 m. Six surface holes and seven deep holes are arranged in the dam mass to dissipate energy by using the water pad pond behind the dam. The hills on the left bank are equipped with three nonpressure straight spill holes; the inlet is arranged between the inlet of the power plant on the left bank and the dam, and the outlet is located on the other side of the beach in Baihetan Village. The three spill holes all adopt the "dragon drop tail" pattern inside the holes. The maximum excavation width of the dam foundation is approximately 100 m. The scale of the dam foundation excavation and treatment project is large, and the geological conditions of the dam foundation are complicated. Therefore, the excavation and treatment of the dam foundation are very difficult. The dam is divided into 31 dam sections. The concrete pad, above 750.0 m in foundation height (dam sections 1 to 3 ), and the dam foundation consolidation grouting project of dam sections 4 to 18 are on the left bank, and the dam foundation consolidation grouting project of dam sections 19 to 31 is on the right bank. 2.2 Geological conditions of the dam foundation (1) Lithological characteristics and distribution Columnar jointed basalt is widely distributed in Baihetan as a special structural rock mass. The columnar joints of the rocks surrounding the underground engineering sites can be divided into three types according to the diameter of the column. Type I columns are generally 13 ~ 25 cm in diameter and 2 ~ 3 m in length. Type II columns are generally 25 ~ 50 cm in diameter and 0.5 ~ 2.0 m in length. Type III columns are generally 0.5 ~ 2.5 m in diameter and 0.5 ~ 2.5 m in length. The length is generally 1.5 to 5.0 m. The elevation from 834 to 735 m on the left bank of the dam is composed of layers of greenish-gray massive basalt and breccia lava. The elevation from 735 to 719 m is composed of layers of breccia lava with massive basalt and thin layers of tuff, and the elevation from 719 to 665 m is composed of layers of massive basalt. The elevation from 665 ~ 600 m is the layer of Type І CJB; for each column, the diameter is 15 ~ 25 cm, the development is irregular, the surface is slightly rough, the intercolumn is closely embedded, and the length is 3 m. Additionally, the fracture in each column is developed, the fracture is arc-shaped, the surface is smooth, and the interfracture is closely embedded. The basalt rock is hard, and the distribution of lithological layers in the foundation of the dam revealed by actual excavation is shown in Fig. 2 . The 834 ~ 665 m elevation section of the foundation of the dam on the left bank is massive basalt, which is dominated by cryptocrystalline basalt, accounting for 60.0% of the basalt. Next most abundant is amygdaloidal basalt, accounting for 23.4% of the total, followed by breccia lava, accounting for 16.3%. The tuff is banded and thin, with an exposed area of approximately 45.3 m2, accounting for only 0.3%. Below 665 m elevation at the foundation of the left bank of the dam, the exposed lithologies are all stratified Type I CJB. The 834–600 m elevation section of the right bank mainly exposes the layers of the Emeishan Group, which are oblique porphyry basalt, Type III CJB, Type II CJB, cryptocrystalline basalt, amygdaloidal basalt, breccia lava and tuff. Below 600 m elevation, the dam foundation mainly consists of layers of Type I CJB and layers of breccia lava. Layers of Type I columnar articulated basalt are found at elevations of 600–570 m on the left bank and 600–540 m on the right bank. For each column, the diameter is generally 15 ~ 25 cm, the development is irregular, the surface is slightly rough, the intercolumnar mosaic is tight, and the length is generally 3 m. Microcracks develop in the column, the cut rock is a 5 ~ 10 cm rock mass, and the mosaic is tight. The subsurface is composed of layers of breccia lava and Type II CJB. The foundation of the dam between 570 m elevation on the left bank and 540 m elevation on the right bank is composed of layers of breccia lava. According to the preliminary investigation and construction details of dam sections 13 and 14, the thickness of each layer of breccia lava is between 4.3 and 17.0 m, with an average thickness of 8.5 m. The address profile is shown in Fig. 3 . (2) Tectonic development The fault structure is more developed at the middle dam site, and there are nine major faults of larger scale. The 834–600 m fault zone of the dam foundation and shoulder on the left bank is mainly developed as F 17 , F 14 , F 16 , f 110 , f 108 , f 145 , etc. The faults exposed at the excavation surface below 600 m height are mainly F 14 , F 16 , f 261 , f 262 , and f 265 in the WNW direction. The 834–600 m fault zone of the dam foundation on the right bank is mainly developed as F 17 , F 14 , F 16 , f 261 , f 262 , and f 265 in the WNW direction. The main faults developed at 600 m elevation are f 232 , f 249 , and f 256 . Except for F 17 , which is in the NE direction, all the other faults are in the NW direction; some of the fault outcropping features are shown in Fig. 3 . The distributions of some faults, fault zones and rock bodies are shown in Fig. 4 . (3) Initial ground stress conditions The Baihetan dam site is a plateau and deep valley located on the east side of the Jiaoji River fracture zone and on the north side of the Xiaojiang River fracture zone. As a result of the tectonic extrusion in the NW-NNW region that occurs after neotectonic movement, the rocks surrounding the underground cave cluster of Baihetan Hydropower Station are mainly under tectonic stress. The ground stress of the primary rocks in the dam site area is generally in the NNW-NW direction, as shown in Fig. 5 . However, the initial stress of the raw rock in the underground cave cluster on the right bank is influenced by the downcutting of the river valley and fault block movement, and the direction of the maximum main stress is deflected to approximately the N-S direction. The horizontal burial depths of the underground plant caverns on the left bank and right bank are 950 ~ 1050 and 630 ~ 800 m, respectively, and the vertical burial depths are 260 ~ 330 and 420 ~ 540 m, respectively. The initial maximum ground stress of the underground cave cluster on the left bank is 19 ~ 23 MPa (where the maximum measured horizontal stress is 33.39 MPa) and is inclined to 5°~13° of the river valley. The maximum main stress on the right bank is 22ཞ26 MPa, and the maximum measured main stress is 30.99 MPa. The intermediate main stress tends to 2°~11° of the river valley in general, but under the local influence of the interlayer zone, the value and characteristics of the ground stress vary. In general, the initial stress level of the surrounding rocks in the underground cave cluster at Baihetan is high, and the local ground stress characteristics are influenced by large tectonic structures. 3 Consolidation Grouting Design For The Dam Foundation 3.1 Grouting process (1) Raw materials Cement: Ordinary Portland cement 42.5R produced by a cement company in Hunan Province is used in this study. The cement is passed through an 80 mm square-hole sieve with a fineness of less than 5% of the sieve volume. The performance is in accordance with the relevant requirements of the Chinese general Portland cement standard (GBl75-2007). The chemical composition of the Portland cement used in this study is shown in Table 1 . The initial setting time is 155 min, the final setting time is 235 min, and the 28 d compressive strength is 46.3 MPa. Table 1 The Chemical constituents of the Portland cement used in this study Constituents SiO 2 Al 2 O 3 Fe 2 O 3 MgO CaO SO 3 Loss on ignition Content/% 22.3 7.1 4.5 2.4 56.6 2.2 2.5 (2) Slurry ratio and particle size Ordinary Portland cement grout is used for consolidation grouting of hole sequence І and hole sequence II, and four levels of the water-cement ratio (water-cement mass ratio) of the ordinary Portland cement slurry are tested (2:1, 1:1, 0.8:1, and 0.5:1). Wet-ground cement grout is used for hole sequence III; similarly, four levels of the water-cement ratio of the cement slurry are tested (3:1, 2:1, 1:1, and 0.5:1). Wet grinding equipment (GJM–FII) from the Wuhan Yangtze River Academy of Sciences Institute of Automation is used for wet grinding in this experiment. The particle size distribution of the wet-ground cement is analyzed by an NSKC-1 laser particle size analyzer from the Wuhan Yangtze River Academy of Sciences Institute of Automation. The results are shown in Fig. 4 . According to Fig. 4 , D 95 (the maximum particle size with a cumulative mass distribution rate of 95%) is equal to 37.46 µm, and D 50 (average particle size) is 11.44 µm. (3) Grouting methods The grouting holes are divided into three sequences. Hole sequences І and II adopt the "top-down, plugging in hole, bottom circulation" grouting method. Hole sequence III is the first grout protective layer below the foundation surface and adopts the "bottom-up, plugging in hole, bottom circulation" grouting method. Grouting pressure: Consolidation grouting adopts a graded pressurized method to cause the grouting pressure to gradually reach the design value, and it adopts the principle of no harmful lifting of the grouting rock surface and concrete. In the process of grouting, the relationship between injection rate and injection pressure is strictly controlled, and the grouting pressure of the protective layer is 0.5 MPa. The grouting pressure of the first section below the foundation surface is 0.8 ~ 1.0 MPa; the pressure gradually increases by 0.5 MPa in each section. The largest grouting pressure is 3.0 MPa, which is the grouting pressure of the concrete conduit, as shown in Table 2 . Grouting end standard: Under the design pressure, the injection rate is not greater than 1.0 L/min, and the grouting operation can end after 30 min of continuous grouting. Table 2 Dam foundation consolidation grouting pressure and section lengths Depth (m) -5 ~ 0 0 ~ 5 5 ~ 10 10 ~ 15 15 ~ 20 20 ~ 25 25 ~ 30 Ⅰ 0.5 0.8 ~ 1.0 1.0 ~ 1.5 