Experimental Study On Engineering Characteristics Of Granite Residual Soil In Shenzhen

Granite residual soil is a regional special soil,which has unique engineering properties.Because the engineering characteristics of granite residual soil are difficult to control in engineering practice,the selection of its strength and deformation characteristic parameters has always been the focus of the majority of engineering circles and geotechnical mechanics researchers.In this paper,the granite residual soil in Shenzhen is taken as the research object,and the engineering characteristics and microstructure influence mechanism of granite residual soil in Shenzhen area are systematically studied by using the method of macro test and microstructure analysis.The research can provide theoretical guidance and technical support for the engineering protection and disaster mechanism research of this kind of soil enrichment area.The main research contents and achievements are as follows:(1)In the natural state,the granite residual soil in Shenzhen has high water content,which belongs to sandy cohesive soil or sandy cohesive soil.Because the soil is rich in Al2O3,Si O2,Fe2O3 and other cementation materials,it has micro structure,the connectivity and wrapping between particles are improved,and the soil has strong resistance to deformation.(2)Considering the influence of iron oxide content,water content and dry density,the disintegration test of compacted granite residual soil in Shenzhen was carried out.It is found that the water resistance of compacted granite residual soil is poor,the disintegration characteristics are mainly affected by the content of iron oxide,and the physical state has little effect on it.When comparing and selecting subgrade fillers,the weathering degree and physical state of soil should be considered comprehensively,and the reasonable selection should be made.(3)Taking the undisturbed and remolded granite residual soil as the research object,the damage degree of soil was simulated by applying different confining pressure to soil,and the triaxial consolidation undrained test was conducted to quantitatively analyze the influence of microstructure damage on the shear characteristics of soil.The results show that the stressstrain relationship of the original sample is mainly shear shrinkage and weak dilatation,which is the shear expansion failure;The whole remolding sample developed in strain hardening mode,which was manifested as shear shrinkage failure.The residual structure of granite soil has some structure because of the existence of the residual structure of parent rock and the structure of free iron oxide glue structure.The yield stress Py of structure is 128.5kpa by double logarithm method,and P < Py,the soil skeleton bears external load with the increase of consolidation pressure;When P > Py,the secondary structure of soil is produced due to the action of secondary carbonate and free oxide,and the consolidation pressure continues to increase,and the structural strength of soil gradually loses.The soil is loaded as the compaction process,and the structural form tends to remould the soil.(4)By introducing structural parameters related to "structural contribution rate",the change rule of "structural contribution rate" in undrained shear test is that the structural damage occurs before the peak strain,and the structure of undisturbed soil experiences the process from strengthening to gradual damage and then tends to be stable.The contribution rate of structure confirms the importance of attaching importance to structure in granite residual soil engineering.The engineering parameters are accurately evaluated by simulating different structural damage degrees,which provides basis for structural design and foundation reinforcement in granite residual soil rich areas.(5)The pore distribution and microstructure characteristics of granite residual soil under different consolidation conditions were analyzed by mercury intrusion and scanning electron microscopy,and the response law of pore distribution and microstructure during deformation was explored.It is found that there is a strong correlation between the deformation characteristics of granite residual soil and its microstructure.In the process of compression,pores and particles affect the compressibility in different ways,and the mechanism of deformation microstructure is different under different stress states.