Search Results (119)

As an innovative foundation type specifically developed for seabed conditions characterized by shallow overburden overlying bedrock, driven embedded rock-socketed jacket offshore wind turbines achieve high bearing capacity by embedding the pile tips into the bedrock. However, the mechanical behavior of this foundation system has not yet been fully clarified. In this study, based on the engineering conditions of an offshore wind power project in Fujian, a 1:100 scaled physical model test is conducted to validate Plaxis 3D finite-element model. On this basis, a parametric sensitivity analysis is conducted to investigate the influences of key geotechnical properties, pile rock-socketed depth, and geometric parameters, with the aim of elucidating the mechanisms governing the lateral loading behavior of the jacket foundation. The results show that the numerical simulations are in good agreement with the experimental measurements. Among all piles, the front-row pile exhibits the most significant displacement at the pile top at the mudline, reflecting the asymmetry in load transfer and deformation of the pile foundation system. The ultimate bearing capacity varies by about 91.7% among different bedrock types, while the influence of rock weathering degree on the lateral bearing performance of the foundation is about 4.7%. The effects of Pile rock-socketed depth and geometric parameters on the lateral bearing capacity of the foundation are approximately 15.2% and 80.8%, respectively. A critical threshold for rock-socket depth exists at about 6D (where D is the pile diameter), beyond which further improvements in embedment depth result in diminishing improvements in lateral bearing capacity. Full article

Safe and efficient coal mining faces a global challenge in predicting sudden surface subsidence whose mechanisms remain unclear. This study, centered on deep coal seams in China’s Ordos Basin, examines the risk of abrupt subsidence controlled by high-positioned, ultra-thick, and weakly cemented key strata. We adopt an integrated “observation–experiment–model” paradigm. First, we construct a spatial decoupling model to analyze errors in 1D SBAS-InSAR monitoring, leading to a refined 2D method that reduces the three-dimensional monitoring error from 50 mm to under 20 mm. Based on this, the subsidence basin’s boundary angles are accurately determined as 52.3°–58.6° (strike) and 44.3°–48.2° (dip). Second, a large-scale physical simulation experiment visualizes the complete process of overburden failure up to the breaking of high-level key strata. Finally, by coupling remote sensing observations with experimental phenomena, a theoretical model is built to quantify the mechanical behavior of key strata, revealing the critical width-to-depth ratios for the rupture of the Yan’an Formation (0.21–0.27), Zhiluo Formation (0.53–0.82), and Zhidan Group (1.22–1.34). The research not only delineates surface subsidence morphology under special geological conditions but also answers the core questions of why subsidence occurs and when mutation may happen, thereby laying a theoretical foundation for a comprehensive early-warning model for mining areas worldwide. Full article

The construction of undersea tunnels involves multiple potential hazards, among which water-related risks are particularly critical during the construction phase. Tunnel water inrush can trigger serious safety incidents and increase maintenance costs during operation. Therefore, accurately predicting water inflow is essential to ensure construction safety and long-term operational reliability. This study calculated the water inflow per meter of an undersea tunnel using the built-in FISH programming language in FLAC^3D 7.0 finite difference software. A series of numerical models was established to examine the effects of eight influencing factors, including seawater depth, permeability of the surrounding rock, overburden thickness, and the thickness and permeability coefficients of both the grouting ring and the lining. The results indicate that water inflow generally increases linearly with greater seawater depth and overburden thickness. Although higher permeability of the surrounding rock leads to increased inflow, the growth rate gradually decreases. When the thickness of the grouting ring exceeds 6 m, the marginal benefit of its effect gradually decreases. The inflow was found to decrease as the lining permeability declined, with a more evident reduction under higher grouting ring permeability. Sensitivity analysis further revealed that seawater depth exerts the most significant influence on water inflow, whereas the thickness of the grouting ring has the least effect. Full article

