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

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

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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

Massive landsliding in Narrabeen sandstones in the Watagan region

The Narrabeen Group is a thick sequence of bedded Triassic sandstones which occupies the stratigraphic interval between the Permian coal measures and the Hawkesbury Sandstone in the Sydney Basin. In the northern Sydney Basin it is laterally extensive, extending throughout the southern Hunter Valley from the Central Coast to beyond the Great Divide. In the Watagans region, a unique situation arises where a disconformity causes the Narrabeen group to be underlain directly by Permian upper marine sediments. The result is a dramatic occurrence of ancient massive landsliding, leading to steep sandstone slopes that break to an elevated detrital plane, of considerable lateral extent. This paper describes the unusual geomorphic features associated with the landslide mass and interprets a variety of individual mass-movement and rockfall mechanisms which have contributed to these impressive features in the various stages of its development

Prehistoric landslides: significance, recognition, examples

Prehistoric landslides with a wide range of ages and sizes exist worldwide in both rock and soil. Many are thought to have occurred during Pleistocene time when climates in some areas were harsher and wetter. Subsequent weathering and erosion have subdued topography and other features of prehistoric landslides, often making them difficult to recognize. Recognition is the key to dealing with prehistoric and other old landslides. Old slide masses are usually only marginally stable because past movements reduced available shear strength on their failure surfaces to residual levels. These masses are susceptible to reactivation by construction activities, heavy precipitation, and earthquakes. If prehistoric landslides are recognized, they can be avoided or steps taken to minimize interference with them. Where they cannot be avoided, they must be stabilized or lived with. Stabilization typically involves robust retaining structures, large buttress fills, or excavation of most of the slide mass - all of which are expensive. Living with old landslides may involve continuing maintenance for distress caused by creep or other movements; this can also be expensive. Problems arise when prehistoric and other old landslides are unrecognized, then reactivated during or after construction. Then, unexpected ground movements cause damage, increase costs, set back construction schedules, and disrupt partially completed or completed facilities and operations. Geologic considerations, features of prehistoric and old landslides, and guidance for recognizing them are presented. Then examples of prehistoric landslides in the United States, Papua New Guinea, and Australia are given

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

Some Comments on the Entropy-Based Criteria for Piping

This paper is an extension of previous work which characterises soil behaviours using the grading entropy diagram. The present work looks at the piping process in granular soils, by considering some new data from flood-protection dikes. The piping process is divided into three parts here: particle movement at the micro scale to segregate free water; sand boil development (which is the initiation of the pipe), and pipe growth. In the first part of the process, which occurs during the rising flood, the increase in shear stress along the dike base may cause segregation of water into micro pipes if the subsoil in the dike base is relatively loose. This occurs at the maximum dike base shear stress level (ratio of shear stress and strength) zone which is close to the toe. In the second part of the process, the shear strain increment causes a sudden, asymmetric slide and cracking of the dike leading to the localized excess pore pressure, liquefaction and the formation of a sand boil. In the third part of the process, the soil erosion initiated through the sand boil continues, and the pipe grows. The piping in the Hungarian dikes often occurs in a two-layer system; where the base layer is coarser with higher permeability and the cover layer is finer with lower permeability. The new data presented here show that the soils ejected from the sand boils are generally silty sands and sands, which are prone to both erosion (on the basis of the entropy criterion) and liquefaction. They originate from the cover layer which is basically identical to the soil used in the Dutch backward erosion experiments

Case Studies and Benchmark Examples for the Use of Grading Entropy in Geotechnics

The grading entropy concept can be adapted to the field of geotechnics, to establish criteria for phenomena such as particle packing, particle migration and filtering, through a quantified expression of the order/disorder in the grain size distribution, in terms of two entropy-based parameters. In this paper, the grading entropy theory is applied in some geotechnical case studies, which serve as benchmark examples to illustrate its application to the characterisation of piping, softening and dispersive soils, and to filtering problems in the context of a leachate collection system for a landfill site. Further, since unstable cohesive (dispersive) soils are generally improved by lime, the effect of lime addition is also considered, on the basis of some measurements and a further application of the grading entropy concept, which allows evolutions in the entropy of a soil to be considered as its grading is modified. The examples described support the hypothesis that the potential for soil erosion and particle migration can be reliably identified using grading entropy parameters derived from grading curve data, and applied through an established soil structure stability criteria and a filtering rule. It is shown that lime modification is not necessarily helpful in stabilizing against particle migration