This study focuses on characterising the pore space in Tamusu mudstone, a preferred nuclear waste disposal host medium in China, using focused ion beam/scanning electron microscopy (FIB-SEM). The investigation is conducted at the mesoscale, with a sample volume of 7·96 × 9·16 × 10·00 μm3 and voxel sizes of 5 × 5 × 10 nm3. The findings reveal that the pores in Tamusu mudstone primarily exist at the nanoscale, typically within its mineral matrix or at interfaces with non-porous minerals. At the FIB/SEM-imaged scale, the pore space in the Tamusu mudstone is mainly unconnected, with an analysed porosity of approximately 3·5%. Pore characteristics within the specimen exhibit relative consistency within a box size of 6–8 μm. Furthermore, the pore paths in Tamusu mudstone exhibit a preferred orientation within the bedding plane, suggesting anisotropy in pore space, possibly attributed to changes in pore path orientation and tortuosity.

This paper outlines a new approach to use coarse-grained molecular dynamics (CGMD) and the Gay-Berne potential to simulate the compression of kaolinite saturated with water at an acidic pH (=4) in a low (1 mM) ion concentration solution. To overcome the limitations of the standard Gay-Berne potential and capture the charge heterogeneity on the surface of kaolinite particles under acidic pH conditions, each clay platelet is modelled using a two-ellipsoid composite particle. The molecular dynamics software LAMMPS was employed to generate virtual monodisperse samples containing 1,000 composite particles and to simulate isotropic compression to 100 kPa. The observed macro-scale response in void ratio – effective stress space lay above the response obtained in a simulation that used an equivalent CGMD model developed to simulate alkaline (pH=8) pore water conditions. This is in qualitative agreement with available experimental data for 1D compression. Post-compression qualitative observation of the two virtual samples revealed a book-house type fabric in the sample with acidic pore-fluid, while a turbostatic fabric was observed when the alkaline pore-fluid was simulated. These observations are also in qualitative agreement with SEM data reported in the literature.

This paper develops an elastoplastic solution for cylindrical cavity contraction in unsaturated soils under constant suction conditions. The elastoplastic cavity contraction problem is formulated into a set of first-order ordinary differential equations by introducing a new auxiliary variable, which is solved as an initial value problem. The new solution is validated by comparison with numerical simulation results. Finally, parametric studies show that, as soil suction increases, the internal support pressure decreases faster with cavity contraction, the unloading-induced plastic zone becomes narrower, and the changes in effective stresses are smaller for a given tunnel convergence.

Data gathered from 65 922 articles published in 30 geotechnical engineering journals between 1998 and 2022 were used to build a topic model and study the evolution of research output in the field. Over this period, the number of journal publications has grown exponentially with the number of articles published per year doubling every 6·3 years. The average citations per article (32·7) are skewed by highly cited articles, which make up 7·8% of the articles but account for 34·5 of the total number of citations. The articles’ country of origin has become increasingly centralised, with nearly half the articles published between 2018 and 2022 coming from China (39%) and the United States (10%). The topic distribution in the field has become highly specialised, with emerging topics being fuelled by: (a) new technologies and methods (i.e. data science and sensing techniques – the fastest-growing topics), and (b) rising applications seemingly related to mitigation (e.g. offshore and energy geotechnics) and adaptation (e.g. geohazards, mass movements) to climate change. As a consequence, traditional topics (e.g. soil and rock mechanics) have reduced their share in the field, but still remain among the most cited topics in geotechnical engineering.

Cracking resulting from drying (constrained dehydration) poses a significant challenge in geomaterials, impacting their mechanical performance. To address this problem, extensive efforts have been made to prevent or mitigate the occurrence of cracks, with recent attention focused on the utilisation of biopolymers. This letter investigates the influence of varying concentrations of the xanthan biopolymer on the mechanical response of granular materials, examining both macro and micro scales. The strength changes of the soil were evaluated through desiccation experiments, analysing the appearance and progression of failure on the macro scale. The findings of this study demonstrate that failure (cracking) progression is mitigated and eventually eliminated by increasing the concentration of the additive xanthan. Additionally, capillary experiments were conducted to assess the changes in attraction and the development of capillary bridges on the micro-scale. They indicate that the formation of hydrogel bridges significantly enhances particle attraction, thereby increasing its macro-resistance to cracking.

