Performance of fully encapsulated rebar bolts and D-Bolts under combined pull-and-shear loading

The performance of two types of rock bolts, fully encapsulated rebar and D-Bolt, under combined pull and shear loading were studied in the laboratory. A new test approach was developed to apply the pull and shear loads to the rock bolt at the same time so that the bolt is displaced in a direction different from the bolt axis. Five displacing angles between 0 degrees (pure pull) and 90 degrees (pure shear) were employed in the tests. The test results show that the linear elastic stiffness of both the D-Bolt and the rebar bolt is mobilised quickly after a small displacement. When the displacing angle is larger than 40 degrees, grout crushing may occur underneath the bolt shank, resulting in reduction in the stiffness of the bolt. The ultimate load of the bolts remains approximately constant no matter what the displacing angle is for both the D-Bolt and the rebar bolt. The displacement capacity of the D-Bolt, however, is dependent on the displacing angle. The ultimate displacement of a 1-m long D-Bolt section varies from 140 mm under pure pull (0 degrees) to approximately 70 mm when the displacing angle is larger than 40 degrees. The ultimate displacement of the rebar slightly increases from 29 mm under pure pull to 53 mm under pure shear. In general, the displacement capacity of the D-Bolt is larger than that of the rebar bolt. It is approximately 3.5 times the rebar under pure pull and 50% higher than rebar under pure shear. The test results show that the displacing angle of the bolt is larger than its loading angle, which is also confirmed by the analytical solutions. (C) 2014 Elsevier Ltd. All rights reserved.