Accurate deformation monitoring is essential for ensuring the stability of deep vertical shafts. In this study, a temperature-compensated fiber Bragg grating (FBG) sensing system was deployed in the 882 m deep Guotun Coal Mine shaft to measure circumferential and vertical strains at six depths. A site-specific mechanical model integrating stratigraphy, dual-layer concrete lining, and the influence radius was developed to analyze shaft wall stresses. The monitoring results reveal pronounced spatial anisotropy, with circumferential compressive and tensile strains at deeper levels nearly twice those at shallow levels. Strain variation also increases over time, reflecting the combined effects of groundwater fluctuations and overburden consolidation. The stresses inferred from measured strains agree well with the analytical solution in both magnitude and depth-dependent trend, with deviations remaining within a reasonable engineering margin. All stresses are below the strength limits of the C70/C50 concrete lining, confirming that the shaft is in a safe stress state. The proposed monitoring–analysis framework provides a reliable basis for evaluating shaft wall behavior under complex hydrogeological conditions. Full article

Large-mining-height technology has been increasingly applied in thick seam mining to enhance productivity and resource recovery. However, it also intensifies strata pressure and complicates surrounding rock control, leading to greater overburden movement, stronger roof weighting, and severe coal wall spalling. Taking the 12306 working face of the Wangjialing Mine as a case, this study employs physical similarity experiments and UDEC numerical simulations to investigate the coupled mechanism of overburden migration and coal wall instability. Results show that abutment stress induces non-uniform deformation, while strata pressure changes directly govern spalling depth. Moreover, coal wall instability is strongly affected by multiple factors: greater burial depth intensifies crack propagation, larger mining height expands failure depth, larger mining step size extends the stress-affected zone, larger dip angle shifts failure upward, and lower support resistance weakens control capacity. These findings clarify the disaster mechanism of deep large-mining-height faces and provide theoretical and engineering guidance for optimizing support design and enhancing coal wall stability. Full article

This study presents a nonlinear regression expansion model tailored to the characteristics of fissured highly expansive soils. Through in-depth investigations, fissure ratio (K_r), dry density (ρ_d), initial water content (w₀), and overburden stress (ln(1 + σ)) were identified as critical factors influencing expansion behavior. Experimental results revealed linear relationships between ultimate expansion (δ_ep) and w₀, ρ_d, and ln(1 + σ), and an exponential relationship with K_r. A multivariate nonlinear regression model was developed and validated, demonstrating high predictive accuracy. The model highlights the significant role of fissure infill materials, particularly gray-green clay, on soil expansiveness. It provides a reliable tool for predicting the expansion characteristics of fissured expansive soils under various conditions, offering theoretical and practical support for engineering applications in expansive soil regions. This study uses a single highly expansive clay from the Nanyang section. The soil is a transported Middle Pleistocene alluvial–proluvial clay (al-plQ2) in which fissures are predominantly filled by 2–5 mm gray-green clay. Accordingly, the proposed regression is most applicable to fissure systems that are largely infilled; extrapolation to open or partially infilled fissures should be made with caution. Full article

Tunnel anchorages are critical components in long-span suspension bridges, transferring immense cable forces into the surrounding rock mass. Although previous studies have advanced the understanding of their pullout behavior through field tests, laboratory models, numerical simulations, and theoretical analyses, significant challenges remain in predicting their performance in complex geological conditions. This study investigates the pullout failure mechanism and bearing behavior of tunnel anchorages situated in heterogeneous conglomerate rock, with application to the Wujiagang Yangtze River Bridge in China to employ a tunnel anchorage in such strata. An integrated research methodology is adopted, combining in situ and laboratory geotechnical testing, a highly instrumented 1:12 scaled field model test, and detailed three-dimensional numerical modeling. The experimental program characterizes the strength and deformation properties of the rock, while the field test captures the mechanical response under design, overload, and ultimate failure conditions. Numerical models, calibrated against experimental results, are employed to analyze the influence of key parameters such as burial depth, inclination, and overburden strength. Furthermore, the long-term stability and creep behavior of the anchorage are evaluated. The results reveal the deformation characteristics, failure mode, and ultimate pullout capacity specific to weakly cemented and stratified rock. The study provides novel insights into the rock–anchorage interaction mechanism under these challenging conditions and validates the feasibility of tunnel anchorages in complex geology. The findings offer practical guidance for the design and construction of future tunnel anchorages in similar settings, ensuring both safety and economic efficiency. Full article