Strain measurement inside the soil body in three-dimensional (3D) experiments is a real challenge for physical modellers in geotechnics. The use of fibre optic sensing offers the possibility of continuous measurement of the strain at depth with high spatial and temporal resolution in small-scale laboratory experiments. Despite the technology not being fully ready yet for centrifuge experiments, this is an important development in geotechnics. This paper explores the capacities of distributed fibre optic sensing (DFOS) as a solution for direct soil strain profile measurement at depth. A series of small-scale plane-strain experiments is used to simulate the simple case of the formation of a downwards subsidence. DFOS cables are laid in the soil specimen, and strains are directly compared with the soil movement, recorded with cameras through particle image velocimetry. Results indicate the ability of DFOS in detecting soil movements and underline the typical signature strain profile expected during this type of experiments. Finite-element analyses are carried out to further underpin the consequences of performing these tests at 1g and extend the findings to potential applications in 3D and on the geotechnical centrifuge. This shows promising results for detection of soil strain profiles inside the soil body in 3D.

Grouting cable is a newly developed technology for the reinforcement of fractured rock mass in coal mines of China. It integrates the procedures of cable anchoring and grouting, thus simplifying the working procedure of roadway support. However, ordinary grouting cable products with a core tube have some significant defects, such as a narrow flow channel, difficulty in slurry diffusion and significant reduction of cable strength. To overcome these shortcomings of ordinary grouting cables, this paper proposes a new kind of grouting cable without a core tube. The ordinary plastic core tube is replaced by a steel core wrapped by several steel strands. The inner gap between the steel strands and steel core is used as the slurry flow channel. The optimised measures can significantly improve slurry diffusion and strength performance of the grouting cable. As a novel idea, several samples of the new grouting cable were produced. Lab testing and field application experiment indicated that slurry diffusion and strength performance of the new grouting cable had been significantly improved compared with ordinary ones.

Soils exhibit non-linear stress–strain behaviour, even at relatively low strain levels. Existing Winkler models for suction caisson foundations cannot capture this small-strain, non-linear soil behaviour. To address this issue, this paper describes a new non-linear elastic Winkler model for the uniaxial loading of suction caissons. The soil reaction curves employed in the model are formulated as scaled versions of the soil response as observed in standard laboratory tests (e.g. triaxial or simple shear tests). The scaling relationships needed to map the observed soil-element behaviour onto the soil reaction curves employed in the Winkler model are determined from an extensive numerical study employing three-dimensional finite-element analysis. Key features of the proposed Winkler model include: computational efficiency, wide applicability (it can be used for caisson design in clay, silt or sand) and design convenience (the required soil reaction curves can be determined straightforwardly from standard laboratory test results). The proposed model is suitable for small and intermediate caisson displacements (corresponding to fatigue and serviceability limit state conditions) but it is not applicable to ultimate limit state analyses.

Uncertainty in the measurement of the cone penetration test with pore-water pressure measurement (i.e. piezocone testing CPTU) can be caused by an equipment malfunction, poor calibration and maintenance of sensors, but also by a lack of saturation of the piezocone. The standards allow for many different options in terms of filters, saturation fluids and methodologies. The novel device described herein aims at measuring in a very simple manner the degree of saturation of the piezocone prior to testing. Because the quality of pore-water pressure measurements can currently only be assessed a posteriori – that is, after the test has been completed, or at best while testing, the methodology proposed herein has the potential to provide quality benchmarks for CPTU. The tool measures a parameter inspired by the well-established Skempton coefficient B, which is routinely used to estimate the sample saturation prior to laboratory testing. Furthermore, by performing the same measurement after a CPTU test, it is possible to assess whether saturation was lost during cone penetration. The paper describes a set of preliminary results that show a clear correlation between the saturation degree of filters and/or of the overall pore-pressure measurement system and the B parameter proposed, thus providing a proof of concept in laboratory settings.

With the goal of promoting the treatment and reuse of fly ash (FA), a series of permeability tests were conducted to investigate the hydraulic conductivity (K) of polymer (chitosan, polyethylene oxide (PEO) and xanthan gum)–FA—kaolinite (KA) systems under different confining pressures and overconsolidation ratios (OCRs). The addition of FA increased the K of KA due to changes in particle size and gradation, and the effect is not significant when the FA content is below 30%. PEO and xanthan gum increased the K of KA, with xanthan gum having a more significant effect, while chitosan reduces it. For FA–KA mixtures, chitosan and xanthan gum had negligible impact on the K, whereas PEO increased it by an order of magnitude. In addition, confining pressure restricts the flow channel while increasing the effective contact area between polymers and soil particles. The Koc/Knc of polymer-modified KA rapidly converges at high OCRs, while that of polymer-modified FA–KA converges at low OCRs. This study provides insight into the effects of polymer modification on the hydraulic conductivity of FA–clay mixtures and provides guidance for the application of polymer modification technology in soil improvement.