Search Results (257)

Tightness of homogeneous embankment dams is often ensured by means of upstream water barriers, such as bituminous concrete facings, concrete slabs, shotcrete membranes, metallic sheets, geomembranes, and cement blankets. The stability analysis of these dams, especially in areas with high seismicity, must include the hydraulic and mechanical effects resulting from an extensive, sudden cracking of the impervious facing. To this purpose, in this paper, simple, original analytical solutions are proposed to estimate the position of the exit point on the downstream slope of the dam, the maximum height of the saturation front at the downstream face, and the time required for the saturation front to reach the downstream face. These variables generally depend on several factors, such as the geometry of the dam, homogeneity or heterogeneity, the permeability coefficient of the dam body materials, and resistance laws to describe the seepage flow. The high number of these factors requires the development of advanced 2D/3D FEM analyses, often computationally heavy and complex to implement. Although approximate, the proposed solutions may however allow us to define the role of the various factors and their interaction, to quickly deduce the main, preliminary design indications. Full article

Soil permeability decreases with reduced saturation, making desaturation an effective strategy for seepage control. Air injection has emerged as a promising technique to induce desaturation in engineering applications that require rapid seepage prevention. Although this method has attracted considerable attention, its specific effects on soil saturation and permeability remain insufficiently understood. In this study, a modified conventional permeameter is used to examine the influence of air injection on the degree of saturation and permeability coefficient of sandy soil; simultaneously, the variation in air injection pressure during the gas injection process was monitored, and the influence of overburden pressure on the initial gas injection value was investigated. The findings reveal the following: (1) When other factors are the same, the increase in the air injection flow rate decreases the degree of saturation of sandy soil, and the air injection rate is 40 mL/min, which results in the degree of Fujian sand to achieve a maximum reduction to about 0.750; the increase in the relative density decreases the degree of saturation of sandy soil. (2) The decrease in the degree of sandy soil decreases the permeability coefficient of sandy soil; the desaturation effect of the air injection method varies for different sand samples, and the air injection method can reduce the permeability coefficient of Fujian sand by about 60% at most. (3) The change trend of air injection pressure is related to the gas migration process. Overburden pressure has a negligible influence on the initial value of air injection pressure; the initial pressure value of the air injection method is mainly related to hydrostatic pressure and is affected by the pore structure of the soil. Full article

The durability of concrete in immersed tunnels is critically influenced by the coupled effects of stress, seepage, and chemical erosion, particularly in inland water environments. However, the spatio-temporal evolution of mechanical property degradation under such multi-field coupling remains insufficiently quantified. Unlike previous studies focused on “load-ion” or “hydraulic pressure-ion” dual coupling, this work introduces a complete stress–seepage–chemical tri-coupling that incorporates the critical seepage effect, representing a fundamental expansion of the experimental scope to better simulate real-world conditions. This study investigates the degradation mechanisms of concrete in the Shunde Lungui Road inland immersed tunnel subjected to such coupled erosion. A novel aspect of our approach is the application of the micro-indentation technique to quantitatively characterize the spatio-temporal evolution of the local elastic modulus at an unprecedented spatial resolution (0.5 mm intervals), a dimension of analysis not achievable by conventional macro-scale testing. Key findings reveal that the mechanical properties of concrete exhibit an initial enhancement followed by deterioration. This behavior is attributed to the filling of pores by reaction products (gypsum, ettringite, and Friedel’s salt) in the short term, which subsequently induces microcracking as the volume of products exceeds the pore capacity. Furthermore, increasing hydro-mechanical loading significantly accelerates the erosion process. When the load increases from 1.596 kN to 3.718 kN, the influence range of elastic modulus variation expands by 9.2% (from 5.186 mm to 5.661 mm). To quantitatively describe this acceleration effect, a novel load-acceleration erosion coefficient is proposed. The erosion rate increases from 0.0688 mm/d to 0.0778 mm/d, yielding acceleration coefficients between 1.100 and 1.165, quantifying a 10–16.5% acceleration effect beyond what is typically captured in dual-coupling models. These quantitative results provide critical parameters for employing laboratory accelerated tests to evaluate the ionic erosion durability of concrete structures under various loading conditions, thereby contributing to more accurate service life predictions for engineering structures. Full article