The Shendong mining area, a pivotal coal production base in China, faces considerable challenges due to extensive mining activities. The significant development of overlying rock fractures and the widespread occurrence of surface cracks present a major challenge to mining safety and ecological preservation in China and other mining nations. This study focuses on the Panel 12,401 fully mechanized longwall face at Shangwan Coal Mine to systematically investigate overburden movement and the evolution of surface fractures. By combining UDEC discrete element modeling with a computational framework that links subsurface strata subsidence and surface settlement, this research examines the spatial and mechanical properties of fracture propagation. Experimental results show that surface fractures continue to develop as the working face advances, with their horizontal apertures gradually decreasing and eventually closing after the face passes. Both the maximum surface subsidence and the maximum fracture aperture exhibit a strong positive correlation with mining height. In contrast, increased mining depth leads to reductions in maximum surface subsidence, the subsidence factor, and the size of surface fracture apertures. These findings provide a theoretical basis for reducing mining-induced damage and promoting ecological restoration in mining areas. Full article

When constructing subway tunnels in composite strata consisting of overlying soil and underlying rock, placing the tunnel within the overburden rock strata and setting a certain thickness of safety cover rock on top is an effective way to ensure the safety of tunnel construction and the stability of the surrounding rock. However, there is currently no unified understanding or standard regarding the safe overburden thickness of the tunnel and its general rules. To investigate the effect of changes in the roof overlying rock thickness on the surrounding rock stability of subway tunnels, this study is based on the typical soil–rock strata of an underground tunnel section of Jinan Metro Line 4 in China. A total of 4 different conditions for the thickness of the overlying soil layer were considered, and 48 comparison schemes were designed. A systematic study of numerical simulation comparisons of tunnel excavation under different cover rock thicknesses was conducted. The deformation and plastic zone evolution characteristics of the surrounding rock were revealed under different cover rock thicknesses, and the existence of an optimal cover rock thickness range for tunnel crowns in soil–rock strata was identified. Based on this, a theoretical analysis model for the failure of the tunnel roof overlying rock was constructed. Using the upper-bound approach limit analysis method, the theoretical formula for the critical overburden thickness of the tunnel crown was derived. The influence of different rock mechanical parameters and tunnel design parameters on the critical overburden thickness was analyzed. The results were compared with numerical simulation results to verify the effectiveness of the proposed method. The research findings provide theoretical references for selecting reasonable buried depths and support designs for mining-bored tunnels in soil–rock composite strata. Full article

The Erlian Basin, an important research area for sandstone-type uranium deposit exploration in China, is affected by overburden layers, resulting in indistinct characteristics of uranium anomalies in airborne gamma-ray spectrometry (AGS). To harness the potential of AGS, it is imperative to develop effective verification methods that can identify the spatial relationship between weak uranium anomalies and deep uranium-rich geological bodies. This study presents a comprehensive investigation of geophysical and geochemical measurements conducted in four distinct areas. There is a significant positive correlation between the ground gamma spectrometry equivalent uranium (eU_GGS) content, soil radon concentration (C_Rn), geoelectrochemical uranium (U_GEC), and metal activity state uranium (U_MAS) content directly above and at the edges of uranium-rich geological bodies. When the buried depth of the uranium-rich geological body exceeds 100 m, the eU_GGS content above these deep uranium bodies increases by (0.4–1.2) × 10⁻⁶ g/g compared to background areas, while the C_Rn levels at the edges of these bodies increase by more than 5000 Bq/m³, which is 3–5 times higher than the regional average. Meanwhile, the U_GEC and U_MAS contents show sawtooth-like uranium peak anomalies on their profiles, and their peak-to-background ratio is greater than 5. The verification methods and corresponding interpretation indicators, namely GGS, C_Rn, GEC and MAS measurements, can quickly reveal the spatial relationship and provide a reliable basis for concealed uranium deposit exploration. Full article

