The influence of geologic structure on design and construction in a moderately deformed paleozoic sequence in Eastern Australia

Abstract This paper presents a case study to illustrate the role played by geologic structures in the design and construction of major transportation infrastructure, in a setting of moderately deformed Paleozoic sedimentary rocks in eastern Australia. It describes a complex development of folding, faulting and jointing that has resulted in significant inclination of beds, juxtaposition of strata and affected the weathering characteristics of a wide range of rock types. The sequence, which displays an upward transition from marine to terrestrial sediments, comprises an interbedded succession of conglomerate, sandstone, shale and erratic volcanics and crystal tuff. Unfavorable relationships between major excavation faces, inclined beds and jointing have resulted in problems with the stability of road cuttings. Also, the presence of faults and dykes at various scales has had a significant effect on weathering and rock strength. The paper demonstrates the importance of the choice of alignment at design stage, and how a basis of good structural interpretation and geologic mapping can be used to avoid problems during construction and issues with ongoing maintenance

Field monitoring of expansive soil behaviour in the Newcastle-Hunter region

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Some consequences of the qualitative analysis of the point-symmetric coupled consolidation models

The point-symmetric linear coupled consolidation models, known from the theory of the oedometric testing and from dissipation testing, can be summarized into a single mathematical model in the function of the embedding space dimension m ([1]). When a set of boundary conditions is specified equally for the 1, 2 and 3 dimensional models (i.e. oedometric, cylindrical and spherical models) then a family of related model: a “modelfamily” is obtained. Some inferences of the results of the qualitative analysis of two model-families are presented and discussed in this paper. These are (i) the similarity of the solution within a model-family, (ii) a direct proof that the uncoupled consolidation theories cannot be considered as a special case of the coupled consolidation theories and (iii) the interesting fact that an instantaneous dissipation may be predicted for the uniform initial pore water pressure distribution if the displacement is specified at both boundaries

Impact of grading on steady-state strength

International audienceIn the mining industry, waste dumps are earthen structures typically built by loose waste tipping. They may reach heights of hundreds of metres and undergo large deformations. For this reason, their stability design is based on the steady-state shear strength of the waste material. Waste materials are widely graded and may contain particles of up to metric order. Particle shape depends on the pattern of dissecting discontinuities at the source rock mass and the relation between the size of the fragments and discontinuity spacing. The shear strength of this material is determined in the laboratory using scaled samples with altered particle-size distribution (PSD). However, altering the PSD is known to impact shear strength, and this impact is poorly studied. The representativeness of laboratory parameters obtained from scaled samples is thus arguable. Discrete-element simulations are used here to investigate steady-state shear strength changes with the alteration of the PSD when particle size and shape are correlated. It is observed that shear strength changes result from the variation of the particle shapes induced by the alteration of the PSD. Consequently, identifying size−shape correlations and their potential impact on shear strength is of paramount importance when scaling materials for laboratory testing

Temporal-spatial frequency rockfall data from open-pit highwalls using a low-cost monitoring system

In surface mining, rockfall can seriously threaten the safety of personnel located at the base of highwalls and cause serious damage to equipment and machinery. Close-range photogrammetry for the continuous monitoring of rock surfaces represents a valid tool to efficiently assess the potential rockfall hazard and estimate the risk in the affected areas. This work presents an autonomous terrestrial stereo-pair photogrammetric monitoring system developed to observe volumes falling from sub-vertical rock faces located in surface mining environments. The system has the versatility for rapid installation and quick relocation in areas often constrained by accessibility and safety issues and it has the robustness to tolerate the rough environmental conditions typical of mining operations. It allows the collection of synchronised images at different periods with high-sensitivity digital single-lens reflex cameras, producing accurate digital surface models (DSM) of the rock face. Comparisons between successive DSMs can detect detachments and surface movements during defined observation periods. Detailed analysis of the changes in the rock surface, volumes and frequency of the rocks dislodging from the sub-vertical rock surfaces can provide accurate information on event magnitude and return period at very reasonable cost and, therefore, can generate the necessary data for a detailed inventory of the rockfall spatial-temporal occurrence and magnitude. The system was first validated in a trial site, and then applied on a mine site located in NSW (Australia). Results were analysed in terms of multi-temporal data acquired over a period of seven weeks. The excellent detail of the data allowed trends in rockfall event to be correlated to lithology and rainfall events, demonstrating the capability of the system to generate useful data that would otherwise require extended periods of direct observation

Suction effects on the shear strength behaviour of compacted dewatered tailings

The paper presents the results from suction-controlled triaxial tests on compacted Dewatered Tailings (DT) carried out to evaluate their shear strength behaviour under rapid loading. Specimens were prepared via static compaction to a target dry density of 1.55 g/cm3 and water content of 18.5%. This produced an initial soil suction around 50 kPa. Compacted specimens were then subjected to a wide range of suction and loading paths prior to shearing. Specimens were finally sheared under ‘undrained’ conditions with suction monitored, not controlled, during the rapid loading. The triaxial results show that, in addition to the influence of confining stress, suction plays a key role on the shearing behaviour of compacted DT specimens. The higher the suction before shearing, the higher the material stiffness and peak deviatoric stress. Triaxial results are analysed using the Bishop’s effective stress concept, assuming that the coupling parameter χ is equal to the degree of saturation (χ=Sr). A unique Critical State Line (CSL) is obtained when adopting this simple approach, which permits the direct comparison of unsaturated and saturated tests results. Finally, the paper discusses the practical implications of the experimental results on the stability of DT deposits