The permeability coefficient of saturated clay plays a crucial role in practical engineering applications. In this paper, based on the fractal geometry theory and combined with the relationship between the flowing water volume and non-flowing water volume in saturated clay, the theoretical formulas for the effective pore specific surface area and the effective void ratio of saturated clay are established. Based on the capillary seepage channel model of saturated clay, combined with Poiseuille’s law and the concept of equivalent hydraulic radius, the theoretical formula for the permeability coefficient of saturated clay is established. Finally, the physical parameters of the remolded clay samples are measured and substituted into the modified Kozeny–Carman equation and the equivalent capillary seepage equation of saturated clay before and after the modification. Through the comparative analysis of the above theoretical values and the measured values of indoor seepage tests, it is found that the saturated clay seepage equation established in this paper is more suitable for dense saturated clay with relatively small pores. It has the characteristics of higher calculation accuracy and easier acquisition of basic parameters. The research results provide important references for practical engineering and the study of saturated clay seepage theory, and have broad prospects for practical engineering applications. Full article

The permeability characteristics of expansive soil have a significant impact on slope stability. This study investigates the permeability evolution of three expansive soils (B, GW, GB) with distinct swelling potentials (68%, 42%, and 28%) under repeated wet–dry cycles, combining laboratory falling-head tests and in situ four-ring infiltrometer measurements. The results demonstrate that the permeability coefficient increases consistently with cycle number. The high-expansivity soil (B) exhibited the most pronounced change, with permeability increasing from 10⁻⁶ cm/s to 10⁻³ cm/s after five cycles, whereas the low-expansivity soil (GB) remained stable. A significant specimen size effect was observed in initial permeability, which stabilized beyond a critical infiltration area of 1102.7 cm². However, this size dependence diminished after three cycles due to extensive cracking and structural homogenization. Crack density analysis further confirmed microstructural stabilization at sample diameters between 32 and 38 cm, validating the adopted in situ seepage diameter of 37 cm. Linear regression revealed greater discrepancies between laboratory and in situ permeability values in high-swelling soils. Empirical formulas incorporating wet–dry cycles were developed to accurately predict in situ permeability, providing practical tools for engineering design and risk assessment. Full article

The high water cut period represents a critical phase in the development of tight oil wells, and accurately forecasting productivity during this stage is essential for effective oilfield development planning. However, traditional reservoir engineering methods find it difficult to handle complex oil-water seepage behaviors and cannot accurately predict the productivity of tight sandstone oil wells in the high water cut period. Therefore, this paper proposes a method for predicting the productivity of tight oil reservoirs based on a hybrid deep learning algorithm, using the geological, engineering, and development parameters of 342 fractured horizontal wells in the Z211 block of Heshui Oilfield. The model was based on the KAN deep learning algorithm, and the WOA meta-heuristic optimization algorithm was used to optimize the KAN model parameters. Combined with multi-dimensional parameters such as oil well geology, engineering and development, an efficient and accurate productivity prediction model was established. Based on the interpretability of the model itself, the key features of the model and the factors affecting productivity are explained in combination with the SHAP (SHapley Additive exPlanations) value and the Pearson coefficient, revealing the changing relationship of productivity and the degree of influence of different parameters on productivity. The results indicate that the KAN-WOA model demonstrates strong performance in both prediction accuracy and robustness for productivity forecasting. For high water cut fractured horizontal wells in tight oil reservoirs, water content and permeability were identified as the primary influencing factors on initial productivity, whereas for low water cut wells, dynamic liquid level, number of fracturing stages, and sand volume were the key determinants. This approach offers a novel data-driven solution for the development and management of tight oil wells, serving as an effective decision-support tool in oilfield development. Full article

