Field Tests and Analytical Model for Estimating the Effects of Anchor-Root at the Bottom of Full-Length Bond Bolt

The enlarged anchor-root at the bottom for rock bolts is considered as the very helpful measure for improving the anti-pullout capacity of transmission tower foundation design in mountain area. It is a key problem for estimating the action of anchor-root at the bottom of full-length bonded rock bolts. Two types of bolts tests were carried out in field to study the action effect of anchor-root. Both the conventional root and the enlarged anchor-root are used for field tests. According to tested results, two types curve characteristics of axis force along depth were compared and studied. The mechanism of anchor-root action effects was investigated on the basis of the fitting analysis on the tested results. Further, the analytical formulation for evaluating the behavior of the enlarged anchor root is derived and obtained. The analytical model results agreed quite well with both the field tested results. On the basis of curve characteristics of bolt axis force, a theory of the anchor-root role is equivalent to bond length added was proposed and the analytical model was presented in this paper. Compared with measured data, this model can accordingly be used to predict the action of anchor-root at the bottom of full-length bond bolt.