Search Results (127)

Karst ground collapses triggered by groundwater fluctuations pose a significant threat to the safety and stability of tunnel engineering. In this study, taking the Yakouzai Tunnel as a case, a combination of physical model tests and numerical simulations was employed to investigate the mechanisms of groundwater-induced karst collapse. A self-designed physical model device reproduced the full process of soil cavity initiation, expansion, and roof failure. Numerical simulations were further conducted to analyze the evolution of pore water pressure, stress distribution, and displacement under both groundwater drawdown and rise conditions. The results indicate that concentrated seepage erosion at the cavity arch foot is the primary driver of cavity initiation, with cyclic suffusion promoting its progressive expansion. Rapid groundwater drawdown generates vacuum suction that markedly reduces roof stability and may induce sudden collapse, whereas groundwater rise, although providing partial support to the roof, intensifies shear stress concentration and leaves the cavity in an unstable state. The findings highlight that karst collapse is governed by the coupled effects of seepage erosion, arching degradation, differential settlement, and vacuum suction, providing a scientific basis for monitoring, prediction, and mitigation of karst hazards. Full article

To investigate the mechanism of road collapse induced by structural defects in underground drainage/sewerage pipelines in water-rich sands, laboratory physical model tests were conducted to reproduce the macroscopic development of surface subsidence. A computational fluid dynamics-discrete element method (CFD-DEM) model was then established and validated against the tests to assess its reliability. Using the validated model, we examined the effects of defect size and groundwater level on the progression of groundwater-ingress-driven internal erosion and tracked the evolution of vertical stress and intergranular contacts around the pipe. Results show that internal erosion proceeds through three stages—initial erosion, slow settlement, and collapse—culminating in an inverted-cone collapse pit. After leakage onset, the vertical stress in the surrounding soil exhibits a short-lived surge followed by a decline on both sides above the pipe. The number of intergranular contacts decreases markedly; erosion propagates preferentially in the horizontal direction, where the reduction in contacts is most pronounced. Within the explored range, higher groundwater levels and larger defects accelerate surface settlement and yield deeper and wider collapse pits. Meanwhile, soil anisotropy strengthens with increasing groundwater level but peaks and then slightly relaxes as defect size grows. These qualitative findings improve understanding of the leakage-induced failure mechanism of buried pipelines and offer references for discussions on monitoring, early warning, and risk awareness of road collapses. Full article

Settlement and deformation of multi-purpose utility tunnels (MUTs) are critical factors affecting their structural integrity and service life; however, effective identification methods remain limited. This study proposes a comprehensive approach integrating Brillouin frequency domain analysis (BOFDA), fiber Bragg grating (FBG), and ground penetrating radar (GPR) technologies, which was successfully applied to an MUT comprising three tanks in Baiyin City, Gansu Province, China. BOFDA enables precise localization of settlement points, FBG-based dislocation meters facilitate posture recognition of the MUT, and GPR is employed for detailed analysis of settlement causes. The results indicate that MUT deformation primarily manifests as displacement at joint locations, supplemented by deformation of the tunnel structure itself. Rotation, even settlement, and uneven settlement were identified through three FBG-based dislocation meters installed on the top and side walls. The primary causes of MUT settlement include mudstone compression and collapse of loess. Full article

Urban underground pipeline aging and leakage can result in soil erosion and ground collapse, constituting a major threat to urban public safety. To investigate this disaster mechanism, this present study established a two-dimensional numerical model based on the computational fluid dynamics–discrete element method (CFD–DEM) two-way fluid–solid coupling approach, simulating and reproducing the entire process from soil erosion, soil arch evolution to ground collapse caused by underground pipeline leakage in water-rich sand layers. The simulation shows that under the action of seepage pressures, soil particles are eroded and lost, forming a cavity above the pipeline defect. As soil continues to be lost, the disturbed zone expands toward the ground surface, causing ground settlement, and in water-rich sand layers, a funnel-shaped sinkhole is eventually formed. The ground collapse process is closely related to the groundwater level and the thickness of the overlying soil layer above the pipeline. Rising groundwater levels reduce the effective stress and shear strength of the soil, significantly exacerbating seepage erosion. Increasing the thickness of the overlying soil layer can enhance the confining pressure, improve soil compactness, and promote the formation of soil stress arch, thereby effectively slowing down the rate of ground collapse. This study reproduces the process of ground collapse numerically and reveals the mechanism of ground collapse induced by underground pipeline leakage in water-rich sand layers. Full article

