Study On The Load Transfer Behavior Of The Rock Bolt And Its Anchoring Efficacy In Jointed Rock Mass Around Highway Tunnel

In current tunnel jointed surrounding rock supporting system and bolt is a widely used way. After decades of practice, bolt for jointed surrounding rock reinforcement plays a very important role, but the mechanism of rock bolt was not very clear,especially study in jointed rock bolt load transfer laws and the anchoring effect was mainly focused on qualitative experience. According to the status of domestic and foreign rock bolt support of theoretical research, this article discussed the bolting mechanism and efficacy of rock bolt in tunneling engineering from different point,based on the present bolting theoretical research and underground engineering. Aim to achieve deeply knowledge of bolting mechanism, provide scientific theoretical research for the blot designing.The several parts below are included in this main research:(1) According to the characteristics of mudstone formation, position of a single joint is taken as a variable. Design and production of single joint at different positions of the cuboid specimen has been done. When joint open a small displacement, strain and displacement distribution of rock bolt is analyzed. Analysis of influence of joint position on bolt stress distribution as the joint opening displacement increasing, and the bolt axial force distribution has been carried on.(2) By introducing displacement discontinuous function, under the single joint and multi joint grouting bolt displacement, axial force and shear should force calculation formula was deduced. To obtain the load transfer rules of rock bolt, analysis of axial force of rock bolt and shear stress distribution with different joint distribution are conducted. Then the theoretical calculation results are compared with experimental results and verify the correctness of the theoretical model in this paper.(3) Considering the anisotropy of the jointed rock cohesion, broken rock zone calculation formula is established by extending Hundson and Harrison tunnel reinforcement model for the jointed rock mass. On the basis of the anchored surrounding rock before and after rupture zone changes, a new assessment method for anchoring efficacy of rock bolt is proposed. Anchoring efficacy of rock bolt in jointed rock mass is discussed under different jointed rock mechanical parameters.(4) The discrete element model is adopted to calculate and analyze the anchoring efficacy, under the conditions of different grade of surrounding rock anchors. Bearingcapacity and efficiency ratio of the tunnel under different geological conditions of various types of supporting type is simulated. Through the parameter sensitivity analysis,the effect of rock strength, joint spacing, anchor length and lateral pressure coefficient of anchor effect is discussed. The anchoring efficacy for rock bolt is low when the rock grade is very poor and good, the highest efficiency of understanding between III and IV surrounding rock. The results make sense for maintaining the stability of the tunnel anchor in the tunnel project to provide theoretical support.(5) The application of this model to the Shigu tunnel anchor effect evaluation,based on the evaluation formula combined with anchor numerical model, the axis force of anchor, the plastic zone of the surrounding rock are obtained. Through the comparison of the axial force and the key monitoring points, the proposed method is verified, and the efficacy evaluation of underground anchor rock joints is obtained.