Bulletin of Engineering Geology and the Environment最新文献

Traditional dual-porosity models average gas pressure within the matrix, failing to account for the uneven gas pressure distribution and the resulting inhomogeneous deformation in the shale skeleton. To this end, we propose a modified dual-porosity model. In the new approach, the gas pressure profile within the matrix is determined using the gas diffusion equation, and the induced deformation is expressed analytically and then integrated into the permeability model to establish a coupling process. The experimental data for both adsorption and non-adsorptive gases are accurately replicated to verify the proposed model. Subsequently, the effects of shale matrix properties -diffusion and geometry characteristics - on permeability evolution are addressed. Both global and local deformations together affect the permeability changes of adsorption gas. In contrast, for non-adsorptive gas, permeability is primarily driven by local deformation, influenced by the competition between inward and outward swelling. As a result, the recovery phase, primarily determined by the swelling transition, is more easily attained for non-adsorptive gas. The decreasing and recovering stages are more pronounced near the injection boundary, while areas farther from the injection boundary continue to experience reduced permeability. An increased diffusion coefficient leads to a reduced equilibrium time and a more pronounced global effect, resulting in an earlier rise in permeability evolution. A larger critical ratio produces a stronger local effect along with a notable decrease in permeability. Additionally, smaller matrix blocks exhibit a shorter equilibrium time and a greater global effect, resulting in a more significant reduction in permeability and a subsequent rebound. This work can provide an accurate method for evaluating the permeability variation in the laboratory and further the gas depletion characteristics at the field scale.

The Qinghai-Tibet Plateau region is showing a trend of climate warming, and the active layer is thickening. The freeze–thaw (FT) cycles change the internal structure of the active layer of lateritic soil slopes, resulting in widespread landslides. At present, the research on the microstructure of Qinghai-Tibet Plateau lateritic soil under climate warming is rare. To simulate the effect of climate warming, FT tests were conducted at both fixed (F-type) and elevated (E-type) freezing temperatures. The microstructure was quantitatively analyzed using X-ray micro-computed tomography (CT), with a focus on pore structure, porosity development, and pore size distribution. Pores evolved from isolated, spherical structure into dendritic and banded structures after successive FT cycles. Surface porosity increased significantly, especially under E-type cycles, which produced a more uneven and distinct distribution due to the enhanced water migration and ice formation. For total porosity, it increased from 5.58% to 17.79% (F-type) and to 26.81% (E-type) after seven cycles. In terms of connected porosity, it rose more sharply after E-type FT tests. A log-normal distribution model was established to analyze the pore size distribution after FT tests. E-type cycles led to a more pronounced shift in the pore size distribution, characterized by a rightward displacement of the curve and a reduction in distribution width. The study shows that elevated freezing temperature FT cycles significantly enhance pore connectivity and structural damage of lateritic soil. In engineering construction in relevant areas, the effects of climate warming on the microstructural deterioration of lateritic soil should be fully considered in design and protection measures. Such consideration is essential to ensure the long-term safety and stability of engineering structures.

Underground engineering is gradually exploring deeper, which puts forward new requirements for hard rock breaking technology. Microwave-liquid nitrogen (LN₂) cooperative assisted rock breaking technology is considered an efficient rock breaking method that can cause a strong thermal shock effect on the rock mass, effectively reduce drill bit wear and improve drilling efficiency in hard rock formations. Therefore, the structural damage and tensile failure properties of the granite under combined microwave and LN₂ are investigated experimentally. The results show that with the increase of the microwave time and thermal shock cycles, the internal structure damage of the granite increases significantly, and the initiation stress, tensile strength, and splitting modulus of the granite decrease. With the deepening of the thermal shock cycle, the number of microcracks in the granite increases and transgranular cracks appear gradually. After 16 min of microwave irradiation at a power of 0.9 kW, the tensile strength and splitting modulus of the granite decreased by 51.8% and 60.1%, respectively. In comparison, following 20 thermal shock cycles, these two mechanical parameters of the granite exhibited more significant reductions, with decreases of 58.6% and 69.7% correspondingly. The microwave-LN₂ treatment can effectively reduce the energy required for mechanical failure of the granite and increase the number of crack propagations. The shear crack proportion and induced crack surface complexity increase with the increase of the microwave time and thermal shock cycles. A thermal-mechanical model with continuous-discrete coupling is established to simulate and reveal the cracking mechanism of the granite under the microwave-LN₂. The research results provide a new idea for increasing speed and reducing cost in deep hard formation drilling.