During the construction of deep underground soft rock strata, the adverse effects of high geostress, unfavorable geological conditions, and excavation disturbances are significant, easily triggering Material-Stress-Induced (MSI) large deformation disasters, leading to the failure of support structures or even collapse, thus posing great challenges to the safe construction of this type of underground engineering. Based on this, this study first classifies the large deformations, analyzes the instability mechanism of material-stress-induced large deformation in soft rock, and identifies the influencing factors of this type of large deformation from three aspects. Subsequently, a numerical investigation (FLAC3D 6.00) is utilized to examine the surrounding rock deformation characteristics under different material factors (uniaxial compressive strength and elastic modulus), stress factors (burial depth and lateral pressure coefficient), and construction factors (excavation method, support pattern, and timing of initial support installation). On this basis, a multi-factor sensitivity comparison analysis is conducted, which clarifies the differences and prioritization of parameter influences on large deformation, and reveals the dominant role of controlling factors such as elastic modulus. The analysis demonstrates a strong negative correlation between the examined material factors (uniaxial compressive strength and elastic modulus) and the magnitude of surrounding rock displacement, with both values eventually converging. A significant positive correlation between the examined stress factors and the magnitude of surrounding rock displacement was observed. A pronounced positive correlation was observed between stress factors and surrounding rock deformation. These factors distinctly have different effects on the peak displacement of different surrounding rock parts. Vault settlement demonstrates the most pronounced displacement, while arch bottom deformation is the least apparent. The three excavation methods exhibit relatively low sensitivity to surrounding rock displacement. Similarly, the support patterns demonstrate limited influence on surrounding rock deformation. The material factor of soft surrounding rock is the main controlling factor of the large deformation of soft surrounding rock in deep underground engineering. The elastic modulus has the strongest influence on the displacement of the surrounding rock. When the elastic modulus is less than 2 GPa, the sensitivity coefficient is much higher than the stress factors. The research results can provide some reference and guidance for similar underground projects. Full article

To overcome the limitations imposed by the anisotropy and heterogeneity of natural loess, this study establishes a novel quantitative macro–micro correlation framework for investigating the deformation mechanisms of artificial structural loess (ASL). ASL samples were prepared by mixing remolded loess with cement (0–4%) and NaCl (0–16%), followed by static compaction (95% degree) and 28-day curing (20 ± 2 °C, >90% RH) to replicate the structural properties of natural loess under controlled conditions. An integrated experimental methodology was employed, incorporating consolidation/collapsibility tests, particle size analysis, X-ray diffraction (XRD), and mercury intrusion porosimetry (MIP). A three-dimensional nonlinear model was proposed. The findings show that intergranular cementation, particle size distribution, and pore architecture are the main factors influencing loess’s compressibility and collapsibility. A critical transition from medium to low compressibility was observed at cement content ≥1% and moisture content ≤16%. A strong correlation (Pearson |r| > 0.96) was identified between the mesopore volume ratio and the collapsibility coefficient. The innovation of this study lies in the establishment of a three-dimensional nonlinear model that quantitatively correlates key microstructural parameters (fractal dimension value (D), clay mineral ratio (C), and large and medium porosity (n)) with macroscopic deformation indicators (porosity ratio (e) and collapsibility coefficient (δ_s)). The measured data and the model’s output agree quite well, with a determination coefficient (R²) of 0.893 for porosity and 0.746 for collapsibility, verifying the reliability of the model. This study provides a novel quantitative tool for loess deformation prediction, offering significant value for engineering settlement assessment in controlled cementation and moisture conditions, though its application to natural loess requires further validation. Full article