The dynamic shear modulus ratios and dynamic damping ratios of soil are critical parameters for soil seismic response analyses and seismic safety evaluation of engineering sites. This study utilized dynamic triaxial test and resonant column test data of 5208 soil samples collected from more than 2500 boreholes across the Beijing-Tianjin-Hebei (BTH) region. Statistical analyses were conducted for five typical soil types (silty clay, clay, silt, silty sand, and fine sand), focusing on their dynamic shear modulus ratios and dynamic damping ratios. Key parameters representing the characteristics of soil dynamics, including the reference strain, the maximum damping ratio, and the damping ratio nonlinearity coefficient, were statistically evaluated. Median values, as well as the values corresponding to 84% and 16% exceedance probabilities, were provided. The median values of the reference strain, the maximum damping ratio, and the damping ratio nonlinearity coefficient were 13.43 × 10⁻⁴, 0.2155, and 0.7799 for silty clay; 16.47 × 10⁻⁴, 0.2266, and 0.7722 for clay; 10.64 × 10⁻⁴, 0.2012, and 0.7856 for silt; 11.98 × 10⁻⁴, 0.1842, and 0.7911 for silty sand; and 12.73 × 10⁻⁴, 0.1803, and 0.8064 for fine sand. Based on these statistics, the influence of various factors on the reference shear strain, maximum damping ratio, and damping ratio nonlinearity coefficient were investigated. The results showed considerable variability, and weak correlations were observed between these parameters and site-related factors such as sampling depth, shear wave velocity at sampling depth, overburden thickness, 30 m average shear wave velocity (V_S30), and 20 m equivalent shear wave velocity (V_se). The coefficients of determination for the linear regressions considering each factor were between 0.001 and 0.274, which were sufficiently close to 0 and indicated a weak predictive ability of the model considering only one factor. Furthermore, multivariate linear regression models incorporating all five influencing factors also achieved a slight reduction in standard deviation compared with directly adopting the mean values—by <5.5% for the reference shear strain, <3.9% for the maximum damping ratio, and <7.3% for the damping ratio nonlinearity coefficient. A case study was conducted to demonstrate the impact of the variability in soil dynamic parameters on both site seismic response and structural seismic response. For the selected ground motion inputs, site model, and structural model, differences in soil dynamic parameters led to variations in structural seismic response up to 54.5%. Comparative analyses with recommended values from existing studies indicate that the dynamic parameters of the five typical soil types in the BTH region investigated exhibited distinct regional characteristics: the dynamic shear modulus ratios were significantly lower, while the dynamic damping ratios were significantly higher. Comparisons with results from other studies on soil dynamic parameters in China showed that the dynamic shear modulus ratios derived from this study were noticeably smaller, while the dynamic damping ratios were significantly larger. At least one of the three soil dynamic parameters for each soil type failed to pass two-side t-tests, which indicated that the statistical data were from two distributions, that is, soil dynamic properties were intrinsically linked to sedimentary environments, exhibiting distinct regional specificity. Therefore, for boreholes lacking laboratory dynamic test data of soil in the BTH region, it was recommended to use the median values of reference shear strains, maximum damping ratios, and damping ratio nonlinearity coefficients provided in this study for the estimation of dynamic shear modulus ratios and dynamic damping ratios, while their variability must be taken into consideration. Full article

The rehabilitation of coal mine sites in semi-arid environments is a step in combating desertification. A promising rehabilitation approach involves the development of anthropic soils that can support vegetation. However, reliable soil quality indicators are needed to evaluate long-term sustainability of rehabilitation strategies. In a coal mine area in northeastern Spain, two anthropic soils (0.5 m thick) were constructed by layering fine-textured coal residues at the bottom, topped with coarse overburden materials. Chemical fertility was enhanced using combinations of semi-liquid manure (25 or 60 mm) and straw (0 or 15 Mg ha⁻¹), resulting in four treatments randomly distributed across both soil surfaces. Two abiotic indicators were selected for sustainability assessment: soil organic carbon (SOC) fractions and microstructure. Seven years after rehabilitation activities were completed, SOC fractions were analyzed. In addition, two years later, soil porosity and specific pore perimeter were also assessed in soil thin section images. The results indicated that the lower manure rate promoted more efficient SOC stabilization, evidenced by a 4–5-fold increase in specific pore perimeter at 0–5 cm depth, and lower fulvic acid content at 5–20 cm depth, compared with the higher manure rate. Micromorphological analysis proved to be a sensitive method for detecting early improvements in the physical quality of anthropic soils, highlighting the importance of adjusting manure rates for sustainable coal mine rehabilitation. Full article