1.5 ~ 2.0 2.0 ~ 2.5 2.5 ~ 3.0 3.0 Ⅱ 0.5 1.0 ~ 1.5 1.5 ~ 2.0 2.0 ~ 2.5 2.5 ~ 3.0 2.5 ~ 3.0 3.0 Ⅲ 0.5 1.0 ~ 1.5 2.0 ~ 2.5 2.5 ~ 3.0 3.0 3.0 3.0 3.2 Consolidation grouting measures In consideration of the specific geological conditions and field test results from the construction of the Baihetan arch dam foundation, consolidation grouting of the dam foundation is performed mainly via four methods: rock overburden grouting combined with shallow concrete overburden grouting, nonoverburden grouting combined with shallow concrete overburden conduit grouting, nonoverburden grouting and reinforcement grouting. (1) Measures for rock overburden grouting and shallow concrete overburden grouting: reservation of a 5 m rock overburden protection layer → top-down, plugging in hole, circulating grouting at hole bottom → anchor pile placement → excavation of overburden layer → shallow conduit formation → concrete pouring → concrete overburden conduit grouting, as shown in Fig. 5 . (2) Nonoverburden grouting and shallow concrete overburden conduit grouting: excavation to foundation surface → top-down, hole jamming, bottom-hole circulating grouting → anchor pile placement → shallow conduit formation → concrete pouring → concrete overburden conduit grouting. (3) Nonoverburden grouting and reinforcement grouting: excavation to the foundation surface → top-down, plugging in hole, circulating grouting at hole bottom → anchor pile placement → inspection hole formation → reinforcement grouting. The distribution of specific grouting methods for the dam foundation area is shown in Fig. 6 . 3.3 Grouting partition To ensure that the high stress of the dam foundation can be distributed evenly and to strengthen the upstream seepage control, the range of consolidation grouting is extended beyond the dam foundation, 5 m upstream to the dam heel and approximately 10 m downstream to the toe (horizontal projection distance). The depth of the grouting hole in the range of the dam foundation is divided into four zones from A to D, corresponding to grouting hole depths of 30, 25, 20 and 15 m. The enlarged grouting zone upstream and downstream is Zone E, which has the same hole depth as the neighboring zone. The partition of consolidation grouting of the Baihetan arch dam foundation is shown in Fig. 7 . As shown in Fig. 8 , the grouting holes are arranged in a grid pattern, the inter-row spacing of CJB is 2×2 m, and the inter-row spacing of the gravel lava dam foundation is 3×3 m. The grouting holes on both shore slopes are perpendicular to the foundation surface. The riverbed dam in sections 13–22 contains a plumb hole, and the transition between the plumb hole and the hole perpendicular to the foundation surface occurs by diverging holes. The holes on the upstream and downstream slopes are diverging holes. 3.4 Evaluation of the consolidation grouting effect (1) Lugeon test The Lugeon test can directly reflect the permeability of a stratum and constitutes the basis for classifying the stratum at the early stage of the injection project. A pressure of 1 MPa is adopted, and after the pressure stabilizes, the pressure inflow rate is measured every 5 min. When the difference between the maximum and minimum values of four consecutive readings is less than 10% of the final permeability or the difference between the maximum and minimum inflow rates is less than 1.0 L/min, the test is considered complete. The final value is then taken as the flow rate to calculate the water permeability. The Lugeon test calculation formula is shown in Eq. (1): where q is the permeability of the test section, Lu; Q is the pressure inflow, L/min; P is the total pressure acting on the test section, MPa; and L is the length of the test section, m. (2) Acoustic test Acoustic wave testing provides an important basis for determining the physical and mechanical parameters of a rock body. The results can be applied to the excavation of rock slopes, providing an effective indicator for blasting excavation. The higher the wave velocity is, the better the physical and mechanical properties of the rock mass and its integrity are. Acoustic testing is performed mainly on the test holes before and after grouting. By comparing the test results before and after grouting, the parameters of the rock integrity changes are obtained, and the grouting quality is analyzed. The acoustic testing device used in this study is an RS-ST01C acoustic control instrument produced by Wuhan Yanhai Engineering Development Co. This test considers the coefficients of geological defects, such as the weathering coefficient, integrity coefficient, anisotropy coefficient, fracture action and karst action. A grouting test borehole is drilled 14 days after the completion of grouting. 4 Analysis Of The Consolidation Grouting Results Quality inspection of the consolidation grouting is conducted based on acoustic wave velocity measurements of the rock mass combined with drilling pressure water tests. For proper completion of the acoustic wave test, the test should be performed for each unit and should be carried out 14 days after the grouting of the corresponding part. To meet the quality inspection standard, more than 90% of the whole dam section should have a value greater than 4200 m/s, and less than 5% of the section should have a value less than 4000 m/s. The consolidation grouting also adopts a pressure water test inspection, which is carried out 7 days after grouting completion in the corresponding part. The quality standard is as follows: when the grouting quality check of the hole is 85% above the pressure water test section, the water permeability is not greater than 3 Lu and is not concentrated. 4.1 Analysis of the Lugeon test results As shown in Fig. 11 , before grouting, the water permeability of dam sections 7–8 is large: that of dam section 7 is 73.7% greater than 3 Lu, and that of dam section 8 is 58% greater than 3 Lu. Figure 11 also shows that the decreases in grouting volume and water permeability of the rock mass after grouting are large. Dam section 7: The grouting volume decreases from 50.81 kg/m to 10.2 kg/m from hole sequence І to hole sequence III, representing a decrease of 80%. Dam section 8: The grouting volume decreases from 40.52 kg/m to 8.55 kg/m from hole sequence І to hole sequence III, representing a decrease of 78.8%. After grouting, the test results are all less than 3 Lu. As shown in the pie charts for each dam section in Fig. 12 , prior to grouting, dam sections 12–15 exhibit high permeability of the rock. The permeability of dam sections 12, 13, 14 and 15 is 96.49%, 98.9%, 97.1%, and 98% greater, respectively, than 3 Lu. After grouting, the test results are all less than 2.8 Lu. Figure 12 also shows that the decreases in grouting volume and permeability of the rock mass after grouting are large. Dam section 12: The quantity of grouting decreases from 83.49 kg/m to 16.34 kg/m from hole sequence І to hole sequence III, representing a decrease of 80.4%. Dam section 13: The injection volume decreases from 46.85 kg/m to 2.35 kg/m, representing a decrease of 95%, from hole sequence І to hole sequence III. Dam section 14: The grouting volume decreases from 67.51 kg/m to 18.54 kg/m from hole sequence І to hole sequence III, representing a decrease of 72.5%. Dam section 15: The injection volume decreases by 77%, from 128.21 kg/m to 29.44 kg/m, from hole sequence І to hole sequence III. After grouting, the test results are all less than 2.75 Lu. 4.2 Analysis of the acoustic test results As shown in Fig. 13 , the mean wave velocity of dam section 7 before grouting is 5210 m/s, and that after grouting is 5255 m/s. The increase in wave velocity after grouting is 0.9%. Among the 22 inspection holes at the foundation of the dam, the percentage with a wave velocity greater than or equal to 4700 m/s is 91.5%, and the percentage with a wave velocity less than 4200 m/s is 3.8%. Thus, the results meet the quality inspection standard. For dam section 8, the average acoustic wave velocities before grouting and after grouting are 5310 m/s and 5342 m/s, respectively, corresponding to an increase of 0.6% after grouting. The percentages of wave velocities greater than or equal to 4700 m/s and less than 4200 m/s are 95.7% and 1.6%, respectively, for the 24 inspection holes at the foundation of the dam, and the wave velocities comply with the standard. After the excavation of the protective layer, more than 90% of the dam foundation from 0 ~ 5 m has a value greater than 4200 m/s, and this result meets the acoustic inspection standard of the dam foundation. As shown in Fig. 14 , for dam section 12, the breccia lava hole section, the percentage of wave velocity values greater than or equal to 4200 m/s after dam foundation grouting is 90.2%, and the percentage of values less than 4000 m/s is 3.6%. Dam section 13: The mean wave velocity before grouting is 4893 m/s, and that after grouting is 5138 m/s, representing an increase of 5.0%. Of the wave velocities of this section of Type І CJB, 90.4% are greater than or equal to 4500 m/s, and 2.6% are less than 4000 m/s. Dam section 14: The percentage of wave velocity values greater than or equal to 4400 m/s in the hole section of Type П CJB after dam foundation grouting is 94.3%, and the percentage less than 4000 m/s is 2.4%. After the excavation of the protective layer, the proportion of values greater than 4200 m/s for the whole dam section from 0 to 5 m is 94.1%. Dam section 15: After dam foundation grouting in hole section of Type П CJB, the percentage of wave velocities greater than or equal to 4400 m/s is 94.8%, and that less than 4000 m/s is 1.8%. After the excavation of the protective layer, the percentage of values greater than 4200 m/s for the whole dam section from 0–5 m is 90.7%. 