Bolting Support Mechanical Mechanism Of Tunnel Surrounding Rock By Considering Post-peak Characteristics

With the continuous development of national economy, the development and utilization of deep underground engineering has become an inevitable trend,especially in tunnel engineering, mining engineering, water and electricity engineering and national defense engineering and other field. The deep rock mass engineering, due to being in a complex and high stress of the engineering geological environment, joints is ordinary existence. Because of high in-situ stress disturbance, the deep surrounding rock behave a very big divergence in the mechanical properties compared with the surrounding rock of shallow. The rock mass displayed post-peak strain softening properties and rock dilatancy properties. Post-peak surrounding rock brings about a series of difficult issues to tunnel surrounding rock support in mining engineering.Therefore, Further study the characteristics of deep post-peak rock and deformation and failure mechanisms has great significance to excavation and support design and the safety and stability of the tunnel surrounding rock.It is supposed to study mechanical mechanism of the post-peak tunnel surrounding rock state under grouted bolting support. The strain softening model was selected to describe the post-peak surrounding rock state. Through the calculated by theoretical derivation, numerical simulation, laboratory test model,respectively, study the influences of bolt supporting on the tunnel surrounding rock’s stress, displacement and the scope of broken rock species distribution. The main contents are as follows:First of all, the bolt axial stress and shear strength equation are obtained based on the bolt bonding resist to sliding deformation principle. Assuming the supporting force, which provided by grouted rock bolt through rock–anchorage face is equivalent to be radial body force of the surrounding rock. And the surrounding rock’s mechanical properties get improved after the bolt applied. Therefore, the balance equation is established under the influence of bolting support. Meanwhile, combining the compatibility equation of residual and softening plastic zone that considering the rock post-peak strain softening and dilatancy with the the balance equation, get the radius of the post-peak residual and softening zone as well as displacement and stress under grouted bolt support. Based on theoretical research cases, it is revealed that the reinforcement effects between grouting anchor and surrounding rock, the bolting pretension have significance effect in improving mechanical properties of softeningand dilatancy characteristic, moreover controlling the development of regional range and deformation of surrounding rock.Then, bolting supporting effect of post-peak surrounding rock was studied through numerical simulation. Firstly, based on Mohr-Coulomb post-peak strain-softening joint model, the coupling relationship between critical plastic shear strain η* and support resistance was established. Secondly, according to bolt reinforcement mechanism, the parameters effected by mechanical anchoring are embedded in the surrounding rock strain softening model. At last, the strain-softening model under the influence of critical plastic softening coefficient η* is embedded into finite difference software FLAC3 D. Through the surrounding rock stress field concussion bolting analyzed under the studied range of stress, the tunnel surrounding rock’s stress, deformation and broken rock species distribution of different length bolt support were discussed. The numerical analysis shows that considering the effect of bolt support, zonal disintegration of the surrounding rock obviously weakened; The surrounding rock stress field, displacement and broken zone under the condition of support are clear difference comparing to not being supported.Finally, the ratio of material experiment is carried out according to the similarity theory, and indoor similar model test research by considering bolt support is constructed, After the cavern excavation, the variability of stress, strain and displacement of surrounding rock both in top of tunnel and in hance of tunnel are monitored. Compared the bolt support tunnel model with unreinforced tunnel, the effectiveness of anchor supporting effect is further confirmed.