Research On The Water-Weakening Microstructure Damage Mechanism Of Carbonaceous Shale

The new excavation of the carbonaceous shale slope is exposed to the air,with the elapse of time and long-term water erosion,mechanical properties of rock mass will gradually deteriorate,resulting in adverse geological disasters.Therefore,it is of great significance to study the water softening micro structural damage mechanism of carbonaceous shale.Research result can provide reference value to failure mechanism and stability of the carbonaceous shale slope.The thesis takes the carbonaceous shale from the reconstruction and expansion project of Guangxi Liuzhou to Nanning Highway slope as the research object.Firstly,a series of laboratory tests carried out to analyze the changes of carbonaceous shale’ water softening process qualitatively and quantitatively;then the different soaking time of carbonaceous shale’s triaxial compression test is simulated and analyzed by PFC2D.The main research results are as followed:(1)X-ray energy spectrum analysis,X-ray diffraction,SEM,nitrogen adsorption measurements were used to analyze the different soaking time of carbonaceous shale.The results show that:when soaked in distilled water for 30 days the mineral composition of carbonaceous shale produce the illite montmorillonite;carbonaceous shale’s main supportive framework is composed of stacked lamellar particles,presenting orderly,dense surface to surface contact form,rock pore size distribution is in the range of 3-28nm,which the proportion of 3-7nm is higher.With the soaking time increased,the lamellar particles are gradually eroded,surface to surface contact forms gradually become the point surface contact form,the micro structure is destroyed gradually,pore diameter becomes smaller but porosity increased.After soaking 30 days later,pore size distribution is in the range of 1～28nm,which the proportion of 1～7nm is higher.(2)Two different conditions of disintegration test and triaxial compression test of different soaking time carried out in carbonaceous shale.The test results analyze its disintegration rule,and the change of carbonaceous shale after water absorption depends on the time,along with the elapse of time it finally become stable.In addition,the carbonaceous shale samples triaxial compression peak intensity is related to the sample’soaking time as well as the confining pressure state of the test:with the same soaking time,the higher of confining pressure,the higher of the peak strength;with the same confining pressure conditions,the longer of the soaking time,the lower of the peak strength.(3)Using PFC2D software to calibrate carbonaceous shale triaxial compression test under two soaking conditions(natural state,after soaking 48h),the micro parameters of carbonaceous shale mechanical characteristics can be obtained.Analyzing the stress-strain curves,strength characteristics and micro fracture failure mode could better reflect the destruction rule of carbonaceous shale’s three-dimensional stress state after water softening,the consistency is also verified by numerical simulation and laboratory test results.