5 Discussion 5.1 Consolidation grouting with no rock mass overburden The Baihetan dam foundation was constructed with consolidation grouting starting on the left bank from dam section 9 and on the right bank from dam section 25. Initially, the grouting adopted nonoverburden grouting combined with shallow concrete overburden conduit grouting. For the cementation grouting in the construction of dam sections 9–11 on the left bank and dam section 25 on the right bank, inspection reveals that the grouting effect is poor, and the relaxation rate and water permeability rate of the rock mass are large. Figure 15 shows the nonoverburden consolidation grouting data of dam sections 9–11 and 25; the results do not meet the grouting quality inspection standard. In summary, it is difficult to guarantee the grouting effect on the surface of the rock mass without overburden grouting technology, and there are problems, such as the interference between the concrete overburden grouting and the concrete pouring process. Before the excavation, the surface of the rock mass of the dam foundation meets the quality inspection standard, but after the excavation and grouting, it does not meet the standard requirement that more than 91% of the wave velocities be greater than or equal to 4200 m/s. One reason for these results is that the excavation adopts blasting, which causes extensive damage to the rock mass. The foundation of Baihetan Hydropower Station is developed in CJB, which easily relaxes and cracks after unloading. The water permeability is high, and misalignment zones, fissures and faults are developed in the dam foundation. The column development is dense, with steeply dipping hidden jointed surfaces and vertical gently dipping hidden jointed surfaces within each column unit. A hidden jointed surface has the characteristics of being wavy and undulating. The microcracks are hard structural surfaces, and the rock mass has a columnar mosaic structure. It is closed under the in situ stress state and easily opens and relaxes after the siege pressure is lifted; the CJB still has a high deformation modulus when the siege condition is maintained, and the rock mass relaxation problem is prominent (Dai et al. 2017 ; Hao et al. 2016 ; Jiang et al. 2014 ; Xiao et al; Xu et al. 2018 ). Additional reasons for the above results are that the excavation extends to the dam foundation surface for grouting, the shallow cracks in the dam foundation are not closed, and it is difficult to increase the pressure of nonoverburden consolidation grouting. Increasing the pressure will lead to stratum elevation, and the low pressure leads to a limited diffusion radius of the slurry, which cannot effectively fill the cracks. When nonoverburden grouting is difficult to obstruct, the obstruction depth is generally 1 ~ 2 m, and the shallow rock mass leaks, leading to a low sonic improvement rate after grouting and difficulty reaching the quality standard. 5.2 Consolidation grouting with rock mass overburden It is difficult to guarantee the grouting effect on the surface of the rock mass without overburden grouting technology. The grouting effect is poor, the relaxation rate and water permeability rate of the rock mass are large, and there are problems due to the interference between the concrete overburden grouting and the concrete pouring process. After discussion with experts and design units, it is proposed that "reserve rock mass, low-pressure thick slurry closed protective layer, overburden consolidation grouting" be adopted. According to the special geological conditions of the Baihetan dam foundation, an approach involving the reservation of a 5 m rock mass overburden, the control of grouting pressure and concentration, and the adoption of methods and materials for dividing holes and sequential grouting was applied. This approach solved the problem of CJB relaxation due to excavation and bare rock mass unloading. The reserved 5 m rock cover is excavated by blasting. (Hu et al. 2018 ; Xia et al. 2020 ) have performed many studies on blasting schemes and have studied the degree of damage of blasting excavation to rock masses, and they proposed a 5 m stage as a reasonable scheme. In the present study, after grouting, the water permeability of the inspection holes is less than 3 Lu, more than 90% of the wave velocities of the rock mass are greater than 4200 m/s, and the integrity of the rock mass is greatly improved. The analysis suggests that reserving a 5 m rock mass without excavation can greatly reduce the damage to the rock mass caused by blasting and excavation and reduce the relaxation of CJB caused by unloading. A second reason for the effectiveness of the approach is that if the 5 m rock mass is closed by thick slurry, the shallow fissure in the dam foundation will be closed, and the pressure of consolidation grouting can be increased, which will increase the diffusion radius of the slurry and allow the fissure to be effectively filled. When there is no overburden and heavy grouting, blocking is difficult, and the blocking depth is generally 1 ~ 2 m. A 5 m rock protection layer is reserved so that there is enough depth for blocking. This series of measures allows the rock mass to be grouted without being disturbed and indirectly leads to increases in rock mass integrity and rock mass wave velocity (Cui et al. 2016 ; Dou et al. 2020 ). Figure 16 shows an image of fissure filling after the excavation of a 5 m protective layer reserved for the dam foundation. This figure shows the diffusion radius of the slurry. The filling of large fissures enables the pressure below the dam foundation to be increased, which has a beneficial effect. 6 Conclusions The basic geological conditions of the Baihetan dam are complex, with the development of a large number of shear zones, cracks and faults. The dam foundation had to be treated to improve the integrity of the dam and reduce the permeability of the rock mass. An analysis of rock overburden grouting in the foundation by Lugeon tests and grout take data leads to the following conclusions: (1) The nonoverburden grouting technique is applied at the surface of the rock mass where the grouting effect is difficult to ensure, and there are problems associated with the interference between the concrete overburden grouting and the concrete pouring procedures. Before excavation, the surface rock of the dam foundation meets the quality inspection standard, but after excavation and grouting, it cannot meet the standard requirement that more than 90% of the wave velocities be greater than or equal to 4200 m/s. (2) Consolidation grouting is proposed for the Baihetan superhigh arch dam foundation to adopt "reserve rock mass, low-pressure thick slurry closed protective layer, overburden consolidation grouting". This approach is designed according to the special geological conditions of the Baihetan dam foundation. By reserving a 5 m rock mass overburden, controlling grouting pressure and concentration, and adopting the methods and materials of dividing holes and sequential grouting, the problem of unloading CJB relaxation due to excavation of the exposed rock mass is solved. The water permeability of the inspection holes after grouting is less than 3 Lu, more than 90% of the wave velocities of the rock mass are greater than 4200 m/s, and the integrity of the rock mass is greatly improved. (3) Rock mass overburden grouting technology addresses the complex geological conditions of the Baihetan dam foundation, solves the problems of conventional consolidation grouting technology, protects the thin layer of gravel lava at the Baihetan dam foundation, and solves the problem of unloading relaxation of CJB due to exposed consolidation grouting. This technology was successfully applied in the Baihetan superhigh arch dam project and has reference significance for the design and construction of consolidation grouting in similar projects. Declarations Acknowledgments This study was supported by the major research and development project of China Three Gorges Corporation ( 20210118). The authors are grateful to our partner in China, Sinohydro Bureau 8 Co., Ltd. The authors are also grateful to the China Three Gorges Corporation. This paper summarizes the results of an investigation and analysis performed over the past several years on columnar jointed basalts (CJBs) at the Baihetan arch dam and combines the findings of all the companies and institutions participating in this project, including its design and construction, as well as the findings of many experts and scholars both at home and abroad. We hereby express our gratitude to all the organizations and individuals involved. Data availability The data used to support the findings of this study are available from the corresponding author upon request. 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Soil Dynamics and Earthquake Engineering, 92:109-121. doi:https://doi.org/10.1016/j.soildyn.2016.09.039 Zhang D, Wang G, Yang T, Zhang M, Chen S, Zhang F (2013) Satellite remote sensing-based detection of the deformation of a reservoir bank slope in Laxiwa Hydropower Station China. Landslides, 10(2):231-238. doi:10.1007/s10346-012-0378-9 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-2449405","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":165668841,"identity":"87d03f91-b4da-4aa3-8a71-8762a4b4e595","order_by":0,"name":"Jinxi 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13","display":"","copyAsset":false,"role":"figure","size":39320,"visible":true,"origin":"","legend":"\u003cp\u003eWave velocity variation of the rock mass after grouting and excavation of dam section 7-8.\u003c/p\u003e","description":"","filename":"13.png","url":"https://assets-eu.researchsquare.com/files/rs-2449405/v1/87b65958bffd10f7871437a6.png"},{"id":31394676,"identity":"d00c9e45-9f41-4cf5-9a7c-8a624e0a1499","added_by":"auto","created_at":"2023-01-10 23:11:02","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":79900,"visible":true,"origin":"","legend":"\u003cp\u003eWave velocity variation of the rock mass after grouting and excavation of dam section 12-15.