Prediction of internal friction angle of Q2-Q3 mixed loess as affected by weight ratio based on modified adhesion theory

Abstract Due to geography and construction technique considerations, Q2-Q3 mixed loess has been used for some loess high-fill slopes in Yan'an, China. The predicting formula for weight ratio and internal friction angle of Q2-Q3 mixed loess with optimal water content is essential for determining the stability of these slopes. This study assumed that the Q2-Q3 mixed loess was a homogeneous, single-species equivalent loess to simplify the derivation of the equation without impacting the research outcomes. This study utilized the stress synthesis law to present a hypothetical stress formula. Two limit cases were considered to determine the formula parameters. Then, the study derived the sliding conditions of equivalent loess soil particles according to the law of bound water. Finally, the study established a formula for predicting the internal friction angle of Q2-Q3 mixed loess based on the definition of the friction factor and the relationship between the water content and the bound water thickness. The results indicate that the predicted internal friction angle of Q2-Q3 mixed loess has minor relative errors, which confirms the accuracy of the formulas developed in this paper. Additionally, as the weight ratio increased, the internal friction angle of the Q2-Q3 mixed loess increased.