The reinforcement provided by discrete fibres is widely reported to be negligible under triaxial extension, a result drawn almost entirely from sands prepared by moist tamping or pluviation, methods that produce a sub-horizontal fibre fabric which unloads as the specimen extends. The results reported here suggest that this finding depends on that fabric rather than on the loading path alone, and the difference in fibre orientation is quantified. Consolidated undrained triaxial compression and extension tests were performed on slurry-consolidated kaolinite reinforced with 2% polypropylene fibre by dry mass, at 18- and 48-mm fibre length and effective confining stresses of 50, 100 and 200 kPa. Each fibre length was consolidated as its own block, and the 48 mm specimens were cut from one block in two directions, with the sampling tube advanced normal to the bedding and within the bedding plane. The fibre orientation distribution, measured on a transparent soil analogue, has a mean inclination of 21° from the horizontal. Extension testing drove effective stress paths beyond the tension cut-off line in every reinforced specimen, a state that undrained compression cannot reach, providing direct evidence of tension within the composite.
This study presents a numerical investigation of ground movements induced by groundwater rise in slopes using a plane strain finite element model with a Mohr–Coulomb constitutive law under drained, steady-state seepage conditions. The main methodological contribution is the definition of a Greenfield Slope Analysis framework, which adapts the Limiting Tensile Strain Method (LTSM) to assess potential damage in shallow-founded buildings affected by slow-moving landslides. Finite element analyses are used to evaluate displacement and strain fields across the slope from which maximum tensile strains are derived, together with the corresponding changes in slope stability. Groundwater rise leads to progressive increase in ground displacements, whereas the spatial distribution of strain is primarily controlled by slope kinematics. For the selected idealised slopes with a layer of uniform thickness, the central portion shows predominantly translational behaviour, while rotation-like components develop near the crest and toe. The crest is mainly associated with tensile horizontal strains, whereas the toe is mainly associated with compressive horizontal strains, resulting in different damage potential depending on the adopted structural idealisation. Sensitivity and parametric analyses indicate that normalised slope-parallel displacement may be used as a proxy for greenfield deformation levels, supporting preliminary damage assessment and interpretation of in-situ monitoring data.
Microcapsule-based technology offers a potential approach for extending the service life of ground infrastructure. This study manufactured gelatin-gum arabic microcapsules containing tung oil (GGTO), sodium silicate (GGSS), or colloidal silica (GGCS) and evaluated their effects on the direct shear behaviour of silica sand after 3-28 days of curing under normal stresses of 10-100 kPa. A structure degradation direct shear (SD-DS) model was developed to represent strength mobilization, post-peak degradation, and contraction-dilation behaviour. All formulations increased shear strength. At 30 kPa after 28 days, GGTO, GGSS, and GGCS increased peak strength by 220.7%, 106.4%, and 56.7%, respectively, and end-of-shearing strength by 179.3%, 79.3%, and 67.6%. Their peak apparent cohesions were 72.2, 43.0, and 30.3 kPa, compared with 6.11 kPa for clean sand. For each material-curing condition, one parameter set represented the responses at 10-100 kPa. These parameters were then fixed and applied to independent 28-day tests at 150 and 200 kPa. The model captured the overall shear responses and material-dependent trends. The results demonstrate post-release reinforcement and out-of-calibration prediction across normal stress for fixed material-curing conditions. These findings may extend the range of microcapsules applicable to granular soils and provide a practical framework for representing their direct shear behavior.
This paper develops a unified critical state model that is applicable to sands of varying densities, and overconsolidated clays, termed as the CASM-SU. A unified hardening parameter is introduced to the original hardening law of the Clay and Sand model with subloading surface, i.e., the CASM-S, where the effects of the unified hardening parameter on the Hvorslev peak stress ratio is well considered. A Lade-based transformed stress method is incorporated to represent intermediate-principal-stress effects without adding an independent parameter. The newly developed CASM-SU shares seven physical parameters with the classical CASM, without introducing a new model parameter u that is given by the CASM-S. This parameter lacks physical meaning, which needs mathematical fitting. A forward Euler integration algorithm is employed for numerical implementation, and the model is validated against drained and undrained tests on clays with various overconsolidation ratios and sands with different relative densities. The comparisons demonstrate that the CASM-SU accurately captures the stress–strain and volumetric responses of both soil types and significantly improves the prediction of peak tensile and compressive strength. The proposed formulation provides a physically based and unified constitutive framework for modelling the behaviour of sands and clays within the critical state framework.
Microbially induced calcite precipitation (MICP) is a promising ground improvement technique involving complex coupling between hydraulic, mechanical, chemical, and biological processes. However, many existing models focus on selected processes or treat key couplings, such as precipitation-induced stress, in a phenomenological manner, while the role of attached biomass is often insufficiently represented. This paper develops a thermodynamically consistent hydro–mechanical–chemical–biological framework for MICP in soils. Within the framework of non-equilibrium thermodynamics, the entropy production associated with all irreversible processes, i.e., transport, reaction, bacterial attachment, and biomass decay, is quantified, and the Helmholtz free energy of the reacting porous medium is rigorously derived. The constitutive relations for stress and porosity are derived from the free energy evolution and expressed in a fully coupled manner, incorporating the hydro–mechanical effects and the contributions of precipitated calcium carbonate and attached biomass to the mechanical response. The resulting governing equations are verified against published numerical results and further applied to two column experiments from the literature. The modelling results show good agreement with experimental observations and reveal that bacterial attachment contributes less than 2% to the overall porosity reduction under typical injection conditions. The proposed framework provides a unified basis for analysing the coupled multiphysics behaviour of MICP-treated soils.
