Abstract: Aiming at the influence of anchorage length on stress conditions in bolt as well as the calculation method for its critical value, a nonlinear stress-slipping model of anchorage interface was introduced to develop shear stress, axial force and displacement solutions of bolts using load transfer method. The influence of anchorage length on stress conditions in bolt, mainly including load-displacement relationship, shear stress distribution as well as softening load and ultimate bearing capacity, was discussed. The calculation method for critical anchorage length was proposed and verified by the engineering applications. The results indicate that the load-displacement relationships of bolts with small anchorage length perform as unimodal curves with low bearing capacities. A slowness changing of the segment aroused accompanying with the increasing of anchorage length. Shear stress distributes uniformly along bolts with small anchorage length and the bearing capacity is very small. The non-uniform characteristics occur with the anchorage length increase and the bearing capacity also increases. The softening loads, ultimate bearing capacities and the bearing capacities of bolts approximate toward constant values after the anchorage length reaches critical value. The calculation results of the critical anchorage lengths show good agreement with the actual values in engineering cases for bearing tests, thus this proposed method is feasible and effective.

Key words: geotechnical engineering, bolts, critical anchorage length, load transfer method, nonlinear interfacial model