ABSTRACT:

Rebar-type rock bolts of 22 mm and a length of 600 mm are instrumented with four resistance strain gauges along the length. A total of 450 mm bolt lengths is embedded with resin grouted inside a cement mortar cast cylindrical sample of diameter 250 mm. Strain gauges are placed on the surface of the rod at four locations. The diameter of the hole is varied as 32 mm, 36mm, and 42 mm. The bolt is embedded cement mortar samples are placed in a pull-testing machine and firmly fixed on the frame by tie-rods. The rod is pulled with three different loading groups of rates. This paper analyzes load-deformation relationship curves for different hole diameters of pulling to observe the variation in peak bond strength and stiffness. The tensile strains obtained at four locations are validated with an analytical equation are in the paper.

INTRODUCTION

Rock bolt is the key reinforcement member used to provide support to rock strata in tunnels, underground mine drives/galleries and other excavations. A bolt enhances mechanical properties of rock masses and reduce deformation and support time (Pinazzi et al., 2020). A fully grouted rock bolt generates shear stress along the interfaces of grout-bolt and grout-rock and resist the movement of rock by increasing overall stiffness of the bolted zone (Cai et al., 2004; Deb & Das, 2010). Every year millions of rock bolts are installed worldwide to support and stabilize engineering structures (Benmokrane et al., 1995).

On other hand, mechanics of shearing along the interfaces of bolt-grout-rock due to pull load was investigated by few researchers. These studies showed that in the absence of rock movement, shear strain along the bolt rod varies non-linearly having the maximum value at the load side and near zero value at the other end (Farmer, 1975). Li & Stillborg, 1999 showed the similar distribution of strain development on the bolt rod considering the deformation of rock. Since then several researchers attempted to simulate the shearing mechanism of bolt-grout and grout-rock interfaces using experimental and numerical models. Significant contribution was made to understand and evaluate the mechanism of bolt-grout interfaces (Hyett et al., 1996). Moreover, extended finite element method (XFEM) were also proposed for analyzing the behavior of grouted rock bolts and applied for simulating reinforcement around tunnels and slopes (Deb and Gujjala, 2018). In the field, Short Encapsulation Pull Tests (SEPT) tests were performed by Pile et al., 2003 and Chugh et al., 2016 to determine anchorage test and optimize roof support systems.This experimental study evaluated the effects of grout types, hole diameter and rate of loading on bond strength, stiffness and distribution of axial strains along the bolt rod. The analytical and solution of displacement and strain proposed by Farmer, 1975 modified to fit the experimental data. Laboratory pull-out tests of instrumented bolts

This content is only available via PDF.
You can access this article if you purchase or spend a download.