Acta Geotechnica最新文献

Microbially induced calcite precipitation (MICP) has emerged as a sustainable technique for constructing horizontal curtains in deep excavations, offering both hydraulic efficiency and environmental benefits. The MICP process is generally governed by complex bio-chemo-hydro-mechanical interactions. However, in practical applications, the injection of bacterial and chemical solutions through pumping and recharge wells induces elevated pore pressures, alters local stress fields, and may initiate microcracking, affecting soil integrity. Moreover, temperature variations significantly influence MICP kinetics and efficiency. Existing models inadequately address these coupled effects, particularly the thermal and damage phenomena. This study presents a comprehensive thermal–hydraulic–mechanical–biochemical–damage (THMBCD) model that integrates temperature-dependent behavior and damage mechanics to simulate the MICP-based formation of horizontal curtains for deep excavation. The model incorporates microstructural changes and fracture evolution based on damage theory. Validation is achieved through experimental data and analytical solutions. Parametric studies reveal that higher bacterial and chemical concentrations, along with increased injection temperatures, enhance calcite precipitation and stiffness while reducing the damage ratio. Among these factors, bacterial concentration exhibits the most pronounced influence. This study offers critical insights into the complex coupled THMBCD mechanisms governing the MICP treatment process during horizontal curtain formation in deep excavations, thereby advancing its applicability in real-world geotechnical engineering design.

In Rock Valley, Nevada, the USA, past earthquake sequences and shallow faulting in Paleozoic carbonates remain poorly understood. Carbonates are typically more ductile rocks that do not experience large stress drops or fracture coalescence, which contradicts previous observations in the region. As part of the Source Physics Experiment, an effort has been made to experimentally characterize the petrophysical and geomechanical properties of carbonates from Rock Valley. Well core and outcrop samples were used to determine the difference between shallow-buried Tertiary limestones and deeply buried Paleozoic limestones and dolostones. The carbonates possessed porosities between 3 and 9%, with V_P and V_S in the Tertiary carbonates around 2700 and 1800 m/s, respectively, and 6000 and 3100 m/s, respectively, in the Paleozoic carbonates. Microstructural characterization revealed that the Paleozoic carbonates contained significantly more pre-existing damage and alteration than the Tertiary carbonates, though the deformation varies from localized to diffuse. Unconfined Brazilian tests and triaxial tests with confining pressures between 0 and 50 MPa showed that, although samples all experienced failure, the dolostones typically failed at greater stresses and possessed greater E/ν ratios than the limestones. The Hoek–Brown failure criterion was used to construct failure envelopes with the compressive and tensile failure tests. Velocity, density, and porosity measurements were used to construct a hypothetical velocity-depth profile and compare the results with the theoretical petrophysical measurements. Using brittleness analysis, the likely failure conditions were determined to be low-porosity dolomitic rock for fault nucleation in the Paleozoic basement.

The cast-in-situ pile and pre-bored grouted pre-stressed high-strength concrete (PHC) pile (Bored PHC pile) are two types of non-displacement pile. Nevertheless, the installation effects of cast-in-situ pile and Bored PHC pile should also be considered when installed in vicinity of some important infrastructures. In this research, the installation effects of cast-in-situ pile and Bored PHC pile were analyzed and compared based on an actual engineering project in vicinity of a subway tunnel. The inclinometers, pore water pressure sensors and soil pressure sensors were equipped between the test piles and adjacent subway tunnel. The test results showed that: the disturbance caused by the Bored PHC pile installation was larger than the disturbance caused by cast-in-situ pile, as the drilling speed of Bored PHC pile was much higher than the drilling speed of cast-in-situ pile; while the disturbance induced by the PHC pile insertion stage of Bored PHC pile was close to the disturbance induced by the concrete placing stage of cast-in-situ pile; the excess pore water pressure and the increase of lateral soil pressure caused by cast-in-situ pile and Bored PHC pile installation all recovered rapidly after cast-in-situ pile and Bored PHC pile installation; the disturbance induced by Bored PHC pile and cast-in-situ pile installation became relatively limited when the radial distance reached 4D (D is pile diameter); the research results could provide a theoretical basis for the application of cast-in-situ pile and Bored PHC pile near some important infrastructures such as subway tunnels.

