Test Study On Granite Residual Soil Under Stress Paths

Granite residual soil is widely distributed in Fujian regions.It is a kind of residual soil formed after its parent rocks'being influenced by a series of physical and chemical weathering,with its specific engineering characteristics of'large porosity ratio,high compressibility and high strength".There is relatively few research on the physical and mechanical properties of granite residual soil,while the related geotechnical engineering problems has been a noticeable increase nowadays.Therefore,this paper takes the Fujian area of granite residual gravel cohesive soil as the research object,to carry out laboratory tests including conventional triaxial consolidated drained test and various stress path tests,comprehensively comparing and analyzing what influence may different soil and changes of its stress-strain curves.In addition,it has compared the difference between granite residual soil undisturbed sample and remolded one about their strength and deformation feature under different stress paths.Furthermore,the applicability of most common constitute model for granitic residual soil has been analyzed by making Duncan-Chang model and Cambridge model to do a stress-strain curves fit.The main work and results of this article is as follows:(1)The five types of tests,including triaxial consolidated drained shear test,K0-consolidation drained shear test,the lateral unloading K0-consolidation test,the lateral unloading axial loading K0-consolidation test and the biaxial unloading K0-consolidation test,were carried out,for the undisturbed samples and remolded samples of granite residual soil.The stress-strain curve of granite residual soil were studied under the different stress paths.The test results show that the stress-stain curves and the parameters of strength obviously different.In the biaxial unloading test,the granite residual soil presents strain softening type,and the stress-strain curve shows strain hardening under the other stress paths.In engineering practice,various working conditions should be considered in order to cope with the influence of soil strength and deformation on the project.(2)By comparing the difference between granite residual soil undisturbed sample and remolded one about their strength and deformation feature under different stress paths,it can be concluded the granite residual soil has strong structural features which leads to the fact that the strength of undisturbed sample is larger than that of the remolded sample under different stress paths.Whereas the tests' s result show the same characteristics of small difference in friction angle and large change in cohesive force under different stress paths.(3)The stress-strain relationship of granite residual soil is preliminarily discussed.According to the test date,the failure constants and initial tangent modulus were obtained in each test.Meanwhile,The relation curve of consolidation drained test of granite residual soil under different compaction degrees is fitted by Duncan-Chang model,and the corresponding model parameters are acquired.At the same time,based on the Cambrige model,the stress-strain curves of undisturbed samples and remolded samples are fitted.So we can draw some rule.Above all,Duncan-Chang model can better fit the stress-strain curve of granite residual soil under different compaction conditions in the triaxial consolidated drained shear test.And the Cambridge model of undisturbed sample and remolded sample of granite residual soil have better fitting effect in the the lateral unloading K0-consolidation test.Furthermore,the fitting effect of modified Cambridge model is better.