Grain-based model (GBM) effectively represents the mineral composition and grain distribution present in natural rock, making it widely used for simulating cracking in crystalline rocks. This study introduces an improved GBM (IGBM) based on the principles of grain seeding, growth, and merging, which allows for the alteration of mineral grain orientation and shape that the conventional GBM can not offer. The microscopic parameters of the IGBM are calibrated based on laboratory test results. Subsequently, 99 models are generated by varying particle size, grain aspect ratio, and grain orientation to investigate the effects of particle size and fabric on the mechanical behavior of crystalline rocks. The study reveals that when the direction of maximum shear stress ((tau_{text{m}text{a}text{x}})) aligns closely with the grain boundary orientation, the uniaxial compressive strength (UCS) of the sample is at its lowest. In contrast, the rock’s strength increases when the grain orientation deviates from the direction of (tau_{text{m}text{a}text{x}}). Additionally, as particle size decreases, both UCS and Young’s modulus increase correspondingly. The tensile strength is barely affected by the particle size. When the grain-to-particle size ratio exceeds a critical threshold of approximately 8, the normalized UCS of the model stabilizes. Therefore, for future applications of the grain-based discrete element method in simulating rock cracking, it is advised that the grain-to-particle size ratio be maintained at a minimum of 8 to ensure accurate results. The proposed numerical method and research findings can provide guidance for future refined simulations in rock mechanics.

In response to the challenge of brittle failure and the lack of nucleation sites in the EICP-solidified soil, a method for mechanical enhancement through the synergistic effect of xanthan gum (XG) and fibers was proposed. The mechanical properties, CaCO₃ content, water stability, and microstructural characteristics of EICP-solidified sand were systematically evaluated. Based on the experimental results, the enhancement mechanism of XG and fiber was then revealed accordingly. The results demonstrate that XG may enhance the immobilization of urease at contact points and provides nucleation sites for CaCO₃ precipitation, while fibers offer additional immobilization sites for urease and delay soil failure through a bridging effect. Under the CaCO₃-fiber-XG reinforcement system, the UCS of EICP-solidified sand was increased by up to 187.51%. Furthermore, the UCS, deformation modulus, and water stability of EICP-solidified sand exhibited a positive correlation with CaCO₃ content. As the CaCO₃ content increased from 1.5% to above 2.25%, the water stability of the EICP-solidified sand rapidly increased from 40% to approximately 90%. When the CaCO₃ content exceeded 2.25%, the water stability remained in the range of 90%-100%, showing excellent water stability.

In split Hopkinson pressure bar (SHPB) tests, the size effects play a crucial role in influencing dynamic mechanical properties of rock-like materials. To explore the influence of specimen size and bar diameter on the dynamic mechanical characteristics of sandstone, dynamic compression experiments were conducted on specimens of varying sizes using a Φ50 mm and a Φ100 mm SHPB device. The results showed that specimens exhibited different test outcomes under the impact of bars with different diameters. In addition, in order to obtain the influence of size effects on axial inertia effects, the concept of dimensionless stress difference was proposed, which can be obtained by installing strain gauges at both ends of specimens. Dimensionless stress difference-time curves can be divided into an oscillation zone and a stable descent zone. Research indicates that the duration of the oscillation zone is largely constrained by the diameter of the bar and the intensity of the impact, and is relatively less affected by the length of specimens. The results can provide theoretical references for designing specimen sizes of rock-like materials in SHPB tests at the macro level, and these findings provide valuable insights for optimizing impact-resistant designs in rock-based engineering structures.

Large paleolandslides in mountainous regions frequently resulted in river blockages, forming dammed-lakes and subsequently outburst floods. Regional landscape evolution and paleoclimatic or neotectonic conditions can be inferred from the remnants of paleolandslides, paleolake shorelines and lacustrine sediments. The paper, through field surveys, satellite imagery interpretation and lacustrine sediment dating, examines these Quaternary landforms along the midstream Tashkurgan river, Chinese Pamir. We identify three large paleolandslides - Xiabandi, Hamletti and Spillway Outlet – that sequentially dammed the river near the current Xiabandi hydro-project dam at approximately 22–26, 12.5 and 6.5 ka BP, respectively. The Xiabandi paleolandslide created an upper paleolake shoreline (3100 m asl) and thick lacustrine sediments, while the Spillway Outlet paleolandslide formed a lower paleolake shoreline (3030 m asl). Lacustrine sediments at the Tashman and Xindi sections contain diverse soft-sediment deformation structures of seismic origin, such as sand dykes, ball-and-pillows, slumps, convolutions and graded faults. These deformation structures, together with paleolandslides, indicate high paleoseismicity in the Tashkurgan region. The older Xiabandi paleolandslide was likely triggered by activity of the Karakax fault, whereas the younger Hamletti and Spillway Outlet paleolandslides were likely associated with activity of the Muztag fault. Our findings provide critical constraints for the seismic and landslide risk assessment of the midstream Tashkurgan river, particularly for the safety of the Xiabandi hydro-project.

