Experimental Study On Shear Strength Parameters Of Freeze-thaw Interface Of Silty Clay

In order to explore the mechanism of the shallow landslide of the channel slope in the seasonally frozen area during the spring thawing period,the shear strength of the frozen thawed interface of silty clay in the seasonally frozen area was studied.According to the needs of the test,a direct shear apparatus for geotechnical engineering is developed,and the improvement of the self-made direct shear apparatus compared with the traditional direct shear apparatus is analyzed.In order to study the shear strength parameters of soil at the freeze-thaw interface,the traditional direct shear apparatus is improved,including sample size,selection of shear test,determination of the freeze-thaw interface and setting of temperature control mode.Based on the test results,the shear strength of remolded silty clay samples,the shear strength of the frozen thawed interface of silty clay and the water migration of the frozen thawed samples are studied.The change of shear strength parameters of the soil at the frozen thawed interface is analyzed.The relationship between the change of shear strength parameters and the change of water at the interface is established.The change of shear strength of the soil at the freeze-thaw interface is discussed cause and mechanism.The corresponding finite element model is established for the shear test of the freeze-thaw interface.The rationality of the finite element model is verified by comparing the calculation results of the finite element software with the results of the physical test,and the micro understanding of the shear test is deepened.The main achievements are as follows:(1)According to the requirements of the research content,the traditional direct shear apparatus is improved.According to the needs of the test,the reasonable structure of the apparatus and the size of the shear box have been designed.The inner diameter of the shear box is 10 cm,10cm in height,matched with the size of the sample,so that the sample in the process of putting into the shear box to avoid new disturbance;the direct shear instrument is equipped with the corresponding data acquisition system,so that the data acquisition is more accurate and convenient.(2)The shear strength parameters of remolded silty clay under different initial water content,internal friction angle?and cohesion c,were studied.For the remolded soil samples with dry density of 1.55 g/cm~3 and moisture content of 18%,20%,22%and 24%,the law is that the internal friction angle?and cohesion c decrease with the increase of moisture content.The water content increased from 18%to 24%,the cohesion of each sample decreased by 21.98%,35.21%and 42.56%,and the internal friction angle of each sample decreased by 13.82%,24.51%and48.58%,respectively.(3)The shear strength parameters cohesion c and internal friction angle?of remolded silty clay at the freeze-thaw interface were studied.When the specimen melts to the designated position,take out the specimen being melted for quick shear test.When the dry density is 1.55 g/cm~3 and the initial moisture content is 18%,20%,22%and 24%,the cohesion of the remolded soil decreases with the increase of the initial moisture content.The initial moisture content increased from 18%to 24%,and the cohesion of each sample decreased by 1.12%,0.51%,4.49%and 10.79%respectively.With the increase of initial moisture content,the internal friction angle decreases slightly,but the degree of decrease is not obvious.Among them,the sample with 22%water content decreased by 3.28%.(4)The law of water redistribution of samples with different initial moisture content during freeze-thaw was studied.The moisture migration of four groups of samples with dry density of1.55g/cm~3 and initial moisture content of 18%,20%,22%and 24%has the same trend when they melt to 5 cm,and the phenomenon of water accumulation appears above the interface of freeze-thaw,and the degree of change increases with the increase of initial moisture content.At the height of 4.5 cm,the initial moisture content of 18%,20%,22%and 24%increased by 0.22%,0.42%,0.81%and 1.13%respectively.(5)The cohesive force of soil at the interface is very sensitive to the change of water content,which shows that the cohesive force decreases with the increase of water content,and the larger the increase of water content,the greater the reduction of cohesive force.The internal friction angle of soil at the freeze-thaw interface is less affected by the change of water content at the interface,but when the increase of water content at the interface gradually increases,the internal friction angle decreases.(6)Through the finite element analysis software,the finite element model of the interface shear test of freeze-thaw is established,and compared with the results of the physical test.The numerical analysis curve under each normal stress,its trend is more consistent with the stress-strain curve of the physical test,and the greater the normal stress,the smaller the difference between the two.It shows that the finite element model can reflect the constitutive relationship of the soil at the shear plane in the physical test,and the finite element model established has certain rationality and reliability,which can provide a numerical reference for the shear test of the freeze-thaw interface.