Effect of fulvic acid contamination on the shear strength and microstructural evolution of red clay

Effect of fulvic acid contamination on the shear strength and microstructural evolution of red clay | 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 Article Effect of fulvic acid contamination on the shear strength and microstructural evolution of red clay Xinhua Dong, Chunxue Du, Kun Yang, Jifeng Wang, Pei Zhang, Jiangfeng Wang, and 2 more This is a preprint; it has not been peer reviewed by a journal.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-8226112/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 14 You are reading this latest preprint version Abstract The influence of fulvic acid (FA) contamination on the residual shear strength of red clay is an important issue in geological engineering. This study examines the effects of FA contamination on the shear strength, mineral composition, and microstructural changes in Guilin red clay using repeated drainage direct shear tests, along with X-ray diffraction (XRD), scanning electron microscopy (SEM), and particle and pore structure analysis system (PCAS). The results indicate that a low FA concentration (m FA /m RC = 2%) combined with short-term immersion (approximately 7 days) enhances the residual shear strength of red clay, primarily through increases in cohesion and internal friction angle. However, higher FA concentrations (m FA /m RC ≥ 4%) and prolonged immersion (≥ 21 days) lead to a significant reduction in shear strength, with the most notable decrease observed at m FA /m RC = 6% and t = 21 days, where cohesion and internal friction angle were reduced by several tens of percentage points. XRD results show that FA contamination does not significantly alter the mineral composition, but it leads to the dissolution and transformation of calcite and illite, thereby altering their relative abundances. SEM observations suggest that short-term FA contamination promotes particle aggregation and pore filling, resulting in a denser microstructure and increased shear strength. In contrast, prolonged contamination causes a reduction in particle size, increased porosity, and a more loosely packed structure, ultimately weakening the soil's shear strength. The study proposes a dual adsorption mechanism: at low FA concentrations, FA enhances soil aggregation through the formation of "organic–inorganic bridges," while at high concentrations, it induces interparticle repulsion through the development of a hydrated organic film, leading to structural loosening and strength degradation. These findings provide insights into the complex mechanisms by which FA contamination affects the mechanical properties of red clay, offering a theoretical foundation for geotechnical design and safety assessments in FA-affected regions. Physical sciences/Engineering Earth and environmental sciences/Environmental sciences Physical sciences/Materials science Earth and environmental sciences/Solid earth sciences Residual shear strength Microstructural evolution Fulvic acid Red clay Geotechnical engineering Full Text Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 20 Mar, 2026 Reviews received at journal 14 Mar, 2026 Reviews received at journal 09 Mar, 2026 Reviewers agreed at journal 06 Mar, 2026 Reviewers agreed at journal 05 Mar, 2026 Reviewers agreed at journal 04 Mar, 2026 Reviewers agreed at journal 04 Mar, 2026 Reviewers agreed at journal 27 Dec, 2025 Reviewers agreed at journal 18 Dec, 2025 Reviewers invited by journal 16 Dec, 2025 Editor invited by journal 02 Dec, 2025 Editor assigned by journal 29 Nov, 2025 Submission checks completed at journal 29 Nov, 2025 First submitted to journal 27 Nov, 2025 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. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-8226112","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":562167286,"identity":"74294037-5f84-463e-995d-f52c12760ac6","order_by":0,"name":"Xinhua Dong","email":"","orcid":"","institution":"Zhumadian Flood and Drought Disaster Prevention Center","correspondingAuthor":false,"prefix":"","firstName":"Xinhua","middleName":"","lastName":"Dong","suffix":""},{"id":562167287,"identity":"e9cf6be7-6b17-4658-85b5-2e4ccce07407","order_by":1,"name":"Chunxue 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Microstructural evolution, Fulvic acid, Red clay, Geotechnical engineering","lastPublishedDoi":"10.21203/rs.3.rs-8226112/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8226112/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe influence of fulvic acid (FA) contamination on the residual shear strength of red clay is an important issue in geological engineering. This study examines the effects of FA contamination on the shear strength, mineral composition, and microstructural changes in Guilin red clay using repeated drainage direct shear tests, along with X-ray diffraction (XRD), scanning electron microscopy (SEM), and particle and pore structure analysis system (PCAS). The results indicate that a low FA concentration (m\u003csub\u003eFA\u003c/sub\u003e/m\u003csub\u003eRC\u003c/sub\u003e = 2%) combined with short-term immersion (approximately 7 days) enhances the residual shear strength of red clay, primarily through increases in cohesion and internal friction angle. However, higher FA concentrations (m\u003csub\u003eFA\u003c/sub\u003e/m\u003csub\u003eRC\u003c/sub\u003e \u0026ge; 4%) and prolonged immersion (\u0026ge;\u0026thinsp;21 days) lead to a significant reduction in shear strength, with the most notable decrease observed at m\u003csub\u003eFA\u003c/sub\u003e/m\u003csub\u003eRC\u003c/sub\u003e = 6% and t\u0026thinsp;=\u0026thinsp;21 days, where cohesion and internal friction angle were reduced by several tens of percentage points. XRD results show that FA contamination does not significantly alter the mineral composition, but it leads to the dissolution and transformation of calcite and illite, thereby altering their relative abundances. SEM observations suggest that short-term FA contamination promotes particle aggregation and pore filling, resulting in a denser microstructure and increased shear strength. In contrast, prolonged contamination causes a reduction in particle size, increased porosity, and a more loosely packed structure, ultimately weakening the soil's shear strength. The study proposes a dual adsorption mechanism: at low FA concentrations, FA enhances soil aggregation through the formation of \"organic\u0026ndash;inorganic bridges,\" while at high concentrations, it induces interparticle repulsion through the development of a hydrated organic film, leading to structural loosening and strength degradation. These findings provide insights into the complex mechanisms by which FA contamination affects the mechanical properties of red clay, offering a theoretical foundation for geotechnical design and safety assessments in FA-affected regions.\u003c/p\u003e","manuscriptTitle":"Effect of fulvic acid contamination on the shear strength and microstructural evolution of red clay","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-19 05:41:44","doi":"10.21203/rs.3.rs-8226112/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-03-20T08:54:12+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-14T17:47:07+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-09T09:48:52+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"45902738788336596565122772762359403044","date":"2026-03-06T13:19:52+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"163948063356296918693424884513659059544","date":"2026-03-05T07:55:55+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"246554375404060405880416035315367209773","date":"2026-03-04T13:47:06+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"74911154913879609688069502941895033861","date":"2026-03-04T06:18:56+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"269766462437771362306950643021288634180","date":"2025-12-27T10:28:24+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"9441701688499779478411318021039952201","date":"2025-12-18T06:16:03+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-12-17T04:07:52+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-12-02T22:40:05+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-11-29T07:13:07+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-11-29T07:12:03+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-11-28T03:15:14+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"1dc52c92-1761-4cbe-be0f-00a714417a93","owner":[],"postedDate":"December 19th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":59861930,"name":"Physical sciences/Engineering"},{"id":59861931,"name":"Earth and environmental sciences/Environmental sciences"},{"id":59861932,"name":"Physical sciences/Materials science"},{"id":59861933,"name":"Earth and environmental sciences/Solid earth sciences"}],"tags":[],"updatedAt":"2026-05-11T09:10:56+00:00","versionOfRecord":[],"versionCreatedAt":"2025-12-19 05:41:44","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8226112","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8226112","identity":"rs-8226112","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}