Laboratory direct shear test results for natural bedding and sawcut defects have been statistical... more Laboratory direct shear test results for natural bedding and sawcut defects have been statistically analysed in shales and banded iron formation materials across BHP Western Australian Iron Ore deposits (BHP WAIO) to prove the hypothesis of similarity of shear strength of defects. The following paper provides typical Hencher corrected friction angles based on statistical methods to group data sharing similar characteristics. This paper justifies the existence of similar populations of shear strength of defects based on rigorous statistical analysis of valid direct shear test samples collected from multiple projects of the Pilbara. Spatial distribution bias effects and normality tests have been checked. Surface 'geotechnical' weathering grades do not explain the reduction of the shear strength of defects in shales. The use of base of completed oxidation and spectral signatures have provided a better explanation for the variability observed on the shear strength of defects. Where weathered shale samples from the Brockman column have greater frictional strength than fresh samples, a paradoxical phenomenon that can be attributed to chemical alteration generating additional textural roughness.
In recent years, an innovative approach has been proposed in using two ground-based synthetic ape... more In recent years, an innovative approach has been proposed in using two ground-based synthetic aperture radars to simultaneously monitor slope stability (Severin et al. 2011; 2014). The technique allows to obtain a detailed pseudo 3D displacements map covering large pit slopes. In October 2014, a similar experiment was conducted at MMG Limited's Century Mine (Queensland), using two real aperture radars. The outcomes of the test have shown that even if reasonable results can be achieved, more precise information can be obtained through the integration with prism data. The technique has produced a much clearer image of the slope deformation, identifying a complex break-up of the slope surface due to the weathering process affecting the shale rock mass.
Safety and efficiency of mining operations depend on the quality of design of mining excavations ... more Safety and efficiency of mining operations depend on the quality of design of mining excavations and sequence. A crucial ingredient in mining design is the adequate information of both the original in situ stress and the stress disturbance caused by mining. The main method of stress determination-the overcoringhas a number of drawbacks. 1. It requires an open access to the location of the measurements, which is especially difficult if the stress is to be measured ahead of deep underground excavation. 2. It presumes the rock to be isotropic, while in many cases the rock anisotropy is significant. Subsequently, the isotropic stress reconstruction procedure of the overcoring method can give erroneous stress magnitudes and directions (e.g. Amadei and Goodman, 1982). The rock memory methods-DRA and the Kaiser effect are free from the influence of anisotropy. Moreover the DRA technique can, in principle, provide as a by-product a sufficient number of measurements to reconstruct the full anisotropic tensor of moduli, or compliances sufficient to characterise rock anisotropy, introduce corrections to the overcoring stress reconstruction procedure and quantify the effect of rock anisotropy on the stress concentrations induced by the excavation. In this paper, we present the procedure for the anisotropy characterisation based on DRA and analyse the sensitivity of the procedure and the effects of the rock anisotropy on stress measurements.
Melt quenched high pressure die casting (MQ-HPDC) is a new die casting process developed recently... more Melt quenched high pressure die casting (MQ-HPDC) is a new die casting process developed recently for improving the casting quality of the conventional high pressure die casting (HPDC) process. In the MQ-HPDC process, an alloy melt with a specified dose and superheat is quenched by directly pouring the alloy melt into a preheated metallic container. The thermal mass and preheating temperature of the container is selected so that the alloy melt is quenched just below the alloy liquidus and heterogeneous nucleation takes place during the melt quenching. The quenched alloy melt is then fed immediately into the shot sleeve for component casting. In this paper we present the MQ-HPDC process and the resultant microstructures and mechanical properties of a MQ-HPDC A3 56 alloy.
The uniaxial compressive strength (UCS) is an essential input parameter of the Hoek & Brown failu... more The uniaxial compressive strength (UCS) is an essential input parameter of the Hoek & Brown failure criterion to represent the shear strength of rock masses, which is frequently used for slope stability analysis in the mining industry. This paper presents the use of the field estimated strength (FES) as a way to estimate the UCS, which is not a new idea but rather a regular practice applied by consultants and internal engineers within BHP Iron Ore for the last 20 years. However, the paper puts emphasis on the practical limitations related to the FES calibration by spot sampling, the bias effects caused by 'length-weighted' calculations due to the skewness distribution on FES and presents a logarithmic transformation on FES as a manner to test similarity of typical values. The paper concludes presenting typical values as defined by statistical similarity 'hypothesis testing' on FES data of the same stratigraphical rock units across different locations in the Pilbara.