\u003c/p\u003e","description":"","filename":"14.png","url":"https://assets-eu.researchsquare.com/files/rs-2449405/v1/42381f87605fe8c082d44065.png"},{"id":31394196,"identity":"96d097ea-0955-4e5d-8593-b8fbcdc6487b","added_by":"auto","created_at":"2023-01-10 23:03:02","extension":"png","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":419212,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of wave velocity of rock mass after uncovered grouting (0~5 m).\u003c/p\u003e","description":"","filename":"15.png","url":"https://assets-eu.researchsquare.com/files/rs-2449405/v1/ea7a123086f423424396e98f.png"},{"id":31394199,"identity":"b114b86b-359b-4101-ab6b-7b62c7bf77ea","added_by":"auto","created_at":"2023-01-10 23:03:02","extension":"png","order_by":16,"title":"Figure 16","display":"","copyAsset":false,"role":"figure","size":1787110,"visible":true,"origin":"","legend":"\u003cp\u003eSlurry diffusion path after excavation of the 5 m protective layer reserved at the dam foundation.\u003c/p\u003e","description":"","filename":"16.png","url":"https://assets-eu.researchsquare.com/files/rs-2449405/v1/c97a41d9081fd235261e8bb3.png"},{"id":33271395,"identity":"a1decf0a-2aa3-4b09-8298-028a91e9bc76","added_by":"auto","created_at":"2023-02-22 07:44:30","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":7892126,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2449405/v1/078e24ee-6268-484f-ba2e-08e5a6342510.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Analysis of a Rock Mass Overburden Consolidation Grouting Method by Lugeon and Acoustic Tests","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eThe quality of the foundation rock mass is important for the overall stability of superhigh arch dams. Scholars have conducted many important studies on the causes and treatment of foundation failure in high dams (Dou et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Fan et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Fan et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Shi et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2020\u003c/span\u003e); for example, cement grouting and concrete plug replacement treatment for the class III rock mass of the Ertan arch dam foundation has been studied (Lin et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). In addition, a study was conducted on grouting treatment measures for the structural surfaces of the left and right shoulders of the Xiaowan arch dam and the rock masses in the alteration zone using thrust piers of resistant rock masses, underground cave plugs, concrete replacement, consolidation grouting and groove plugs of the foundation surface (Lin et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). The following principle was proposed for the Xiluodu arch dam: \"rock grade as the foundation and safety as the criterion. The weakly weathered rock masses should be reasonably utilized as the foundation rock, and the thrust at the arch end should be divided into elevation sections to determine the degree of utilization\" (Fan et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). In recent years, some scholars have explored self-flow controlled grouting technology in the treatment of dam foundations where bedrock is broken and cracks are developed (Fan et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). The integrated construction technique of foundation consolidation grouting is one of the main measures to improve the integrity and deformation resistance of a dam foundation. Dam foundation stability is a critical issue for the overall safety of dams and is especially relevant to the foundation treatment of 300 m class high arch dams.\u003c/p\u003e \u003cp\u003eAccording to the geological and construction conditions, consolidation grouting technology for dam foundations can generally be divided into nonoverburden grouting technology, concrete overburden grouting technology, lead pipe grouting technology and grouting technology derived from a combination of the above three types. In addition, different hydropower projects often adopt different foundation grouting schemes. The dam foundation of Ertan Hydropower Station has good geological conditions; cementation grouting was adopted in a \"non-overburden grouting, high-pressure pilot pipe\" grouting scheme for the first time in the project there, with high-pressure pilot pipe grouting being employed to target shallow or unqualified rock masses after grouting (Yang et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Laxiwa Hydropower Station adopted the technique of \"grouting without overburden in the first phase and concrete overburden in the second phase\" (Zhang et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2013\u003c/span\u003e), and the Jinping first-level hydropower station applied \"grouting without overburden, concrete overburden drilling and grouting in the section of a riverbed and slow slope dam\" (Zhang et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). In the case of Wudongde Hydropower Station (under construction), the foundation of the riverbed dam is grouted with nonoverburden and concrete conduit grouting. Nonoverburden grouting is mainly applied in cases where the geological conditions are favorable and the foundation rock is not affected by long-term exposure. This approach has the advantages of convenient construction and no interference with concrete construction. The main drawbacks are as follows: it is difficult to improve the grouting pressure, with the effect of surface rock grouting being difficult to guarantee; it is difficult to clear the foundation after grouting; and the ground surface easily forms a series of emergent slurries, resulting in a large amount of slurry waste. Therefore, the application of nonoverburden consolidation grouting technology has limitations. To improve the effect of surface rock grouting, the riverbed dam foundation projects of Xiaowan Hydropower Station (Wang et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) and Xiluodu Hydropower Station (Lin et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) both adopt concrete overburden consolidation grouting and perform warehouse operation preparation and consolidation grouting concurrently during the interval between concrete pouring so that the grouting equipment can be withdrawn for pouring. Overburden grouting usually requires \"three in and three out\". Overburden concrete consolidation grouting is suitable for many kinds of geological conditions, and its main advantages include improving grouting pressure, guaranteeing grouting quality, reducing surface cascading slurry, and saving pulp materials. Its main disadvantages are that it interferes extensively with concrete construction, is unconducive to concrete maintenance, requires long-term occupation of the concrete pouring bin surface, increases the concrete cracking risk, poses the risk of drilling through cooling water pipes and instrument lines, and causes drilling damage to concrete. Moreover, with overburden concrete consolidation grouting, it is very difficult to clean up the warehouse surface, the amount of concrete drilling work is increased, and the equipment is repeatedly dumped and left idle, which increases the investment.\u003c/p\u003e \u003cp\u003eLarge blast excavations have significant impacts on the physical, mechanical and hydraulic properties of the rock mass at the excavation boundary. In addition, they can lead to damage and stress redistribution within the rock mass, resulting in shallow rock unloading and increasing the permeability of the rock mass of a dam foundation and dam shoulder (Xia et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The geological conditions of the dam foundation of Jinshajiang Baihetan Hydropower Station are complex, and the dam foundation is mainly composed of Type І columnar jointed basalt (CJB), which is a special rock mass with undulating and irregular columnar jointed surfaces, irregular and incomplete cutting of column sections (Yan et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2011\u003c/span\u003e), the development of saphenous cracks within the column, and a low deformation modulus. In the dam foundation, misalignment zones develop within the interlayer, the deformation and shear strength are low, and some lithologic sections have dense cleavage zones (Chen et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Due to the developmental characteristics of the structural surface and the stress state of the rock mass, the horizontal deformation modulus of Type I CJB is significantly larger than the lead deformation modulus. The columnar joints and microcracks in fresh CJB are hard structural surfaces that are closed under the siege state and easily opened and relaxed after lifting the siege state; thus, CJB in the siege state still has a high deformation modulus (Shi et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The rock mass of an arch dam foundation is required to have sufficient bearing overburden and stability. One of the main engineering geological problems of Jinsha River Baihetan Hydropower Station is that the special rock structure and structural surface development characteristics of Type І columnar joints cannot meet the strict deformation requirements for the foundation of a high arch dam. The objectives of the project there are to increase the deformation resistance of the foundation, improve the shear and seepage resistance of the structural surface, avoid unloading and relaxation of the surface bedrock, reduce the impact of excavation and blasting crack surface opening of the dam foundation, and improve the integrity of the dam foundation. Therefore, it is necessary to consolidate the dam foundation and carry out consolidation grouting.\u003c/p\u003e \u003cp\u003eIn this study, we analyzed the complex geological conditions and difficulties of consolidation grouting of the Baihetan arch dam, proposed the key technology of \"reserving rock mass overburden weight, low-pressure thick slurry closure, overburden concrete consolidation grouting\", and proposed special antilifting measures for this technology. According to these special grouting measures, we carried out a large number of grouting inspections and performed data collection. Based on Lugeon tests and the analysis of grout take data and rock mass wave velocity data, we determined the grouting effect of the proposed method. The results are expected to provide a reference for the construction and design of similar projects.