Pipeline exfiltration from damaged water-supply systems frequently causes soil erosion and ground subsidence, which jeopardizes the safety of pedestrians and vehicles and even causes casualties. Despite the severe consequences, it is difficult for engineers to give reliable assessments of pipeline exfiltration hazards. In this study, erosion processes were explored using model tests and coupled computational fluid dynamics–discrete element method (CFD-DEM) simulations. It was discovered that the erosion zone can be divided into two zones—the exfiltration zone and the seepage diffusion zone. When water pressure reached 2.412 × 10⁻² MPa, local porosity approached 1.0, indicating there were no soil particles remaining. As pipeline pressure increased from 2.122 × 10⁻³ MPa to 2.412 × 10⁻² MPa, ground failure transitioned from downward settlement to upward bulge, and the ground failure duration of the fractured prototype pipe was reduced by 22–28% (from 125 s to 98 s), with a standard deviation of less than 5. The established exponential decay model ($\mathrm{v}\left(\mathrm{t}\right)={\mathrm{v}}_0{\mathrm{e}}^{(-\mathsf{\alpha }\mathrm{t})},{\mathrm{R}}^2>0.89$) enabled prediction of erosion duration. Based on the erosion height curve, the erosion duration and erosion area in similar engineering environments can be estimated, providing a reference for evaluating the risk of ground collapse due to pipe exfiltration. Full article

Focusing on the issues of severe mining pressure and discontinuous surface deformation caused by the large-scale mining of multiple coal seams, and taking into account the research background of Shigetai Coal Mine in Shendong Mining Area, this study adopts physical similarity simulation, theoretical analysis, and on-site verification methods to carry out research on rock migration, stress evolution, and overlying rock fracture mechanism at shallow burial depths and in multiple-coal-seam mining. The research results indicate that as the working face advances, the overlying rock layers break layer by layer, and the intact rock mass on the outer side of the main fracture forms an arched structure and expands outward, showing a pattern of layer-by-layer breaking of the overlying rock and slow settlement of the loose layer. The stress of the coal pillars on both sides in front of and behind the workplace shows an increasing trend followed by a decreasing trend before and after direct top fracture. The stress on the bottom plate of the goaf increases step by step with the collapse of the overlying rock layer, and its increment is similar to the gravity of the collapsed rock layer. When mining multiple coal seams, when the fissures in the overlying strata of the current coal seam penetrate to the upper coal seam, the stress in this coal seam suddenly increases, and the pressure relief effect of the upper coal seam is significant. Based on the above laws, three equilibrium structural models of overlying strata were established, and the maximum tensile stress and maximum shear stress yield strength criteria were used as stability criteria for overlying strata structures. The evolution mechanism of mining damage caused by layer-by-layer fracturing and the upward propagation of overlying strata was revealed. Finally, the analysis of the hydraulic support working resistance during the backfilling of the 31,305 working face in Shigetai Coal Mine confirmed the accuracy of the similarity simulation and theoretical model. The above research can provide support for key theoretical and technological research on underground mine safety production, aquifer protection, surface ecological restoration, and source loss reduction and control. Full article

