Analysis Of Shear Properties Of Collapsible Red Sandstone Under Different Water Content

Rock,as the main component of the earth's lithosphere,is a solid aggregate with stable shape composed of one or more minerals,which has been widely used in human life and production.As a common easily disintegrating rock,red sandstone is widely distributed all over the country,so red sandstone layers are often encountered in actual engineering construction.Similarly,the red sandstone in the Lanzhou area belongs to the strongly weathered sandstone,which is easily disintegrated when it encounters water,which weakens the engineering properties,partially reduces or even completely loses the bearing capacity,resulting in slow construction and correspondingly prolonged construction period.In order to study the variation law of shear strength of red sandstone after encountering water,the red sandstone in Lanzhou area was taken as the research object.First,red sandstone samples with different water contents were prepared,and the direct shear test was carried out to analyze the relationship between the cohesion,internal friction angle and water content of red sandstone,and then to analyze the relationship between the shear strength and water content of red sandstone.In the research,the two concepts of cohesion change rate and internal friction angle change rate are innovatively proposed,and the influence law of water content on the shear strength of red sandstone is analyzed more deeply.Disintegrate and remake the samples that have completed the direct shear test,and carry out the direct shear test according to the soil mechanics sample method,and obtain the relationship between cohesion,internal friction angle and moisture content,and then obtain the shear resistance.The relationship between strength and moisture content.Similarly,the relationship between water content and shear strength was further analyzed by using the cohesion change rate and the internal friction angle change rate.Finally,the expression of the generalized roughness coefficient JRC is deduced,and the roughness coefficients of the red sandstone samples before and after disintegration are calculated respectively from the expression,and then the relationship between shear strength and water content is analyzed from the angle of roughness coefficient.Through research,it is found that before disintegration,when the moisture content of red sandstone samples is 5.918%,the cohesion is zero;when the moisture content is 2.880%,its influence rate on the shear strength of red sandstone samples reaches the maximum.After disintegration,when the moisture content of the red sandstone sample is 2.539%,the change rates of cohesion and the angle of internal friction are zero;when the moisture content is 6.242%,the change rates of the cohesion and the angle of internal friction of the sample reach the maximum value;when the moisture content is 14.020%,it can be considered that the change rate of the cohesion of the sample reaches the minimum value;when the moisture content is 18.745%,the change rate of the internal friction angle reaches the minimum value.When the moisture content of red sandstone samples is 1.078% and 19.016%,the cohesion is zero,and the generalized roughness coefficient is also zero,which also proves the correctness of the derived expression and the relationship between moisture content and shear resistance.It shows that the relationship between generalized roughness coefficient and shear strength is consistent with the relationship between c,? and shear strength.