Study On Loading Rate Effect Of Joint Normal Deformation

Joint normal deformation characteristic is one of the main research problems of rock mechanics and Engineering.Previous studies had been done on the joint normal closure characteristics under static conditions.However,rock masses are not simply subjected to static loads.In conditions like mining,road construction,earthquake,landslide and so on,It is also relatively common that rock masses are subjected to dynamic loads such as blasting load and earthquake load However,the study of joint normal closure characteristics under dynamic loading is still in the preliminary stage now.Therefore,Studies on the loading rate effect of joint normal deformation characteristics and its mechanism are of important theoretical and engineering significance.In this paper,the samples of standard cylinder,dentate and rough joint were made of plaster,and the dynamic characteristics of the joints dynamic characteristics under static and quasi-static conditions(10-2 MPa/s to 100 MPa/s)were investigated.The main results obtained are as follows:1.Under static and quasi-static conditions,the gypsum material compressive strength increases with the increasing of loading rate,and is linearly related to the logarithm of loading rate.The uniaxial compression modulus of gypsum material changes little with the increase of loading rate.2.Fitting the test data of first cycle of two types joint with five kinds of commonly used function model.The results show that,besides the exponential function model,the other four functions model(hyperbolic function,improved exponential function,semi-logarithmic function,power function)can better describe the joint closure character.3.Under static and quasi-static conditions,the normal closure properties of dentate joints and rough joints have obvious loading rate effects during the initial loading process.The initial normal stiffness of joint increases with the increase of loading rate,and be linearly related to the logarithm of loading rate.The joint maximum allowable closure decreases with the increase of loading rate,and it also linearly with the logarithm of loading rate.With the increase of initial contact area or joint roughness coefficient(JRC),the initial normal stiffness of joint becomes more and more sensitive to the loading rate,and the joint maximum allowable closure becomes less and less sensitive to the loading rate.The initial normal stiffness of joint increases with the increases of initial contact area or joint roughness coefficient(JRC)at the same loading rate,but joint maximum allowable closure decreases with the increase of initial contact area of joint or joint roughness coefficient(JRC).4.Under elastic condition(after multiple cycles,the maximum stress does not exceed the maximum cyclic load before),the failure of joint surface will no longer occurred.At this point,the loading rate has little influence on the joint normal deformation characteristics.5.The joint changes from elastic state to plastic state(after multiple cycles,again load maximum stress exceeds the maximum cycle load before),In the process of joint deformation,the material failure of the joint surface will occur.At the same time,the normal deformation behavior has the loading rate effect again.6.In combination with Standard cylindrical sample and two types joint test results,it is preliminarily considered that the loading rate effect on failure of joint surface is the root cause of loading rate effect of joint normal deformation.That is to say,when the joint surface does not produce material failure,the loading rate has little influence on the joint normal deformation characteristics what be neglected.When the material failure occurs on the joint surface,the joint normal deformation has loading rate effect.