Experimental Study On Clay Migration-Agglomeration Process Of Granite Binary Structure Slope Under Seepage Action

Granite is widely distributed in Fujian and shows obvious uneven weathering phenomenon.Under the long-term rainfall leaching environment,the deep granite weathering crust will produce strong internal erosion.When the fine clay particles in the upper weathered soil move to the differential weathering interface in the large pore coarse-grained soil overhead structure,it will easily produce clay particles gathering and form low-strength viscous layer.It has an important influence on the failure mode and stability of granite binary structure slopes.This paper focuses on the migration-aggregation phenomenon of clay particles in granite dual structure slopes.Through engineering geological investigation,indoor geotechnical test and physical model test,the characteristics and laws of clay particles migration and movement in weathered granite crusts are found,the formation process and evolution mechanism of the weak zone of the granite differential weathering interface are reappeared,and the mechanism of triggering the deformation and failure of granite binary structure slope under the conditions of excavation unloading,top loading and rainfall infiltration is revealed.The main research work and achievements are as follows:(1)The investigation and analysis of the weathering and erosion characteristics of granite in Fujian Province found that obvious clay migration-agglomeration phenomenon is widespread in the granite binary structure slope,which is mainly reflected in the clay migration phenomenon of the granite weathering crust and the remaining joints of the granite weathering crust,the clay migration-agglomeration phenomenon of the channel and the clay migration-agglomeration phenomenon of the concealed sliding zone of the weathered granite crust.The formation of a sudden change in permeability and a weak zone that induces the deformation and failure of the slope have an important impact on the stability of the dual structure slope.(2)An experimental study on the migration process of clay particles in weathered granite soil was carried out.It is found that the formation of clay migration is affected by the factors such as particle size distribution and porosity of weathered soil.The soil sample with large proportion of gravel and sand has obvious macropore structure,which is easier to form a connected dominant seepage channel in the process of groundwater seepage.As a result,the migration of fine clay particles is active,which further aggravates the coarsening of granite weathered soil particles and the destruction of soil structure,and increases the intensity of soil erosion.(3)A model experiment on the migration-agglomeration process of clay particles in granite weathering crust under rainfall infiltration conditions was conducted to verify the process and phenomenon of clay particle agglomeration at the differential weathering interface to form a weak zone.It is found that in the loose and porous granite weathering soil,the migration of finer particles with infiltration water in the coarse pore space to the differential weathering interface slows down significantly and forms a low-strength mud film by adhering to the differential weathering interface,which is magnified to the engineering scale as a weak zone with high content of cohesive particles and low strength,controlling the deformation and damage mode and stability of the binary structure slope.(4)A model test on the evolution of granite binary structure slope instability was conducted to study the effects of three conditions such as excavation unloading,slope top loading and rainfall infiltration on the evolution of granite binary structure slope instability.It is found that the slope is prone to slope erosion damage under the condition of rainfall adjacent to the top line of the slope,is prone to folded line landslide along the bedrock surface under the condition of rainfall far from the top line of the slope,and is prone to local slope landslide damage under the condition of rainfall and loading on the top of the slope.