A Study On Physical And Mechanical Properties Of Granite Residual Soil

Granite residual soil are widely distributed in southeast region in our country,which is the product of the combination of the certain geography,climate and geological environment,so it is a regional special soil.With the rapid development of China's economy,granite residual soil has gradually become the common carrier and geotechnical material in construction.We study the basic physical properties and triaxial test on the granite residual soil in Bozhi city of Guangdong province to provide reference and basis for related engineering application.The basic physical properties test includes the limit moisture content test,the compaction test,the mineral composition analysis test,the particle analysis test.Meanwhile,we also do the analysis of XRD test.According to the analysis of the experimental results,the natural moisture content of the granite residual soil is 21.45%,the liquid limit is 18.21,and the plastic limit is-0.337,so the soil is in a hard state.The composition of soil samples is mainly Kaolinite and Quartz,while other mineral components are less.And we can found that it belongs to the residual sand viscous soil based on the existing classification methods.Triaxial test includes consolidated drained test and consolidated-undrained test of the granite residual soil under different confining pressure and different particle grading.We can obtain a series of corresponding curves which includes the relation curve of the partial stress q-axial strain?₁,the relation curve of the volumetric strain?_v-axial strain?₁ and so on.We can conclude that the stress and strain relations of all specimens are non-linear strain hardening,and the peak stress of the sample increases with the increase of confining pressure;In consolidation-drainage test,the volume of original grading sample decrease and then increase in the process of shearing when the confining pressure is relatively small,while the volume of original grading sample is decreaseing when the confining pressure is relatively large.In the case of grading change?after adding sand?,the volume of samples are always decreasing in the shear process.With the increase of sand content,the cohesion c and the friction angle?increase with the increase of sand content.At the same time,it can be seen that the influence of grading on cohesion is larger than the influence on friction angle.In consolidated-undrained tests,the pore pressure of all specimens remain stable when axial strain reach to 5%.At the same time,the stable value of pore pressure increases with the increase of confining pressure.We obtain some relation curves through the consolidated-drained test and the consolidated-undrained test with different gradation under different confining pressures.We can conclude that the parameters of Duncan-Chang model vary with the different grading by analysising the results.In the consolidated-drainage test,the initial deformation modulus increases greatly when the confining pressure is smaller,while it increase slowly when the confining pressure is larger.The parameters of Duncan-Chang model show the trend whether it is in consolidated-drained or consolidated-undrained:except for n and R_f,the parameter of k are significantly affected by gradation.