Search Results (68)

Vertical shafts are key channels for underground energy storage, mineral exploitation, and related engineering fields. Yet in deeply buried complex strata and high ground stress environments, traditional passive supports are prone to lining failure, while linear yield criteria cannot accurately characterize rock masses’ nonlinear mechanical behavior, limiting their use in shaft analysis. The core mechanical process of shaft construction aligns with the cavity contraction–expansion mechanism: excavation induces cavity unloading and contraction, causing shaft deformation and plastic zone expansion in surrounding rock; support enables cavity reverse expansion via preset shaft wall counter loads to actively control surrounding rock deformation. Based on this, this study integrates the Hoek–Brown nonlinear yield criterion, large-strain theory, and non-associated flow rules; couples cavity contraction–expansion semi-analytical solutions with the composite shaft wall mechanical model; and establishes a composite shaft wall–surrounding rock interaction analysis method. This research clarifies excavation-induced surrounding rock mechanical responses, reveals shaft wall counter loads’ regulatory effect on surrounding rock, and develops a systematic excavation support calculation workflow. Parameter analysis shows that increasing lining thickness is the most direct way to reduce inner wall tensile stress and improve safety; composite linings optimize stress distribution and enhance structural collaborative performance; and safety assessment confirms the lining inner wall as a structural weak zone. The proposed method and findings fill the gap in applying cavity contraction–expansion theory to shaft construction, providing reliable theoretical and practical guidance for deep shaft design, construction, and safety evaluation. Full article

To investigate the mechanical properties, energy evolution, and failure behavior of coal–rock composite structures under mining disturbances, a mining-induced stress path was designed based on the actual stress evolution ahead of a mining face. Triaxial tests were carried out under these stress conditions on coal–rock composite samples at various confining pressures, supplemented by conventional triaxial compression tests for comparison. The results show that the coal–rock composite samples exhibited marked brittle failure under mining-induced stress, with no sign of the brittle–ductile transition observed in conventional triaxial tests as the confining pressure increased. Using dual circumferential extensometers, it was found that the circumferential deformation of the coal and rock was initially governed by their intrinsic mechanical properties and later controlled by crack propagation. At higher confining pressures, the growth rate of circumferential strain at failure increased significantly, indicating that deeper excavations result in more severe unloading-induced failure. Comparative analysis revealed that the coal component had a higher elastic energy density and faster energy accumulation and release rates than the rock, identifying coal as the dominant medium for elastic energy storage and release within the composite samples. Furthermore, at peak stress in mining-induced stress tests, the coal showed less circumferential deformation than in conventional tests, while the rock exhibited the opposite trend, confirming the presence of a bonding constraint effect at the coal–rock interface. These findings enhance our understanding of the mechanical behaviors and failure mechanisms of coal–rock composites under mining disturbances, thus providing practical guidance for ensuring safety and efficiency in deep coal mining. Full article

The development of underground space in the South China Sea islands is an important way to enhance their protection capabilities. This study focuses on the stress loading and unloading conditions of surrounding rock during the excavation of underground caverns in island reefs. Laboratory variable confining pressure permeability tests were conducted to quantify the stress sensitivity of permeability in coral reef limestone based on Darcy’s law and the stress sensitivity index model equation for permeability. In addition, the use of nuclear magnetic resonance technology reveals the microscopic mechanism of coral reef limestone permeability evolution. The results of the experiments show that the permeability of coral reef limestone sample is mainly controlled by the advantaged permeable channels formed by large pores. During the stress loading stage, the pore structure inside the sample changes, with compression of large pores and generation of smaller pores, resulting in a decrease in effective permeable pathways and a decrease in permeability. When the stress loading reaches 4 MPa, the damage rate of the sample’s permeability is 19.6%. During the stress unloading stage, the recovery of the sample’s permeability shows a significant hysteresis effect. Due to the irreversible damage caused by the compression and collapse of the pore structure during the loading stage, the permeability of the sample cannot fully recover when unloaded to the initial stress state. Based on the experimental results, calculations show that the stress sensitivity coefficient of coral reef limestone permeability is 1.1 × 10⁻¹ MPa⁻¹, which is higher than that of conventional land-based rocks. The conclusions of this study can provide important design references for the stability control of surrounding rocks and geological hazard prevention during the excavation of underground chambers on the islands. Full article

