Research On Mechanical Properties And Damage Constitutive Model Of Soft And Hard Interbedded Rock Mass

Layered rock mass is a common type of rock mass in nature.Compared with single rock,it has significant characteristics such as heterogeneity and anisotropy,and its mechanical properties are more complex.At present,there are relatively few studies on layered rock mass,and the theory is still immature.Therefore,it is of great significance to study the mechanical properties and damage evolution law of soft and hard interbedded rock mass for evaluating the stability of rock mass engineering and guiding engineering design.This paper mainly adopts the method of combining laboratory test and theoretical analysis,using similar materials to prepare soft and hard interbedded rock mass,analyzes the pore structure of soft and hard interbedded rock mass based on nuclear magnetic resonance technology,and carries out uniaxial compression test and triaxial compression test.In the experiment,the strength characteristics and failure modes of the soft and hard interbedded rock mass were analyzed,and the damage constitutive model of the soft and hard interbedded rock mass was established based on the Weibull distribution statistical strength theory.The main findings of this paper are as follows:(1)Using cement,gypsum powder and quartz sand materials,single rocks with different mechanical properties were prepared through the ratio test.Select the mix ratio of expected target strength to prepare layered rock mass,and use different pads to drill standard test blocks with different joint inclination angles.There are two combinations of layered rock samples(hard-soft,hard-soft-hard),and each combination corresponds to five joint dip angles(0°,10°,30°,45°,60°)The T2 spectral distribution,spectral area and porosity of the layered rock samples were analyzed by nuclear magnetic resonance technology,which showed that the sample preparation effect was good,and the pore structure was mainly composed of tiny pores.(2)The uniaxial compression test was carried out on the layered rock samples,and the strength law with the change of the joint inclination angle was a "U"-shaped distribution that first decreased and then increased,and the failure characteristics changed from splitting failure to shearing failure.In addition,the acoustic emission technology is supplemented in the uniaxial compression test to monitor the acoustic emission characteristics of the uniaxial compression test and the crack expansion of the sample.The triaxial compression test was carried out on the layered rock mass sample.The strength law of the two-layer rock mass first increased and then decreased with the change of the joint inclination angle,while the strength law of the three-layer rock mass was gradually decreased with the change of the joint inclination angle.Due to the influence of confining pressure,the failure characteristics are mainly shear failure.By comparing the mechanical characteristics of the two groups of tests,it is shown that the confining pressure has a significant influence on the strength and failure characteristics of the layered rock samples.(3)The damage equation is established by introducing Weibull statistical strength theory,and the damage variable is introduced into the rock constitutive equation to construct a statistical damage constitutive model to describe the pre-peak stage of the test curve.The rationality of the model is verified by comparing the theoretical curve of the model with the experimental curve.By analyzing the effects of joint inclination and thickness ratio on damage variables,the sensitivity of joint inclination and thickness ratio to damage variables is revealed.The results show that the joint inclination has a great influence on the damage variables.