Experimental Study On The Shear Strength Of Fully Weathered Mudstone In Seasonal Permafrost Areas

Seasonal permafrost is very widespread in China,occupying about half of the total land area.The soil properties of seasonally frozen soils,especially the shear strength of soils,are also affected by seasonal temperature changes,which in turn have an impact on overwintering works.In this paper,the shear strength of fully weathered mudstone and saturated fully weathered mudstone at different freezing temperatures and pressures were analysed according to the results of the indoor triaxial tests,taking the fully weathered mudstone in the typical monsoon freezing area of Changchun as an example,and the results were applied to the numerical simulation and analysis of overwintering foundation works.The main research contents and results include:1.Considering that most of the undisturbed samples are in an unsaturated state,it is necessary to determine the SWCC curve of the completely weathered mudstone in the area in advance to provide data support for subsequent triaxial tests.Based on the VG model,the measured soil water characteristic curve is fitted to obtain a high-precision conversion formula for matrix suction and volumetric moisture content.2.Through indoor triaxial test,the variation trend of shear strength parameters of fully weathered mudstone under different temperature and confining pressure in seasonal frozen area is analyzed,the factors affecting analysis of the variation in cohesion and internal angle of friction of fully weathering claystone,and the difference in shearing parameters of fully weathering claystone with two different saturations is compared and analyzed.Shear strength was found to be significantly influenced by temperature variation.When temperature drops,significant increase in soil shear strength.When the temperature decreases from 20 °C to-20 °C,the cohesion of fully weathered mudstone increases continuously,and the increase of unsaturated mudstone is significantly higher than that of saturated mudstone,and the internal friction angle increases first and then decreases.3.The soil parameters obtained through the test are applied to the numerical simulation study of overwintering foundation pit engineering problems,and the influence of the change of shear strength parameters on the strength and deformation of the foundation pit engineering under different temperatures is analysed.The simulation results show that as the temperature decreases,the soil of the foundation pit becomes frosty and swollen,and there is a significant increase in the value of pit bottom elevation,horizontal displacement of supporting piles and soil pressure on the side of piles;the soil shear strength parameters that change with temperature are chosen for the numerical simulation analysis of overwintering engineering,and the simulation analysis results are more accurate and more in line with the engineering reality.