Research On Slope Stability Of The Quaternary Thick Alluvium Of Yanshan Iron Mine Under Repeated Wetting And Drying Cycles

Most of the soil in slope engineering is in the non-saturation. Under the effects of natural conditions, long-term drying evaporation, rainfall infiltration or other factors, deformation, strength and other physical or mechanical property of soil is usually changed. Landslides or other natural disasters would be induced, which greatly threat life and property security.In order to grasp the law between wet or dry cycles and unsaturated soil slope stability to evaluate slope stability of Quaternary alluvium, an in-depth analysis and research to changes in the characteristics of unsaturated soil strength under repeated wetting-drying cycles was carried out based on experiments and field test.Through on-site sampling, the variation law of shear strength was studied under the condition that the internal structure and characteristics of the soil is the same as direct shear test. Finally, the limit equilibrium analysis code was applied to evaluate the slope stability and ultimately make reasonable suggestions.The main research work and results are summarized as follows:1) Taking Yanshan Iron Quaternary alluvial silt and silty clay for repeated wet and dry cycles direct shear tests, the variation of shear strength parameters were analyzed. It was found that undisturbed soil shear strength parameters state on a downward trend in a number of wet and dry cycles and stabilized after five wet and dry cycles.2) Through the field situ constant head permeability test, the influencing depth of repeated wetting-drying cycles was below the surface of 4-5m. Under long term water-saturated conditions, the top soil was controlled by cohesion and friction angle instead of static shear yield strength, which will cause the increase likelihood of debris flow.3) Taking the typical profile of Yanshan iron mine eastern slope for example, a two-dimensional numerical model was established considering the silt, silty clay affected by wet and dry cycles and other factors affecting slope stability characteristics. The safety factors of the slope stability under different conditions through GEO-Slope software were obtained to evaluate the slope stability. Under the influence of repeated wet and dry cycles, slope safety factor decreased and the stability became worse. The Quaternary slope stability could not assured by single curtain grouting. After applying slope revetment and underground water prevention measures such as three-dimensional water control measures, safety coefficients were 1.204(Section 5-5),1.238(Section 6-6), which achieved reserve requirements.4) Measures were raised to control slope water and ecological slope protection, such as platform cut drainage, slope ecological protection, underground water shutoff curtain, drain hole on bedrock, or water control recommendations. It would deepen the understanding of nature, general knowledge of grouting process high-pressure grouting and diaphragm walls curtain grouting techniques.