Search Results (221)

This paper presents an analytical model for one-dimensional consolidation analysis of multi-layered unsaturated soils under depth-dependent initial conditions. The general solutions are derived explicitly using the Laplace transform. By combining these general solutions with interfacial continuity conditions between layers and the boundary conditions, the reduced-order system is solved via the Euler method to obtain analytical solutions in the Laplace domain. Numerical inversion of the Laplace transform is then performed using Crump’s method to yield the final analytical solutions in the time domain. The model incorporates initial conditions that account for both uniform and linear distributions of initial excess pore pressure within the soil stratum. The proposed solution is verified by reducing it to degenerated cases (e.g., uniform initial pressure) and comparing it with existing analytical solutions, showing excellent agreement. This confirms the model’s correctness and demonstrates its generalization to multi-layered systems with depth-dependent initial conditions. Focusing on a double-layered unsaturated soil system, the one-dimensional consolidation characteristics under depth-dependent initial conditions are investigated by varying the physical parameters of individual layers. The proposed solution can serve as a theoretical reference for the consolidation analysis of multi-layered unsaturated soils with depth-dependent initial conditions. Full article

To investigate the influence of different water-rich conditions on tunnel excavation stability, three typical working conditions were designed based on the engineering characteristics of tunnels in water-rich areas (with groundwater levels 70 m, 55 m, and 40 m from the tunnel bottom, respectively). Numerical simulation research on tunnel excavation stability was carried out using the finite difference method. The results show that the influence of surrounding rock mechanical strength indexes on pore water pressure distribution is significantly greater than that of water-rich conditions; under the action of pore water pressure, the displacements of different parts of the tunnel structure exhibit differentiated characteristics, with the displacement of the arch foot being larger than that of the vault; the tunnel bottom is a high-risk area for geological hazards such as shear failure and mud burst, which requires key prevention and control. The research results can provide data support and technical reference for disaster early warning and support design optimization of tunnel projects in water-rich areas. Full article

In the wave theory of saturated soils, pore tortuosity is an important physical property for quantifying the added mass force caused by the relative acceleration between solid and liquid phases. However, this inertial force is often ignored for simplicity in practical applications. To investigate the influence of pore tortuosity on the propagation of compressional waves in saturated soils, a system of generalized governing equations for one-dimensional infinitesimal strain elastic waves is solved using the Laplace transform method. Semi-analytical solutions are obtained for the spatiotemporal distributions of the excess pore water pressure, the pore water velocity, and the soil particle velocity caused by a step load perturbation under undrained conditions. These solutions are used to evaluate the effects of pore tortuosity on the velocities and amplitudes of fast and slow compressional waves. The results show that pore tortuosity has an insignificant effect on the propagation of fast compressional waves, but for slow compressional waves, the larger the pore tortuosity is, the lower the wave velocity and the larger the wave amplitude. Ignoring the influence of pore tortuosity can lead to an underestimation of the arrival time of slow compressional wave. The propagation of this wave is limited to a distance of approximately 1 m away from the loading boundary. This research finding is purely theoretical. For further experimental validation, it is suggested to detect the slow compressional wave by placing miniature acoustic receiving transducers as close as possible to the loading or transmitting surface. The proposed solutions are also useful for calibrating sophisticated numerical codes for dynamic consolidation of saturated soils and wave transmission in porous media. Full article

Liquefaction in urban areas has repeatedly caused severe damage to infrastructure, including manhole uplift, road subsidence, and failure of buried utility lines, as evidenced by reports during major earthquakes such as the 1964 Niigata earthquake and the 2011 Great East Japan Earthquake. Although natural sand has been widely used as backfill, excess pore water pressure leads to rapid loosening. This study evaluates slag–dried sludge mixed soil as a new liquefaction-resistant backfill that improves disaster mitigation while promoting resource recycling. Compaction, cone penetration, and shaking table tests were conducted with sludge mixing ratios of 0–30%, identifying 20% as optimal. Liquefaction in slag-only soil occurred at 1013 s (7 m/s²), whereas the 20% mixture delayed it to 1380 s (11 m/s²), increasing the acceleration threshold by 1.5 times and extending the onset time by 36%. Therefore, the acceleration required for liquefaction to begin was approximately 1.5 times higher, and the occurrence time was extended by approximately 36%. Also, the cone index reached 7750 kPa, exceeding the traffic load requirement of 1200 kN/m², while still allowing for sufficient permeability and workability compared to the use of natural clay particles. The improved backfill material proposed is promising as a sustainable urban infrastructure technology that simultaneously reduces liquefaction damage, improves the resilience of urban infrastructure, and reduces environmental impact through waste recycling. Full article

