Acta Geotechnica最新文献

A THMC coupled phase field framework for modeling fractures in porous rocks is proposed in this study. The framework introduces additionally the damage variable governed synergistically by the phase field and chemical field to account for dual-fracture mechanisms. Through this damage variable, full coupling of the temperature, hydraulic, mechanical, chemical, and phase fields is achieved. Implemented on the COMSOL Multiphysics platform, this multi-field coupling framework is solved by using a staggered iteration algorithm. The proposed framework was verified through fracture propagation induced by various factors. Furthermore, two-dimensional case studies are conducted to investigate the effects of acid concentration, heterogeneity, injection rate, specific surface area, and scale parameters on fracture morphology, fluid pressure distribution, temperature distribution, pressure evolution, and fracture propagation range. Numerical results demonstrate that the predictions of the proposed THMC coupled phase field model for fracture evolution and acid breakthrough consumption align with existing studies, while effectively characterizing the influence of sensitivity parameters.

To explore the dynamic response of sand–irregular concrete interface, a series of cyclic direct shear tests were conducted under dynamic normal loading, with different joint roughness coefficient ((it {text{JRC}})) and dynamic normal loading frequency. DEM models were developed to analyze its microscopic behavior. Research results indicate that there was a critical (it {text{JRC}}) that maximized the interface shear strength. Maintaining a constant frequency of dynamic horizontal loading, changing the dynamic normal loading frequency resulted in changes in the shape of the shear stress–displacement hysteresis loops. The increase in dynamic normal loading frequency led to an increase in energy dissipation coefficient, which ranged from approximately 0.85 to 0.95. Energy introduced into the system by shearing was predominantly dissipated by internal mechanisms, mainly through slip and rolling slip. Dynamic horizontal loading would result in a decrease in the average force chain length and strength. As shearing, the anisotropy of the contact normal direction and tangential contact force of specimens significantly decreased. When the specimens were at shear stress reversal point, the anisotropic orientation of contact normal direction, normal contact force, and tangential contact force rotated toward the shear direction, and the rotation angle increased with the increase in (it {text{JRC}}).

This study investigates the impacts of shearing and volume change on the evolution of particle size distribution in silica (Ottawa) and calcareous (Fiji Pink) sands, during the direct shear test. Results reveal Fiji sand's higher shear resistance and extensive grain crushing compared to Ottawa sand, due to differences in mineralogy and grain shape. The findings provide insights into granular soil behavior under increasing stress denoted as phase transition points that naturally occur with increasing shear. It was observed in the particle size distribution (PSD) of both sands that grain crushing initially increases the shear fraction of fines but then gradually reduces the percentage of larger grain diameters. The analysis of PSD evolution during shear was conducted using Hardin's B_r, Lade's B₁₀, and Marsal's B_m breakage index frameworks. The micro- and macro-mechanical aspects of direct shear show that to model shear effects on grain breakage, the effects of dilation (− dε_v/dε_h), internal grain friction (μ), and vertical effective stress (σ′_v) conditions must be considered. The combination of these effects leads to the proposition of the particle partition potential (P₃) parameter, which represents the average stress conditions acting on sand during shear. P₃ can be computed from stress, strain, and volumetric change data only, but it nevertheless shows a strong linear correlation with Hardin’s B_r parameter, which is measured by comparing pre- and post-test PSDs. Particle breakage was also related to the loading intensity (L_I) parameter which combines the magnitude of force chains formed within particles and the duration of loading. P₃ is linearly correlated with both P₃ and B_r, thus pointing to the effectiveness of L_I in quantifying particle breakage across different sands. Finally, three additional datasets from the literature were used to calculate L_I and P₃ from stress–strain data and compute B_r. The computed and measured B_r values were well correlated with R² = 0.91.

