Experimental And Numerical Simulation Of Dynamic Mechanical Properties Of Anchored Jointed Sandstone

At present,the development and utilization of underground space has become one of the key focus areas.Not only mining projects,but also civil engineering,water conservancy and hydropower projects are often disturbed by dynamic loads such as earthquakes and blasts during development and use.Therefore,it is very important to study the stability of underground engineering under dynamic loads such as earthquakes and blasting.There are a lot of defects such as joints and cracks in the engineering rock mass,and the joints have an important influence on the dynamic mechanical properties and failure mechanism of the rock mass.In recent years,anchor reinforcement is the most effective,economical and most widely used support method.Studying the dynamic mechanical properties of anchored jointed rock mass is helpful to fully understand the destruction mechanism,strength and deformation of anchored jointed rock mass and the importance of studying stability control of underground space.In order to study the dynamic mechanical properties of anchored jointed rock masses under impact loading,this paper uses a combination of indoor physical tests and mesoscopic numerical simulations to carry out indoor physical impacts of prefabricated test pieces under different test systems and different working conditions test,in further carry out numerical simulation impact test with reference to physical test.The main research contents and conclusions are as follows:（1）Based on the Hopkinson pressure bar test,an impact test is performed on the complete sandstone specimen,and the dynamic characteristics and failure modes of sandstone specimens under different impact loads are studied.The results show that the strain rate of the sandstone specimen is in the range of 10¹¹0²s^-1,and the dynamic compressive strength and peak strain have obvious strain rate effects.When the average strain rate of the specimen is 75.62s^-1,the dynamic compressive strength is about twice the static compressive strength.The failure morphology of the complete sandstone specimen has a significant strain rate effect,and the particle size decreases with the increase of the strain rate.（2）Based on the drop weight impact test system,impact tests were performed on unanchored and anchored joint specimens,and the dynamic characteristics and failure morphology of sandstone specimens under the same impact load were studied.The results show that the anchoring effect of the anchor rod improves the dynamic compressive strength and overall toughness of the joint specimen,and also plays a restrictive role in its failure and deformation.The peak load of 45°,60°,30°and 90°inclination test specimens with anchor joints increases in sequence,and the vertical compression displacement decreases in sequence.The peak load of the complete specimen is the largest,and the vertical compression displacement is the smallest.The peak load of the 45°joint specimen is increased by 16%after anchoring.The failure morphology of the anchored joint specimens exhibited both split failure and tensile failure,and the failure morphology of the unanchored joint specimens and the complete specimen mainly exhibited split failure.（3）Based on the RFPA2D numerical simulation software,the numerical simulation test is carried out to compare the indoor physical experiment,and the failure process and failure morphology of the complete specimen under different impact loads and the same penetration joint specimen under the same impact load are studied.The results show that the results of numerical simulation and the results of indoor physical tests are in agreement with each other.The failure process and failure form of the specimen are closely related to the stress wave peak value and joint inclination angle;The larger the stress wave peak is,the more obvious the damage form,and the joint angle with the most obvious damage effect is between 45°and 60°.The dynamic failure process and failure morphology of unanchored and anchored specimens with the same joint length and different joint inclination angles are studied.The results show that the projected length of the joint in the horizontal direction has a positive correlation with the cumulative rate of the AE cumulative number.The failure mode of the anchored specimen is that the development of micro-cracks is mainly concentrated around the joints of the upper part of the bolt,and the development of micro-cracks around the joints of the lower part of the bolt is obviously weaker,and the failure form of the unanchored specimen is mainly manifested by the micro-cracks surrounding the joint.The main penetrating cracks of the failure form of the numerical simulation test specimens are similar to the laboratory physical tests.Under the impact load,the anchor has the function of restraining the deformation and displacement of the specimen and preventing the development of cracks,and the presence of the anchor improves the dynamic stability of the specimen.