Supercritical CO₂ modifies deep coal reservoirs through the coupled effects of adsorption-induced deformation and geochemical dissolution. CO₂ adsorption causes coal matrix swelling and facilitates micro-fracture propagation, while CO₂–water reactions generate weakly acidic fluids that dissolve minerals such as calcite and kaolinite. These synergistic processes remove pore fillings, enlarge flow channels, and generate new dissolution pores, thereby increasing the total pore volume while making the pore–fracture network more heterogeneous and structurally complex. Such reservoir restructuring provides the intrinsic basis for CO₂ injectivity and subsequent CH₄ displacement. Both adsorption capacity and volumetric strain exhibit Langmuir-type growth characteristics, and permeability evolution follows a three-stage pattern—rapid decline, slow attenuation, and gradual rebound. A negative exponential relationship between permeability and volumetric strain reveals the competing roles of adsorption swelling, mineral dissolution, and stress redistribution. Swelling dominates early permeability reduction at low pressures, whereas fracture reactivation and dissolution progressively alleviate flow blockage at higher pressures, enabling partial permeability recovery. Injection pressure is identified as the key parameter governing CO₂ migration, permeability evolution, sweep efficiency, and the CO₂-ECBM enhancement effect. Higher pressures accelerate CO₂ adsorption, diffusion, and sweep expansion, strengthening competitive adsorption and improving methane recovery and CO₂ storage. However, excessively high pressures enlarge the permeability-reduction zone and may induce formation instability, while insufficient pressures restrict the effective sweep volume. An optimal injection-pressure window is therefore essential to balance injectivity, sweep performance, and long-term storage integrity. Importantly, the enhanced methane production and permanent CO₂ storage achieved in this study contribute directly to greenhouse gas reduction and improved sustainability of subsurface energy systems. The multi-field coupling insights also support the development of low-carbon, environmentally responsible CO₂-ECBM strategies aligned with global sustainable energy and climate-mitigation goals. The integrated experimental–numerical framework provides quantitative insight into the coupled adsorption–deformation–flow–geochemistry processes in deep coal seams. These findings form a scientific basis for designing safe and efficient CO₂-ECBM injection strategies and support future demonstration projects in heterogeneous deep coal reservoirs. Full article

Offshore wind farm construction faces significant geotechnical challenges posed by tidal mudflat sediments, including high moisture content, low bearing capacity, and high sensitivity to disturbance. Utilizing MgO—a material characterized by abundant raw materials, low embodied energy, and environmental compatibility—for the stabilization of such soft soils represents a promising and sustainable approach worthy of further investigation. This study elucidates the carbonation-induced stabilization mechanism of coastal mucky soil from Ningbo, Zhejiang Province, through systematic monitoring of reaction temperature and unconfined compressive strength (UCS) testing under varying levels of reactive MgO content, carbonation duration, and initial moisture content. Microstructural characterization was performed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) to reveal the evolution of mineralogical and pore structure features associated with carbonation. The results indicate that increasing MgO content leads to higher peak reaction temperatures and shorter time-to-peak values. However, the rate of reduction in time-to-peak diminishes beyond 20% MgO. A secondary temperature rise is commonly observed between 3–3.5 h of carbonation in most specimens. When the MgO content is below 30%, UCS peaks within 6–10 h, with the peak time decreasing as MgO content increases. When MgO exceeds 45%, strength deterioration occurs due to structural damage. The correlation between deformation modulus and UCS is found to be comparable to that of conventional cement-stabilized soils. Microstructural analysis reveals that, with increased MgO dosage and prolonged carbonation, carbonation products progressively fill voids and bind soil particles, resulting in reduced total porosity and a refinement of pore size distribution—evidenced by a leftward shift in the most probable pore diameter. Nevertheless, at excessively high MgO levels (e.g., 50%), crystallization pressure from rapid product formation may generate macro-pores, compromising soil fabric integrity. This study presents a low-carbon and efficient ground improvement approach for access road construction in tidal mudflat wind farm developments. Full article