The presence of adjacent tall buildings significantly affects the mechanical response of water-rich strata during metro station excavations. This study focuses on the deep construction pit excavation project of the Houhu Fourth Road Metro Station on Wuhan Metro Line 12. The deformation of the retaining structure and the surface settlement behind the wall obtained from field monitoring data are analyzed. Finite difference numerical simulations are conducted to investigate the responses of water-bearing strata adjacent to tall buildings during the excavation process of the construction pit. The numerical simulation results show that during the excavation process, the maximum deformation of the diaphragm wall is approximately 25.1 mm. It occurs at the position where the wall is buried 28 m deep. The maximum value of ground settlement is approximately 11.9 mm. Furthermore, an empirical formula for predicting the ground settlement under the influence of adjacent buildings and construction pit excavation—applicable to water-bearing sandy strata with conditions similar to those of the Houhu Fourth Road Metro Station—is proposed. The results, derived from the Houhu Fourth Road Metro Station case, demonstrate that the ground surface settlement profile in its water-bearing sandy stratum is significantly altered due to groundwater seepage and the additional loads from nearby buildings. The settlement predicted by the empirical formula shows good agreement with both measured and simulated data: the correlation coefficient (R²) between the predicted values and measured data is above 0.92. Full article

To elucidate the lost circulation mechanism in naturally fractured shale, this study employs fluid seepage theory and fracture deformation theory, assumes the polymer-based drilling fluid system behaves as a Herschel–Bulkley (H–B) fluid, and develops a calculation model for lost circulation pressure that comprehensively incorporates fracture geometry, fracture stress state, drilling fluid properties, and the pressure differential between the wellbore and the formation. Research shows that the lost circulation rate of drilling fluid increases with greater initial fracture width, fracture deformation index, fluid consistency coefficient, yield stress, and pressure differential between the wellbore and the formation, while it decreases with increasing fracture radial extension length, fracture roughness, drilling fluid density, and normal stress on the fracture surface. The initial fracture width, fracture radial extension length, and fluid consistency coefficient have a significant influence on the lost circulation rate of drilling fluid. In contrast, the effects of the fracture deformation index and dynamic yield stress are relatively minor, indicating that they are not the primary controlling factors of fracture-induced lost circulation. Full article

Heavy rainfall infiltration is a key disaster-inducing factor that triggers the softening of surrounding rock and deformation of support structures in tuff gully tunnels. Based on the gully section of the left line of the Dabao Tunnel of the Leigongshan–Rongjiang Expressway in Guizhou Province, this study systematically reveals the synergistic disaster-inducing mechanism of “topography-seepage-softening” in tuff gully tunnels under heavy rainfall infiltration through laboratory tests and FLAC3D 3D numerical simulations. The main innovative conclusions are as follows: (1) The “phased” attenuation law of tuff mechanical parameters was quantified, and the critical water content for significant strength deterioration was determined to be 2.5%, with a saturated softening coefficient of 0.59. These results provide key data for early warning and evaluation of similar projects. (2) A “convergence-disorder” distribution pattern of pore water pressure controlled by gully topography was revealed. It was found that the rock mass directly below the aqueduct exhibits a disordered zone with downward-extending pore water pressure due to fluid convergence, with the maximum pore water pressure reaching 0.55 MPa. This clarifies the essence that tunnel stability is controlled by the coupling of topography and seepage field. (3) The key sensitive areas for tunnel stability—namely the gully bottom, arch haunches, and the area below the aqueduct—were accurately identified. The significant increase in displacement of these areas after rock stratum softening was quantified (e.g., the displacement at the crown of the secondary lining increased from 3 mm to 4 mm, and the influence range expanded to the arch haunches). This study clarifies the deformation characteristics and instability mechanism of tuff gully tunnels under heavy rainfall from two aspects: the “internal mechanism of rock mass softening” and the “external condition of topographic seepage control.” It can provide a theoretical basis and key technical pathway for disaster prevention and control as well as stability design of similar tunnels. Full article

