Civil and Resources

Various numerical techniques now exist to predict the performance of rocksocketed piles. These have generally ignored the influence of socket wall roughness on the pile capacity because no technique was available to include this effect. This paper examines the application of a simple model, which accounts for socket wall roughness and provides a shearing mechanism at the pile-rock interface, to predict the performance of side-resistance-only piles socketed in weak rock. Good agreement was obtained between the predicted load-settlement response using the proposed technique and the actual results of I0 pile tests.

The stress path for a series of constant stiffness direct shear tests has been predicted using the Ladanyi and Archambault variable dilation shear equation. The tests were performed on highly weathered mudstone abutting concrete, to simulate side resistance socketed pile performance. The joint prbfiles have been analysed statistically to determine relevant properties for use in a simple triangular model for the purposes of this prediction. The proposed method has been tested in the prediction of a side resistance socketed pile load test. Remarkably good agreement is achieved.

136A strata contain 'underclays' or other low strength strata. A study to evaluate the geotechnical properties of the strata and to determine the geological factors contributing most significantly to strength development was carried out. Both laboratory and in situ tests were performed, and floor movement was monitored. Results indicate that underclay shear strength and stratigraphy of the subcoal strata are important, shear strength affecting load carrying ability ani the stratigraphy affecting the failure mechanism. A method of bearing capacity ar~lysis developed by Vesic for two layer systems is used to define pillar stability. Results of this analysis agree well with observations.

This paper presents the results of a program of determining the current insitu stress based on testing under cores taken from exploration drilling. The analysis of the results uses the deformation rate technique (DRA) developed by Yamamoto and published in1990. The results when rotated into the appropriate direction are confirmed in direction and magnitude by two independent stress measurement programs using Hydraulic Fracture. Work has also been undertaken to confirm the technique with CSIRO Hollow Inclusion (HI) tests. The initial testing which established the veracity of the method was undertaken in May 2002. Confirmatory testing of previously tested under cores was completed in August 2004. These tests not only showed the current insitu stress, but also confirmed the Kaiser Effect stresses measured by the Acoustic Emission (AE) technique, as well as revealed the maximum load that the samples had been tested. Six independent test programs have been undertaken using different personnel and different laboratories to confirm that the approach is robust, simple and elegant.

Rock mass classification systems are extensively used in rock engineering design work, and mine design is no exception. Among the systems most widely used for mining-related design work are the NGI Q-system (Barton et al., 1974), the RMR system (Bieniawski, 1976), the MRMR system (Laubscher and Taylor, 1976) and, more recently, the GSI system (Hoek et al., 1998). Classifying the

Rock mass classification systems are extensively used in rock engineering design work, and mine design is no exception. Among the systems most widely used for mining-related design work are the NGI Q-system (Barton et al., 1974), the RMR system (Bieniawski, 1976), the MRMR system (Laubscher and Taylor, 1976) and, more recently, the GSI system (Hoek et al., 1998). Classifying the rock mass is widely seen as being the fieldwork required to characterize the rock mass and enable the application of empirical design methods associated with the different classification systems. This paper argues that it is fundamentally important to recognize the distinction between rock mass characterization and rock mass classification. These two processes should, in most cases, be separated from each other. Rock mass characterization should be used to determine the intrinsic properties of the rock mass independently of the application; i.e. independent from the infrastructure to be designed, the size, shape, and orientation of the excavation(s) or pillar(s), etc. Rock mass characterization should also be compatible with most classification systems and empirical design methods to be used. Rock mass characterization is the background fieldwork required to perform rock mass classification and/or engineering design work. Rock mass classification is the subsequent step to the characterization, and an integral part of the design process. Parameters that vary according to the design, such as the relative orientation of geological structures compared to the opening or the mine-induced stresses, should be calculated as part of the rock mass classification and design process, rather than during the rock mass characterization process. The failure to distinguish between rock mass characterization and rock mass classification can lead to major design errors and poor results.

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.

The aim of the present work is to assess whether a single fibre pull-out test can be related to the behaviour of multiple fibres in fibre reinforced concrete under bending condition. A simple model based on the stress block theory is described and compared with experimental results on three point bending tests with aligned fibres.

A series of tests are described in which the in situ stress has been recovered using the rock memory technique, known as deformation rate analysis (DRA), where the samples have been subjected to confinement (30 and 50 MPa). The rock samples comprised Urad Aplite Porphyry and were recovered from oriented core, drilled from a depth of approximately 1,550-1,650 m below surface lower than the current mine development. The oriented core is subsampled to obtain the test samples in six directions. The tests were performed in a sophisticated, very stiff triaxial stress cell. The unconfined compressive strength (UCS) of the rock was approximately 70 MPa. The maximum in situ stress was determined to be approximately 70 MPa. Based on experience the test procedure adopted typically loads the samples to a stress equal to three times the estimated overburden stress. In this case, that would be approximately 120 MPa, which would clearly exceed the UCS and hence the unconfined memory test would not have been applicable. Testing under confinement can increase the measurable stress difference, i.e. 1-3, and thus significantly extend the depth to which this technique can be undertaken when compared with unconfined tests suitable for other memory techniques. In particular, in the tests conducted, the confinement of 30 and 50 MPa raised the strength (1-3) from 70 MPa to between 170-270 MPa. Such an approach has implications for testing rock samples recovered from deep drilling where conventional testing could not reach the expected in situ stress without premature failure of the samples.

An experimental study of post-peak behaviour of rock models in uniaxial compression under different controlling methods is presented. A series of mortar samples with different compositions are firstly tested into post-peak stages using the axial strain control. In axial strain control, all types of mortar samples including pure cement samples have unavoidable sudden failure beyond the peak stress at different stages, and therefore only limited post-peak stress-strain curves can be captured. In order to capture the post-peak stress-strain curves beyond the sudden failure, a failure control method based on controlling the rate of lateral strain is proposed in this study. Using this method, post-peak stress-strain curves with positive modulus could be obtained for class II behaviour. The failure modes of the samples tested in both axial strain control and failure control show similarity. Also, the failure-controlled experiments indicate that despite the unstable fracture growth in the samples being considerable after peak stress, it may not lead to the uncontrolled sudden failure of the whole sample but could produce a class II stress-strain curve.

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.