Study On The Relationship Between Microstructure And Shear Strength Of Red Mudstone And Its Remolded Soil

This paper mainly studies the microstructure and shear strength of mudstone remodeling in Cangxi Formation and Guankou Formation.Among all that,the basic physical and mechanical properties and microstructure characteristics of red mudstone are studied by geotechnical test,X-ray Diffraction,SEM,IPP and ArcGIS software.What's more,the effects of moisture content,dry density and sample preparation methods on shear strength parameters are investigated.Meanwhile,qualitative and quantitative methods are used to study the relationship between the shear strength and the microstructural characteristics which contain roundness,fractal dimension,particle morphology,contact relationship,arrangement and combination characteristic,particle area ratio,pore type and porosity,etc.Besides,the differences between the original and reconstructed samples are analyzed.And the main results are as follows:1.The lithology characteristics of the red beds around Longquan Mountain are:The Cretaceous sandstone accounted for 62.17%,the Guankou Formation is dominated by mudstone(about 84.5%),the other rock groups are mainly sandstone;At the same time,the Jurassic sandstone accounts for 57.47%,and the Lianhuakou Formation is dominated by sandstone(about 87%),the proportion of sandstone mudstones in other rock groups is relatively average.2.The cohesion c of the remolded samples in both the Cangxi Formation and the Guankou Formation increase at the first time and then decrease with the increase of water content,and the characteristic water content is 20.1% and 19.43%.Meanwhile,the internal friction angle ? of the Cangxi Formation generally fluctuated,while the internal friction angle ? of the irrigation group fluctuated between 21° and 27.5°.The higher the dry density,the larger the cohesion c,and the dry density has a significant effect on the cohesion c of the low water content(w<24%),however,the dry density has little effect on the internal friction angle ?.The sample preparation method mainly affects the cohesion c at low moisture content,when the water content of the Cangxi Formation and the Guankou Formation are 10.1%-18% and 12%-19%,respectively,the cohesion c of the consolidated sample is significantly lower than the compacted sample.3.The shear strength of the remolded samples of Cangxi Formation increases with the increase of the proportion of particles,and decreases with the increase of porosity;Besides,the shear strength parameters are negatively correlated with porosity and positively correlated with particle roundness.The shear strength of the remolded specimens in the Guankou Formation increased with the increase of the ratio of particles with an equivalent diameter greater than 5?m;And the cohesion c is positively correlated with the porosity of the pores and the ratio of particles with an equivalent diameter greater than 5?m;While the internal friction angle ? and pore fractal dimensions are negatively correlated and positively correlated with particle roundness.In addition,the structural differences between undisturbed and reconstructed samples are mainly reflected in the morphology of particles,contact relationship,alignment and orientation,cementation,pore characteristics and shear strength variation.Besides,with the same water content,the cohesion c of the original sample is obviously greater than that of the remodeled sample,but the internal friction angle ? is slightly smaller than that of the remolded sample.4.The moderately inclined rock landslides in the eastern Sichuan Basin are mostly developed in the Cretaceous Cangxi Formation and the Jurassic Penglai Formation,accounting for 71.4% of the total statistical data.Moreover,landslide sliding is mainly caused by the softening of granular skeleton of mudstone under the action of water-soil,the failure of cementing material flow and the destruction of the whole structure,resulting in the reduction of shear strength.Besides,the hazard value of landslide moisture content can be determined by the characteristic value of indoor direct shear test of remolded samples.