With the continuous development of cities, underground space has become increasingly crowded, making the efficient and safe utilization of underground space an urgent issue to address. At present, research on foundation pit construction adjacent to existing subway structures mainly focuses on the impact of pit excavation on tunnels. While these studies have established a basic understanding of how pit excavation affects tunnels, research on adjacent subway stations and tunnels is nearly nonexistent—especially regarding the impact of the coupling effect between stations and tunnels during the excavation process. Additionally, most studies are conducted in soft soil areas, with no research yet on the impact in loess areas. To study the impact of foundation pit construction on subway tunnels and stations and reveal their coupling mechanism, model tests and numerical simulations were conducted based on actual engineering conditions. The model box had dimensions of 1.5 m in length, 1 m in width, and 1.2 m in height, while numerical simulations adopted the same dimensions as the actual project. Two different support structures—pile-anchor support and double-row pile support—were used for separate research and comparative analysis. The results show that with the increase in excavation depth, the foundation pit unloading effect becomes increasingly obvious. The pressure borne by both support structures increases, and the disturbance to the subway structure also becomes more significant. The maximum disturbance of tunnel earth pressure under the double-row pile support is 7.92 kPa, which is 224% higher than that under the pile-anchor support. The impacts on the subway tunnel and station under the double-row pile support are significantly greater than those under the pile-anchor support. Additionally, affected by the station, the locations of maximum tunnel deformation are not at the positions corresponding to the center of the foundation pit, but offset 10 m away from the station. Both the station and the tunnel exhibit a certain degree of uplift deformation, and the tunnel has significant convergence deformation in the horizontal direction. The maximum disturbance of the bending moment under the double-row pile support is 101.87 N·m, which is 19.8% higher than that under the pile-anchor support. This study reveals the coupling mechanism of the impact of adjacent foundation pit excavation on subway structures (including subway stations and tunnels) and presents the corresponding causes and phenomena, and it is of great significance for the development of related projects in loess areas and the protection of subway structures. Full article

As metal mines advance into deep mining, the increase in tectonic stress and horizontal stress leads to a higher degree of joint and fissure development in roadway surrounding rocks, along with a significant rise in both the fragmentation degree of the rock mass and the support cost. This paper adopts field monitoring and numerical simulation methods to analyze the characteristics of mining-induced stress rotation after unloading due to deep roadway excavation in the Jinchuan mining area, and proposes corresponding surrounding rock control countermeasures and optimized schemes for the original support. The research results show that after the unloading caused by the excavation of deep roadway surrounding rock, the magnitudes and directions of the maximum, intermediate, and minimum principal stresses all exhibit a trend of slow change, followed by drastic change, and finally gradual stabilization. When the roadway advances to 4 m in front of the monitor section, the adjustment of the magnitude of principal stress of the surrounding rock is the most drastic. Moreover, as the working face moves away from the monitor section, the principal stress gradually stabilizes and becomes lower than the initial stress value. When the roadway advances to 6 m in front of the monitor section, the adjustment of the direction of the principal stress of the surrounding rock is the most drastic. The rotation angle of the maximum principal stress shows a trend of first increasing and then decreasing with the increase in the excavation step, while the rotation angles of the intermediate and minimum principal stresses show a trend of first decreasing and then increasing as the excavation step increases. Based on the spatial distribution characteristics of joints and fissures in the roadway surrounding rock, the sensitive area for the rotation of mining-induced stress direction is defined. By changing the advancing direction of the roadway, the rotation trajectory of the principal stress can be deviated from the sensitive area, thereby improving the self-stabilization ability of the roadway surrounding rock. It is proposed that asymmetric coupling support be adopted to reinforce the positions where the principal stress rotation of the rock mass around the anchorage is severe, which can effectively reduce the range of the plastic zone in the roadway surrounding rock. The research results provide new ideas for the surrounding rock control of deep roadways, as well as a theoretical basis for the design and optimization of roadway support parameters in similar mines. Full article

