Damage Evolution Characteristics And The Accumulation Damage Model Of Sandstone Under Dry-Wet Cycle

There are three big roles of water on rock mass: chemistry,physics and mechanics,water rock interaction problems of Geotechnical Engineering is one of the topics of basic research,and the dry wet cycling process is an important part of water rock interaction.In this paper,combined with the National Natural Science Fund Project "the cycle of dry and wet rock under macro and meso damage model of cumulative"(project number: 51308567),on the basis of referencing the results of previous studies,using laboratory drying-saturated-drying process to simulate the Three Gorge in the riparian zone of typical rocks affected by reservoir water level repeated movements,through indoor experiment,combining theoretical analysis and numerical simulation methods,the deterioration mechanism of different rocks under wet and dry cycle accumulation were studied deeply.The research on bank slope stability prediction,rock life,provide theoretical basis for the disaster prevention and mitigation measures.The main contents and research conclusions of this paper were as follows:(1)Based on Hertz contact theory,the theoretical mechanism of the prediction of rock strength nondestructive micro damage comprehensive screening method,established the multiple regression model of rock compressive strength and density,longitudinal wave velocity,rebound value,higher accuracy of empirical formula with the previous prediction of strength;scale effect equation of sandstone "lossless micro damage" different moisture detection parameters through experiment,macro parameters of sandstone and scale effects of meso parameters restricts and affects each other,"lossless micro damage" comprehensive screening method can be used as reference for mechanical testing,the original rock group,with the same lithology,the same size,the same moisture content rock.(2)The experiment selects the diameter of D=50mm,height of the sandstone were 25 mm,50mm,100 mm,Its 0,1,3,6,10 times of "drying-saturated-drying" effect,the three sizes in the cycle under the " saturation " state of the water content and permeability analysis of the relationship,saturated water absorption rate and initial permeability and the number of cycles.(3)The whole section CT scanning experiments were conducted on three different sizes of sandstone under Dry-Wet Cycle,the CT image pseudo color by Matlab software to enhance the analysis and processing,the best threshold value of the edge detection and fractal characteristics,obtained under the different cycles of rock skeleton not damaged area ratio,the initial defects(microcracks and pores)the fractal dimension and area ratio of CT images(fractal dimension and the number of cycles of n,the moisture content of the linear correlation);Mean CT value defined by damage variable with the increase of N,the nonlinear accumulation of different sizes,different sandstone accumulation coefficient(h=50mm coefficient),two samples h=25mm and h=100mm(the ratio of length to width are 2)the micro structures are similar and can be classified as a class analysis.(4)The sandstone wetting drying test design of the "dry" and "saturated" state of split test,uniaxial compression test,three axial compression test,cyclic loading and unloading test,and the different stages in the process of mechanical energy conversion is analyzed,various mechanical parameters of sandstone varies with the n the "saturated" state of the samples the variation is "dry" condition is more obvious,namely "saturated" state "dry" sandstone mechanical properties of the rock was partially recovered;mechanical parameters of rock affected of the strength is not a performance under Dry-Wet Cycle,sensitivity of rock resistance to water tension is greater than the compressive properties.(5)Rock material strain hardening and softening behavior in the Peak District,through the indoor mechanical test results of sandstone under Dry-Wet Cycles,the pre peak of the modified Duncan-Chang model and verified its uniqueness,the peak maximum principal strain softening as parameters,based on the M-C criterion of rock strain softening model is deduced the sandstone and Dry-Wet Cycles of nonlinear elastic plastic constitutive model,the model parameters is given;Based on the theory of damage mechanics,respectively to the energy index defined damage variable of rock elastic stage and plastic stage,given without considering Dry-Wet Cycle of initial damage and damage evolution equations of different initial damage state of sandstone under consideration.(6)Based on the finite difference theory,deduced the finite difference nonlinear elasto plastic constitutive model of sandstone in the form of expression,and combined with the two software development platform FLAC3 D good,achieved two times the development of different condition of sandstone under Dry-Wet Cycle under elastoplastic damage constitutive model using VC++ program,the dynamic link this model shows the simulation calculation program;using this model and the experimental results(uniaxial compression,three axial compression),they are close to two times the development of this model proves the correctness and rationality of the calculation program;and through the establishment of a simple slope model of case analysis,to develop two times the constitutive model and the Mohr-Columb model were compared.