Oases are the core carriers of societal development in arid regions, and their spatial patterns have changed significantly, driven by climate change and anthropogenic activities. This study integrates historical documents, archeological materials, maps, and remote sensing data. The changes in the temperature, precipitation, settlements, war frequency, and oasis area were identified by combining quantitative and qualitative methods, and the partial least squares path model (PLS-PM) was utilized to quantify the natural and human driving factors. The results show that the oasis development in the Tarim and Heihe River Basins exhibits distinct spatio-temporal variability and phased characteristics and is comprehensively shaped by both natural and anthropogenic drivers. The Tarim Basin’s natural oases demonstrate a “fluctuating recovery” pattern. The cultivated oases gradually expanded. The natural oases within the Heihe River Basin have persistently decreased, and cultivated oases show a “U”-shaped evolution pattern. This reflects the strong intervention of human reclamation in the cultivated oases. The introverted social ecosystem has endowed the Tarim River Basin with the ability to self-repair and achieve a periodic recovery. The Heihe River Basin serves as a strategic corridor for national external engagement, relying on regime stability. A regime collapse led to its lack of a stable recovery period. The PLS-PM reveals that the Tarim River Basin oasis evolution is predominantly driven by climate fluctuations. The path coefficient of natural factors for artificial oases is 0.63, and extreme drought leads to natural oasis contraction. The human influence dominates the Heihe River Basin, with a −0.93 path coefficient linking the cultivated oasis area to human factors. The frequency of wars (load 0.74) and changes in settlements (load −0.92) are the key factors. This study provides a powerful case for the analysis of the evolution and driving mechanism of future oases in drylands. Full article

In recent years, the region of Valparaíso has faced devastating fires, notably the Viña del Mar fire on 2 February 2024, which affected 9252 hectares. This study analyzes fire behavior in informal settlements and assesses the effectiveness of different construction materials through scaled prototypes of dwellings made from MDF, OSB, TetraPak, and flame-retardant resin composites. Controlled fire experiments were conducted, recording fire spread times and atmospheric conditions. Results confirm significant differences in fire spread rates and structural survival times between materials, highlighting the practical benefit of fire-resistant alternatives. The Kaplan–Meier survival analysis indicates critical time thresholds for rapid flame escalation and structural collapse under semi-open conditions, supporting the need for improved safety measures. Burn pattern observations further revealed the role of wind, thermal radiation, and material properties in fire dynamics. Overall, this study provides experimental evidence aligned with real fire scenarios, offering quantified insights to enhance fire prevention and response strategies in vulnerable settlements. These findings provide an exploratory basis for understanding fire dynamics in informal settlements but do not constitute definitive design prescriptions. Full article

Given the increasing challenges posed by frequent extreme climatic events, understanding the climate–human connection between the climate system and the transitions of ancient civilizations is crucial for addressing future climatic challenges, especially when examining the relationship between the abrupt events of the Holocene and the Neolithic culture development. Compared with the globally recognized “4.2 ka collapse” of ancient cultures, the initial start time and the cultural significance of the 5.5 ka climatic fluctuation are more complex and ambiguous. The Hongshan culture (6.5–5.0 ka) is characterized by a complicated society evident in its grand public architecture and elaborate high-status tombs. However, the driving mechanisms behind cultural changes remain complex and subject to ongoing debate. This paper delves into the role of climatic change in Hongshan cultural shifts, presenting an integrated dataset that combines climatic proxy records with archaeological data from the Hongshan culture period. Based on synthesized aeolian, fluvial-lacustrine, loess, and stalagmite deposits, the study indicates a relatively cold and dry climatic fluctuation occurred during ~6.0–5.5 ka, which is widespread in the Horqin dune field and adjacent areas. Combining spatial analysis with ArcGis 10.8 on archaeological sites, we propose that the climatic fluctuation between ~6.0–5.5 ka likely triggered the migration of the Hongshan settlements and adjustment of survival strategies. Full article

This study addresses the critical challenge of excavation face instability in rectangular pipe jacking through systematic physical model tests. Utilizing a half-section symmetry apparatus with non-contact photogrammetry and pressure monitoring, the study investigates failure mechanisms under varying overburden ratios and sand densities. Key findings reveal that support pressure evolution follows a four-stage trajectory: rapid decline (elastic deformation), slow decline (soil arching development), slow rise (arch degradation), and stabilization (global shear failure). The minimum support pressure ratio Pmin decreases by 39–58% in loose sand but only 10–37% in dense sand due to enhanced arching effects. Distinctive failure mechanisms include the following: (1) failure angles exceeding 70°, substantially larger than theoretical predictions; (2) bimodal ground settlement characterized by without settlement followed by abrupt collapse, contrasting with gradual transitions in circular excavations; (3) trapezoidal settlement surfaces with equilibrium arch angles ranging 41°–48°. These new discoveries demonstrate that real-time support pressure monitoring is essential for risk mitigation, as ground deformation exhibits severe hysteresis preceding catastrophic rapid collapse. The experimental framework provides fundamental insights into optimizing excavation face support design in shallow-buried rectangular tunneling. Full article