Electric rope shovels play a critical role in open-pit mining, where their automation and operational efficiency directly affect productivity. This paper presents a LiDAR-based relative positioning method to determine the spatial relationship between the ERS and mining trucks. The method utilizes dynamic DBSCAN for noise removal and RANSAC for truck edge detection, enabling robust and accurate localization. Leveraging this positioning data, a time-optimal trajectory planning strategy is proposed specifically for autonomous swing motion during the unloading process. The planner incorporates velocity and acceleration constraints to ensure smooth and efficient movement, while obstacle avoidance mechanisms are introduced to enhance safety in constrained excavation environments. To execute the planned trajectory with high precision, a neural network-based sliding-mode controller is designed. An adaptive RBF network is integrated to improve adaptability to model uncertainties and external disturbances. Experimental results on a scaled-down prototype validate the effectiveness of the proposed positioning, planning, and control strategies in enabling accurate and autonomous swing operation for efficient unloading. Full article

Urban rail transit networks’ rapid expansions have led to increasing intersections between existing and new lines, particularly in dense urban areas where new stations must underpass existing infrastructure at zero distance. Deformation controls during construction are critical for maintaining the operational safety of existing stations, especially in soft soil conditions where construction-induced settlement poses significant risks to structural integrity. This study systematically investigates the influence mechanisms of different construction schemes on base plate deformation when an open-top UBIT (underground bundle composite pipe integrated by transverse pre-stressing) underpasses existing stations. Through precise numerical simulation using PLAXIS 3D, the research comparatively analyzed the effects of 12 pipe jacking sequences, 3 pre-stress levels (1116 MPa, 1395 MPa, 1674 MPa), and 3 soil chamber excavation schemes, revealing the mechanisms between the deformation evolution and soil unloading effects. The continuous jacking strategy of adjacent pipes forms an efficient support structure, limiting maximum settlement to 5.2 mm. Medium pre-stress level (1395 MPa) produces a balanced deformation pattern that optimizes structural performance, while excavating side chambers before the central chamber effectively utilizes soil unloading effects, achieving controlled settlement distribution with maximum values of −7.2 mm. The optimal construction combination demonstrates effective deformation control, ensuring the operational safety of existing station structures. These findings enable safer and more efficient urban underpassing construction. Full article

With the rapid urbanization and increasing development of underground spaces, foundation pit groups in complex geological environments encounter considerable challenges in deformation control. These challenges are especially prominent in cases of adjacent constructions, complex geology, and environmentally sensitive areas. Nevertheless, existing research is lacking in systematic analysis of construction sequencing and the interaction mechanisms between foundation pit groups. This results in gaps in comprehending stress redistribution and optimal excavation strategies for such configurations. To address these gaps, this study integrates physical model tests and PLAXIS 3D numerical simulations to explore the Nanjing Jiangbei New District Phase II pit groups. It concentrates on deformations in segmented and adjacent configurations under varying excavation sequences and spacing conditions. Key findings reveal that simultaneous excavation in segmented pit groups optimizes deformation control through symmetrical stress relief via bilateral unloading, reducing shared diaphragm wall displacement by 18–25% compared to sequential methods. Sequential excavations induce complex soil stress redistribution from asymmetric unloading, with deep-to-shallow sequencing minimizing exterior wall deformation (≤0.12%He). For adjacent foundation pit groups, simultaneous excavation achieves minimum displacement interference, while phased construction requires prioritizing large-section excavation first to mitigate cumulative deformations through optimized stress transfer. When the spacing-to-depth ratio (B/He) is below 1, horizontal displacements of retaining structures increase by 43% due to spacing effects. This study quantifies the effects of excavation sequences and spacing configurations on pit group deformation, establishing a theoretical framework for optimizing construction strategies and enhancing retaining structure stability. The findings are highly significant for underground engineering design and construction in complex urban geological settings, especially in high-density areas with spatial and geotechnical constraints. Full article

