Abstract:

Three new methods for identifying axial forces in ground anchor or rock bolt are presented. Unlike in traditional methods that rely on the use of an electronic device, such as strain gauges or load cells, these new methods do not use electronic devices for reading data, but instead use mechanical schemes to measure axial forces at the same time. Since the methods are electricity free, they are maintenance free, long-lasting and can be produced at low costs. The methods are also beneficial in terms of safety management since the costs of axial forces measurements are low and can visualized for workers at all times. The concepts for designing the new devices, lab test results and some field application examples are introduced in this paper.

Introduction

It is of primary importance to grasp axial forces in ground supporting members, such as rock bolts or ground anchors as pointed by Conover (2010). As they are installed with an important mission to suppress deformation of rock masses, it is ideal that axial forces acting in them are grasped at all times for the purpose of safety management. Standard methods for monitoring axial forces are based on use of load cell inserted behind a base plate, or strain gauges attached to main tendon or rock bolt (for example, Hyett and Spearing, 2012). These schemes require electronics hardware for data collection. On-Site Visualization of measured axial force, using electricity, has been proposed by Akutagawa (2012) and the importance of sharing measured information on a real-time basis has been pointed out by Izumi et al. (2014). However, it is often the case that axial forces of up to only 5% of all the ground supporting members are usually monitored, if at all, because of required cost to do so. In order to increase the ratio of monitored ground anchors or rock bolts, for the sake of safety management, a new series of techniques, all of which work without using electricity, were developed to measure axial forces as 1) needle rotation, 2) magnified deformation between a specially created gap on an anchor plate and 3) change in crack patterns appearing on a bearing plate of a rock bolt. Principles and applications of these new techniques are introduced in this paper.

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