Shallow-buried pipelines are susceptible to uplift buckling when the vertical stress exceeds the overburden pressure, particularly in unsaturated soils where uplift capacity remains poorly understood. This study investigates the uplift behavior of pipelines in unsaturated ground through uplift trapdoor tests and proposes a limit equilibrium theory to evaluate uplift capacity under unsaturated conditions. The proposed theory, validated against experimental results, reveals that uplift capacity increases as the groundwater level becomes deeper due to enhanced shear strength in unsaturated soils. Application of the theory to sand, silty clay, and loam soils with realistic pipeline dimensions showed that fine-graded soils exhibit higher uplift capacity than sand, indicating greater risks for pipeline stability. These findings advance the understanding of uplift mechanisms in unsaturated soils and provide practical insights for pipeline design and safety assessment.

Owing to the insufficient bearing capacity of monopile foundations in the deep sea, pile–bucket foundations, which consist of a traditional monopile and a wide-shallow bucket and can effectively improve lateral performance, are receiving increasing attention. This paper describes the results obtained from a large-scale model testing campaign on laterally loaded pile–bucket foundations in clay. The results obtained from monotonic tests performed on pile–bucket foundations with three different bucket sizes are presented, and a monopile is used as a comparison. The pile–soil interaction was investigated in terms of the overall load–displacement behavior, distribution of the bending moment, pile (bucket) deflection, net soil resistance, and p–y curves. The monotonic test results show that with the addition of the bucket, the ultimate bearing capacity and initial stiffness of the hybrid foundation obviously increase. Compared with that of the monopile foundation, the displacement at the mud surface of the hybrid foundation is 80–90% lower under the same load, and the peak soil resistance of the hybrid foundation is approximately 12–15 times greater than that of the monopile foundation. Furthermore, supplementary 3D FEM analyses were also performed to reveal the foundation failure mode and soil flow mechanism of pile–bucket foundations. This study provides design references for further practical applications of hybrid foundations.

This study presents a modified two-phase relationship model to effectively predict changes in soil structure and consolidation behavior when superabsorbent polymer (SAP) is introduced. Laboratory experiments are conducted to examine the effects of SAP on water retention, compressibility, and permeability under different conditions. The findings indicate that a 0.6% SAP dosage forms a gel-like matrix that enhances soil structure, increases drainage efficiency, and improves consolidation performance in high-water-content dredged clay. Key factors influencing these changes, such as SAP dosage, initial water content, and particle interactions, are analyzed. The traditional phase relationship model is modified to incorporate the unique properties of SAP, revealing how it alters the distribution and connectivity of solid, liquid, and void phases within the soil. This refined model provides improved accuracy in predicting soil behavior under varying initial water contents and consolidation stresses, addressing limitations in conventional methods. Additionally, the study highlights the nonlinear relationship between water absorption and volume expansion of SAP, emphasizing its role in enhancing pore structure and soil stability. Overall, this study provides a reliable predictive framework for SAP-treated soils and offers valuable guidance for sustainable sediment treatment in geotechnical engineering applications.

This study derives theoretical solutions for the lateral response of a scoured fixed-head pile in elastoplastic soil and investigates the effects of soil nonlinearity and foundation exposure on the pile’s ductile behavior. The theoretical model considers both pile plastic hinging, assuming the pile section follows a bilinear moment–curvature relationship, and soil plasticity, assuming elastoplastic behavior. The ultimate state of the pile–soil system is determined by either pile-head bending failure or in-ground plastic hinging. Examples are presented to demonstrate the application of the proposed solutions to derive theoretical pushover curves, the accuracy of which is validated by comparing them with numerical and experimental results. In addition, the examples show that with increasing scour depth, the possibility of the occurrence of in-ground plastic hinging increases, but the effect of soil nonlinearity decreases. This study further conducts a parametric investigation to examine the effect of soil nonlinearity on the displacement ductility capacity and system overstrength ratio. The results indicate that the normalized yield moment can be regarded as a factor normalizing the effect of soil nonlinearity. A higher normalized yield moment value indicates a more significant effect of soil nonlinearity. This can cause increased displacement ductility capacity and a reduced system overstrength ratio.

