A Numerical Study of the Behaviour of Fully Grouted Cable Bolts Under Static and Dynamic Loading

Tahmasebinia, F. (University of New South Wales) | Zhang, C. (University of New South Wales) | Canbulat, I. (University of New South Wales) | Vardar, O. (University of New South Wales) | Saydam, S. (University of New South Wales)

OnePetro 

Abstract

Stability of underground excavations in mining and tunneling is one of the most significant concerns of geotechnical engineers. Rock reinforcement methods can be used to increase rock strength and minimise the displacement of unstable rock mass. It is important to understand how the reinforcement systems work to ensure the stability of underground excavations. Rock bolts together with cables bolts have been commonly used as an effective underground support system and an element of reinforcement to improve excavation stability. The principle of rock bolting is one of the most researched aspects of ground control as they are used under a variety of loading conditions and geological environments. Both support systems are usually considered to be subjected to static loads under relatively low stress conditions; however, under high stress conditions, especially burst-prone conditions, they may be subjected to dynamic loading. Cable bolts and other support elements in such conditions are used to absorb the kinetic energy of the removed rock to avoid sudden and violent failures. Therefore, cable bolts that have high energy-absorption capability are becoming more widely used for burst control. In this paper, numerical simulation analyses are developed for cable bolts, grout and rock mass, as well as the interactions between them under static and dynamic loading, to evaluate the performance of cable bolts and surrounding materials. To validate the suggested numerical models, the simulated results are compared with the reported experimental observations in the literature. A novel numerical model is suggested to predict the dynamic behaviour of the cable bolts under impact loading.

1. Introduction

Rock reinforcement methods have been used to increase rock mass stability by increasing its strength and minimising the displacement of unstable rock mass in underground excavations. Both rock bolts and cable bolts are widely used in underground mines and tunnels. A rock bolt is usually a steel bar, which is fixed into rock mass either by grouting or mechanically, and it can be pre-tensioned. A cable bolt is a flexible tendon that is made of twisted steel wires, with high tensile strength to support rock mass, and it is usually fixed into rock by resin and/or grouting. There are various types of rock bolts which vary in size, capacity and geometry to suit different ground conditions.

A large amount of research, including experiments, has been conducted to investigate the tensile failure and load transfer capacity of rock bolts and cable bolts. The pull test and the shear test are the two methods used to examine rock bolt performance. The short-encapsulated pull test, which can be carried out in both the laboratory and the field, evaluates the axial reinforcement behaviour of rock bolts and cable bolts. The shear test is normally undertaken in the laboratory and it includes two methods: the single shear test and the double shear test. The single shear test can underestimate the shear strength of the bolts under certain circumstances. The double shear test is usually conducted on fully grouted and axially tensioned bolts installed in different types of three-piece adjoining concrete blocks.

Rock bolts and cable bolts are usually considered to experience static loads under relatively low stress conditions. However, in burst-prone conditions, support elements are subjected to dynamic loading. Therefore, it is important to understand the bolt behaviour under dynamic loading conditions, especially from the perspective of energy absorption. This paper presents the results of explicit modelling of cable bolt behaviour and interactions with the host rock mass under static and dynamic loading to improve the understanding of support responses under dynamic loading conditions, which can assist in controlling dynamic failures.