Profile of Sheared Cable Bolts Strand Wires

For the past several decades cable bolt technology has been used for ground reinforcement in civil, mining and other construction projects. The strength properties of these cables, used as cable bolts, have been evaluated mainly by their ultimate tensile strength as this kind of test could be carried out in the field as well as in the laboratory. Only recently there has been a growing interest in cable bolt failures in shear because of documented field failure evidence. A series of single and double shear tests were carried out to study the extent shear failure of cable bolts in concrete blocks. Tests were made using both single and double shear rigs at the University of Wollongong. Various types of marketed cable bolts were tested using both types of shearing equipment. Various pertinent parameters were examined with direct influence on the failure characteristics of cable bolts were examined. This paper illustrates the strand wires failure profiles in both test methods and with particular focus being directed to the shear failures of both plain and indented cable bolts currently used in Australian mines. The nature of cable failure and the extent of sheared cable displacement affecting the profile of broken strands wires are reported to indicate the way the cable bolt has failed and its failure load

Single shear testing of various cable bolts used in Australian mines

Sixteen single shear tests were carried out on eight geometric cable variations provided for testing from Australian suppliers – Jennmar, Megabolt and Minova. Each test was subjected to varying pre-tension values of zero and 15 tonnes, exploring the effect of plain, spiral, bulbed, indented and a combination of plain and indented wire strands. The results obtained demonstrated that the shear strength of plain strand cable was higher than the spiral and/or indented profiled cables with direct correlation to the strands ultimate tensile strength. All the plain profiled cables experienced an element of partial debonding suggesting that their application at embedment length less than 1.8 m each anchor side may not be adequate. The spiral and indented profile strands provided greater bond strength at the cable-grout interface due to the surface roughness of the wires imposing an interlocking effect, leading to reduced shear displacement. The data suggests that the spiral profile was superior to the indented profile due possibly to the compromised integrity of the strand from the impact of stress raisers when creating the indented profile. No study was carried on the button indented profile cable bolts. This report is the first validation that type of apparatus selected to test the shearing capacity of a cable strand will not affect results

Double shear testing of cable bolts with no concrete face contacts

A new series of double shear tests were carried out using a newly modified double shear apparatus which prevented contacts between concrete block surfaces during shearing. 13 double shear tests were carried out using 21 mm diameter 19 (9 × 9 × 1) seal construction wire strand cable (also called Superstrand cable), Plain SUMO, Indented SUMO, Spiral MW9 and Plain MW10 cable bolts. These cables were tested subjected to different pretension loads. Concrete blocks with Uniaxial Compressive Strength (UCS) of 40 MPa and Stratabinder grout were used for all the tests to maintain test consistency. The results show that the peak shear load and the corresponding shear displacement decrease by increasing the pretension load of the tested cable. The Ultimate tensile strength, lay length, number of wires and cable bolt surface profile type (plain and spiral/indented) are important factors in total shear strength of the cable bolt

Angle Shear Testing of 15.2 mm Seven Wire Cable Bolt

This paper focuses on the experimental study of shear testing of 15.2 mm, 25 t capacity seven wire cables at zero, 30° and 45° angles using two different shear testing facilities at the University of Wollongong (UOW) and the University of Southern Queensland (USQ) in Toowoomba. A circular double-shear rig MK-IV was used for testing cable perpendicular to the sheared joint faces (zero angle of orientation), while testing the cable at 30° and 45° was carried out using a larger-size rectangular-shaped rig. Testing was carried out based on the double-shear testing methodology wherein cable bolts were fully encapsulated using Stratabinder HS inside of three concrete blocks representing host rocks. This study was part of the tri-universities-funded ACARP project C27040 awarded jointly to the University of New South Wales, University of Wollongong and University of Southern Queensland. The objective of the experimental testing programme was to provide the essential information for the development of numerical models that included not only the technical parameters, but also the behavioural outcomes from various tests with respect to the angles of testing and their effect on the nature of cable failure, be it pure shear, tensile shear or shear tensile, cable pretension and the credibility of the effectiveness of the Barrel and Wedge (B&W) anchorage system were evaluated. Laboratory facilities at both UOW and USQ were used in the study. The prepared double-shear samples were then positioned inside of compression testing machines and were subjected to shear testing. The values of shear load and displacement were recorded for various inclinations angles. It was found that increased angle of shear contributes to increased stiffness of the cable in shear with other parameters being equal. Subroutine codes were developed in UDEC and 3DEC to simulate shear behaviour of cable bolts installed in angles for different pretension loads. The numerical simulations indicated that UDEC and 3DEC can simulate the general shear behaviour of cable bolts reasonably well for various inclination angles and pretension values