Rockslides and their cascading hazards, such as river blockage and outburst flooding, pose significant threats to infrastructure and human lives, particularly in mountainous and seismically active regions. To enhance hazard forecasting and risk mitigation, it is helpful to develop accurate numerical models for analysing the failure mechanisms of rock slopes under external loadings. Traditional two-dimensional numerical simulations have constraints in capturing the anisotropic stress distribution and complex evolution of failure mechanisms in three-dimensional space. Moreover, most three-dimensional numerical models typically treat rock slopes as homogeneous media, rarely accounting for the natural fractures within rock blocks. To address these limitations, this study introduces a novel three-dimensional material point method (MPM), combined with the discrete fracture network (DFN) to dynamically simulate the initiation and evolution of rockslides under seismic loading, along with the subsequent river blockage phenomenon. The DFN is explicitly incorporated into MPM using a projection algorithm by mapping fracture geometries onto the computational domain and then assigning the physical properties of fractures to specific material points, enabling a more realistic representation of fractured rock masses. The reliability of the proposed framework in addressing complex dynamic contact problems is verified through four numerical case studies. The motion of rockslides under seismic loading and the deposition of fragmented rock blocks within a river channel are then studied, revealing that fracture intensity and fracture orientation significantly influence the failure modes of rock slopes and the extent of river blockage. This research provides valuable insights into the complex failure processes of fractured rock slopes and interactions between rockslides and river systems, contributing to the advancement of hazard assessment and mitigation strategies.

Particle breakage and morphology evolution significantly impact the mechanical properties of soils. However, the morphology evolution patterns of each fraction within the total grading remain unclear due to the difficulty of particle tracing. This study involved conducting a series of one-dimensional compression tests on stained coral sands, examining both well-graded and poorly graded samples. Results indicated that for well-graded coral sands, large particles exhibited a lower survival rate and transformed into rounder and more regular shape after compression, whereas the morphology of finer particles rarely changed. Within a specific fraction of the total grading, the survival particles of the same size tended to be rounder and more regular, while the newly created finer fragments would be sharper. Besides, the average values of circularity and solidity for a given grading in well-graded samples were higher than those in poorly graded conditions. To investigate the influence of initial particle shape and mineral composition on morphology evolution, additional compression tests were conducted on shell sands and completely decomposed granite (CDG) sands. The results indicate that mineral composition, rather than initial particle shape, significantly affects particle morphology evolution. After compression, all CDG sand particles became less round and more irregular, demonstrating a contrasting morphology evolution compared to that observed in calcareous sands.

Grid-type walls are extensively used as the foundation or ground improvement against soil liquefaction, while little is known concerning the stress path of the enclosed soil subjected to shaking events. Simulation results from a 2D finite element model unveil the symmetric jump rotation of principal stress within grid-type walls owing to dynamic soil-wall interaction. Subsequently, a systematic hollow cylinder torsional apparatus tests were conducted under this stress path, using clayey sands incorporating varied cyclic stress ratios (CSR), maximum principal stress rotation angles α_σ,m, and relative densities. The experimental results indicate that, in most cases, the soil liquefaction resistance increased as increasing α_σ,m, attributed to the shear stress acting on the bedding plane. A correlation between the principal stress rotation angle and the number of cycles required for initial liquefaction was established, characterising α_σ,m-dependent undrained liquefaction responses. Interestingly, an inverse trend was found at CSR = 0.2 and α_σ,m = 90° cases, indicating the coupled effect of shear stress and normal stress difference acting on the bedding plane. Furthermore, a new mechanism of liquefaction mitigation by grid-type walls is identified as rotating the maximum shear stress away from the bedding plane.