The freezing method is widely employed in the construction of a vertical shaft in soft soil and water-rich strata. As the construction depth increases, investigating the water–heat–force coupling effects induced by the hydration heat (internal heat source) of concrete is crucial for the safety of the lining structure and its resistance to cracking and seepage. A three-dimensional coupled thermal–hydraulic–mechanical analysis model was developed, incorporating temperature and soil relative saturation as unknown variables based on heat transfer in porous media, unsaturated soil seepage, and frost heave theory. The coefficient type PDE module in COMSOL was used for secondary development to solve the coupling equation, and the on-site temperature and pressure monitoring data of the frozen construction process were compared. This study obtained the model-related parameters and elucidated the evolution mechanism of freeze–thaw and freeze–swelling pressures of a frozen wall under the influence of hydration heat. The resulting model shows that the maximum thaw depth of the frozen wall reaches 0.3576 m after 160 h of pouring, with an error rate of 4.64% compared to actual measurements. The peak temperature of the shaft wall is 73.62 °C, with an error rate of 3.76%. The maximum influence range of hydration heat on the frozen temperature field is 1.763 m. The peak freezing pressure is 4.72 MPa, which exhibits a 5.03% deviation from the actual measurements, thereby confirming the reliability of the resulting model. According to the strength growth pattern of concrete and the freezing pressure bearing requirements, it can provide a theoretical basis for quality control of the lining structure and a safety assessment of the freezing wall. Full article

The seepage characteristics and heat transfer efficiency in rough fractures are indispensable for assessing the lifetime and production performance of geothermal reservoirs. In this study, a two-dimensional rough rock fracture model with different secondary roughness is developed using the wavelet analysis method to simulate the coupled flow and heat transfer process under multiscale roughness based on two theories: local thermal equilibrium (LTE) and local thermal nonequilibrium (LTNE). The simulation results show that the primary roughness controls the flow behavior in the main flow zone in the fracture, which determines the overall temperature distribution and large-scale heat transfer trend. Meanwhile, the nonlinear flow behaviors induced by the secondary roughness significantly influence heat transfer performance: the secondary roughness usually leads to the formation of more small-scale eddies near the fracture walls, increasing flow instability, and these changes profoundly affect the local water temperature distribution and heat transfer coefficient in the fracture–matrix system. The eddy aperture and eddy area fraction are proposed for analyzing the effect of nonlinear flow behavior on heat transfer. The eddy area fraction significantly and positively correlates with the overall heat transfer coefficient. Meanwhile, the overall heat transfer coefficient increases by about 3% to 10% for eddy area fractions of 0.3% to 3%. As the eddy aperture increases, fluid mixing is enhanced, leading to a rise in the magnitude of the local heat transfer coefficient. Finally, the roughness characterization was decomposed into primary roughness root mean square and secondary roughness standard deviation, and for the first time, an empirical correlation was established between multiscale roughness, flow velocity, and the overall heat transfer coefficient. Full article

This study develops a novel analytical solution for three-dimensional axisymmetric consolidation of unsaturated soils incorporating radial–vertical composite seepage mechanisms and anisotropic permeability characteristics. A groundbreaking dual orthogonal expansion framework is established, utilizing innovative Bessel–trigonometric function coupling to solve the inherently complex spatiotemporal coupled partial differential equations in cylindrical coordinate systems. The mathematical approach synergistically combines modal expansion theory with Laplace transform methodology, achieving simultaneous spatial expansion of gas–liquid two-phase pressure fields through orthogonal function series, thereby transforming the three-dimensional problem into solvable ordinary differential equations. Rigorous validation demonstrates exceptional accuracy with coefficient of determination R² exceeding 0.999 and relative errors below 2% compared to numerical simulations, confirming theoretical correctness and practical applicability. The analytical solutions reveal four critical findings with quantitative engineering implications: (1) dual-directional drainage achieves 28% higher pressure dissipation efficiency than unidirectional drainage, providing design optimization criteria for vertical drainage systems; (2) normalized matric suction variation exhibits characteristic three-stage evolution featuring rapid decline, plateau stabilization, and slow recovery phases, while water phase follows bidirectional inverted S-curve patterns, enabling accurate consolidation behavior prediction under varying saturation conditions; (3) gas-water permeability ratio k_a/k_w spanning 0.1 to 1000 produces two orders of magnitude time compression effect from 10⁻² s to 10⁻⁴ s, offering parametric design methods for construction sequence control; (4) initial pressure gradient parameters λ_a and λ_w demonstrate opposite regulatory mechanisms, where increasing λ_a retards consolidation while λ_w promotes the process, providing differentiated treatment strategies for various geological conditions. The unified framework accommodates both uniform and gradient initial pore pressure distributions, delivering theoretical support for refined embankment engineering design and construction control. Full article

