Study On Similar Material Simulation Test And Damage Constitutive Model Of Cross Jointed Rock Mass

Cross jointed rock mass is widely distributed engineering geological bodies in nature.It is very important to understand the strength and deformation characteristics of cross jointed rock mass for the safety and stability of related rock mass engineering accurately.In this paper,using similar materials to make jointed rock mass specimens,through changing the dip angle and length of joints to simulate cross jointed rock mass under different working conditions.uniaxial compression tests are carried out on cross jointed rock mass specimens under different working conditions.In the test process,digital image correlation method(DIC)is used to measure the full field strain near the joint tip under different loads in real time.On the basis of classification and comparison of test results,in-depth analysis is carried out;Based on the combination of fracture mechanics,energy theory and damage mechanics,the meso damage and macro damage of rock mass are coupled into macro meso composite damage according to Lemaitre strain equivalence principle,and the equivalent elastic model of cross jointed rock mass is constructed;Finally,the model calculation results is compared with the experimental results,and they are in good agreement,which proves the rationality of the model.The macro damage variables of the model take into account both the initial damage of rock mass under the interference effect of cross joints and the additional damage caused by wing crack propagation.The main research results are as follows:(1)The results show that the strength of rock mass with single joint first decreases and then increases between 0 ° and 90 ° with the lowest strength between 45 ° and 60 ° and the strength of rock mass with 0 ° joint is weakened to a great extent,while the strength and deformation characteristics of rock mass with 90 ° joint are less affected;(2)The existence of cross joints has little influence on the deformation modulus of rock mass at the initial stage of loading,but the interference effect between cross joints has a great influence on the stress intensity factor at the tip of main joints,which makes the peak strength of rock mass have significant difference;(3)Due to the interference effect between the cross joints,the strength of the rock mass with the same dip cross joint is lower than that of the rock mass with two joints alone,and the strength of the rock mass with the opposite dip cross joint is higher than that of the rock mass with two joints alone when the angle between the primary and secondary joints is close to90 ° and greater than 90 °;(4)When the vertical joint plane is under load,the joint plane produces tensile deformation.The opening of vertical joint plane is beneficial to the coordinated deformation of inclined joint plane,which makes the rock strength higher than that of inclined joint plane alone.(5)In the case of damage shielding of cross jointed rock mass,the strength of cross jointed rock mass can be improved with the increase of the length of secondary joint,but with the increase of the length of secondary joint,the secondary joint can develop into the main joint of cross jointed rock mass,which makes the strength of cross jointed rock mass lower than that of the main joint.