Seismic resilience plays a crucial role in assessing structural seismic performance. However, there is currently a lack of assessment regarding the seismic resilience of mountain tunnels. We developed a mountain tunnel model that considers terrain features, selected appropriate evaluation indicators, and conducted incremental dynamic analysis (IDA) to obtain seismic fragility curves based on different damage states. By establishing rational functionality restoration functions, we calculated the resilience index of tunnels, thus constructing an assessment framework for evaluating the seismic resilience of mountain tunnels. We conducted seismic resilience analysis on mountain tunnels under near-fault (NF) and far-field (FF) earthquakes, aiming to reveal the impact of different ground motion characteristics on the seismic resilience of mountain tunnels. The research findings indicate that various types of ground motion have significantly different effects on the seismic resilience of mountain tunnels, with NF pulse-like ground motions leading to more severe structural damage. Compared to other types of ground motion, seismic effects from near-fault fling step (NFFS) and near-fault forward directivity (NFFD) ground motions result in a significant decrease in post-earthquake residual functionality, leading to a noticeable reduction in tunnel seismic resilience, with the resilience index of NFFS lower than that of NFFD. Furthermore, the PGV/PGA ratio significantly affects the seismic resilience of mountain tunnels in near-fault earthquakes. Compared to a low PGV/PGA ratio, a high PGV/PGA ratio results in greater damage to mountain tunnels and smaller resilience indices.

Subsurface heterogeneity poses a significant challenge for geotechnical experts, particularly in hazard-prone regions susceptible to earthquakes, landslides, and ground subsidence. This study presents the development of geotechnical soil maps (GSMs) by incorporating an improved version of the modified Shepard-based Inverse Distance Weighting (IDW) method utilizing the Google Earth Engine (GEE) platform. This approach integrates monotonization equations to improve accuracy and ensure smoother transitions in complex subsurface formations and compares with the traditional Kriging technique. Essential geotechnical parameters, i.e., SPT-N, shear wave velocity (Vs), soil classification, plasticity index (P.I), and linear shrinkage (L.S), were used to develop GSMs. Analysis revealed that superficial depths (1.5–3.0 m) predominantly consist of silt and clay sediments, with SPT-N and Vs values ranging from 0–10 and 0–222 m/s, respectively, while L.S ranged between 0 and < 7%. In contrast, deeper layers (> 3.0 m) transitioned to cobbles, boulders, and rock strata. However, isolated zones exhibiting low strength or stiffness characteristics may pose stability challenges under hazard conditions. The advanced IDW algorithm demonstrated superior performance, achieving root mean square error (RMSE) and mean absolute error (MAE) values ranging from 0.12 to 1.45, and Nash Sutcliffe Efficiency (NSE) and correlation coefficients (R²) between 0.88 and 0.98, along with up to error mitigation of 48% against the conventional techniques. Additionally, it reduced areal coverage differences (2–18%), eliminated sharp ridges, and maintained geotechnical accuracy, aligning well with Tobler’s First Law of Geography. These findings highlight the effectiveness of this approach in enhancing hazard mitigation strategies and supporting the resilience of infrastructure.

Clay exhibits strong water sensitivity and low strength, making it highly susceptible to undesirable phenomena in engineering applications. To address this issue, the enhancement of soil properties through the addition of solidifying materials is considered, particularly in light of the low utilization rate of phosphogypsum slag. Therefore, phosphogypsum is employed as a PS cementitious material (comprising phosphogypsum, slag, and calcium oxide), combined with basalt fiber (BF) as a novel green material to synergistically solidify the soil. The effects of fiber content, PS content, and curing time on the performance of the solidified soil were investigated through various tests, including compaction tests, unconfined compressive strength tests, Brazilian split strength tests, falling head penetration tests, scanning electron microscopy, and X-ray diffraction tests. The results indicated that as the PS mix content and curing time increased, the compressive strength of the soil gradually improved and exhibited significant brittleness. The strength of the PS-solidified soil could reach 2118 kPa at 28 days, representing a 1340% enhancement compared to that of raw soil. An optimal fiber content was identified in the PS-BF solidified soil (0.6% BF), which resulted in a 54% increase in strength compared to PS solidified soil. As fiber content increased, the energy absorption capacity initially rose and subsequently declined, while the permeability coefficient exhibited the opposite trend. The fibers and the hydration products adhering to the surface collaboratively contribute to the strengthening of the soil. These research findings can provide theoretical and technical guidance for subgrade improvement and slope protection.