Study On The Synergetic Support Of Bolt Andanchor-cable Based On Energy Analysis

In the deformation and failure process of surrounding rock energy is always conversed and transferred, and in the deformation and instability process of surrounding rock energy also changes. Support system have a certain control effect on the deformation and instability of surrounding rock, so it must have the influence on energy conversion and transfer in the surrounding rock. Therefore, the characteristic of energy change in supported surrounding rock of underground projects must be analyzed to provide guidance for strengthening surrounding rock. First of all, in the view of energy analysis, the elastic and plastic strain energy distribution in surrounding rock is studied by theory analysis method based on Mohr-Coulomb yield criterion after circular tunnel is excavated. The involved parameters and the synergic effect of main parameters are analyzed. Then, the synergic effect existing in some support parameters of bolt and anchor-cable are analyzed to prove the conclusions from theoretical analysis. In this paper, the main conclusions are as follows:(1) Total energy density and elastic energy density in surrounding rock are calculated by making use of stress and displacement formula about circular roadway. Then, the change and distribution law of total energy density and elasticity energy density of surrounding rock is revealed.(2) It is discovered that the displacement formulae based on plastic position potential theory is not right by analyzing the characteristic of energy distribution in surrounding rock. In some plastic regions total energy based on these displacement formulae is less than elastic energy in surrounding rock that contrary to energy conservation law, so it is not applicable to plastic zone.(3) The sensitive factors which affect elastic and plastic energy in surrounding rock are the original rock mechanics parameters and primary stress. In particular, the cohesion has more obvious influence on the energy of surrounding rock than friction angle in broken rock zone. Energy of surrounding rock in broken rock zone can be reduced when elastic modulus is increased. Furthermore, when supporting force is increased plastic energy of surrounding rock in broken rock zone can be decreased, the degree of energy concentration in surrounding rock can be lessened, and elastic energy of surrounding rock can be increased, so that all these can lead to more stability of surrounding rock.(4) The cohesion of surrounding rock can be enlarged when pre-stress of bolt is increased, then the broken rock zone can be lessened, but the degree of plastic energy concentration can be aggravated. Thus, combined anchor-cable which cooperates with bolt is needed to provide uniform force for surrounding rock in order to reduce the degree of plastic energy concentration. But the increase of cohesion and supporting force could aggrandize elastic energy of surrounding rock, so higher elastic modulus of blots and anchor-cables is needed to increase elastic modulus of entirety and reduce elastic energy and displacement of surrounding rock so that surrounding rock can be in the steady status of fewer damage, uniform cracks and lower energy.(5) Prestress of cable is a sensitive factor of the energy in surrounding rock and the length of cable has no impact on the energy of surrounding rock. In view of effect of tensile stress around anchorage section on energy of surrounding rock, the length of cable within 5m to 7.5m is advised under conventional conditions.(6) The effect of combination cable is superior to the effect of single cable. There is coordination matching effect between prestress and interval of cable. The interval of cable should be reduced when prestress is low, likewise, the interval of cable can be increased when prestress is high.(7)The purpose of support should not limited to control deformation of surrounding rock and increase rock strength, it should be to improve stability of cracked rock under the condition of reducing plastic energy and the degree of plastic energy concentration in surrounding rock as soon as possible.