Shear behavior of clayey infilled rock joints having triangular and sinusoidal asperities

Rock joints govern an important role in the overall stability of rock slope which may be filled with infill material due to transported materials with water, weathering as well as joint shearing. There are two methods of testing rock joint shear behavior, one is Constant Normal Load (CNL), and another is Constant Normal Stiffness (CNS). The CNL is found suitable in slope stability where sliding mass can move freely without any restriction while CNS is suitable in underground excavation, pile socketed in rock and reinforced rock slope where the stiffness of boundary restricts dilation during the shearing process. This study investigates the shear behavior of clay infilled rock joints with triangular and sinusoidal asperities under CNL conditions. The pair of triangular and sinusoidal asperities is Type 1T, Type 2T and Type 1S, Type 2S respectively where prefix represent asperity height and suffix represent the type of asperity. Joint Roughness Coefficient () obtained from back-calculation of Barton equation using experimental data is 7, 9, 9 and 12 for Type 1T, Type 2T, Type 1S and Type 2S respectively. The direct shear test was performed on two campaigns, among these, was one of understanding shear behavior of infilled rock joints under various normal loads and another was the shear behavior of infill rock joints under various infill thicknesses. During the first campaign shear behavior of clayey infilled rock joint fewer than three different normal loads were tested. Likewise, in the second campaign shear behavior of clayey infill rock joint under three infill thickness were performed. Overall this study provides better insights into shear behavior clayey infilled rock joints having different joint morphology

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

Axial Performance of Cable Bolts Under Various Bonding and Loading Conditions

Cable bolts are one of the main methods of support for many mining and civil engineering projects. This study focused on the axial performance of the cable bolts under various conditions. A large scale pull out apparatus was designed to support the testing of various mainstream cables in the Australian mining industry. An additional small scale test was also devised to provide comparative results with the large scale test. Six cable types, ranging from plain to indented and bulbed, were encapsulated using two types of cementitious and resin based bonding agents. The cables were first tested in each testing scale in monotonic and cyclic loadings to simulate varying stress paths for the service life performance of the cables. The results showed much higher stiffness for the large scale tests compared to the small scale sleeve pull out tests. All grouted cables consistently illustrated higher load values in all tests compared to the resin sample. The bulbed cable indicated that the presence of a bulb structure on a cable tends to overshadow other attributes. Cyclic tests in both testing setups suggested a low to almost non-existing adverse effect on the pull out test compared to the monotonic tests. Surface indentation clearly increased the performance of the cable bolts in all cases. The radial stiffness value on the large scale tests was a determining factor. In the end, a series of numerical models using finite element was calibrated by the results of the large scale tests. The sensitivity analysis of the numerical model exhibited a similar effect for the elastic modulus of confinement and the uniaxial compressive strength of the concrete and grout for plain and bulbed cables. Finally, in the numerical model, the most important factor proved to be the bulb size; with a high potential to alter the load values with even small changes

Effect of surface profile on axial load transfer mechanism of tendons

ABSTRACT: Cable bolts as one of the most common means of ground support in surface and underground projects are attracting more attention due to their advantages over more expensive and cumbersome support elements. Thus, newer cables with new configurations and surface properties are emerging on a regular basis. Conventionally, the performance of cable bolts is studied in two main categories of axial and shear load transfer mechanisms. This paper focuses on the former by developing and proposing an experimental plan to cast light on the effect of surface profile on axial performance of cable bolts. Consequently, 15 representative surface profiles were designed and machined on metal base plates using a CNC machine. Later, these plates were used as moulds for casting cylindrical samples of Stratabinder cementitious grout. Three curing times of one day, 7 days, and 28 days were studied under static compression loading. It was observed that the surface roughness of the samples plays a major role in failure as it inhibits free movement of grout metal interface and inflicts end effect as well as introducing stress concentration point. These two drastically reduce the performance of grout and cause tensile crack growth

Numerical simulation of stress distribution in longwall panels during the first caving interval

Reliable prediction of induced stress distribution in longwall panels enhances safety in longwall mining. This paper presents the results of numerical simulation intended to examine stress distribution in terms of peak abutment pressures during the first caving of longwall mining. Longwall mining was simulated by incorporating Universal Distinct Element Code (UDEC). Several conceptual models were developed and subsequently analyzed to investigate the effects of five critical parameters on peak abutment pressures. Critical parameters that were studied as a part of this investigation included roof strata uniaxial compressive strength, immediate roof height, spacing of bedding planes and Vertical and horizontal in situ stresses. The results of numerical simulation increased the current understanding of rear and front abutment pressures in longwall mining under various geo-mining conditions