Foamed concrete is a lightweight, environmentally friendly civil engineering material with excellent absorption capacity. It has been widely applied in engineering fields such as building thermal insulation and pore filling of underground buried pipelines. But the mechanical properties of existing foamed concrete cannot meet the engineering requirements for support, pressure relief and filling of weak surrounding rock. The mechanical properties of foamed concrete were improved with CNTs to prepare CNT foamed concrete (CNTFC) pressure-relieving filling materials. The effects of five factors (the fly ash (FA) incorporation rate, aggregate–cement ratio, water–binder ratio, CNT incorporation rate and foam volume fraction) on the density and 2:1 cylinder strength (the ratio of uniaxial compressive strength to apparent density), splitting tensile (the ratio of splitting tensile strength to apparent density) and specific strength of the CNTFC were analyzed. By combining stress–strain and scanning electron microscopy analyses, the mechanism of improvement of the mechanical strength of CNTFC due to CNTs was clarified. The results show that the foam volume fraction, water–binder ratio and aggregate–cement ratio are the top three factors affecting its strength, followed by the CNT incorporation rate and FA incorporation rate. Among the five influencing factors, only the incorporation of CNTs increases the 2:1 cylinder strength, splitting tensile strength and specific strength. When the doping rate is 0.05%, this ratio specifically refers to the mass of CNTs accounting for 0.05% of the mass of the total cementitious materials of cement and fly ash. At this doping dosage, compared with the condition without CNTs (0% doping dosage), the uniaxial compressive strength increased from 6.23 MPa to 7.18 MPa (with an increase rate of 15.3%). The splitting tensile strength increased from 0.958 MPa to 1.02 MPa (with an increase rate of 6.5%). The density only slightly increased from 0.98 g/cm³ to 1.0 g/cm³ (with an increase rate of 2.0%), achieving the balance of “high strength-low density”. CNTs and cement hydrates are interwoven into a network structure, and the mechanical properties of the CNTFC are effectively improved by the excellent nanoscopic tensile properties. Excessive doping of CNTs takes 0.05% as the threshold. Exceeding this doping dosage (such as 0.10% and 0.15%) leads to a decrease in its strength and ductility due to CNT agglomeration and deterioration of pore structure. And 0.05% is the ratio of the mass of CNTs to the total cementitious materials of cement and fly ash. At this doping dosage, CNTs are uniformly dispersed and can balance the strength and density of CNTFC. The optimum proportion of CNTs is 0.05%. Full article

This study presents a validated numerical investigation into the seismic liquefaction potential of fine-grained reclaimed sediments commonly encountered in coastal, containment, and reclamation projects. Fine-grained reclaimed sediments pose a particular challenge for seismic liquefaction assessment due to their low permeability, high fines content, and complex cyclic response under earthquake loading. A fully coupled, nonlinear finite element model was developed using the Pressure-Dependent Multi-Yield (PDMY) constitutive framework, calibrated against laboratory Cyclic Direct Simple Shear (CDSS) tests and verified using in situ Cone Penetration Tests with pore pressure measurement (CPTu). The model effectively captured the dynamic response of saturated sediments, including excess pore pressure generation, cyclic mobility, and post-liquefaction behavior, under three earthquake ground motions: Livermore, Chi-Chi, and Loma Prieta. Results showed that near-surface layers (0–2.3 m) experienced full liquefaction within two to three cycles, with excess pore pressure ratios (R_u) approaching 1.0 and peak pressures closely matching laboratory data with less than 10% deviation. The numerical approach revealed that traditional CPT-based cyclic resistance methods underestimated liquefaction susceptibility in intermediate layers due to limitations in accounting for pore pressure redistribution, evolving permeability, and seismic amplification effects. In contrast, the finite element model captured progressive strength degradation, revealing strength gain in deeper layers due to consolidation, while upper zones remained vulnerable due to low confinement and resonance effects. A critical threshold of R_u ≈ 0.8 was identified as the onset of rapid shear strength loss. The findings confirm the advantage of advanced numerical modeling over empirical methods in capturing the complex cyclic behavior of reclaimed sediments and support the adoption of performance-based seismic design for such geotechnically sensitive environments. Full article