\u003c/p\u003e"},{"header":"2 Project Overview","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Background of the Baihetan project\u003c/h2\u003e \u003cp\u003eBaihetan Hydropower Station is located in the lower reaches of the Jinsha River in Ningnan County, Sichuan Province, and Qiaojia County, Yunnan Province. The station controls a basin area of 430,300 km\u003csup\u003e2\u003c/sup\u003e, accounting for 91% of the Jinsha River basin. The main application of the power plant is power generation; it is also used for flood control and shipping and to promote local economic and social development. The total overburden of the reservoir is 20.627\u0026nbsp;billion m\u003csup\u003e3\u003c/sup\u003e, the regulation overburden is 10.436\u0026nbsp;billion m\u003csup\u003e3\u003c/sup\u003e, and the flood control overburden is 7.50\u0026nbsp;billion m\u003csup\u003e3\u003c/sup\u003e. The hub project of Baihetan Hydropower Station mainly consists of river barrage and flood relief energy-dissipation structures, water diversion and power generation systems, and other components, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The barrage dam is a concrete double-curved arch dam with a peak height of 834.0 m and a maximum height of 289 m. Six surface holes and seven deep holes are arranged in the dam mass to dissipate energy by using the water pad pond behind the dam. The hills on the left bank are equipped with three nonpressure straight spill holes; the inlet is arranged between the inlet of the power plant on the left bank and the dam, and the outlet is located on the other side of the beach in Baihetan Village. The three spill holes all adopt the \"dragon drop tail\" pattern inside the holes.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe maximum excavation width of the dam foundation is approximately 100 m. The scale of the dam foundation excavation and treatment project is large, and the geological conditions of the dam foundation are complicated. Therefore, the excavation and treatment of the dam foundation are very difficult. The dam is divided into 31 dam sections. The concrete pad, above 750.0 m in foundation height (dam sections \u003cspan refid=\"Sec1\" class=\"InternalRef\"\u003e1\u003c/span\u003e to \u003cspan refid=\"Sec5\" class=\"InternalRef\"\u003e3\u003c/span\u003e), and the dam foundation consolidation grouting project of dam sections \u003cspan refid=\"Sec10\" class=\"InternalRef\"\u003e4\u003c/span\u003e to 18 are on the left bank, and the dam foundation consolidation grouting project of dam sections 19 to 31 is on the right bank.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Geological conditions of the dam foundation\u003c/h2\u003e \u003cp\u003e(1) Lithological characteristics and distribution\u003c/p\u003e \u003cp\u003eColumnar jointed basalt is widely distributed in Baihetan as a special structural rock mass. The columnar joints of the rocks surrounding the underground engineering sites can be divided into three types according to the diameter of the column. Type I columns are generally 13\u0026thinsp;~\u0026thinsp;25 cm in diameter and 2\u0026thinsp;~\u0026thinsp;3 m in length. Type II columns are generally 25\u0026thinsp;~\u0026thinsp;50 cm in diameter and 0.5\u0026thinsp;~\u0026thinsp;2.0 m in length. Type III columns are generally 0.5\u0026thinsp;~\u0026thinsp;2.5 m in diameter and 0.5\u0026thinsp;~\u0026thinsp;2.5 m in length. The length is generally 1.5 to 5.0 m.\u003c/p\u003e \u003cp\u003eThe elevation from 834 to 735 m on the left bank of the dam is composed of layers of greenish-gray massive basalt and breccia lava. The elevation from 735 to 719 m is composed of layers of breccia lava with massive basalt and thin layers of tuff, and the elevation from 719 to 665 m is composed of layers of massive basalt. The elevation from 665\u0026thinsp;~\u0026thinsp;600 m is the layer of Type І CJB; for each column, the diameter is 15\u0026thinsp;~\u0026thinsp;25 cm, the development is irregular, the surface is slightly rough, the intercolumn is closely embedded, and the length is 3 m. Additionally, the fracture in each column is developed, the fracture is arc-shaped, the surface is smooth, and the interfracture is closely embedded. The basalt rock is hard, and the distribution of lithological layers in the foundation of the dam revealed by actual excavation is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The 834\u0026thinsp;~\u0026thinsp;665 m elevation section of the foundation of the dam on the left bank is massive basalt, which is dominated by cryptocrystalline basalt, accounting for 60.0% of the basalt. Next most abundant is amygdaloidal basalt, accounting for 23.4% of the total, followed by breccia lava, accounting for 16.3%. The tuff is banded and thin, with an exposed area of approximately 45.3 m2, accounting for only 0.3%. Below 665 m elevation at the foundation of the left bank of the dam, the exposed lithologies are all stratified Type I CJB.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe 834\u0026ndash;600 m elevation section of the right bank mainly exposes the layers of the Emeishan Group, which are oblique porphyry basalt, Type III CJB, Type II CJB, cryptocrystalline basalt, amygdaloidal basalt, breccia lava and tuff. Below 600 m elevation, the dam foundation mainly consists of layers of Type I CJB and layers of breccia lava. Layers of Type I columnar articulated basalt are found at elevations of 600\u0026ndash;570 m on the left bank and 600\u0026ndash;540 m on the right bank. For each column, the diameter is generally 15\u0026thinsp;~\u0026thinsp;25 cm, the development is irregular, the surface is slightly rough, the intercolumnar mosaic is tight, and the length is generally 3 m. Microcracks develop in the column, the cut rock is a 5\u0026thinsp;~\u0026thinsp;10 cm rock mass, and the mosaic is tight. The subsurface is composed of layers of breccia lava and Type II CJB. The foundation of the dam between 570 m elevation on the left bank and 540 m elevation on the right bank is composed of layers of breccia lava. According to the preliminary investigation and construction details of dam sections 13 and 14, the thickness of each layer of breccia lava is between 4.3 and 17.0 m, with an average thickness of 8.5 m. The address profile is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e(2) Tectonic development\u003c/p\u003e \u003cp\u003eThe fault structure is more developed at the middle dam site, and there are nine major faults of larger scale. The 834\u0026ndash;600 m fault zone of the dam foundation and shoulder on the left bank is mainly developed as F\u003csub\u003e17\u003c/sub\u003e, F\u003csub\u003e14\u003c/sub\u003e, F\u003csub\u003e16\u003c/sub\u003e, f\u003csub\u003e110\u003c/sub\u003e, f\u003csub\u003e108\u003c/sub\u003e, f\u003csub\u003e145\u003c/sub\u003e, etc. The faults exposed at the excavation surface below 600 m height are mainly F\u003csub\u003e14\u003c/sub\u003e, F\u003csub\u003e16\u003c/sub\u003e, f\u003csub\u003e261\u003c/sub\u003e, f\u003csub\u003e262\u003c/sub\u003e, and f\u003csub\u003e265\u003c/sub\u003e in the WNW direction. The 834\u0026ndash;600 m fault zone of the dam foundation on the right bank is mainly developed as F\u003csub\u003e17\u003c/sub\u003e, F\u003csub\u003e14\u003c/sub\u003e, F\u003csub\u003e16\u003c/sub\u003e, f\u003csub\u003e261\u003c/sub\u003e, f\u003csub\u003e262\u003c/sub\u003e, and f\u003csub\u003e265\u003c/sub\u003e in the WNW direction. The main faults developed at 600 m elevation are f\u003csub\u003e232\u003c/sub\u003e, f\u003csub\u003e249\u003c/sub\u003e, and f\u003csub\u003e256\u003c/sub\u003e. Except for F\u003csub\u003e17\u003c/sub\u003e, which is in the NE direction, all the other faults are in the NW direction; some of the fault outcropping features are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The distributions of some faults, fault zones and rock bodies are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e(3) Initial ground stress conditions\u003c/p\u003e \u003cp\u003eThe Baihetan dam site is a plateau and deep valley located on the east side of the Jiaoji River fracture zone and on the north side of the Xiaojiang River fracture zone. As a result of the tectonic extrusion in the NW-NNW region that occurs after neotectonic movement, the rocks surrounding the underground cave cluster of Baihetan Hydropower Station are mainly under tectonic stress. The ground stress of the primary rocks in the dam site area is generally in the NNW-NW direction, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. However, the initial stress of the raw rock in the underground cave cluster on the right bank is influenced by the downcutting of the river valley and fault block movement, and the direction of the maximum main stress is deflected to approximately the N-S direction. The horizontal burial depths of the underground plant caverns on the left bank and right bank are 950\u0026thinsp;~\u0026thinsp;1050 and 630\u0026thinsp;~\u0026thinsp;800 m, respectively, and the vertical burial depths are 260\u0026thinsp;~\u0026thinsp;330 and 420\u0026thinsp;~\u0026thinsp;540 m, respectively. The initial maximum ground stress of the underground cave cluster on the left bank is 19\u0026thinsp;~\u0026thinsp;23 MPa (where the maximum measured horizontal stress is 33.39 MPa) and is inclined to 5\u0026deg;~13\u0026deg; of the river valley. The maximum main stress on the right bank is 22ཞ26 MPa, and the maximum measured main stress is 30.99 MPa. The intermediate main stress tends to 2\u0026deg;~11\u0026deg; of the river valley in general, but under the local influence of the interlayer zone, the value and characteristics of the ground stress vary. In general, the initial stress level of the surrounding rocks in the underground cave cluster at Baihetan is high, and the local ground stress characteristics are influenced by large tectonic structures.