As metal resource extraction increases, heavy metal ion pollution in the saturated zone intensifies. Hence, research on the migration of heavy metal ions in aquifers and the efficacy of protective measures is essential to inform pollution prevention and control engineering. This study focuses on the slag pond and its surrounding area of a smelting plant. Utilizing field hydrological surveys and experiments, and data from previous studies, we employed FEFLOW7.0 simulation software to model the groundwater system of the boulder aquifer in this region. The model divides the domain based on natural topography: the eastern river serves as a constant-head boundary, while other areas are set as specified-flux boundaries. The impermeable layer at the bottom is treated as a no-flow boundary, with a maximum simulation period of 2500 days. The simulation examines the natural movement of zinc ions and how the construction of the wall impacts their migration, as well as the wall’s effectiveness in preventing seepage. Findings indicate that the movement of zinc ions is significantly influenced by the reaction coefficient. When the reaction coefficient exceeds 10⁻⁸ s⁻¹, zinc ions decrease rapidly in the area. After the construction of the cutoff wall, the maximum migration distance of zinc ions within 2500 days decreased from 220 m to 77 m, demonstrating its effectiveness in controlling zinc transport in groundwater. Full article

This study incorporates a nonlinear seepage relationship into Biot’s consolidation theory and simulates the consolidation of a single vertical drain under vacuum preloading using the finite element method. The model, simplified via the equal-strain assumption, is validated against theoretical predictions. Under the axisymmetric Biot’s framework, consolidation behavior is analyzed in detail. The results show that in the early stages of consolidation, excess pore water pressure in the vicinity of the prefabricated vertical drain (PVD) does not fully dissipate and may even increase, indicating the occurrence of the Mandel–Cryer effect. As the consolidation process advances, the consolidation front gradually extends outward, and the void ratio near the PVD decreases rapidly, leading to the formation of a clogging zone. In contrast, the reduction in the void ratio in the non-clogging region is relatively slow. The progressive development of the clogging zone significantly impedes the overall consolidation rate. Furthermore, this study explores the influence of key parameters—including the compression index, permeability coefficient, well diameter ratio, smear effect, and well resistance—on the formation of the clogging zone and the Mandel–Cryer effect. Full article

The gas desorption behavior of coal is a key basis for guiding gas parameter determination, optimizing gas extraction, and preventing gas-related disasters. Coal in mine working faces typically exhibits a mixed particle size distribution. However, research on the gas desorption behavior of mixed-size coal samples and comparative studies with single-sized samples remains insufficient. This study employed a self-developed experimental system for the multi-field coupled seepage desorption of gas-bearing coal to conduct comparative experiments on gas desorption behavior between single-sized and mixed-size coal samples. Systematic analysis revealed significant differences in their desorption and diffusion patterns: smaller particle sizes and higher proportions of small particles correlate with greater total gas desorption amounts and higher desorption rates. The desorption process exhibits distinct stages: the initial desorption amount is primarily influenced by the particle size, while the later stage is affected by the proportion of coal samples with different particle sizes. The desorption intensity for both single-sized and mixed-size samples decays exponentially over time, with the decay rate weakening as the proportion of small particles decreases. The gas diffusion coefficient decays over time during desorption, eventually approaching zero, and increases as the proportion of small particles rises. Conversely, the gas desorption attenuation coefficient increases with a higher proportion of fine particles. Based on the desorption laws of coal samples with single and mixed particle sizes, this study can be applied to coalbed gas content measurements, emission prediction, and extraction design, thereby providing a theoretical foundation and technical support for coal mine operations. Full article