The precise prediction of soil settlement under applied loads is of paramount importance in the field of geotechnical engineering. Conventional analytical approaches often lack the capacity to accurately represent the rate-dependent deformations exhibited by soft soils. Creep affects the integrity of geotechnical structures and can lead to loss of serviceability or even system failure. Over time, they deform, the soil structure can be weakened, and consequently, the risk of collapse increases. Despite extensive research, regarding the creep characteristics of soft soils, the prediction of creep deformation remains a substantial challenge. This study explores soil consolidation settlement by employing three different material models: the Soft Soil Creep (SSC) model implemented in PLAXIS 2D, alongside two user-defined elasto-viscoplastic models, specifically Creep-SCLAY1S and the non-associated creep model for Structured Anisotropic Clay (n-SAC). Through the simulation of laboratory experiments and the Lilla Mellösa test embankment situated in Sweden, the investigation evaluates the strengths and weaknesses of these models. The results demonstrate that the predictions produced by the SSC, n-SAC, and Creep-SCLAY1S models are in close correspondence with the field observations, in contrast to the more simplistic elastoplastic model. The n-SAC and Creep-SCLAY1S models adeptly represent the stress–strain response in CRS test simulations; however, they tend to over-predict horizontal deformations in field assessments. Further investigation is advisable to enhance the ease of use and relevance of these sophisticated models. Full article

The Tunnel Boring Machine (TBM) method has gained attention as an eco-friendly tunneling technique, effectively reducing noise, vibration, and carbon emissions compared to conventional blasting methods. However, ground settlement and volume loss are inevitable during TBM excavation due to the deformation of the surrounding ground, which may even lead to ground collapse in severe cases. In this study, a Shield TBM model, validated using field data, was employed to perform numerical analyses on parameters such as tunnel diameter, ground elastic modulus, face pressure, and backfill pressure. Based on the simulation results, the influence of each parameter on settlement was evaluated, and a predictive model for estimating maximum settlement was developed. The proposed model was statistically validated using p-value assessment, variance inflation factor (VIF), coefficient of determination (R²), and residual analysis. Furthermore, the prediction model showed high agreement with the field data, yielding a prediction error of 8.25%. This study emphasizes the applicability of verified numerical modeling for accurately predicting ground settlement in Shield TBM tunneling and provides a reliable approach for settlement prediction under varying construction conditions. Full article

This study aimed to uncover how harm is normalised in migrant communities using rationalisations, power imbalances, and emotional distancing. This research counters the dominant discourse that migrant communities are cohesive, altruistic, and protective by critically analysing the psychological and moral mechanisms of intra-community harm. Migration scholarship has long extolled the contribution of migrant networks to settlement, employment, and integration. Using a qualitative ethnographic approach, data were gathered using participant observation and semi-structured interviews with twelve purposively sampled migrants. The aim of applying a primary qualitative study was to capture a detailed, first-hand understanding of participants’ lived experiences and social relations. It permitted the in-depth examination of how people rationalise and navigate intra-community harm in the actual contexts of their lives. Thematic analysis yielded four significant findings: one, injustices in the community are frequently met with silence and inaction due to fear and moral disengagement; two, assistance is extraordinarily situational and gendered, often falling disproportionately on women or being mediated by institutions; three, internal exploitation—like rent gouging and manipulation of aid—is justified through community narratives; and four, people increasingly feel isolation, emotional burnout, and only symbolic unity at communal events. The research suggests that, although migrant networks can offer critical resources, they are not invulnerable to internal hierarchies and moral collapses. To create effectively inclusive and nurturing settings, future interventions must account for more than mere structural barriers, intra-group processes, and psychological rationalisations allowing intra-community injury. Full article