Slope design in the regolith comprising weathered rock and transported materials is often very co... more Slope design in the regolith comprising weathered rock and transported materials is often very conservative. This arises from the use of conventional laboratory testing using saturated samples. In Western Australia, many of the mines are located in areas of high salinity. When materials recovered for testing are located above the water table they are most likely to be affected by suction. In this paper the authors will present the results of testing materials recovered from a gold mine where the in situ water content was approximately 20% while the saturated water content was approximately 50%. The material had a permeability of approximately 10⁻¹⁰ m/s and comprised over 40% clay size material. The salinity was approximately 7,000 ppm. Suction comprises matric and osmotic suction. The test work shows that the osmotic suction had the most significant effect on reducing the in situ water content and raising the shear strength parameters. This had a big impact on understanding of slope stability in these materials. The dispersive nature of the material subsequently influenced stability when approaching the ground water table but for unforeseen reasons. The paper shows how the slope was then stabilised.
International Journal of Rock Mechanics and Mining Sciences, Sep 1, 2014
The sources of nonlinear deformation in hard rock under short term uniaxial compression can be at... more The sources of nonlinear deformation in hard rock under short term uniaxial compression can be attributed to crack closure, sliding, compaction and crack generation. The common approach to finding the Young's modulus of a "hard rock" is to determine the linear part of stress-strain curve. However, it is usually a difficult task, although several methods of resolving it have been proposed in the past. We believe that in some rock types there is no linear part as such and provide evidence to support the fact that nonlinear deformation contributed by crack closure, sliding and compaction in different degrees could co-exist within the same stress range. We demonstrate that the change in tangent modulus under different stress levels is attributable to the combination of crack closure, sliding and dilatancy. The difference in tangent modulus under different stress levels could reach more than 20GPa in some rocks. We have also found that the nonlinear deformation contributed by irreversible sliding, compaction and even dilatancy increases the rock stiffness in the second loading. This phenomenon was found under loads ranging from 15% to 95% of UCS.
An experimental study of 3-D crack growth from initial cracks of different shapes and inclination... more An experimental study of 3-D crack growth from initial cracks of different shapes and inclinations in biaxial compression with different biaxial load ratios (x ∕ y) is presented. Unlike 3-D crack growth in uniaxial compression, which is characterised by the presence of intrinsic limits on 3-D growth of wing cracks associated with wing wrapping, in biaxial compression the wing crack can grow extensively and is parallel to the free surfaces of the specimen as long as the x ∕ y ratio exceeds a threshold. Surprisingly, the threshold is extremely low: around 0.05 for all cases considered; below this threshold, the wing crack growth is restricted. It is found that the shape and inclination of the initial crack have minor effect on this transition process.
Laboratory direct shear test results for natural bedding and sawcut defects have been statistical... more Laboratory direct shear test results for natural bedding and sawcut defects have been statistically analysed in shales and banded iron formation materials across BHP Western Australian Iron Ore deposits (BHP WAIO) to prove the hypothesis of similarity of shear strength of defects. The following paper provides typical Hencher corrected friction angles based on statistical methods to group data sharing similar characteristics. This paper justifies the existence of similar populations of shear strength of defects based on rigorous statistical analysis of valid direct shear test samples collected from multiple projects of the Pilbara. Spatial distribution bias effects and normality tests have been checked. Surface 'geotechnical' weathering grades do not explain the reduction of the shear strength of defects in shales. The use of base of completed oxidation and spectral signatures have provided a better explanation for the variability observed on the shear strength of defects. Where weathered shale samples from the Brockman column have greater frictional strength than fresh samples, a paradoxical phenomenon that can be attributed to chemical alteration generating additional textural roughness.
In recent years, an innovative approach has been proposed in using two ground-based synthetic ape... more In recent years, an innovative approach has been proposed in using two ground-based synthetic aperture radars to simultaneously monitor slope stability (Severin et al. 2011; 2014). The technique allows to obtain a detailed pseudo 3D displacements map covering large pit slopes. In October 2014, a similar experiment was conducted at MMG Limited's Century Mine (Queensland), using two real aperture radars. The outcomes of the test have shown that even if reasonable results can be achieved, more precise information can be obtained through the integration with prism data. The technique has produced a much clearer image of the slope deformation, identifying a complex break-up of the slope surface due to the weathering process affecting the shale rock mass.
Safety and efficiency of mining operations depend on the quality of design of mining excavations ... more Safety and efficiency of mining operations depend on the quality of design of mining excavations and sequence. A crucial ingredient in mining design is the adequate information of both the original in situ stress and the stress disturbance caused by mining. The main method of stress determination-the overcoringhas a number of drawbacks. 1. It requires an open access to the location of the measurements, which is especially difficult if the stress is to be measured ahead of deep underground excavation. 2. It presumes the rock to be isotropic, while in many cases the rock anisotropy is significant. Subsequently, the isotropic stress reconstruction procedure of the overcoring method can give erroneous stress magnitudes and directions (e.g. Amadei and Goodman, 1982). The rock memory methods-DRA and the Kaiser effect are free from the influence of anisotropy. Moreover the DRA technique can, in principle, provide as a by-product a sufficient number of measurements to reconstruct the full anisotropic tensor of moduli, or compliances sufficient to characterise rock anisotropy, introduce corrections to the overcoring stress reconstruction procedure and quantify the effect of rock anisotropy on the stress concentrations induced by the excavation. In this paper, we present the procedure for the anisotropy characterisation based on DRA and analyse the sensitivity of the procedure and the effects of the rock anisotropy on stress measurements.