Shear characterisation of various cable bolts using single and double shear techniques

The application of cable bolts in Australian coal mines has been increasingly widespread over the past few decades. Cable bolts initially are installed as a secondary means of support systems in underground coal mines to complete the action of primary supports, rock bolts. Over the years, several investigations have been undertaken in order to better understand the mechanisms of rock and strata control to be able to more appropriately manage the environment of the ground. One of the most concerns amongst all researchers, which have been on increase, is to understand better the mechanism of load transferring systems in cable bolts. As a matter of fact, several investigations have been performed through utilizing Single and Double shear load test methodology to address the deficiency of previous studies and provide more credible and accurate database to be utilized by engineers and designers in order to create safer and more reliant environment in underground mining industry. The University of Wollongong in this regard has been playing a pivotal role to deal with the shortage of previous research studies in the field of Double and Single shear load tests and this thesis study continues the research work currently is going on at the research and development section of the University of Wollongong to enhance the scope of the previous studies

Investigation of the behaviour of rock bolts and tendons in shear under static and dynamic loading conditions

The instability of the rock surrounding underground excavations and engineering tunnels is an ever-present threat to both the safety of human life and equipment. To eliminate or minimise these threats, it is necessary to understand the root cause of the instability of the rock mass in underground structures. Two groups of reinforcements are adopted to reinforce the unstable rock mass, namely, rock bolts and cable bolts. Rock bolts are applied immediately after excavation, as a primary support system, to connect the fractured bedding plane to the immediate strata to create a beam. On the other hand, to enhance the durability of the excavation, long cable bolts are used as a secondary support system to connect and bind the bolted fractured zone to the higher competent stratification layers. Extensive research in the area of rock bolting with the aim of improving the load transferring mechanism of the bolting system has led the rock bolting technology to be enhanced enormously over the past four decades. Axial loading tests, known as the pull out test, have always been an accepted testing method to examine the tensile strength of tendons and load transfer capacity. Tendons refers to both rock bolt as well as cable bolts in this thesis. This type of test is relatively simple to design and perform both in the field and in the laboratory. Therefore, most available data on tendon performance deals with axial tensile testing. On the other hand, studies on shear behaviour of tendons are limited as shear tests can only be performed in the laboratory. The shear performance of tendons can be significantly affected by the ultimate tensile strength of the bolt, pretension load, rock mass strength, cable bolt surface profile, and cementitious/chemical resin properties. However, there is little known about the shear performance of tendon when installed at varying angles under quasi-static loading conditions. In addition, seismic events and rockburst are a pervasive problem in mines which operate at high extraction ratios and involve release and transmission of energy from the zone of influence of mining. Shear failure of rock bolts in mines are relatively prevalent, in particular in deep mines, which requires extensive research to understand the dynamic shear behaviour of tendons under high impact velocity loading conditions. Nevertheless, there is a lack of knowledge regarding the shear response of tendons under high impact loading condition such as rockburst events in underground mines and tunnels. Therefore, the current research study aims to provide a better understanding concerning the shear response of conventional rock bolts under high velocity impact loading conditions with the help of the laboratory experimental tests as well as numerical modelling approaches