When deep-buried tunnels are excavated using the drill-and-blast method, the surrounding rock is subjected to combined cyclic blasting loads and excavation-induced stress unloading. Understanding the distribution characteristics of rock damage zones under these conditions is crucial for the design and safety of building-integrated underground structures. This study investigates the relationship between surrounding rock damage and in situ stress conditions through numerical simulation methods. A constitutive model suitable for simulating rock mass damage was developed and implemented in the LS-DYNA (version R12) code via a user-defined material model, with parameters determined using the Hoek–Brown failure criterion. A finite element model was established to analyze surrounding rock damage under cyclic blasting loads, and the model was validated using field data. Simulations were then carried out to explore the evolution of the damage zone under various stress conditions. The results show that with increasing hydrostatic pressure, the extent of the damage zone first decreases and then increases, with blasting-induced damage dominating under lower pressure and unloading-induced shear failure prevailing at higher pressure. When the hydrostatic pressure is less than 20 MPa, the surrounding rock stabilizes at a distance greater than 12.6 m from the tunnel face, whereas at hydrostatic pressures of 30 MPa and 40 MPa, this distance increases to 29.4 m. When the lateral pressure coefficient is low, tensile failure occurs mainly at the vault and floor, while shear failure dominates at the arch waist. As the lateral pressure coefficient increases, the failure mode at the vault shifts from tensile to shear. Additionally, when the horizontal stress perpendicular to the tunnel axis (σ_H) is less than the vertical stress (σ_v), variations in the axial horizontal stress (σ_h) have a significant effect on shear failure. Conversely, when σ_H exceeds σ_v, changes in σ_h have little impact on the extent of rock damage. Full article

This study investigates the deformation characteristics and control measures for existing metro shield tunnels induced by large-section rectangular pipe jacking over-crossing, focusing on the Chengbei Road Comprehensive Utility Corridor project in Suzhou. A 9.1 m × 5.5 m pipe gallery was installed 73.6 m through clay strata over operational subway tunnels, with a minimum clearance of 4.356 m above the tunnel. Finite element simulations and field monitoring were employed to analyze the deformation of the existing tunnels, particularly the effectiveness of anti-uplift counterweights. The results revealed that excavation-induced unloading caused significant tunnel uplift, with maximum vertical displacements of 5.51 mm and 4.95 mm for the down line (DL) and up line (UL) tunnels, respectively. The addition of counterweights reduced these displacements by 30.3% and 37.1%, while also decreasing lateral displacements by up to 61.6% and bending moments by approximately 33%. The study demonstrates that counterweights, combined with slurry lubrication, real-time monitoring, and over-excavation control, effectively mitigate deformation and stress variations during large-section pipe jacking. The successful completion of the project without disrupting subway operations highlights the practical applicability of these measures. Full article

In deep foundation pit engineering, the rational arrangement of internal struts plays a crucial role in controlling diaphragm wall displacement and minimizing environmental impacts. This study investigates the effects of servo steel struts through model tests, analyzing diaphragm wall displacement, bending moment, surface settlement, and surrounding soil pressure during both excavation and active servo control phases. The results show that installing servo struts near the pit bottom significantly improves deformation control, whereas strut placement in shallow zones more effectively mitigates surface settlement. The servo system dynamically adjusts strut displacements, thereby inducing internal force redistribution in the diaphragm wall and modifying the stress field in surrounding soils. This mechanism leads to an increase in positive bending moments on the wall’s backside, which may necessitate the localized reinforcement of the diaphragm wall at servo strut connections to ensure structural integrity. The lateral wall and surrounding soil pressure exhibit further increase, effectively compensating for the pressure loss induced by excavation unloading. Notably, the influence on soil pressure demonstrates a dissipating trend with an increasing distance from the excavation. Full article

The unloading effect induced by foundation pit excavation leads to soil deformation, which may adversely affect the underlying tunnel. Foundation pit excavation is a three-dimensional (3D) deformation process, whereas most existing methods are based on a two-dimensional (2D) plane assumption. To improve conventional 2D analysis methods, this study considers the influence of the actual construction sequence on tunnel deformation. A 3D analytical method for evaluating tunnel deformation and stress induced by foundation pit excavation is proposed, based on the image source method and the rotational dislocation-coordinated deformation model. The proposed method is validated through comparative analysis with other methods using monitoring data from three engineering cases. Furthermore, the study examines and discusses the impact of excavation sequences on the final longitudinal displacement of the tunnel. The results indicate that the proposed method provides more accurate predictions of tunnel deformation induced by foundation pit excavation in actual projects. Staged and segmented excavation reduces bottom heave of the foundation pit, thereby mitigating its impact on the underlying tunnel. When the segmentation efficiency is positive, increasing the number of excavation blocks contributes to better tunnel deformation control. However, when the segmentation efficiency is negative, an increase in excavation blocks has an insignificant effect on deformation control or leads to excessive construction workload. Full article

