Research On The Damage Evolution And Failure Law Of The Jointed Rock Mass During Excavation

Jointed rock mass is ubiquity in actual projects such as Mining Engineering, Tunneling and Highway Engineering, etc. Joints with different shapes and sizes, which are divided in rock mass, have a profound influence on the character of rock mass. Therefore, they are regarded as the initial damage of rock mass. It has been proved that a large majority of disasters, such as landslide, collapse of tunnel and goaf, etc, are the results of the failure of joints in the rock mass. So, it is vital to study on the influence of the joints on the damage of rock mass. Taking the zinc copper ore body of Tongkeng Mine, Huaxi Group for research background, this paper have studied the damage evolution and failure law of the jointed rock mass excavation in deep mine. The main research contents and results are as following:(1) On the basis of the current related documents, the author has summarized the research status of contents, which are related to the jointed rock mass. At the same time, numerous theories and numerical analysis methods, which can be used in the study on jointed rock mass, are concluded.(2) The main contents and methods in damage mechanics are introduced. After that, the author has summarized the methods that are used to depict the rock mass damage parameters, including area damage parameter, elastic modulus damage parameter and strength damage parameter. Meanwhile, strength damage parameter is chosen to measure the damage of jointed rock mass after analyzing the merits and demerits the methods(3) Damage revolution and damage characteristics about rock mass, which are under different loads, are studied by using the nuclear magnetic resonance technique and Electro-hydraulic servo rock uniaxial tester. main conclusions are as following:1) Tiny pores and holes are common seen in the rock mass, and when the loads gradually become larger, they experience the stages of stitching, generation of new fissures, expansion and through of fissures and formation of macroscopic fracture surface.2) there is no close correlation between the changes of rock porosity and rock macroscopic strength. For example, when the load is low, the rock porosity will become dismiss, while rock macroscopic strength is lower.3) the relationship between microscopic pore change of rock mass and macroscopic mechanical strengthen is established on the basis of the combination of the magnetic resonance analysis results and uniaxial loading analysis results. And then, rock mass strength nondestructive testing is realized.(4) Through using the RFPA software and multistage stressing, the author has studied the damage and failure laws of pillars, which contain numerous joints. main conclusions are as following:1) rock heterogeneity has remarkable influence on its mechanical properties. As the rock heterogeneity increase, the damage evolution mode of rock changes from ductile failure into brittle failure, and the dispersivity of macroscopic unstable failure decrease. At the same time, peak strength of rocks increases ceaselessly, and finally reaches to a stable value. It is also found that when the rock heterogeneity is low, acoustic emission of rocks under uniaxial loading reflects a property of low intensity and high frequency. Acoustic emission strength and mutagenicity of rocks increase with higher rock heterogeneity.2)With the increase of the joint Angle, rock macroscopic strength will be reduced and the maximal acoustic emission energy is lower. Joints in rock mass transform from pressure state to Pull and shear states.3) when there exists the same angle of joints, the more the number, the lower the rock mass strength. And when there exists the same number of joints, the larger the angles, the lower the rock mass strength. That is to say, the big angle joint Occupies dominant factors on the failure of rock mass.(5) Taking the a stope in initial minery at Tongkeng Mine for study object, the author has studied the damage law of jointed rock mass in deep mine after excavating through the UDEC software. The results indicates that if we do not design the pillars, the goaf tends to collapsed for the failure of big angle joints when excavates at the second step(about20m). However, pillars(2.0m×2.0m), which are arranged in the goaf, can obviously enhance the safety of goaf and guarantee Safety mining. Besides, the deformation of pillar located in the mid-goaf is bigger than that located in the rim. so we can appropriately increase the size of central pillar, whilst reduce the size of pillar located in the edge.