Study On Achoring Characters Of Interior Bond Section And Achoring Structure For Soft Rock Within Bolt

Anchor engineering is a very important branch in the field of geotechnical engineering , and Study on anchoring characters of interior bond section is one of the key issues in anchor engineering. In this paper, anchoring characters of interior bond section in bolt are studied with elasticity model and shear lag debonding model. Based on the anchoring characters of soft rock, a new type of structure about interior bond section is designed, and is validated with pull-out tests and numerical simulation in laboratory. The main contents are as follows:1,Based on the elastic theory, Model research on distribution regularity of shear stress on anchorage end of prestressing bolt is carried out in both tension-type and pressure-type prestressing bolt. The non-uniform distribution of shear stress is obtained, and their peak shear stress points are not in the location of the endpoint. The shear stress peak point of tension-type anchor occurred in about 10cm away from the starting point of bond section, and the shear stress peak point of pressure-type anchor occurred in the vicinity of the bearing plate.2,Analysis of the displacement changing result from the impact of pre-stressed physical point of the surrounding rock, in pull-type bolt, prestressing force is transferred to the surrounding space with the semi-circular shape by the symmetry axis of bolt and the top interface of bond section in rock and soil. However, prestressing force is transferred to the surrounding space with the 'U' shape in the pressure-type bolt.3,Setting up the shear-lag debonding model in external interface of bolt, analysing in the mechanics in the process of destruction and studying on bonding length, the following is obtained. From the loading to the damaging on anchor section, there are three phase, including elastic deformation, plastic-slip deformation, debonding deformation. According to the static balance equation, Coulomb yield conditions and non-associated flow rule, the shift differential equations about the external interface of bolt-grouting section is deduced and the expression of Shear stress in the sliping part of bolt-grouting section is solved out.4,Considering the process of shear-lag debonding, the method of the length of interior bond section is proposed. When prestress is less than the largest prestress, the interface is in elastic stage, and bonding length is solved through the flexible formula; when prestress is greater than the largest prestress, the interface is in three stages, and bonding length is determined through the same area integral approach.5,Based on the anchor properties of soft rock, combined key strata theory for control of strata movement with the ideas of the deformation on compound beams, anchored-wall theory is brought out on describing the soft rock anchoring mechanism. the taper structure in structural engineering is introducted in the rock anchoring engieering, and the taper bolt is designed.6,Through the similarity experiment of soft rock, pull-out tests and numerical simulation, the displacements of both tension-type bolt and pressure-type bolt are transfered gradually from the buttom of the hole. Howerver, tension-type anchor is not. Compared the chart of stress vector and the chart of displacement vector, This taper structure of cone-shaped bolt has the effect on the scattering of the direction of stress, but the role of decentralization is very limited. Optimizing its structure is the further need.