This study investigates damage characteristics of red sandstone under dynamic loads to clarify the effects of construction disturbances and blasting on the stability of surrounding rock during mountain tunnel construction in water-rich strata. Dynamic impact experiments at various loads were conducted using the Split Hopkinson Pressure Bar (SHPB) instrument, complemented by simulations of the fracturing process in saturated sandstone using finite element software. This analysis systematically examines the post-fracture granularity mass fraction, stress-strain curves, peak stress-average strain rate relationship, and fracture patterns. The dynamic response mechanism of red sandstone during the process of tunnel blasting construction was thoroughly investigated. Experimental results reveal that the peak stress and failure strain exhibit strain rate dependency, increasing from 45.65 MPa to 115.34 MPa and 0.95% to 5.23%, respectively, as strain rate elevates from 35.53 s⁻¹ to 118.71 s⁻¹. The failure process of red sandstone is divided into four stages: crack closure, nearly elastic phase, rapid crack development, and rapid unloading. Dynamic peak stress and average strain rate in sandstone demonstrate an approximately linear relationship, with the correlation coefficient being 0.962. Under different impact loads, fractures in specimens typically expand from the edges to the center and evolve from internal squeezing fractures to external development. Peak stress, degree of specimen breakage, and energy dissipation during fracturing are significantly influenced by the strain rate. The numerical simulations confirmed experimental findings while elucidating the failure mechanism in surrounding rocks under varying strain rates. This work pioneers a multiscale analysis framework bridging numerical simulation with a blasting construction site, addressing the critical gap in time-dependent deformation during tunnel excavation. Full article

Dewatering and excavation are fundamental processes influencing soil deformation in deep foundation pit construction. Excavation causes stress redistribution through unloading, while dewatering lowers the groundwater level, increases effective stress, and generates seepage forces and compressive deformation in the surrounding soil. To systematically investigate their combined influence, this study conducted a scaled physical model test under staged excavation and dewatering conditions within a layered multi-aquifer–aquitard system. Throughout the experiment, soil settlement, groundwater head, and pore water pressure were continuously monitored. Two dimensionless parameters were introduced to quantify the contributions of dewatering and excavation: the total dewatering settlement rate ${\eta }_{dw}$ and the cyclic dewatering settlement rate ${\eta }_{dw,i}$. Under different experimental conditions, ${\eta }_{dw}$ ranges from 0.35 to 0.63, while ${\eta }_{dw,i}$ varies between 0.32 and 0.82. Both settlement rates decrease with increasing diaphragm wall insertion depth and increase with greater dewatering depth inside the pit and higher soil permeability. An analytical formula for dewatering-induced soil settlement was developed using a modified layered summation method that accounts for deformation coordination between soil layers and includes correction factors for unsaturated zones. Although this approach is limited by scale effects and simplified boundary conditions, the findings offer valuable insights into soil deformation mechanisms under the combined influence of excavation and dewatering. These results provide practical guidance for improving deformation control strategies in complex hydrogeological environments. Full article

Predicting rock failure under excavation-induced non-uniform stress remains challenging due to the inability of conventional homogeneous specimens to replicate field-scale stress gradients. A novel trapezoidal sandstone specimen with adjustable top-surface inclinations (S75/S85) is proposed, uniquely simulating asymmetric stress gradients to mimic excavation unloading. Geometric asymmetry combined with multi-scale characterization (CT, SEM, PFC) decouples stress gradient effects from material heterogeneity. The key findings include the following points. (1) Inclination angles > 15° reduce peak strength by 24.2%, transitioning failure from brittle (transgranular cracks > 60) to mixed brittle-ductile modes (2) Stress gradients govern fracture pathways: transgranular cracks dominate high-stress zones, while intergranular cracks propagate along weak cementation interfaces. (3) PFC simulations reveal a 147% stress disparity between specimen sides and validate shear localization angles θ = 52° ± 3°), aligning with field data. This experimental–numerical framework resolves limitations of traditional methods, providing mechanistic insights into non-uniform load-driven failure. The methodology enables targeted support strategies for deep asymmetric roadways, including shear band mitigation and plastic zone reinforcement. By bridging lab-scale tests and engineering stress states, the study advances safety and sustainability in deep roadway excavation. Full article