Search Results (128)

With the rapid advancement of urban underground space development, shield tunnel construction has seen a significant increase. However, at the initial launching stage of shield tunnels in shallow-buried weak strata, engineering risks such as face instability and sudden surface settlement frequently occur. At present, there are relatively few studies on the reinforcement technology of the initial section of shield tunnel in shallow soft ground and the evolution law of ground disturbance. This study takes the launching section of the Guanggang New City depot access tunnel on Guangzhou Metro Line 10 as the engineering background. By applying MIDAS/GTS numerical simulation, settlement monitoring, and theoretical analysis, the reinforcement technology at the tunnel face, the spatiotemporal evolution of ground settlement, and the mechanism of soil disturbance transmission during the launching process in muddy soil layer are revealed. The results show that: (1) the reinforcement scheme combining replacement filling, high-pressure jet grouting piles, and soil overburden counterpressure significantly improves surface settlement control. The primary influence zone is concentrated directly above the shield machine and in the forward excavation area. (2) When the shield machine reaches the junction between the reinforced and unreinforced zones, a large settlement area forms, with the maximum ground settlement reaching −26.94 mm. During excavation in the unreinforced zone, ground deformation mainly occurs beneath the rear reinforced section, with subsidence at the crown and uplift at the invert. (3) The transverse settlement trough exhibits a typical Gaussian distribution and the discrepancy between the measured maximum settlement and the numerical and theoretical values is only 3.33% and 1.76%, respectively. (4) The longitudinal settlement follows a trend of initial increase, subsequent decrease, and gradual stabilization, reaching a maximum when the excavation passes directly beneath the monitoring point. The findings can provide theoretical reference and engineering guidance for similar projects. Full article

Cylindrical retaining structures are widely adopted in intercity railway tunnel engineering due to their exceptional load-bearing performance, no need for internal support, and efficient utilization of concrete compressive strength. Measured deformation data not only comprehensively reflect the influence of construction and hydrogeological conditions but also directly and clearly indicate the safety and stability status of structure. Therefore, based on two geometrically similar cylindrical shield tunnel shafts in Shenzhen, the surface deformation, structure deformation, and changes in groundwater outside the shafts during excavation were analyzed, and the deformation characteristics under the soil–rock composite stratum were summarized. Results indicate that the uneven distribution of surface surcharge and groundwater level are key factors causing differential deformations. The maximum horizontal deformation of the shafts wall is less than 0.05% of the current excavation depth (H), occurring primarily in two zones: from H − 20 m to H + 20 m and in the shallow 0–10 m range. Vertical deformations at the wall top are mostly within ±0.2% H. Localized groundwater leakage in joints may lead to groundwater redistribution and seepage-induced fine particle migration, exacerbating uneven deformations. Timely grouting when leakage occurs and selecting joints with superior waterproof sealing performance are essential measures to ensure effective sealing. Compared with general polygonal foundation pits, cylindrical retaining structures can achieve low environmental disturbances while possessing high structural stability. Full article

Settlement analyses of foundation soils are very important for the investigation, design, and construction of buildings. However, due to complex natural sedimentary processes, soil-forming environments, and geological tectonic stress histories, settlement properties show obvious spatial variability and autocorrelation. Moreover, measurement data on the physical and mechanical parameters of building foundation soils are limited. This limits the accuracy of formation stability analyses and safety evaluations. In this study, a series of field tests of building foundation soils were carried out, and the statistical physical and mechanical properties of the clay strata were obtained. A random field method and copula functions of uncertain geotechnical properties with limited survey data are proposed. A dual-yield surface constitutive model of the soil properties and a stability analysis method for uncertain deformation were developed. The detailed analytical procedures for soil deformation and stratum settlement are presented. The reliability functions and failure probabilities of variable settlement processes are calculated and analyzed. The impact of the spatial variation and cross-correlation of geotechnical properties on the probabilistic stability of variable land subsidence is discussed. This work presents an innovative analysis approach for evaluating the variable settlement properties of building foundation soils. The results show that the four different mechanical parameters can be regressed to linear equations. The horizontal fluctuation scale is significantly larger than the vertical scale. Copula theory provides a powerful framework for modeling limited geotechnical parameters. The bootstrap approach avoids parametric assumptions, leveraging empirical data to enhance the reliability analysis of variable settlement. The variability parameter exerts a greater influence on land subsidence processes than the correlation structure. The failure probabilities of variable stratum settlement for different cross-correlations of building foundation soils are different. These results provide an important reference for the safety of building engineering. Full article