Firstly, based on one-dimensional Terzaghi consolidation theory, we derived and established the analytical solution of excess pore water pressure and average consolidation degree of double-layered foundation, which can reflect the effect of fiber reinforcement. Meanwhile, the one-dimensional consolidation test of a double-layered foundation was carried out by means of a modified WG-type (product series code) consolidation instrument. The accuracy of the theoretical solution was verified by designing different consolidation parameters of the basalt fiber-reinforced solidified lightweight soil (BF-SLS) layer. Secondly, our findings suggest that the settlement rate of the double-layered foundation decreased with the increase in thickness, compression modulus and fiber mixing ratio of the BF-SLS layer. Nevertheless, the average pore pressure dissipation rate changed in the opposite trend. Both increased with increasing permeability coefficient of the BF-SLS layer. Within the thickness ratio range of 0 to 1/2 between the upper and lower layers, the thickness of the BF-SLS layer significantly influenced the consolidation process of the double-layer foundation. At equivalent T_v levels, the difference in consolidation degree exceeded 60%. Finally, a comparison of various simplified methods for calculating the average consolidation degree of double-layer foundations reveals that neither the weighted consolidation coefficient method nor the average index method yields results that are in good agreement with theoretical solutions. The difference between U_s (defined by sedimentation) and U_p (defined by pore pressure) cannot be distinguished. This research can further refine the consolidation theory of “upper hard and lower soft” double-layer foundations. Full article

Spontaneous liquefaction in the Lusatian lignite dump sites has raised significant geotechnical and environmental concerns. While mechanical influences have been extensively studied, hydrochemical investigations suggest an inner initial that is highly correlated to CO₂ generation, attributed to buffering reactions, which lays the foundation for this study. This study aims to understand the process behind and to quantify the transient evolution of excess pore-pressure induced by CO₂ accumulation, both dissolved and as free gas, in saturated medium using a series of column experiments. Excess pore-pressures up to 7.7 kPa were recorded following a period of buffering reaction, with discharged gas confirmed as CO₂. The results demonstrate that the buffering process strongly influences the elevated pressure, while, in turn, elevated pressures affect the chemical conditions within the column. Secondary mineral precipitation, as one of the effects, was observed to reduce buffering reactivity and modify pore structure, thereby altering pore-pressure response. These findings highlight hydrochemical feedback as critical internal triggers and amplifiers in liquefaction events, complementing mechanical explanations and advancing understanding of coupled hydro-chemo-mechanical processes in dump site stability. Full article

Installation in sand is sensitive to its evolving pore structure, yet design models rarely update permeability for real-time fabric changes. This study tracks the stress-dependent pore size distribution of coarse sand under laterally constrained compression using high-resolution X-ray nano-CT. Scans taken at six axial stress levels show that the distribution shifts toward smaller radii while keeping its log-normal shape. A single shifting factor, defined as the current median radius normalized by the initial value, captures this translation. The factor decays with axial stress according to a power law, and the exponent as well as the reference pressure are calibrated from void ratio data. The resulting closed-form expression links mean effective stress to pore radius statistics without extra fitting once the compressibility constants are known. This quantitative relation between effective stress and pore size distribution has great potential to be embedded into coupled hydro-mechanical solvers, enabling engineers to refresh hydraulic permeability at every computation step, improving predictions of excess pore pressure and soil resistance during suction anchor penetration for floating wind foundations. Full article

Scrap tire-derived geomaterial has been gaining attention recently as an alternative material for improving the ground. This paper presents a fundamental experimental investigation into sand–rubber mixtures using hollow cylinder torsional shear apparatus, with the aim of enhancing our understanding of the integrated effects of rubber content and cyclic stress ratio (CSR) on the liquefaction characteristics of the mixtures. The results show that the incorporation of granular rubber into sand not only reduces excess pore water pressure during cyclic loading but also alters the generation mode of pore water pressure. The liquefaction resistance of the sand–rubber mixture increases significantly when the rubber gravimetric proportion exceeds 10%. The energy dissipation per loading cycle decreases with increasing rubber content, whereas the cumulative dissipative energy exhibits an opposite trend, showing a positive correlation with rubber content. In addition, this rubber-enhanced effect shows CSR dependence; the cumulative energy dissipation significantly diminishes at a high CSR. Therefore, the effect of granular rubber addition to sand on pore water pressure tends to become more pronounced at higher rubber contents. Full article

