Effects Of Clay Mineral Content On The Physical And Mechanical Properties Of The Granite Residual Soil

Granitoid is one of the most widespread igneous rocks.Under the effects of physical weathering and chemical weathering,granite residual soils formed in various areas have the differences in soil layer thickness,clay content and mineral composition.Therefore,the regional differences in geological and mechanical characteristics of granite residual soils are often observed.In this study,the granite residual soil in Fuzhou,China was selected as the original soil,and granite residual soil samples with different contents of clay were compounded by adding different amounts of kaolinite and illite.A series of limit moisture content test,permeability test,one-dimensional compression test,conventional triaxial consolidation-undrained test and triaxial compression test of decompression are further carried out for the prepared soil samples,which provided reasonable solutions to related engineering problems.Some research works and the main conclusions can be drawn as follows:(1)We experimentally analyzed the specific gravity,particle size,and limit moisture content of the granite residual soil with different clay contents.The changes of the specific gravity,particle size distribution and limit moisture content of the granite residual soil under the influence of the clay content was also discussed.The results show that the specific gravity of granite residual soil increases with the increase in clay content.The higher the clay content,the smoother the cumulative curve of granite residual soil particle size.Both kaolin and illite clay minerals would decrease the liquid limit and plastic limit of granite residual soil and increase the plasticity index.However,the effect of content of kaolin on granite residual soil was less sensitive than that of illite.(2)The permeability test and one-dimensional compression test were conducted for the granite residual soil with different clay content.The effect of different clay contents on the permeability coefficient and soil compression parameters of granite residual soil was also investigated.The experimental results show that increasing the content of the two clay minerals,the permeability coefficients of the granite residual soil both nonlinearly decrease.The soil compressibility index and compressibility coefficient increases with an increase in clay content,and the compression modulus decreases with increasing clay content.(3)The undrained shear strength characteristics of granite residual soil were further examined through the conventional triaxial compression tests on granite residual soil with different clay contents.The characteristics of the triaxial compression stress-strain relationship,Mohr failure envelope and stress-path of granite residual soil composed of kaolin or illite clay minerals were studied.It is found that the shear strength of granite residual soil varies with the content of clay particles.The internal friction angle decreases with the increase in clay content.Cohesion increases with increasing clay content.The critical state stress ratio decreases with an increase in clay content.(4)The triaxial decompression test was carried out to explore the compression characteristics of granite residual soil.The results indicate that the stress-strain relationship of the granite residual soil obtained from the conventional triaxial compression test is similar with that from triaxial decompression test.Most of them appeared to be strain-hardening.However,the accompanied Mohr-circle characteristics and the stress path were significantly different with those from conventional triaxial compression test.The obtained varying trends of soil shear strength,internal friction angle,cohesion,and critical state stress ratio with clay content were is similar to those from conventional triaxial compression tests.Finally,it summarized the main content of this paper,pointed out the limitations of this paper,and prospected the suggestions for future scientific research.