Acta Geotechnica最新文献

This paper introduces a new hypoplastic model characterized by a simple and elegant formulation. It requires only 7 material parameters to depict salient mechanical behaviors of granular materials. The numerical implementation employs an explicit integration method, enhanced by a best-fit stress correction algorithm in a smoothed particle hydrodynamics code. The performance of this model in capturing soil behavior across a range of scenarios is demonstrated by conducting various numerical tests, including triaxial and simple shear at low strain rates, as well as granular collapse, rigid penetration and landslide process at high strain rates.

The hydromechanical behavior of compacted bentonite in near-field salinity groundwater environment is of great importance for achieving the low-permeability sealing capacity in deep geological repositories. Within this context, swelling pressure and hydraulic conductivity of compacted bentonites with technological voids were evaluated under simulated site water salinity conditions. Water content, dry density and pore size distribution were measured after hydration. Results showed that the swelling pressure shows a trend of rapid rise and reach the peak value, then drop sharply and stabilized. The rapid decrease in the hydraulic conductivity for all salinity is the salient features, and then, it reduces slowly. The above evolution behavior is dominated by the swelling mechanisms and the self-sealing of technological void under different salinity conditions. Adequate water and space provided by technological void lead to gradient evolution of geotechnical properties, such as water content, dry density and pore size distribution. The density increase mechanism derived from salinity fails to compete with the density decrease mechanism derived from sufficient space sourced from technological void. Therefore, the dry density at the external sampling site decreases with increasing salinity. At high salinity, the compressed diffuse double layer not only increases the inter-aggregate pores but also widens the water flow channels. As a result, hydraulic conductivity increases with increasing salinity. Considering the influence from groundwater salinity, it is necessary to improve basic properties and technological void dimensions of bentonite blocks for the safety of long-term operation of deep geological repository.

Dispersive soil is a widely distributed problematic soil in arid or semiarid areas of the world and can cause pipe erosion, gully damage and other seepage failures. This study analyzed the effect of environmentally friendly enzyme-induced carbonate precipitation (EICP) on the dispersivity of dispersive soils. This methodology was tested for the stabilization of three dispersive soil types (two high-sodium soils, two low-clay-content soils, and two soils with both high sodium and low clay contents) to examine the impact on dispersivity based on the results of pinhole tests and mud ball tests. Physical, chemical, mechanical, and microscopic tests were also conducted to investigate the effects of the components in the EICP reaction solution on dispersive soil modification. The experiments showed that the concentration of the reaction solution and the curing time required to limit the dispersivity decreased with increasing clay content in the soil. Ca²⁺ limited the dispersivities of dispersive soils via four distinct mechanisms. The first mechanism was ion exchange; Ca²⁺ decreased the percentage of exchangeable sodium ions to less than 7% while reducing the thickness of the diffuse double layer such that the spacings between soil particles were reduced and the chemical dispersivity was limited. Second, Ca²⁺ increased the viscosity of the solution by salting out the organic matter present in the soybean urease. Subsequently, the D1-class physically dispersive soil was converted into an ND2-class nondispersive soil. Third, Ca²⁺ decreased the soil pH by reducing the CO₃²⁻ content, which could hydrolyze to increase the soil alkalinity. Finally, the presence of Ca²⁺ led to the generation of cementitious minerals through the precipitation of CaCO₃ crystals that continuously generated CO₃²⁻, filling and cementing soil particles and thereby limiting their physical dispersivity. These results indicated that a low-concentration EICP reaction solution efficiently controlled the dispersivities of the three dispersive soils.

The lateral load-carrying mechanism of vertically installed and battered minipiles is evaluated using 1g-physical and numerical modelling. Single minipiles with batter angles of 0°, ± 25° and ± 45° are tested under lateral load in medium dense and dense sand. The minipiles are instrumented with fibre Bragg grated optic fibres to obtain a strain profile (two-dimensional) along the minipile shaft. A calibrated numerical model is further adopted to produce p–y curves for battered minipiles at various node deflections. The ratio of soil reaction of battered minipiles to vertically installed minipiles is observed to change with both deflection and depth of the minipile. An analytical solution is developed based on the decomposition of lateral load into skin friction and passive pressure for battered minipiles. A reduction factor is proposed that considers a decrease in passive pressure when the minipile is loaded in the opposite direction of the batter. The analytical solution is capable of accounting for soil properties, pile rigidity and the angle of inclination of battered minipiles. The analytical method is subsequently verified for cohesive soils using full-scale field results. The ratio of the ultimate lateral load of battered minipiles to vertical minipiles presented in the literature corroborated the findings of this study.

This paper focuses on the impact of elevated temperatures on the adsorptive and capillarity water retention mechanisms of unsaturated soils under constrained (constant volume) conditions. This topic is critical for simulating the thermo-hydraulic behavior of soils in hydrogeological or geotechnical applications, including climate change effects on near surface soils, energy piles or soil borehole thermal energy storage systems in unsaturated soil layers, and buffers for geological nuclear waste repositories. A nonisothermal soil water retention curve (SWRC) that separately considers the temperature-dependency of the key parameters governing adsorptive and capillarity water retention mechanisms and soil physical parameters (e.g., surface tension, contact angle, adsorption capacity, cation exchange capacity, mean cavitation suction, air entry value and equilibrium film thickness) was developed to provide insights into the impact of temperature on water retention over the full suction range. The nonisothermal SWRC was validated using experimental data on high plasticity clays, with a good prediction of temperature effects on adsorption and capillarity water retention mechanisms in constrained unsaturated soils.