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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.

The application of cable bolts as a secondary support system is an increasing trend in underground coal mines worldwide. The performances of cable bolts have been evaluated under both axial and shear loading conditions. Two methods of testing cables for shear, single and double shear, have been recognised. This paper examines the shear behaviour of a variety of cable bolts under different pre-tension loads by double shear testing. Plain, spiral and the combination of both cable types were used in this study. The initial axial load and the type of cable bolts are the main factors affecting their shear strength. By increasing the axial pre-tension load, the peak shear load occurs at lower shear displacement. The failure angle due to cable bending across the joint at different pre-tension loads varied between 41° and 49°. This demonstrates that the ratio of axial and perpendicular displacements is almost constant and on average the failure occurs at about 45°. A novel analytical model is proposed to evaluate the shear behaviour of pre-tensioned fully grouted cable bolts subjected to double shearing. Energy and Fourier Series methods were incorporated in the model to simulate the shear behaviour of cable bolts. The comparison of the experimental results with the proposed model shows a good agreement.

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.

The load transfer mechanisms of cable bolts differ from normal rebar bolts. Cable bolts used in mines are basically steel strands with different constructions depending on the number of wires or elements and the way that these elements are laid. Tendon bolts (rebar and cable) are normally evaluated for strength and load transfer properties. The strength of tendon can be carried out by tensile failure tests, while the load transfer strength is evaluated by pull and shear strength tests. Short Encapsulation Pull Testing (SEPT) is used to study of the load transfer capacities of tendons, and can be undertaken both in the laboratory and in situ. A new apparatus known as Minova Axially Split Embedment Apparatus (MASEA) was used to study load-displacement characteristics of smooth versus spiral profile cable bolts. Minova Stratabinder grout was used for encapsulating 400 mm long 19 wire 22 mm diameter superstrand cable in the embedment units. The anchorage of the cable on two sides of the embedment apparatus were intentionally installed at different lengths, to allow the cable to be pulled out from one side of the anchorage. The spiral wire strand cable bolts achieved higher peak pull-out load at minimum displacement in comparison with smooth surface wire strand. The peak pull out force increased with the age of encapsulation grout. The MASEA was easier to assemble and test at a short period of time, thus allowing quick and repeated tests to be undertaken.

A mathematical model which is able to determine the pure shear strength of cable bolt was introduced and calibrated for various conditions. The proposed equation is developed based on the Fourier series concept and a linear relationship between shear and normal forces generated during cable bolt shearing. The conventional double shearing instrument was up to date to evaluate the pure shear strength of cable bolt by removing the contribution of concrete block frictional force. The experimental data obtained from the revised double shear instrument was in good agreement with the prediction of the proposed mode.

The application of cable bolts as a secondary support system in coal mines has substantially increased over the last decades. This development emphasises a prerequisite for a better understanding of the mechanical behaviour of cable bolts in combination of shear and axial loads, which is of interest to geotechnical engineers and designers of underground structures. Based on various research studies undertaken, analytical models have been proposed to assess the shear performance of cable bolts with the aim of designing safe and sustainable rock structures. Recently, a shear strength model for cable bolts was proposed by Aziz et al., (2015). The model was based on Mohr-Coulomb failure criterion and the Fourier series concept. The proposed analytical model was associated with a set of systematic experimental studies by which model coefficients were calibrated. This paper compares the performance of a number of proposed mathematical models against the experimental data and presents a model that simulates the shear behaviour of cable bolts, which is in agreement with the experimental results.

This paper experimentally compares the shear behavior of fiber glass (FG) bolt, rock bolt (steel rebar bolt) and cable bolt for the bolt contribution to bolted concrete surface shear strength, and bolt failure mode. Two double shear apparatuses of different size were used for the study. The tensile strength, the shear strength and the deformation modulus of bolt control the shear behavior of a sheared bolted joint. Since the strength and deformation modulus of FG bolt, rock bolt and cable bolt obtained from uniaxial tensile tests are different, their shear behavior in reinforcing joints is accordingly different. Test results showed that the shear stiffness of FG bolted joints decreased gradually from the beginning to end, while the shear stiffness of joints reinforced by rock bolt and cable bolt decreased bi-linearly, which is clearly consistent with their tensile deformation modulus. The bolted joint shear stiffness was highly influenced by bolt pretension in the high stiffness stage for both rock bolt and cable bolt, but not in the low stiffness stage. The rock bolt contribution to joint shear strength standardised by the bolt tensile strength was the largest, followed by cable bolts, then FG bolts. Both the rock bolts and cable bolts tended to fail in tension, while FG bolts in shear due to their low shear strength and constant deformation modulus.

Bolting is currently the most commonly accepted rock reinforcing method of dealing with rock strata instability in both surface and underground mines as well as civil engineering. Bolts are installed in fractured rock mass to build composite beams in weak strata or to attach weak excavation surfaces to deeper and competent rock layers to achieve stability. After opening, rock mass around the excavation space experiences stress redistribution and rock fracturing occurs in this process. Bolts installed in the fractured rock mass around excavations normally bear combined tensile and shear loads due to the opening and sliding of rock fractures. Direct shear restraint and high normal stress are applied by the bolt to the fracture surfaces to minimise their displacements. This mechanism allows the excavation surfaces to stabilise and makes them self-supporting. In the interactive process of rock mass and bolt, two load transfer mechanisms are involved: the axial tensioning (axial shearing at the bolt-grout interface, in essence) and the lateral shearing. Axial tensioning was the common focus in past studies, whereas lateral shearing is attracting more attention at present. The strength of the bolt when subjected to both shear and tensile loads is smaller than bolt strength when subjected to tensile load only. Thus, ignoring the shear load in bolting design probably leads to a higher safety factor. Hence, a deep understanding of bolt behaviour subjected to combined loads is essential in bolting system design and assessment. In the past, a number of experimental and theoretical investigations were conducted on the shear behaviour of the rock discontinuity reinforced by rock bolts and a few preliminary conclusions were drawn. Yet, few studies were performed on the shear behaviour of cable bolted rock discontinuities. Thus, this research investigated the shear performance of cable bolted rock discontinuities both experimentally and theoretically to provide more knowledge in t