Particle size and shape significantly influence the crushing behaviors of rockfill materials. In this study, single-particle crushing tests were conducted on Baihetan rockfill particles with four size groups. Particle shape was quantified using parameters derived from 3D scanning. The results show that both particle size and shape significantly affect the crushing behaviors. The particle crushing modes are categorized into splitting, chipping, and explosive. Larger particles and particles with shapes closer to ellipsoids and cuboids are more prone to explosive failure, whereas smaller particles and particles with reduced corner sharpness tend to experience major splitting without prior localized fragmentation. The crushing force, crushing energy, and their variability all increase with particle size, and the effect of shape on the crushing behaviors also increases with particle size. The applicability of the Weibull model in describing the size effects on the crushing strength was evaluated. The particle shape effect was incorporated into the calculation of crushing strength using a shape factor determined by an artificial neural networks algorithm. A probabilistic model was developed to predict the crushing strength distribution based on the particle size and shape parameters.

Non-circular piles exhibit remarkable superiority in lateral bearing capacity and seismic performance due to their geometric advantages. However, the complex boundary effects induced by their asymmetric cross sections pose significant theoretical challenges to the analytical characterization of dynamic soil–pile interaction mechanisms at the interface. To address these challenges, an analytical–numerical coupling calculation framework for non-circular pile dynamics is established, where the fundamental dynamic equation of the coupled pile-viscoelastic soil system is derived through variational formulations and Hamilton's principle. The proposed method effectively reduces the three-dimensional (3D) pile–soil interaction problem under dynamic loading to a coupled solution between soil dynamics equations in two-dimensional (2D) space and one-dimensional (1D) pile governing equations. An adaptive numerical iteration algorithm is subsequently employed to solve the governing equations, significantly improving computational efficiency for lateral dynamic pile–soil interaction problems. The proposed approach demonstrates its reliability when evaluated against finite element simulations and existing analytical solutions. A detailed analysis is performed to examine how soil layer properties, the cross-sectional geometry of non-circular piles, and slenderness ratios influence the lateral dynamic response behavior.

Directly carbonating MgO (magnesia) through gaseous CO₂ is a sustainable method in the treatment of sandy and silty soils. However, it is challenging to use this method to stabilize clayey soils as the low permeability of such soils may block the CO₂ flow. This study proposed a new method (named as ‘indirect MgO carbonation’) that used NaHCO₃ as a CO₂ carrier and then mixed with MgO and clayey soils to achieve MgO carbonation and stabilization of clayey soils. To clarify the effectiveness of the indirect MgO carbonation, small-scale and large-scale carbonation tests in the laboratory were conducted to compare direct and indirect carbonation methods in treating clayey soils. The physical, mechanical, microstructural, and mineralogical properties of the soils subjected to direct and indirect carbonation were investigated. The results showed that indirect MgO carbonation achieved higher unconfined compressive strength (UCS) values and water content in clayey soils compared to direct carbonation at MgO/NaHCO₃ ratios of 1:0.25 to 1:0.5. Large-scale laboratory carbonation tests demonstrated that indirect carbonation produced more uniform strength and moisture distribution, as evidenced by lower coefficient of variation values. Independent of CO₂ flow conditions, indirect MgO carbonation presents a viable solution for in situ clayey soil stabilization.

The characteristics of cement-stabilised clays (CSC) primarily depend on the initial water content relative to the liquid limit of the soil, cement dosage and curing duration. In this study, considering high water content and low-plastic clays, the existence of different zones of improvement based on the strength (compression and tension) and compressibility behaviour of CSC with increasing cement dosage is identified through comprehensive mechanical and microstructural investigations. The characteristics of the identified inactive, active and transition zones with different binder dosages, remoulding water content and clay types are studied. The behaviour of the sample across various cementation zones for low-plastic clay-I can be approximated by an S-shaped curve comprising an initial nonlinear segment in the inactive zone (0–5%), a linear segment in active zone-I (5–10%), and an asymptotic segment in the transition zone (10–15%). In contrast, the response in active zone-II follows a distinct linear trend. From the microstructural studies, the transition zone exhibits negligible strength enhancement ((-)5 to +5%) even when there is no hindrance in the formation of C–S–H gel and a decrease in porosity. Samples in active zone-I exhibited a significant increase of about 95–100% in compressive and tensile strength due to effective cementation, while those in active zone-II showed a moderate gain of 50–80%, influenced by remoulding water content. Finally, two prominent mechanisms (predominantly pore filling and pore filling + cementation) that control the formation of different zones of strength enhancement with cement dosage are delineated.