This issue of Geotechnical Engineering (volume 176, issue 3) includes nine papers discussing a wide range of topics. One paper revisits the standard relationship between plasticity index and linear shrinkage; another analyses the reinforcement effect on the end soil of rectangular pipe jacking; one paper is on the design life of clay cut slopes; and the other five are related to research on tailings.
Thaimo et al. (2023) use extensive data to evaluate the plasticity index (PI) equation in view of its existing wide practical use in both geotechnical laboratories and industry practice. In an attempt to assess its veracity, data from 180 soil samples were employed to evaluate the equation statistically. Results show that the proposed method appears to be correct only up to PI values not exceeding 25% and has greater accuracy at lower PI values (<15%). Other studies in the literature also show that the equation may not apply to some soil types or to soils of particular clay mineral types.
Sun et al. (2023) focus on an underground pedestrian passage project and carry out a series of investigations on the influencing factors and evaluation methods of reinforced end soil. The optimal reinforcement scheme is determined and applied to the underground pedestrian passage engineering through direct analysis and variance analysis of the results of the orthogonal test. The research results could serve as a guide in the construction of future rectangular pipe jacking, and the research methodology developed provides a reference for similar underground pedestrian passage projects.
Huang et al. (2023) used a numerical approach to construct a synthetic rock mass model to represent the jointed rock mass and then obtained the strength of the rock mass. In a case study (Hongtuzhang tunnel in China), the micro properties of granite cores with different degrees of weathering were determined and the representative elementary volume of the surrounding rock was set as 15 × 15 m. The surrounding rock grades obtained using geological surveys were found to be higher than those predicted by the numerical method.
Hosseini et al. (2023) developed a novel computational code to calculate the permeability of three-dimensional discrete fracture network models using the effective medium theory method, and the results were compared with numerical results. This computational code is user-friendly and can calculate permeability faster than the numerical method. The results showed that when the aperture was correlated or uncorrelated with trace length, the calculated mean permeability values by the effective medium theory method agreed well with numerical modelling.
Postill et al. (2023) investigate shallow first-time failures in clay cut slopes due to seasonal stress cycles using a validated numerical model capable of capturing seasonal ratcheting and progressive failure. It was found that fully softened strength criteria are inappropriate for the assessment of shallow first-time failures due to seasonal ratcheting, and slopes at angles between the material's fully softened and residual friction angle may be at risk of failure in the future due to this behaviour. Also, the strain-softening behaviour of clay defines the rate of strength deterioration and the operational life of engineered slopes.
Shuttle et al. (2023) show that data from a campaign of self-bored pressuremeter (SBP) testing in an oil-sand tailings impoundment have been analysed using the iterative ‘forward‘ modelling based on the non-associated Mohr–Coulomb cavity expansion theory of Carter et al. (1986). Finite SBP geometry has been included, based on the extensive testing by Ajalloeian and Yu (1998). This modelling shows a baseline geostatic stress ratio K0=0.6 for tailings that are truly normally consolidated.
Ma et al. (2023) investigated the permeability and consolidation characteristics of fine-grained tailings under normal and high pressure, and explored the effects of various flocculants on the permeability and consolidation of fine tailings. First, the geometric characteristics of fine tailings particles treated with different flocculants were investigated by studying the microscopic morphology of coarse, fine and flocculant-treated tailings. All of the tailings were then subjected to conjoined consolidation permeability tests. The results showed that a composite flocculant could have a considerable effect on the geotechnical properties of fine tailings due to changes in the double diffusion layer (DDL) of the particles. However, the DDL theory is not applicable for a consolidation pressure more than 2 MPa.
Islam et al. (2023) give a better simulation of fine-grained mine tailings slurry on disposal in a tailings storage facility (TSF), by applying accelerated loading in a slurry consolidometer to allow for the increased drainage path length, where the proper simulation of such field deposition of tailings in conventional laboratory consolidation testing is challenging. The objective of this research is to simulate the continuous disposal of tailings in the TSF, which creates incremental stress by applying a high constant rate of loading and accelerated loading on coal tailings, red mud and gold tailings in a slurry consolidometer. The findings of this study showed that the consolidation behaviour of the tailings studied varied with the nature of the tailings and with the loading applied.
Bruschi et al. (2023) aim to evaluate the parameters controlling the loss of mass and stiffness degradation of ‘green‘ stabilised bauxite tailings (BT), by applying the porosity/binder index (η/Biv) as a rational dosage method. The stabilisation technique is alkali activation, with a binary system composed of sugar cane bagasse ash and carbide lime with sodium hydroxide (NaOH) as the activator. As a control group, the same BT were also stabilised using Portland cement with high early strength. Diverse stiffness behaviours were observed due to the different curing periods needed for the development of chemical reactions for each binder. Through the porosity/binder index, engineers can choose the best option for a project by decreasing porosity (increasing soil compaction) and reducing the binder content or, inversely, increasing porosity while raising binder content.