Melt quenched high pressure die casting (MQ-HPDC) is a new die casting process developed recently... more Melt quenched high pressure die casting (MQ-HPDC) is a new die casting process developed recently for improving the casting quality of the conventional high pressure die casting (HPDC) process. In the MQ-HPDC process, an alloy melt with a specified dose and superheat is quenched by directly pouring the alloy melt into a preheated metallic container. The thermal mass and preheating temperature of the container is selected so that the alloy melt is quenched just below the alloy liquidus and heterogeneous nucleation takes place during the melt quenching. The quenched alloy melt is then fed immediately into the shot sleeve for component casting. In this paper we present the MQ-HPDC process and the resultant microstructures and mechanical properties of a MQ-HPDC A3 56 alloy.
The uniaxial compressive strength (UCS) is an essential input parameter of the Hoek & Brown failu... more The uniaxial compressive strength (UCS) is an essential input parameter of the Hoek & Brown failure criterion to represent the shear strength of rock masses, which is frequently used for slope stability analysis in the mining industry. This paper presents the use of the field estimated strength (FES) as a way to estimate the UCS, which is not a new idea but rather a regular practice applied by consultants and internal engineers within BHP Iron Ore for the last 20 years. However, the paper puts emphasis on the practical limitations related to the FES calibration by spot sampling, the bias effects caused by 'length-weighted' calculations due to the skewness distribution on FES and presents a logarithmic transformation on FES as a manner to test similarity of typical values. The paper concludes presenting typical values as defined by statistical similarity 'hypothesis testing' on FES data of the same stratigraphical rock units across different locations in the Pilbara.
Slope design in the regolith comprising weathered rock and transported materials is often very co... more Slope design in the regolith comprising weathered rock and transported materials is often very conservative. This arises from the use of conventional laboratory testing using saturated samples. In Western Australia, many of the mines are located in areas of high salinity. When materials recovered for testing are located above the water table they are most likely to be affected by suction. In this paper the authors will present the results of testing materials recovered from a gold mine where the in situ water content was approximately 20% while the saturated water content was approximately 50%. The material had a permeability of approximately 10⁻¹⁰ m/s and comprised over 40% clay size material. The salinity was approximately 7,000 ppm. Suction comprises matric and osmotic suction. The test work shows that the osmotic suction had the most significant effect on reducing the in situ water content and raising the shear strength parameters. This had a big impact on understanding of slope stability in these materials. The dispersive nature of the material subsequently influenced stability when approaching the ground water table but for unforeseen reasons. The paper shows how the slope was then stabilised.
International Journal of Rock Mechanics and Mining Sciences, Sep 1, 2014
The sources of nonlinear deformation in hard rock under short term uniaxial compression can be at... more The sources of nonlinear deformation in hard rock under short term uniaxial compression can be attributed to crack closure, sliding, compaction and crack generation. The common approach to finding the Young's modulus of a "hard rock" is to determine the linear part of stress-strain curve. However, it is usually a difficult task, although several methods of resolving it have been proposed in the past. We believe that in some rock types there is no linear part as such and provide evidence to support the fact that nonlinear deformation contributed by crack closure, sliding and compaction in different degrees could co-exist within the same stress range. We demonstrate that the change in tangent modulus under different stress levels is attributable to the combination of crack closure, sliding and dilatancy. The difference in tangent modulus under different stress levels could reach more than 20GPa in some rocks. We have also found that the nonlinear deformation contributed by irreversible sliding, compaction and even dilatancy increases the rock stiffness in the second loading. This phenomenon was found under loads ranging from 15% to 95% of UCS.
An experimental study of 3-D crack growth from initial cracks of different shapes and inclination... more An experimental study of 3-D crack growth from initial cracks of different shapes and inclinations in biaxial compression with different biaxial load ratios (x ∕ y) is presented. Unlike 3-D crack growth in uniaxial compression, which is characterised by the presence of intrinsic limits on 3-D growth of wing cracks associated with wing wrapping, in biaxial compression the wing crack can grow extensively and is parallel to the free surfaces of the specimen as long as the x ∕ y ratio exceeds a threshold. Surprisingly, the threshold is extremely low: around 0.05 for all cases considered; below this threshold, the wing crack growth is restricted. It is found that the shape and inclination of the initial crack have minor effect on this transition process.
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