The Effect Of Clay Content On The Mechanical Properties Of Silt Soil In Zhengzhou Area And The Study Of Its Micro-mechanism

Due to long-term exposure to the natural environment,the performance of the site is very easy to deteriorate,the shear resistance is poor,and it is easy to produce cracks,erosion,collapse and other diseases.The soil sites in the Zhengzhou are mainly composed of silt or silty sand(clay content < 10%),and the soil site diseases are concentrated in the shallow part.The method of adding clay conforms to the principles of "using ancient materials" and "repairing the old as the old" in the protection of soil sites.It is widely used in the preventive protection of soil sites,but different from pure sand or clay,the existence of fine particles,especially clay,makes the shear behavior of fine-grained sand(such as silty sand,etc.)very complex,and the mechanism of clay action is not clear.Therefore,it is necessary to carry out the research on the influence of clay content on the mechanical properties of soil sites in the Central Plains.In this paper,the silt of Yuanling ancient city,a typical earth site in Zhengzhou,is taken as the research object,and the shallow destruction of earth site is taken as the research background.Firstly,based on the basic physical property test,the particle grading characteristics and liquid plastic limit index under 0,5,10,15,20,25% clay content are studied;Secondly,the effects of clay content(5-25%)and stress conditions(1,5,10,25,50,100,200,400kPa)on the shear mechanical properties of silty sand at the site were studied by direct shear and triaxial shear tests.The differences of mechanical parameters under low stress(1-25kPa)and high stress(50-400kPa)were emphatically analyzed.Finally,the content of clay was explored by SEM micro test.The research can provide the basis for the preventive protection of earth sites.The main research contents and achievements are as follows:(1)The results of direct shear and triaxial shear tests show that the shear strength of the low stress point obtained by the standard fitting formula is far greater than the measured value,which is dangerous when used for the stability analysis of soil sites.Therefore,the low stress condition must be included in the site soil strength test,in order to obtain the true strength index value in accordance with the shallow failure state of soil sites.(2)Under the condition of high and low stress,the cohesion value of direct shear test is greater than that of triaxial shear test,with a difference of 7-10kPa;under the condition of low stress,the internal friction angle value of direct shear test is smaller than that of triaxial shear test,with a difference of 6-11°,while under the condition of high stress,the internal friction angle value of both is similar.(3)Direct shear test and triaxial shear test show that under the same stress and dry density conditions,the increase of strength of silty sand with clay is mainly due to the increase of cohesion.With the increase of clay content,the cohesion increases in a two-stage broken line(on the whole,the inflection point of the curve is at 10% of the clay content),and the difference of cohesion between high and low stress sections tends to decrease gradually.When the clay content is more than 10%,the silty sand of the site undergoes the transformation from "similar sand" to "similar clay",and the shear strength of the soil sample is significantly improved.When the clay fully covers the sand,the increase of the clay content will not cause the change of the cohesion value.(4)In direct shear and triaxial shear tests,when the dry density is the same,with the increase of clay content,the absolute growth rate of shear strength in low stress section is higher than that in high stress section;the increase of dry density under different stress conditions leads to different increase of shear strength,so the appropriate dry density should be selected for different stress conditions.(5)In view of the clay content of earth sites in Zhengzhou is less than 10%,in the protection of earth sites,we should strengthen the contrast between low stress and high stress,and obtain reasonable strength parameters according to the actual protection conditions.In addition,in the restoration project of earth sites,the sampling work of obtaining the bulk strength parameters is "contrary" to the principle of "minimum intervention" and other cultural relics protection principles,while the soil properties of some earth sites in the ZhengzhouTherefore,the strength index obtained from the test can provide a reference for determining the mechanical parameters of the body.