Experimental Study On The Strength Properties Of Sand-Clay Mixtures With Different Proportions

Qanat is an important way for people in Northwest China and the Middle East to get water.The implementation of China’s "One Belt One Road" strategy requires transportation first.The construction of high-speed rail in these areas will inevitably cross the Qanat region.Preliminary investigations found that with the increase of the overburden load,the Qanat will spall and collapse in the cave.If the relevant measures are not taken,the safety operation of the upper railway will be seriously threatened.According to geological survey data,it is learned that the foundation soils in the Qanat area are mostly unsaturated sand-clay mixtures.However,domestic and foreign research on the basic soil properties of unsaturated sand-clay mixtures is scarce and lacks systemicity.Therefore,it is urgent to carry out research on unsaturated sand-clay mixtures.Research on basic soil properties.This paper systematically carried out lab tests of sand-clay mixtures with different proportions under constant moisture content.On the basis of conventional tests,suction was introduced as a variable.The factors affecting the strength characteristics of sand-clay mixtures are clarified,and the mechanism of sand-clay mixtures being damaged under load was also revealed.The main research results are as follows:1)Through specific gravity test,liquid plastic limit test,maximum and minimum dry density test,the relevant parameters of sand-clay mixtures with different proportions were obtained,and the influence of sand content on the plasticity of the mixture was clear;2)The compaction test was carried out on mixtures of different proportions,revealing the compaction mechanism of sand-clay mixtures.A compaction test was done on mixtures of different proportions,and the relationship curve between the suction force of the sand-clay mixture and the moisture content was obtained.3)Through a large number of direct shear tests,The mechanism of action of the two variables of water content and sand content on the direct shear characteristics of sand-clay mixtures is clarified,and a new parameter δ was introduced to determine the dilatancy of sand-clay mixtures.At the same time,suction was introduced as a variable as the third axis,based on the Fredlund bivariate model formula,the influence of suction on the direct shear properties was explored,and the contribution of suction to the direct shear strength of sand-clay mixtures was clarified;4)Triaxial shear tests were carried out on sand-clay mixtures with different proportions of constant moisture content,and the influence of sand content on the triaxial shear strength of the mixture was explored,and the“optimal sand content” that maximizes the strength of the mixture was determined.Between 15% and 30%.The Duncan-Chang model was used to analyze the changes in the strength of the sand-clay mixture during the shearing process.Subsequently,the relevant characteristics of the sand-clay mixture in the shear process(including dilatancy and softening)were explained in the stress ratio-dilatancy plane,and the Bolton formula was used to explore the relationship between the sand content and the consolidation stress and the peak dilatancy angle.Finally,the suction axis was introduced,and the influence of suction on the triaxial shear strength and shear parameters was analyzed.