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"3 Consolidation Grouting Design For The Dam Foundation","content":"\u003cdiv class=\"Section2\" id=\"Sec6\"\u003e\n \u003ch2\u003e3.1 Grouting process\u003c/h2\u003e\n \u003cp\u003e\u003cstrong\u003e(1) Raw materials\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003eCement: Ordinary Portland cement 42.5R produced by a cement company in Hunan Province is used in this study. The cement is passed through an 80 mm square-hole sieve with a fineness of less than 5% of the sieve volume. The performance is in accordance with the relevant requirements of the Chinese general Portland cement standard (GBl75-2007). The chemical composition of the Portland cement used in this study is shown in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. The initial setting time is 155 min, the final setting time is 235 min, and the 28 d compressive strength is 46.3 MPa.\u003c/p\u003e\u0026nbsp;\u003ctable border=\"1\" id=\"Tab1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eThe Chemical constituents of the Portland cement used in this study\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eConstituents\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMgO\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCaO\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eLoss on ignition\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eContent/%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e22.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e56.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(2) Slurry ratio and particle size\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003eOrdinary Portland cement grout is used for consolidation grouting of hole sequence І and hole sequence II, and four levels of the water-cement ratio (water-cement mass ratio) of the ordinary Portland cement slurry are tested (2:1, 1:1, 0.8:1, and 0.5:1). Wet-ground cement grout is used for hole sequence III; similarly, four levels of the water-cement ratio of the cement slurry are tested (3:1, 2:1, 1:1, and 0.5:1). Wet grinding equipment (GJM–FII) from the Wuhan Yangtze River Academy of Sciences Institute of Automation is used for wet grinding in this experiment.\u003c/p\u003e\n \u003cp\u003eThe particle size distribution of the wet-ground cement is analyzed by an NSKC-1 laser particle size analyzer from the Wuhan Yangtze River Academy of Sciences Institute of Automation. The results are shown in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e. According to Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e, D\u003csub\u003e95\u003c/sub\u003e (the maximum particle size with a cumulative mass distribution rate of 95%) is equal to 37.46 µm, and D\u003csub\u003e50\u003c/sub\u003e (average particle size) is 11.44 µm.\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(3) Grouting methods\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003eThe grouting holes are divided into three sequences. Hole sequences І and II adopt the \"top-down, plugging in hole, bottom circulation\" grouting method. Hole sequence III is the first grout protective layer below the foundation surface and adopts the \"bottom-up, plugging in hole, bottom circulation\" grouting method.\u003c/p\u003e\n \u003cp\u003eGrouting pressure: Consolidation grouting adopts a graded pressurized method to cause the grouting pressure to gradually reach the design value, and it adopts the principle of no harmful lifting of the grouting rock surface and concrete. In the process of grouting, the relationship between injection rate and injection pressure is strictly controlled, and the grouting pressure of the protective layer is 0.5 MPa. The grouting pressure of the first section below the foundation surface is 0.8 ~ 1.0 MPa; the pressure gradually increases by 0.5 MPa in each section. The largest grouting pressure is 3.0 MPa, which is the grouting pressure of the concrete conduit, as shown in Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e. Grouting end standard: Under the design pressure, the injection rate is not greater than 1.0 L/min, and the grouting operation can end after 30 min of continuous grouting.\u003c/p\u003e\u0026nbsp;\u003ctable border=\"1\" id=\"Tab2\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eDam foundation consolidation grouting pressure and section lengths\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDepth (m)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e-5 ~ 0\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e0 ~ 5\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e5 ~ 10\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e10 ~ 15\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e15 ~ 20\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e20 ~ 25\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e25 ~ 30\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eⅠ\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.8 ~ 1.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.0 ~ 1.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.5 ~ 2.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.0 ~ 2.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.5 ~ 3.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eⅡ\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.0 ~ 1.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.5 ~ 2.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.0 ~ 2.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.5 ~ 3.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.5 ~ 3.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eⅢ\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.0 ~ 1.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.0 ~ 2.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.5 ~ 3.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec7\"\u003e\n \u003ch2\u003e3.2 Consolidation grouting measures\u003c/h2\u003e\n \u003cp\u003eIn consideration of the specific geological conditions and field test results from the construction of the Baihetan arch dam foundation, consolidation grouting of the dam foundation is performed mainly via four methods: rock overburden grouting combined with shallow concrete overburden grouting, nonoverburden grouting combined with shallow concrete overburden conduit grouting, nonoverburden grouting and reinforcement grouting.\u003c/p\u003e\n \u003cp\u003e(1) Measures for rock overburden grouting and shallow concrete overburden grouting: reservation of a 5 m rock overburden protection layer → top-down, plugging in hole, circulating grouting at hole bottom → anchor pile placement → excavation of overburden layer → shallow conduit formation → concrete pouring → concrete overburden conduit grouting, as shown in Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e\n \u003cp\u003e(2) Nonoverburden grouting and shallow concrete overburden conduit grouting: excavation to foundation surface → top-down, hole jamming, bottom-hole circulating grouting → anchor pile placement → shallow conduit formation → concrete pouring → concrete overburden conduit grouting.\u003c/p\u003e\n \u003cp\u003e(3) Nonoverburden grouting and reinforcement grouting: excavation to the foundation surface → top-down, plugging in hole, circulating grouting at hole bottom → anchor pile placement → inspection hole formation → reinforcement grouting.\u003c/p\u003e\n \u003cp\u003eThe distribution of specific grouting methods for the dam foundation area is shown in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec8\"\u003e\n \u003ch2\u003e3.3 Grouting partition\u003c/h2\u003e\n \u003cp\u003eTo ensure that the high stress of the dam foundation can be distributed evenly and to strengthen the upstream seepage control, the range of consolidation grouting is extended beyond the dam foundation, 5 m upstream to the dam heel and approximately 10 m downstream to the toe (horizontal projection distance). The depth of the grouting hole in the range of the dam foundation is divided into four zones from A to D, corresponding to grouting hole depths of 30, 25, 20 and 15 m. The enlarged grouting zone upstream and downstream is Zone E, which has the same hole depth as the neighboring zone. The partition of consolidation grouting of the Baihetan arch dam foundation is shown in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e.\u003c/p\u003e\n \u003cp\u003eAs shown in Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e, the grouting holes are arranged in a grid pattern, the inter-row spacing of CJB is 2×2 m, and the inter-row spacing of the gravel lava dam foundation is 3×3 m. The grouting holes on both shore slopes are perpendicular to the foundation surface. The riverbed dam in sections 13–22 contains a plumb hole, and the transition between the plumb hole and the hole perpendicular to the foundation surface occurs by diverging holes. The holes on the upstream and downstream slopes are diverging holes.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec9\"\u003e\n \u003ch2\u003e3.4 Evaluation of the consolidation grouting effect\u003c/h2\u003e\n \u003cp\u003e\u003cstrong\u003e(1) Lugeon test\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003eThe Lugeon test can directly reflect the permeability of a stratum and constitutes the basis for classifying the stratum at the early stage of the injection project. A pressure of 1 MPa is adopted, and after the pressure stabilizes, the pressure inflow rate is measured every 5 min. When the difference between the maximum and minimum values of four consecutive readings is less than 10% of the final permeability or the difference between the maximum and minimum inflow rates is less than 1.0 L/min, the test is considered complete. The final value is then taken as the flow rate to calculate the water permeability. The Lugeon test calculation formula is shown in Eq.