Numerical approach towards dynamic double shear testing of tendons using LS-DYNA

ABSTRACT: Underground support systems using tendons has been one of the significant achievements in Civil and Mining engineering endeavors in facing the challenges of ground control. However, shear failure of rock bolts is a concern in underground excavations particularly with respect to seismic events. The understanding of the performance of rock bolts under dynamic loading condition requires a great deal of research. A series of tests were undertaken utilising a drop hammer mass of 592 kg dropped from a maximum height of 2 m onto grouted rock bolts encapsulated in concrete blocks in the double shear box to investigate the performance of rock bolts under dynamic shear load. Load cells, a displacement laser and high-speed camera were used to monitor the tests. Results from the data analyses are presented in the form of displacement, hammer mass drop velocity, force variation with time for all components involved in each test. A numerical simulation using ANSYS/LS-DYNA was used to simulate the behavior of 18 mm conventional rock bolts under high impact velocity loading conditions. The numerical simulation model was found to be in good agreement with the experimental results

Development of double shear testing of tendons

More than 25 years of uninterrupted research on ground support technology for underground mines has been undertaken at the University of Wollongong. This research has resulted in significant findings on tendon characteristics and strength properties. The paper focuses on the development of a fourth generation of cylindrically shaped shear test apparatus for assessing tendon performance in shear. This shear apparatus is known as the MK-IV Double Shear Box or Naj Aziz Double Shear Box (NADSB), and is based on the experience gained from the development of previous versions of rectangular double shear boxes. The new NADSB is circular in shape and is fitted with a truss system, which permits friction free shear testing of tendons across joint planes. A series of double shear tests were carried out on a number of cable bolts commonly used in Australian mines, both plain and indented wires, under varied pretension loads. The results were compared with similar test results using rectangular shaped double shear apparatus, with and without friction across joint faces. The significance of wire surface roughness and increased initial pretension loads are discussed and conclusions made, suggesting that indented wires are inferior in shear compared with plain cable bolts. The general test procedure of the NADSB is described and different concrete reinforcement technics are reported. The influence of external and internal confinement of the concrete medium blocks in circular double shear box contributed to consistent test results with a minimum of lateral and axial cracks occurring in the host medium

Static and dynamic testing of tendons

Underground support system using tendons has been one of the significant achievements in Civil and Mining engineering endeavours in facing challenges of ground control. However, shear failure of rock bolts is still one of the least monitored phenonmenon in underground excavations with respect to seismic events. The understanding of the performance of rock bolts under dynamic loading condition requires a great deal of research. A series of tests were undertaken utilising a drop hammer mass of 600 Kg from a maximum height of 3.7 m over concrete blocks in the double shear box with chemical resin encapsulated a rock bolt to investigate the performance of rock bolts under dynamic shear load. Load cells, displacement laser and high speed camera were used to monitor the test. Results from the data analyses are presented in the form of displacement, hammer mass drop velocity, acceleration and force variation with time for all components involved in each test. The time factor was found to contribute 30 % of the shear load in static testing in comparison with dynamic; In particular, the force-displacement curve and energy absorption for the reinforcement system are presented to examine the performance of rock bolts and conclusion drawn

Performance of bolting systems in tension and the integrity of the protective sleeve coating in shear

A series of laboratory tests were carried out on sleeved bolt and domed washer plates and nuts to determine; • the tensile strength properties of 24 mm (200 mm core) diameter rock bolts (M24 Bolt), • pull through testing of the bolting system consisting of bolt, domed washer plate and nut integrity, • Integrity of the rock bolt fitted with protective plastic sleeve subjected to shearing. All these tests were carried out on rock bolts and dome washer plates supplied by Dextra / Pretec. Pull testing was carried out in accordance with British Standard (BS 7861.1:2007). It was found that the average strength of tested bolts was 32.5 t, elongation 14.5 %. The maximum dome plate deformation load was in the order of 275 kN. No visible deterioration of the protective plastic sleeves was observed when bolts were sheared for vertical shear displacement of up to 25 mm