The accumulation of industrial waste materials (e.g., coal wash and steel furnace slag) has become a critical environmental problem in Australia in recent years. The possible re-use of these types of materials as structural fill for transport embankments and land reclamation is one of the preferred options from a waste management perspective. Consequently, an experimental testing program was undertaken using the triaxial apparatus to evaluate the shear behavior of compacted mixtures of coal wash (CW) and steel furnace slag (SFS). The effect of varying the confining pressure and the percentage of coal wash on the isotropic compression line, the stress-strain behavior, and particle degradation during drained shearing was evaluated. The percentage of coal wash was found to influence the shearing behavior of the CW-SFS mixtures. When the content of coal wash increased, the shear strength of the CW-SFS mixtures decreased and the axial strain corresponding to the peak stress ratio increased. Moreover, the incidence of particle breakage increased for those mixtures with a higher CW content due to the low particle strength of CW. This paper also provided a non-linear strength envelope and a corresponding empirical equation to capture the shear strength of CW-SFS mixtures.

Coal wash (CW) and basic oxygen steel slag fines (BOS) are by-products of the coal mining and steel industries, respectively. Their effective reuse and recycling through large-scale geotechnical projects, such as port reclamation, is economically beneficial and environmentally sustainable. In this study, CW and BOS were blended in order to explore the possibility to obtain synthetic fills having geotechnical properties similar or superior to conventional fills, therefore suitable as a structural fill for the Port Kembla Outer Harbour reclamation near Wollongong City, Australia. A framework with four levels of acceptance is proposed in this paper to select granular waste as structural fill materials. This framework was used for optimising the CW-BOS blend. It was found that for the Port Kembla Outer Harbour reclamation, a CW-BOS blend with a BOS content between 30 and 45% can meet most geotechnical specifications (i.e. high shear strength and bearing capacity, low swelling and particle breakage levels, and adequate permeability) required for a suitable structural fill above the high tidal level.

Shale gas has recently gained significant attention as one of the most important unconventional gas resources. Shales are fine-grained rocks formed from the compaction of silt- and clay-sized particles and are characterised by their fissured texture and very low permeability. Gas exists in an adsorbed state on the surface of the organic content of the rock and is freely available within the primary and secondary porosity. Geomechanical studies have indicated that, depending on the clay content of the rock, shales can exhibit a brittle failure mechanism. Brittle failure leads to the reduced strength of the plastic zone around a wellbore, which can potentially result in wellbore instability problems. Desorption of gas during production can cause shrinkage of the organic content of the rock. This becomes more important when considering the use of shales for CO₂ sequestration purposes, where CO₂ adsorption-induced swelling can play an important role. These phenomena lead to changes in the stress state within the rock mass, which then influence the permeability of the reservoir. Thus, rigorous simulation of material failure within coupled hydro-mechanical analyses is needed to achieve a more systematic and accurate representation of the wellbore. Despite numerous modelling efforts related to permeability, an adequate representation of the geomechanical behaviour of shale and its impact on permeability and gas production has not been achieved. In order to achieve this aim, novel coupled poro-elastoplastic analytical solutions are developed in this paper which take into account the sorption-induced swelling and the brittle failure mechanism. These models employ linear elasticity and a Mohr–Coulomb failure criterion in a plane-strain condition with boundary conditions corresponding to both open-hole and cased-hole completions. The post-failure brittle behaviour of the rock is defined using residual strength parameters and a non-associated flow rule. Swelling and shrinkage are considered to be elastic and are defined using a Langmuir-like curve, which is directly related to the reservoir pressure. The models are used to evaluate the stress distribution and the induced change in permeability within a reservoir. Results show that development of a plastic zone near the wellbore can significantly impact fracture permeability and gas production. The capabilities and limitations of the models are discussed and potential future developments related to modelling of permeability in brittle shales under elastoplastic deformations are identified.

The effective reuse and recycling of granular waste materials, namely coal wash (CW) and basic oxygen steel slag (BOS), are economically beneficial and environmentally sustainable. Nevertheless, due to the heterogeneity of these granular waste materials, the ultimate adoption of CW and BOS as structural fills must be supported by constitutive relationships capable of accurately describing the stress–strain behaviour under representative field loading conditions. In this paper, a critical state surface generalized plasticity model is presented, and its predictive capability using an explicit set of soil parameters is demonstrated for drained triaxial compression tests.