The application of cable bolts in underground mines is an increasing trend all over the world; therefore, it is necessary to determine the axial and shear stresses on cable bolts. One important factor is to determine the coefficient of friction of concrete joint surface. This paper examines the contact coefficient of several cabled strata under various pre-tension loads subject to double shearing test. The result shows that the contact surface area can vary between 70-90% of the total surface area. This empirical value helps to figure out shear and axial stresses, where it is impossible to determine the exact amount of contact coefficient.

Cable bolting and rock/rebar bolting are the two main reinforcement techniques used in underground coal mines to maintain the stability of openings. Due to the structural features of cable strands, cables and solid bolts behave differently in reinforcing rock strata. Since the generation of a cable model is different in a numerical program, and especially impossible in a 2D program, some researchers tend to replace cable bolts with rebar bolts in numerical models, which is still pretty suspicious. To compare their performance differences when subjected in tension and/or in shear, numerical models of cable and rebar bolt were built and analysed using Flac3D program. The generated models of cables and rebar bolts were assigned identical geometrical dimensions and basic mechanical properties to ensure comparability. Attention was mainly given to the strength and stiffness of cables and rebar bolts both in tension and in shear. Conclusions are drawn from these models, which can be a reference for other studies in this area.

The application of cable bolts for ground support is on the increase in underground coal mines worldwide. Currently, two methods of evaluating the performance of the cable bolt are favoured; the short encapsulation pull test and shear test. The former method can be used both in the laboratory and the field, while the latter can be undertaken mainly in the laboratory. There are two methods of shear strength testing, single and double shear tests. This paper examines the double shear testing of several cable bolts currently marketed in Australia under various pre-tension stresses. Both plain and indented wire cable bolts were tested. It was found that, the shear strength of the cable bolt was a function of the wire geometry and initial pre-tension. Indented wire cable bolts were lower in shear strength than the plain wire cable bolts. A mathematical model was proposed to evaluate the shear strength of cable bolts using Fourier series and Mohr-Coulomb failure criterion. The model coefficients were determined based on the experimental results. The findings from the mathematical modelling tallied well with the experimental results.

The strength properties of Secura Hollow Groutable Cable-bolts (HGC) were examined for tensile and shear failures. The 30 mm diameter, nine strand, cable bolt consisted of a mixture of five 7.5 mm plain and four 7.0 mm indented strands wrapped around a central 14 mm steel grouting hole to make a round cable with lay length of 500 mm with bulbs at 500mm centres of diameter 35mm. The tensile strength of the cable was tested in accordance with the British Standard (BS7861-part 2:2009) using the double embedment pull test. The shear strength of the cable bolt was tested by both the BS7861 single and UOW double shear methods. The single shear double test used a guillotine shear frame of double embodiment tendon/grout assembly in a steel tube, while the double shear method enabled shear testing of the cable bolt in concrete to simulate rock. It was found that the tensile strength of the cable was in the order of 680 kN, the shear load by single shear test, based on the average of three tests, was around 448 kN. The shear failure load of the cable bolt from double shear testing based on two tests averaged around 786 kN which is significantly higher than achieved from the single shear test. Thus the shear value, obtained from the double shear method was between 13 and 18 % greater than the single shear test method. The use of the guillotine shear frame for the single shear method was considered an unrealistic method of evaluating the shear characteristics of the cable bolts in rock.

Glass-Reinforced Polymer (GRP) bolts, commonly known as Fibre Glass (FG) dowels are increasingly applied for strata reinforcement in mines. The most popular dowels used in coal mines are the 22 mm diameter fully threaded type. A series of tests were undertaken to evaluate various strength properties of FG dowels. These include tensile failure tests by the double-embedment method, single and double guillotine shear tests, double shear tests in concrete medium and punch shear tests. Punch shear tests were used to evaluate the dowel shear strength parallel and perpendicular to the fibre glass strands or elements direction of extrusion. The study found that the tensile strength of the 22 mm diameter fibre glass dowels was in the order of 30 t. In the shear testing, the peak shear load was influence by the encapsulation grout type and the level of fibre glass axial pre-tension. Also, there was a nearly fivefold difference in the shear strength value of fibre glass dowels tested parallel as against perpendicular to the dowel axis.

In the absence of bolting standards for strata reinforcement in the Australian mines, though individual mines or companies have their in house practices, there remains a visible vacuum in assessing credibly the various properties of chemical resins and cementitious grouts. Currently, all methods used in evaluating the mechanical properties of both chemical resins and other bolting reinforcement grouts are dependent on the American, British and South African standards and accordingly there is no uniform and unified methodology of testing. A simplified approach has been discussed to enable mine operators and other interested parties to determine various pertinent properties of chemical resins and grouts in the bolting system only and this paper describes the various methods used to test a set of resin properties. A special Resin Mixing Container (RMC) was developed to permit multiple resin samples to be cast with consistent resin / grout quality. Various conclusions were drawn from the study enabling a better understanding between suppliers and end users.