We examine the tribological behavior of particle–particle and particle-shale rock systems in the presence of hematite film (iron oxide nanoparticles) simulating iron oxide development on the surfaces of geological materials. By applying different boundary conditions and loading patterns to the samples, we examined the interfaces in both full and partial slip as well as under the influence of a sudden change of the normal load during shearing. We observed that the influence of hematite film (iron oxide nanoparticles) on the normal contact stiffness may alter depending on whether shear stresses are induced or not. In steady-state sliding, the data show that the hematite film (iron oxide nanoparticles) has a greater influence in grain-rock than that in grain-grain systems; however, both the normal contact and shearing behavior depend, primarily, not on the presence of the iron oxide nanoparticles alone, but the combination of surface film and loading pattern. In part of our grain-scale data, we could provide inferences on previous macroscopic test results as we observed similar patterns of behavior at different scales.

Fines detachment, migration, and settling leads to internal erosion of the skeleton structure and clogging of pores, which is an intricate process during the extraction of gas hydrate from marine sediments. Particularly, fines cemented around gas hydrate particles may detach during the dissociation process. The intricacy of this process has not been well characterized in current mathematical models or numerical modeling. In this paper, a mesoscale numerical model coupling solid particle and fluid seepage for gas hydrate-bearing sediments is developed and employed to simulate the fines erosion process, revealing three different mechanisms for the erosion of fines. Fines detach from the soil or gas hydrate particles during the hydrate phase transition and are subject to the Stokes drag force, frictional force, buoyancy force, capillary force, and interparticle interactions within pore space. Based on the established model, the pore clogging due to either physical aggregation or bridging can be clearly identified. The numerical model was initially calibrated with microfluidics experiments, followed by a series of sensitivity analyses to assess the impacts of porosity, fines content, gas hydrate saturation, and pressure gradient on gas and sand production. Results indicate that the interparticle forces play a significant role in pore clogging, which is crucial for gas hydrate-bearing silty sands. The sand production or physical pore clogging is a multi-stage process due to the dissociation of gas hydrates.

Urban sludge, characterized by its large volume and poor engineering properties, has become a significant environmental issue in the southeastern coastal regions of China. This research investigates a method for transforming urban sludge into a usable soil resource through the utilization of a low–carbon binder (CFS), providing a novel approach for sludge treatment and resource recycling. To achieve this, multi–scale experimental research and mechanistic analysis were conducted, focusing on the unit and microscopic experiments of industrial waste slag in collaboration with CFS solidification of engineering waste sludge. The materials used in CFS included Portland cement (PC), fly ash (FA), and steel slag (SS), with the incorporation of response surface methodology (RSM). The findings indicate that the singular addition of FA and SS exhibits a limited solidification effect on the sludge. However, significant synergistic interactions were observed between PC and FA, and between FA and SS. Based on the unconfined compressive strength test results of sludge cured for 7 days, the optimal ratio of the CFS was determined to be PC: FA = 40.7%:40.7%:18.6%, demonstrating the most effective sludge enhancement. The falling head permeability test results showed that the stabilized sludge had permeability approximately two orders lower in magnitude than the untreated sludge. Characterization techniques, including X–ray diffraction (XRD), scanning electron microscopy (SEM), energy–dispersive spectroscopy (EDS), thermogravimetric analysis (TGA) and identified the primary products within the stabilized sludge matrix as ettringite (Aft), calcium–silicate–hydrate (C–S–H) gel, and calcite. Additionally, cured sludge had a lower pore volume than its raw counterpart, according to mercury intrusion porosimetry (MIP) data, which suggests a stronger microstructural structure after stabilization. The improvement in sludge properties attributed to CFS is primarily due to the hydration reaction, pozzolanic reaction, ion exchange, and carbonation. Compared to traditional Portland cement, the CFS curing agent offers comparable economic benefits and substantial environmental advantages.