Correlation Between Microstructure Characteristics And Mechanical Properties1 Of Carbonaceous Mudstone Coarse-grained Soil

Carbonaceous mudstone has unstable engineering mechanical properties such as easy disintegration,low strength and easy weathering in water.The macroscopic mechanical properties of carbonaceous mudstone are essentially caused by the rearrangement of its microstructure under the action of force and environmental factors.Therefore,it is extremely one-sided to describe the mechanical properties of soil solely from a macro perspective.Therefore,this paper studies the macroscopic mechanical variation law of carbonaceous mudstone coarse-grained soil from a micro perspective.Firstly,the influence of mesoscopic parameters on the macroscopic mechanical properties of carbonaceous mudstone coarsegrained soil was analyzed by using discrete element particle flow numerical simulation method.Secondly,based on the electron microscope scanning test and mercury injection test,the microstructure parameters were extracted by digital image processing technology,and the change rules of pores and particles under different working conditions were studied from the size and morphology of microscopic units.Finally,based on the experimental results,the multiple linear regression method and grey correlation method are used to establish the analysis model,and the influence order of the microstructure parameters on the shear strength index is obtained.The error between the measured value and the predicted value of the shear strength index is analyzed.The main conclusions are as follows:(1)The peak strength of numerical samples of carbonaceous mudstone coarse-grained soil increases with the increase of friction coefficient,and the increase rate of peak strength increases with the increase of confining pressure.When the friction coefficient increases from 0.4 to 0.6,the peak strength increases by 12.67%,16.1%and 21.7%respectively when the confining pressure is 60 kPa,120 kPa and 180 kPa.When the porosity increased from 0.25 to 0.35,the peak strength decreased by 36%,11%and 8%respectively when the confining pressure was 60 kPa,120 kPa and 180 kPa.(2)Most of the carbonaceous mudstone coarse-grained soil samples are pores in the range of 0.01μm～0.1μm and greater than 1μm,and the particle composition is mainly clay particles with particle size less than 1μm.With the increase of confining pressure,the particle orientation of carbonaceous mudstone soil samples increases,and the smaller the distribution dimension,the greater the particle orientation;in terms of morphology,the porosity and particle roundness of carbonaceous mudstone increased first and then decreased with the increase of confining pressure,and the fractal dimension decreased first and then increased.Under different confining pressures,the average abundances of particles and pores in the four graded soil samples were basically unchanged,which were between 0.46 and 0.52,and the shapes of particles and pores in the soil samples were flat.(3)Whether it is cohesion or internal friction angle,the shape of microstructure unit is the most influential factor,while the size of unit has little effect on the shear strength index.The prediction error between the predicted value of cohesion obtained by regression analysis and the measured value is large,which is 11%,9%and 5%,respectively.The prediction error of internal friction angle is small,which is 1%,2%and 9%,respectively.