Study On Seepage,Mechanical Properties And Fracture Evolution Of Silty Mudstone Under Hygrothermal Action

Silty mudstone is a kind of expansive soft rock concentrated in Hunan,Guangdong and Guizhou Provinces which locate in the southern China.It has the characteristics of easy shrinkage and fracturing after water losing,as well as swelling and softening after water encountering.With the rapid development of infrastructure constructing in the southern region,a large number of silty mudstone engineering bodies are inevitably formed.The southern of China is the region with the subtropical monsoon climate,then the ambient temperature and humidity fluctuate frequently in time and space which will be easy to cause silty mudstone fracture problem,strength damage and large deformation,and create the crucial negative impact for the stability and safety of the engineering structure.Therefore,this paper combines the National Natural Science Foundation project "Study on the damage evolution and catastrophic mechanism of silty mudstone slope under the interaction of temperature and humidity(51578079)",uses indoor experiments,theoretical analysis and numerical simulation to understand the composition and basic physical properties of silty mudstone,analyzes the unsaturated seepage characteristies of silty mudstone and the influence of the different factors in detail,reveals the spatio-temporal evolution of silty mudstones fracture propagation under hygrothermal alternation.At the same time,study the mechanical properties evolution law of silty mudstones under hygrothennal action and fissures systematically,and invert mesoscopic parameters of silty mudstone by discrete element method based on this.The main researching contents and conclusions are as follows:(1)Reduce dispersion by using ultrasonic longitudinal wave velocity analysis to screen silty mudstone samples.Carry out component analysis to obtain the types and contents of minerals and chemical components of silty mudstones,conduct basic physical property tests to master the particle density,dry bulk density,porosity,water absorption,saturated water absorption,swelling and water-rock properties of silty mudstones,and analyze the relationship between water absorption,saturated water absorption,swelling,water-rock properties and porosity.(2)Using self-made mudstone environment control test box and unsaturated infiltration model,saturated-unsaturated one-dimensional seepage tests were carried out for silty mudstone under the influence of different factors.Analyze the unsaturated seepage law of silty mudstone and the influence of porosity,temperature,water cover height and seepage direetion on the unsaturated seepage law of silty mudstone.And then based on Gompertz curve model,a spatio-temporal prediction model of water content in unsaturated infiltration of silty mudstone is established.(3)The top surface of the self-made silty mudstone fracture propagation model was subjected to damp heat cycle,and the industrial CT scanning was used to obtain the CT images of the fractures at different positions under the variety hygrothermal cycles.The imaging technique was used to reconstruct the fracture 3D images,and the information of the fractured feature was extracted to analyze the spatiotemporal evolution of the fracture.(4)For silty mudstone samples treated by different methods of wet heat treatment,the longitudinal wave velocity and water content of ultrasonic wave were measured,and uniaxial compression and Brazilian splitting experiments were carried out.According to the experimental results,the variation of longitudinal wave velocity,water content and uniaxial mechanical properties of the silty mudstone under temperature action,humidity action and damp heat were analyzed,what is more the relationship between longitudinal wave velocity,water content and uniaxial strength of silty mudstone were analyzed.(5)Rock triaxial tests of complete silty mudstone under different confining pressures and loading rates were carred out.Rock triaxial tests of fissured silty mudstone samples under different confining pressures,different fissure dips and different fissure connectivity were carried out.Based on these experiments,the triaxial stress-strain curves of complete and fissured silty mudstone under different conditions were obtained.The effects of confining pressure and loading rate on triaxial strength of silty mudstone were analyzed.As the next step,the damage law of fissured silty mudstone under different confining pressure,different fissure inclination and different fissure connectivity is also analyzed.(6)Based on the discrete element method,the numerical model of triaxial loading test for silty mudstone was established.According to the results of triaxial loading test for silty mudstone,the meso-parameters of the numerical model for silty mudstone were inverted,which made the computational model better describe the mechanical behavior of silty mudstone under triaxial loading.What is more,the effects of loading rate and confining pressure on the meso-parameters of the numerical model were also analyzed.