The Philippines, located along the Pacific Ring of Fire, is highly susceptible to significant seismic activity arising from the active convergence of major tectonic plates. These seismic events often induce ground shaking intense enough to trigger soil liquefaction, particularly in geologically sensitive regions such as Davao del Sur. This study presents a nonlinear static and dynamic analysis of a mat foundation for a proposed midrise building located within the liquefaction-prone zone of Padada, Davao del Sur. Geotechnical data were obtained through rotary drilling and Standard Penetration Tests (SPTs), which provided the basis for developing the numerical model. Liquefaction assessment was conducted using the PLAXIS Liquefaction Model (UBC3D-PLM), confirming that the site adjacent to the Padada–Mainit River exhibits a high liquefaction potential. Subsequently, finite element analyses were performed in PLAXIS 3D using ground motion records from the 2013 Bohol Earthquake, scaled to 1.0 g, and modeled under the Hardening Soil Model with Small-Strain Stiffness (HSsmall). Results showed excess pore pressure ratios approaching 1, and vertical displacements of the mat foundation exceed 100 mm. These results suggest severe degradation in soil strength, as well as reduced friction angles and mobilized pressure. Full article

Conventional tunnel face stability models are constrained by idealized steady-state seepage assumptions, one-dimensional formulations for inherently three-dimensional flow, and the neglect of transient filter-cake effects. To address these limitations, this study focuses on blowout failure triggered by excess slurry pressure in slurry pressure balance shield tunneling. We establish a limit-analysis framework that couples slurry infiltration with transient seepage, developing a work rate-balance formulation and a three-dimensional rotational failure mechanism. This framework incorporates heterogeneous, time-dependent filter-cake pressure transfer and the spatiotemporal evolution of pore pressure—key factors overlooked in traditional models. Transient seepage simulations demonstrate that the spatiotemporal heterogeneity of the dynamic filter cake provides the fundamental pressure basis for blowout failure. A prominent hydraulic gradient within the potential core failure zone (Z/R ≤ 2.0, Y/R ≤ 2.0) drives failure initiation and propagation, with the vertical hydraulic gradient in the high-risk subregion (Z/R < 0.5) reaching values as high as 12. Results indicate that passive failure risk increases markedly when excess slurry pressure exceeds 200 kPa, accompanied by a sharp decline in the safety factor. Validation against the Heinenoord No. 2 Tunnel case confirms that the proposed three-dimensional model more accurately captures 3D seepage characteristics and critical failure pressures compared to traditional wedge–prism approaches. By overcoming steady-state and one-dimensional simplifications, this framework deepens the understanding of blowout evolution and provides theoretical guidance for the rational control of slurry pressure and improved tunnel-face stability assessment under complex transient conditions. Full article

China possesses abundant tight conglomerate oil resources. However, these reservoirs are typically characterized by low porosity and permeability, high clay mineral content, and complex pore structures, resulting in poor performance of conventional waterflooding development. Challenges including insufficient energy replenishment and high flow resistance ultimately lead to low oil recovery factors. This study systematically investigates surfactant-assisted CO₂ huff-n-puff (SA-CO₂-HnP) for enhanced oil recovery in tight conglomerate reservoirs. For a tight conglomerate reservoir in a Xinjiang block, a fully implicit, multiphase, multicomponent dual-porosity numerical model was established. By integrating pore–throat distributions acquired through high-pressure mercury intrusion with a self-developed MATLAB PVT package, nanoconfinement-induced shifts in the phase envelope were rigorously embedded into the simulation framework. The calibrated model was subsequently employed to conduct a comprehensive sensitivity analysis, quantitatively delineating the influence of petrophysical, completion, and operational variables on production performance. Simulation results demonstrate that compared to conventional CO₂ huff-n-puff, the addition of surfactants increases the cumulative recovery factor by 3.5 percentage points over a 20-year production period. The enhancement mechanisms primarily include reducing CO₂–oil interfacial tension (IFT) and minimum miscibility pressure (MMP), improving reservoir wettability, and promoting CO₂ dissolution and diffusion in crude oil. Sensitivity analysis reveals that injection duration, injection pressure, and injection rate significantly influence recovery efficiency, while soaking time exhibits relatively limited impact. Moreover, an optimal surfactant concentration (0.0003 mole fraction) exists; excessive concentrations lead to diminished enhancement effects due to competitive adsorption and pore blockage. This study demonstrates that SA-CO₂-HnP technology offers favorable economic viability and operational feasibility, providing theoretical foundation and parameter optimization guidance for efficient tight conglomerate oil reservoir development. Full article