\u0026nbsp;(1):\u003c/p\u003e\n \u003cp\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003ewhere \u003cem\u003eq\u003c/em\u003e is the permeability of the test section, Lu; \u003cem\u003eQ\u003c/em\u003e is the pressure inflow, L/min; \u003cem\u003eP\u003c/em\u003e is the total pressure acting on the test section, MPa; and \u003cem\u003eL\u003c/em\u003e is the length of the test section, m.\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(2) Acoustic test\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003eAcoustic wave testing provides an important basis for determining the physical and mechanical parameters of a rock body. The results can be applied to the excavation of rock slopes, providing an effective indicator for blasting excavation. The higher the wave velocity is, the better the physical and mechanical properties of the rock mass and its integrity are. Acoustic testing is performed mainly on the test holes before and after grouting. By comparing the test results before and after grouting, the parameters of the rock integrity changes are obtained, and the grouting quality is analyzed. The acoustic testing device used in this study is an RS-ST01C acoustic control instrument produced by Wuhan Yanhai Engineering Development Co. This test considers the coefficients of geological defects, such as the weathering coefficient, integrity coefficient, anisotropy coefficient, fracture action and karst action. A grouting test borehole is drilled 14 days after the completion of grouting.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4 Analysis Of The Consolidation Grouting Results","content":"\u003cp\u003eQuality inspection of the consolidation grouting is conducted based on acoustic wave velocity measurements of the rock mass combined with drilling pressure water tests. For proper completion of the acoustic wave test, the test should be performed for each unit and should be carried out 14 days after the grouting of the corresponding part. To meet the quality inspection standard, more than 90% of the whole dam section should have a value greater than 4200 m/s, and less than 5% of the section should have a value less than 4000 m/s. The consolidation grouting also adopts a pressure water test inspection, which is carried out 7 days after grouting completion in the corresponding part. The quality standard is as follows: when the grouting quality check of the hole is 85% above the pressure water test section, the water permeability is not greater than 3 Lu and is not concentrated.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Analysis of the Lugeon test results\u003c/h2\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e, before grouting, the water permeability of dam sections 7\u0026ndash;8 is large: that of dam section 7 is 73.7% greater than 3 Lu, and that of dam section 8 is 58% greater than 3 Lu. Figure\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e also shows that the decreases in grouting volume and water permeability of the rock mass after grouting are large. Dam section 7: The grouting volume decreases from 50.81 kg/m to 10.2 kg/m from hole sequence І to hole sequence III, representing a decrease of 80%. Dam section 8: The grouting volume decreases from 40.52 kg/m to 8.55 kg/m from hole sequence І to hole sequence III, representing a decrease of 78.8%. After grouting, the test results are all less than 3 Lu.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs shown in the pie charts for each dam section in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e, prior to grouting, dam sections 12\u0026ndash;15 exhibit high permeability of the rock. The permeability of dam sections 12, 13, 14 and 15 is 96.49%, 98.9%, 97.1%, and 98% greater, respectively, than 3 Lu. After grouting, the test results are all less than 2.8 Lu. Figure\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e also shows that the decreases in grouting volume and permeability of the rock mass after grouting are large. Dam section 12: The quantity of grouting decreases from 83.49 kg/m to 16.34 kg/m from hole sequence І to hole sequence III, representing a decrease of 80.4%. Dam section 13: The injection volume decreases from 46.85 kg/m to 2.35 kg/m, representing a decrease of 95%, from hole sequence І to hole sequence III. Dam section 14: The grouting volume decreases from 67.51 kg/m to 18.54 kg/m from hole sequence І to hole sequence III, representing a decrease of 72.5%. Dam section 15: The injection volume decreases by 77%, from 128.21 kg/m to 29.44 kg/m, from hole sequence І to hole sequence III. After grouting, the test results are all less than 2.75 Lu.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Analysis of the acoustic test results\u003c/h2\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e, the mean wave velocity of dam section 7 before grouting is 5210 m/s, and that after grouting is 5255 m/s. The increase in wave velocity after grouting is 0.9%. Among the 22 inspection holes at the foundation of the dam, the percentage with a wave velocity greater than or equal to 4700 m/s is 91.5%, and the percentage with a wave velocity less than 4200 m/s is 3.8%. Thus, the results meet the quality inspection standard. For dam section 8, the average acoustic wave velocities before grouting and after grouting are 5310 m/s and 5342 m/s, respectively, corresponding to an increase of 0.6% after grouting. The percentages of wave velocities greater than or equal to 4700 m/s and less than 4200 m/s are 95.7% and 1.6%, respectively, for the 24 inspection holes at the foundation of the dam, and the wave velocities comply with the standard. After the excavation of the protective layer, more than 90% of the dam foundation from 0\u0026thinsp;~\u0026thinsp;5 m has a value greater than 4200 m/s, and this result meets the acoustic inspection standard of the dam foundation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e14\u003c/span\u003e, for dam section 12, the breccia lava hole section, the percentage of wave velocity values greater than or equal to 4200 m/s after dam foundation grouting is 90.2%, and the percentage of values less than 4000 m/s is 3.6%. Dam section 13: The mean wave velocity before grouting is 4893 m/s, and that after grouting is 5138 m/s, representing an increase of 5.0%. Of the wave velocities of this section of Type І CJB, 90.4% are greater than or equal to 4500 m/s, and 2.6% are less than 4000 m/s. Dam section 14: The percentage of wave velocity values greater than or equal to 4400 m/s in the hole section of Type П CJB after dam foundation grouting is 94.3%, and the percentage less than 4000 m/s is 2.4%. After the excavation of the protective layer, the proportion of values greater than 4200 m/s for the whole dam section from 0 to 5 m is 94.1%. Dam section 15: After dam foundation grouting in hole section of Type П CJB, the percentage of wave velocities greater than or equal to 4400 m/s is 94.8%, and that less than 4000 m/s is 1.8%. After the excavation of the protective layer, the percentage of values greater than 4200 m/s for the whole dam section from 0\u0026ndash;5 m is 90.7%.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"5 Discussion","content":"\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e5.1 Consolidation grouting with no rock mass overburden\u003c/h2\u003e \u003cp\u003eThe Baihetan dam foundation was constructed with consolidation grouting starting on the left bank from dam section 9 and on the right bank from dam section 25. Initially, the grouting adopted nonoverburden grouting combined with shallow concrete overburden conduit grouting. For the cementation grouting in the construction of dam sections 9\u0026ndash;11 on the left bank and dam section 25 on the right bank, inspection reveals that the grouting effect is poor, and the relaxation rate and water permeability rate of the rock mass are large. Figure\u0026nbsp;\u003cspan refid=\"Fig15\" class=\"InternalRef\"\u003e15\u003c/span\u003e shows the nonoverburden consolidation grouting data of dam sections 9\u0026ndash;11 and 25; the results do not meet the grouting quality inspection standard.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn summary, it is difficult to guarantee the grouting effect on the surface of the rock mass without overburden grouting technology, and there are problems, such as the interference between the concrete overburden grouting and the concrete pouring process. Before the excavation, the surface of the rock mass of the dam foundation meets the quality inspection standard, but after the excavation and grouting, it does not meet the standard requirement that more than 91% of the wave velocities be greater than or equal to 4200 m/s. One reason for these results is that the excavation adopts blasting, which causes extensive damage to the rock mass. The foundation of Baihetan Hydropower Station is developed in CJB, which easily relaxes and cracks after unloading. The water permeability is high, and misalignment zones, fissures and faults are developed in the dam foundation. The column development is dense, with steeply dipping hidden jointed surfaces and vertical gently dipping hidden jointed surfaces within each column unit. A hidden jointed surface has the characteristics of being wavy and undulating. The microcracks are hard structural surfaces, and the rock mass has a columnar mosaic structure. It is closed under the in situ stress state and easily opens and relaxes after the siege pressure is lifted; the CJB still has a high deformation modulus when the siege condition is maintained, and the rock mass relaxation problem is prominent (Dai et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Hao et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Jiang et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Xiao et al; Xu et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Additional reasons for the above results are that the excavation extends to the dam foundation surface for grouting, the shallow cracks in the dam foundation are not closed, and it is difficult to increase the pressure of nonoverburden consolidation grouting. Increasing the pressure will lead to stratum elevation, and the low pressure leads to a limited diffusion radius of the slurry, which cannot effectively fill the cracks. When nonoverburden grouting is difficult to obstruct, the obstruction depth is generally 1\u0026thinsp;~\u0026thinsp;2 m, and the shallow rock mass leaks, leading to a low sonic improvement rate after grouting and difficulty reaching the quality standard.