Reaserch On The Energy System Of Deep Granite Considering The Stored Energy And Dissipated Energy Characteristics

Deep mining is not only the inevitable trend of mining industry,but also the important development direction of "Deep earth" in our country.In deep underground,the rock expresses high nonlinear characteristics,because of the high geostress conditions.Also,the rockburst and other deep dynamic disasters will be much more serious due to the strong disturbance during excavation process.Researches show that the energy theory is an optimal theory for studying rockburst,and it is more close to the essential mechanism of rockburst.In this study,the energy theory was used to study rockburst and other deep underground disasters,based on the 1000 m excavation of Sanshandao Gold Mine.The characteristics of stored energy and dissipated energy were researched,and a suppositional state of energy uniformity in the hostrock was proposed.(1)Linear elastic stored energy is an important index parameter for studying the rockburst disaster with energy criterion.The key to study the linear elastic stored energy storage is to determine the elastic-plastic boundary point.This paper employed the initial point of fracture,which was obtained by acoustic emission monitoring,as the demarcation point between the elastic stored energy and plastic dissipated energy.The linear elastic stored energy under typical confining pressures could be calculated by carrying out the uniaxial and triaxial compression tests.However,whether the initial point of fracture is the real elastic plastic cut-off point is doubt.Taking advantage of high accuracy of MTS815 rock testing experimental equipment,a step cyclic loading and unloading test with increasing stress were designed.And the real elastic plastic cut-off point under confining pressures of 10MPa,20MPa and 30MPa were confirmed.Comparative analysis shows that the elastic plastic cut-off point is a little larger than the nitial point of fracture,and this point shows clearer physical significance and smaller errors.(2)Previous researches show that the linear elastic storage energy ignores the part of energy storage capacity between the elastic plastic cut-off point and the peak strength.In this loading phase,the rock has been damaged,but it also has certain energy storage capacity.In this paper,full cycle loading and unloading tests under 5 typical confining pressures were carried out.The rock stored energy value was calculated by the peak unloading curve,and the results shown that the value calculated by peak unloading curve was 1.2 times of that of the linear stored elastic energy.Meanwhile,considering the elastic strain time-delay characteristic of deep granite,stage loading and unloading tests were studied.After 20 days monitoring on the elastic strain release,the monitoring results present that there is about 5.6%elastic strain of the total strain can not release immediately.Based on this,the maximum stored energy characterization system could be established considering time-delay characteristics of the deep granite.(3)Taking advantage of fracture mechanics theory,for rock and other brittle materials,the energy will dissipate at the creation of new cracks and friction between structural surfaces during the whole damage process,which are,namely,fracture dissipated energy and frictional dissipated energy.The dynamic SHPB tests with different strain rate of deep granite were conducted,and the fracture dissipated energy model with the energy density was confirmed preliminarily.Considering the real geostess conditions,a high confining pressure and self seals device in dynamic SHPB system was developed by our research group.And dynamic SHPB tests with 4 typical confining pressures(10 MPa,20 MPa,30 MPa and 40 MPa)and 3 typical stress ratios(1:1,1:1.5 and 1:2)were finished.The racture dissipated energy model of deep granite was improved furtherly.(4)At present,the studies are mainly focused on the fracture dissipated energy,the researches on the frictional dissipated energy are not adequate,but the frictional dissipated energy is an important part in the dissipated energy system.Especially for jointed rock mass,frictional dissipated energy makes up the majority of dissipated energy during rockburst.This paper designed a set of shearing frictional tests for deep granite,and the frictional dissipated energy characteristics of deep granite were obtained by conducting shearing frictional tests under different vertical stresses.Meanwhile,binocular laser scanning,fractal theory and PFC numerical simulation method were used to disscuss frictional dissipated energy mechanism.The studies indicate that the frictional dissipated energy of deep granite is mainly dissipated on the macroscopic waviness,and along with increase of vertical stress,the energy dissipated way will transfer from climbing to shearing.(5)At last,based on the above researches on the maximum stored energy mechanism,fracture dissipated energy and frictional dissipated energy,taking example of 1000m deep excavation of Sanshandao Gold Mine,and taking the measured in-situ stress data as the stress boundary of the model,the rockburst disaster situation of 90 pillars in 6 stopes were simulated.Then,one-dimensional propagation and scattering laws of rock energy was discussed preliminarily by carring the long rock samples SHPB dynamic tests.It is realized that energy can be regulated.To reduce the energy accumulation after excavation disturbance,the concept of energy homogenization of stored energy in the host rock of deep tunnel was presented,a cooperative support system of anchor net and arch was built after exploring.The research results can realize the suppositional state of energy uniformity in the hostrock of tunnel in the deep mine,which provides a new method for the prevention of rockburst and other deep dynamic disasters.