Engineering Geological Characteristics Of Granite Residual Soil

Granite residual soil is widely distributed in the Fujian coastal areas.Due to the special engineering geological characteristics and its strong regional characteristics of granite residual soil,the study of its physical and mechanical characteristics is not sufficiently,which makes the geotechnical engineering problems frequently occur in granite residual soil area.The granite gravel clay soil obtained from a slope in Fuzhou was taken as the research object.Through the laboratory tests such as material composition analysis,compressibility test,collapsibility test,disintegration test and stress path triaxial test,the engineering geological characteristics of granite residual soil are studied,and its essential reason is discussed.The main work and research results of this paper are as follows:(1)Analysis of material composition of granite residual soil.The results show that the clay minerals in the residual granite are dominated by kaolinite and illite,lack of montmorillonite,and its development process has undergone obvious processes of aluminum enrichment and salt leaching.The content of soluble salts and organic matter in granite residual soil is less,meantime it has smaller cation exchange capacity and smaller specific surface area.At the same time,granite residual soil has a large number of micro-pores and small pores,indicating that the particles within the granular particles arranged more closely,and the cementation is stronger.(2)Study on structural effects on compressive and collapsibility of granite residual soil.The results show that the granite residual soil belongs to the medium compressibility soil and collapsible is not obvious.The compression coefficient of the undisturbed sample is smaller than that of the remodeled sample.However,the compression characteristics of the two samples tend to be consistent with the increase of load.The effect of the drying-wetting cycle has a greater impact on the structure of granite residual soil,which makes it more prone to compression deformation,and the more cycles,the more obvious the impact.However,due to the small amount of collapsibility,the influence of remodeling and drying wetting cycle on the collapsibility is not obvious.(3)Effect of pH value and soaking time on the disintegration characteristics of granite residual soil.The results showed that the amount of disintegration of granite residual soil increased with the soaking time under the same pH conditions.The longer the soaking time,the larger the increase.When soaking time is certain,the disintegration amount of granite residual soil increases with the decreasing of pH,and the stronger the acidity,the greater the increase.(4)Triaxial test of stress-path of granite residual soil.The results show that the stress-strain curves of increasing P and equivalent P triaxial tests are strain hardening type,while the stress strain curve of decreasing P triaxial tests is strain softening type,and the failure modes are both drum-shaped failure.The undisturbed samples of granite residual soil showed stronger structural characteristics than the remolded samples except for the equivalent P stress path.The strength index of equivalent p and decreasing p triaxial tests compared with the strength index of increasing p triaxial test:the cohesion c' of undisturbed sample has a certain reduction,while the internal friction angle ?' rises to a certain extent,and the change of the index is more obvious under equivalent P triaxial tests.The corresponding shear strength index of the remodeling sample is all increased,of which the index change of decreasing p relative to increasing p is smaller.