Experimental Study On Dynamic And Static Reloading Mechanical Properties Of Damaged Marble

The surrounding rock mass will inevitably be subject to disturbances such as unloading damaged and cyclic loading damaged during the excavation of underground engineering.The mechanical properties of the damaged surrounding rock mass is one of the important factors to determine the bearing capacity of the surrounding rock and the stability of the underground project.Therefore,it is great significance to study the acoustic emission characteristics,damage evolution,mechanical properties and energy dissipation of marble damaged by unloading and cyclic loading.In this paper,damaged marble is taken as the research object.Unloading damaged marble samples are prepared by setting different unloading paths,unloading points and unloading rates in unloading confining test,and cyclic loading damaged marble is obtained by setting different cycles and the maximum cycling stresses in cyclic loading test.Static and dynamic uniaxial compression test is performed on the damaged marble sample based on the MTS815.03 electro-hydraulic servo rock mechanics test system and split Hopkinson pressure bar system(SHPB).Acoustic emission monitoring is used for the static uniaxial compression process.The research conclusions are as follows:(1)In the unloading test,unloaded damaged rock samples can be prepared when the confining pressure is unloaded to 0 and the volumetric strain is positive.During the process of unloading,the volumetric strain is divided into three stages: the volumetric strain stable stage,the slowly decreasing stage,and the significant increasing stage.(2)The cumulative ringing count has a negative correlation with the unloading point.As the unloading point increases,the b value generally increases.Acoustic emission b value of the damaged rock samples increase with the normalized axial strain and can be divided into slow increase,sharp increase and rapid decline.(3)The static and dynamic compressive strength and elastic modulus of the unloading damaged rock samples decrease with the damage variables present a negative exponential function and the brittle failure characteristics tend to be insignificant.The degree of fragmentation of rock samples increases significantly with the increase of damage variable.(4)When the damage variable is lower than the critical value Dc=0.17,the dynamic enhancement factor stable around 1.5.The dynamic elastic modulus decreases rapidly while the static elastic modulus does not change significantly.(5)The ratio of breakage energy divided into two stages and the critical point damage variable is D=0.343.When D<0.343,the breakage energy ratio is stable at about 10%,and the value is about 13 J.When D>0.343,the ratio of breakage energy increases with the increase of damage variable.There are 77 figures,10 tables and 132 references in this paper.