Anchor's Stress And Numerical Simulation On Rock Mass Connect Effect In Loose Circle Of Surrounding Rock

Loose circle will form and produce unloading phenomena in surrounding rock after a tunnel is excavated. So the rock mass will not endure overlying strata's load, and only bear its own gravity. If tunnel roof is layered rock mass, masonry structure will form. And if the structure can't be in self-stability, we should adopt anchoring to enhance its stability. Based on FEM, the mechanics characteristic of fully grouted bolt is simulated, and gains the shearing stress distribution law and its relation to lithology. Based on surrounding rock loose circle theory and 'S-R' stability theory on bond beam, model of anchoring connected rock masses structure in loose circle is built, the interaction relationship of bolt and rock mass, the stress distribution of anchoring body and mechanics characteristic of bolt are numerical analyzed.1) The max shearing stress value of fully grouted bolt is large and close to orifice. The harder the rock mass is, the more centralized is the shearing stress, and the softer the rock mass is, the more uniformity is the shearing stress.2) The stress distribution of anchoring body concentrates on contact surface. The axial stress distribution curves of bolts show that, the maximum axial stress of bolt is on contact surface and the minimum is on two ends. For 2 strata structure, tensile stress is effect on the bolts, for 3 strata structure and more, the side bolts are compressed, and the inner bolts are tensioned.3) Through the max axial stress variation curve along with E and C, show that the rock's elastic modulus is in proportion with axial stress and the change of cohesion does no effect on force changes of bolts. The safety of bolt express that the anchoring connected rock mass is in stability.