To investigate the impact of Integrated Mining-Backfill-Roof Contact (IMBR) synergy on strata subsidence in metallic deposits and analyze strata/surface movement patterns, this study enables safe, efficient, environmentally conscious, and sustainable mining development. Focusing on a representative metal mine, we integrated laboratory testing, theoretical analysis, and numerical modeling to determine experimental parameters. Utilizing MIDAS GTS NX, numerical models incorporated four orebody dip angles (30°, 50°, 70°, 90°), five stress release coefficients (20–100%), and contacted/uncontacted conditions to assess IMBR’s control efficacy on surrounding rock stability and surface subsidence. By examining strata/surface movement under variable dip angles and stress release coefficients, displacement control mechanisms were quantified, revealing strata movement evolution principles. Key findings indicate: (1) For all dip angles, the increase rate of displacement progressively intensifies as the excavation stress release coefficient decreases. Notably, at a 30° dipping angle, the most pronounced reduction occurs under declining stress release coefficients, with overall displacement reduction rates reaching 17% for ground surface and 18% for surrounding rock, respectively. (2) Surface displacement impacts intensify as dip angles flatten. (3) Shallower dips induce more pronounced stress disturbance, expanding overburden movement domains and exacerbating surface impacts. Finite element numerical modeling enables accurate and effective analysis of strata and ground movement patterns under varying orebody dipping angles and mining-backfill stress release coefficients. Findings demonstrate that IMBR technology, compared to conventional roof-contacted backfilling methods, achieves timely roof support through immediate backfill-roof contact, significantly reduces overburden fracture propagation depth, and offers valuable insights for controlling surface subsidence in complex mining conditions—particularly for mining under surface structures. Full article

The shear strength and bearing characteristics of lunar soil have a strong connection with its compactness. The compactness varies significantly with depth and has an important effect on engineering activities on the lunar surface. In this study, lunar soil simulant samples of four compactness levels were prepared to explore the relationship between compactness and cone tip resistance in static cone penetration tests (CPTs). The compactness values at different depths were measured layer by layer, and CPTs were carried out. The results indicate that the cone tip resistance continuously increases with the increase in the penetration depth until it reaches a peak, and then remains constant for a certain depth. The cone tip resistance after the normalization of the overburden stress gradually increases and then decreases after reaching the peak. Models of the relationship between cone tip resistance before and after normalization and compactness were constructed using a regression algorithm. The variation in lunar soil compactness with depth can be determined by measuring cone tip resistance with this model. The research findings can provide a theoretical basis for in situ testing, site selection for lunar bases, and other related aspects on the lunar surface. Full article

Pore pressure prediction gives drillers an early warning of potential oil and gas kicks, enabling them to adjust mud weight pre-emptively. A kick causes a delay in drilling practices, blowouts, and jeopardization of the wells. Changes in pore pressure affect the type of fluid contact in the reservoir. This study predicted the pore pressure and determined fluid contacts within the Lower Cretaceous and early Upper Cretaceous (Barremian to early Cenomanian) sandstone reservoirs of the Bredasdorp Basin using well logs and repeat formation test (RFT) data from three wells: E-BK1, E-AJ1, and E-CB1. Eaton’s method of developing a depth-dependent Normal Compact Trend (NCT), using resistivity and sonic wireline logs, as well as other methods including the Mathews and Kelly, Baker and Wood, and Modified Eaton and Bowers methods, were employed for pore pressure prediction. Eaton’s method provided reliable pore pressure results in all the wells when compared to alternative methods in this study. Overburden gradient and predicted pore pressures ranged from 1.84 gm/cc to 2.07 gm/cc and from 3563.74 psi to 4310.06 psi, respectively. Eaton’s resistivity and density/neutron log method results indicated normal pressure in E-BK1 and E-AJ1, as well as overpressured zones in E-AJ1. However, in E-CB1, the results showed only overpressured zones. The E-AJ1 significant overpressures were from 2685 m to 2716 m and from 2716 m to 2735 m in the pores exceeding 7991.54 psi. Gas–water contact (GOC) was encountered at 2967.5 m in E-BK1, while oil–gas contact (OGC) was at 2523 m in E-CB1, and gas–oil and oil–water contacts (GOC and OWC) were at 2699 m and 2723 m, respectively, in E-AJ1. In E-CB1, oil–water contact (OWC) was at 2528.5 m. Fluid contacts observed from the well logs and RFT data were in close agreement in E-AJ1, whereas there was no agreement in E-CB1 because the well log observations showed a shallower depth compared to RFT data with a difference of 5.5 m. This study illustrated the significance of an integrated approach to predicting fluid contacts and pore pressure within the reservoirs by showing that fluid contacts associated with overpressures were gas–water and oil–water contacts. In contrast, gas–oil contact was associated with normal pressure and under pressure. Full article