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e5.2 Consolidation grouting with rock mass overburden\u003c/h2\u003e \u003cp\u003eIt is difficult to guarantee the grouting effect on the surface of the rock mass without overburden grouting technology. The grouting effect is poor, the relaxation rate and water permeability rate of the rock mass are large, and there are problems due to the interference between the concrete overburden grouting and the concrete pouring process. After discussion with experts and design units, it is proposed that \"reserve rock mass, low-pressure thick slurry closed protective layer, overburden consolidation grouting\" be adopted. According to the special geological conditions of the Baihetan dam foundation, an approach involving the reservation of a 5 m rock mass overburden, the control of grouting pressure and concentration, and the adoption of methods and materials for dividing holes and sequential grouting was applied. This approach solved the problem of CJB relaxation due to excavation and bare rock mass unloading. The reserved 5 m rock cover is excavated by blasting. (Hu et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Xia et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) have performed many studies on blasting schemes and have studied the degree of damage of blasting excavation to rock masses, and they proposed a 5 m stage as a reasonable scheme. In the present study, after grouting, the water permeability of the inspection holes is less than 3 Lu, more than 90% of the wave velocities of the rock mass are greater than 4200 m/s, and the integrity of the rock mass is greatly improved. The analysis suggests that reserving a 5 m rock mass without excavation can greatly reduce the damage to the rock mass caused by blasting and excavation and reduce the relaxation of CJB caused by unloading. A second reason for the effectiveness of the approach is that if the 5 m rock mass is closed by thick slurry, the shallow fissure in the dam foundation will be closed, and the pressure of consolidation grouting can be increased, which will increase the diffusion radius of the slurry and allow the fissure to be effectively filled. When there is no overburden and heavy grouting, blocking is difficult, and the blocking depth is generally 1\u0026thinsp;~\u0026thinsp;2 m. A 5 m rock protection layer is reserved so that there is enough depth for blocking. This series of measures allows the rock mass to be grouted without being disturbed and indirectly leads to increases in rock mass integrity and rock mass wave velocity (Cui et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Dou et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Figure\u0026nbsp;\u003cspan refid=\"Fig16\" class=\"InternalRef\"\u003e16\u003c/span\u003e shows an image of fissure filling after the excavation of a 5 m protective layer reserved for the dam foundation. This figure shows the diffusion radius of the slurry. The filling of large fissures enables the pressure below the dam foundation to be increased, which has a beneficial effect.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"6 Conclusions","content":"\u003cp\u003eThe basic geological conditions of the Baihetan dam are complex, with the development of a large number of shear zones, cracks and faults. The dam foundation had to be treated to improve the integrity of the dam and reduce the permeability of the rock mass. An analysis of rock overburden grouting in the foundation by Lugeon tests and grout take data leads to the following conclusions:\u003c/p\u003e \u003cp\u003e(1) The nonoverburden grouting technique is applied at the surface of the rock mass where the grouting effect is difficult to ensure, and there are problems associated with the interference between the concrete overburden grouting and the concrete pouring procedures. Before excavation, the surface rock of the dam foundation meets the quality inspection standard, but after excavation and grouting, it cannot meet the standard requirement that more than 90% of the wave velocities be greater than or equal to 4200 m/s.\u003c/p\u003e \u003cp\u003e(2) Consolidation grouting is proposed for the Baihetan superhigh arch dam foundation to adopt \"reserve rock mass, low-pressure thick slurry closed protective layer, overburden consolidation grouting\". This approach is designed according to the special geological conditions of the Baihetan dam foundation. By reserving a 5 m rock mass overburden, controlling grouting pressure and concentration, and adopting the methods and materials of dividing holes and sequential grouting, the problem of unloading CJB relaxation due to excavation of the exposed rock mass is solved. The water permeability of the inspection holes after grouting is less than 3 Lu, more than 90% of the wave velocities of the rock mass are greater than 4200 m/s, and the integrity of the rock mass is greatly improved.\u003c/p\u003e \u003cp\u003e(3) Rock mass overburden grouting technology addresses the complex geological conditions of the Baihetan dam foundation, solves the problems of conventional consolidation grouting technology, protects the thin layer of gravel lava at the Baihetan dam foundation, and solves the problem of unloading relaxation of CJB due to exposed consolidation grouting. This technology was successfully applied in the Baihetan superhigh arch dam project and has reference significance for the design and construction of consolidation grouting in similar projects.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was supported by the\u0026nbsp;major research and development project of China Three Gorges Corporation\u0026nbsp;( 20210118).\u0026nbsp;The authors are grateful to our partner in China, Sinohydro Bureau 8 Co., Ltd.\u0026nbsp;The authors\u0026nbsp;are also\u0026nbsp;grateful to the China Three Gorges Corporation. This paper summarizes the results of an investigation and analysis performed over the past several years on columnar jointed basalts (CJBs) at the Baihetan arch dam and combines the findings of all the companies and institutions participating in this project, including its design and construction, as well as the findings of many experts and scholars both at home and abroad. We hereby express our gratitude to all the organizations and individuals involved.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data used to support the findings of this study are available from the corresponding author upon request.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eChen BR, Li QP, Feng XT, Xiao YX, Feng, GL, Hu LX (2014) Microseismic monitoring of columnar jointed basalt fracture activity: a trial at the Baihetan Hydropower Station, China Journal of Seismology, 18(4):773-793. doi:10.1007/s10950-014-9445-0\u003c/li\u003e\n \u003cli\u003eCui Z, Sheng Q, Leng X (2016) Control Effect of a Large Geological Discontinuity on the Seismic Response and Stability of Underground Rock Caverns: A Case Study of the Baihetan #1 Surge Chamber. 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Landslides, 10(2):231-238. doi:10.1007/s10346-012-0378-9\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Consolidation grouting, Baihetan super-high arch dam, Grout take, Lugeon test, Columnar joints","lastPublishedDoi":"10.21203/rs.3.rs-2449405/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-2449405/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe Baihetan superhigh arch dam is the largest hydropower station under construction in the world. Columnar jointed basalt (CJB) is widely distributed and densely jointed at the foundation of the Baihetan superhigh arch dam and poses a potential risk to its overall stability. A method of overburden consolidation grouting of the rock mass is proposed that solves the problem of unloading relaxation of CJB due to excavation of the exposed rock mass. The results show the following. 1) The method of nonoverburden grouting cannot achieve the quality inspection standard requirement that at least 90% of the wave velocities be greater than or equal to 4200 m/s, and the overall wave velocity of the rock mass before excavation is greater than that after grouting. 2) After overburden consolidation grouting of the rock mass, which includes controlling grouting pressure and concentration and performing perforation and sequence grouting, the water permeability of the inspection holes is less than 3 Lu, more than 90% of the wave velocities in the rock mass are greater than 4200 m/s, and the integrity of the rock mass is greatly improved. 3) The problems of conventional consolidation grouting technology are solved to protect the thin layer of breccia lava at the foundation of the Baihetan dam. In addition, the problem of unloading relaxation of CJB due to exposure to consolidation grouting is solved in the Baihetan superhigh arch dam project. This application has reference significance for the design and application of consolidation grouting in similar projects.\u003c/p\u003e","manuscriptTitle":"Analysis of a Rock Mass Overburden Consolidation Grouting Method by Lugeon and Acoustic Tests","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-01-10 23:02:56","doi":"10.21203/rs.3.rs-2449405/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"8adccbb5-cf5c-4560-8c38-3e76fcb127a1","owner":[],"postedDate":"January 10th, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2023-02-22T07:44:19+00:00","versionOfRecord":[],"versionCreatedAt":"2023-01-10 23:02:56","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-2449405","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-2449405","identity":"rs-2449405","version":["v1"]},"buildId":"_2-kVJe1T_tPrBINL-cwx","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}