Shear strength properties of artificial rock joints

The shear strength property of artificial rock joints with triangular and sinusoidal roughness was investigated in the laboratory by the aid of direct shear test machine. In particular, this paper includes literature review of past studies on shear strength properties of unfilled and infilled rock joints, experimental studies on shear strength properties of artificial rock joints with triangular, sinusoidal and plain roughness under various normal load and comparison between shear behaviour of these rock joints having different roughness patterns. This research presents the concepts development essential to envision the shear behaviour of rock slopes aided by artificial rock joints. It was concluded that the shear behaviour of rock joints is a function of normal stress, roughness value and pattern of asperity

Effect of surface profile on load transfer mechanism of tendons

Cable bolts as one of the most common means of ground support in surface and underground projects are attracting more attention due to their advantages over more expensive and cumbersome support elements. Thus, newer cables with new configurations and surface properties are emerging on a regular basis. Conventionally, the performance of cable bolts is studied in two main categories of axial and shear load transfer mechanisms. This paper focuses on the former by developing and proposing an experimental plan to cast light on the effect of surface profile on axial performance of cable bolts. Consequently, 15 representative surface profiles were designed and machined on metal base plates using a CNC machine. Later, these plates were used as moulds for casting cylindrical samples of Stratabinder cementitious grout. Three curing times of one day, 7 days, and 28 days were studied under static compression loading. It was observed that the surface roughness of the samples plays a major role in failure as it inhibits free movement of grout metal interface and inflicts end effect as well as introducing stress concentration point. These two drastically reduce the performance of grout and cause tensile crack growth

Shear behavior of clayey infilled rock joints having triangular and sinusoidal asperities

Rock joints govern an important role in the overall stability of rock slope which may be filled with infill material due to transported materials with water, weathering as well as joint shearing. There are two methods of testing rock joint shear behavior, one is Constant Normal Load (CNL), and another is Constant Normal Stiffness (CNS). The CNL is found suitable in slope stability where sliding mass can move freely without any restriction while CNS is suitable in underground excavation, pile socketed in rock and reinforced rock slope where the stiffness of boundary restricts dilation during the shearing process. This study investigates the shear behavior of clay infilled rock joints with triangular and sinusoidal asperities under CNL conditions. The pair of triangular and sinusoidal asperities is Type 1T, Type 2T and Type 1S, Type 2S respectively where prefix represent asperity height and suffix represent the type of asperity. Joint Roughness Coefficient (JRC) obtained from back-calculation of Barton equation using experimental data is 7, 9, 9 and 12 for Type 1T, Type 2T, Type 1S and Type 2S respectively. The direct shear test was performed on two campaigns, among these, was one of understanding shear behavior of infilled rock joints under various normal loads and another was the shear behavior of infill rock joints under various infill thicknesses. During the first campaign shear behavior of clayey infilled rock joint fewer than three different normal loads were tested. Likewise, in the second campaign shear behavior of clayey infill rock joint under three infill thickness were performed. Overall this study provides better insights into shear behavior clayey infilled rock joints having different joint morphology

A look at the performance of barrel and wedge assembly in cable bolts applications

Abstract Pretensioning is one of the most common practices in cable bolting. A barrel and wedge is typically used in the free end of the cable to hold the pretension load. This study investigates the performance of barrel and wedge in cable bolt large-scale laboratory pull out tests. Twenty-five experiments have been completed containing various barrel and wedge and cable sizes under different loading conditions, namely monotonic and cyclic. The results indicated barrel and wedges undergo constant displacement throughout the experiment. The cyclic tests suggest that the barrel and wedge assembly displacement are almost entirely non-reversible. Two distinct behaviours, namely exponential and deflection point based, were observed. The study concludes that barrel and wedge assemblies can significantly influence the performance of cable bolts under axial load

Axial response of resin-encapsulated cable bolts in monotonic and cyclic loading

The ease of use and the design flexibility of cable bolts have made them a popular choice for rock support. Cable bolts can be encapsulated with cementitious grout or resin. There is a need to better understand the impact of resins on the behaviour of cable bolts under varying load and stress regimes over their long service life. This study reports on 18 large-scale resin pull-out tests. The testing apparatus minimised the rotational movement of the cable at the exit point by using a fully grouted anchor tube. Six cable bolts, ranging from 50 to 100 tonnes in capacity, anchored using a fast-curing urea silica resin, were tested under monotonic and cyclic loading. Each cable type was tested twice in monotonic loading, and then the average initial peak load was used to generate a cyclic loading pattern. The study found that the resin product had a relatively low load capacity regardless of the cable type, and that loading type had a minimal impact on the results. The cable diameter had a minor influence on the pull-out results. The resin provided a stiff behaviour and an excellent response to repeated loading