Based on the construction project of Guangzhou Metro Line 13, this paper explores the special construction scheme for the safety of horizontal small-clear-distance shield tunnel construction, which adopts the construction of a tunnel first and a station later in the actual project to reduce the impact on the tunnel segment and the existing bridge piles. At the same time, the MIDAS GTS(2022R1) geotechnical and structural finite element analysis software is used to simulate and analyze the shield excavation process by using the stratum–structure modeling method, and the effect of grouting reinforcement in the tunnel is compared and analyzed. Through the research and analysis of the displacement and deformation of the model, the rationality and effectiveness of grouting reinforcement are explored to ensure the smooth implementation of the special construction scheme. The test results show that the implementation of grouting reinforcement measures in the tunnel can effectively control the horizontal deformation of the existing bridge piles and the horizontal deformation of the left line segment of the small-clear-distance section, and the above two deformation indexes are reduced by 67.7% and 72.1%, respectively, compared with the non-reinforcement condition. The settlement deformation of the segment and the surrounding existing bridge piles meets the requirements of the code, so the construction scheme is basically feasible. Full article

Exploration in the Tarim Craton has established that small-displacement strike–slip faults control carbonate reservoirs’ development and oil and gas accumulation. Oil and gas primarily accumulate within a defined lateral distance from these faults. Material point method (MPM) simulations of such fault systems revealed a functional relationship between the regular spacing of initial oblique Riedel fractures and brittle layer thickness under simple shear. This thickness critically governs the spatial organization of the resultant fault system. Riedel shear zones propagate upwards from the base in a semi-elliptical pattern, producing fewer, but longer, shear zones with increasing brittle layer thickness. Stratum thickness exerts a first-order control on fault configuration during strike-slip deformation, modulating both fault segmentation patterns and interconnectivity. Key quantitative relationships emerged: (1) an inverse proportionality between stratum thickness and Riedel shear zone density and (2) a positive correlation between shear zone length and stratum thickness. This article provides experimental evidence and theoretical guidance for exploring deep-seated strike-slip faults in cratonic basins. Full article

The use of the vertical shaft sinking machine (VSM) for shaft construction can effectively improve construction safety and efficiency. This study focused on analyzing the internal forces and deformation characteristics of a 50.3 m deep shaft constructed by the VSM method. Findings reveal that the external pressure of the shaft is positively correlated with the excavation depth, increasing as the depth grows. Pumping water inside the shaft disrupts the balance of the soil behind it, leading to a reduction in the external pressure of the shaft wall. During the excavation and sinking stage, the bottom connecting beam mainly endures compression. After water pumping, the coupling and restrictive effect between the bottom connecting beam and the shaft wall strengthens, significantly boosting the internal compressive stress. The stress states of the segments above and below the shaft vary: the upper segments are under pure compression, while the lower ones may experience uneven deformation due to multiple factors. Moreover, the cast-in-place piles and surrounding stratum show a “bulging” deformation pattern during sinking, greatly influenced by the shaft’s attitude deviation, whereas grouting at the shaft bottom and internal water pumping have minimal impact on the surrounding stratum. Full article

Addressing the critical technological needs for the real-time monitoring of stress distribution in mining areas, a new method for inverting goaf pressure using distributed optical fiber monitoring data is proposed. By coupling the key stratum fracture mechanics model with the subsidence trajectory function model, a theoretical model is established to accurately describe spatial stress evolution during coal mining. The model quantifies the relationship between goaf pressure changes and key stratum failures through a two-stage analysis of the subsidence process, based on distinct mechanical properties before and after key stratum fracture. Physical model experiments (3 m × 0.2 m × 1.1 m) using Brillouin Optical Time Domain Analysis (BOTDA) technology validated the proposed method, with comprehensive monitoring of key stratum deformations. By coupling the fracture mechanics model of the critical layer and the settlement trajectory function model, the dynamic transformation of the pre-fracture and post-fracture stages is realized, and the stress evolution can be monitored and predicted in real time. The results demonstrate spatial consistency between key stratum fracture locations and goaf peak stress positions. High-precision optical fiber sensing detected an ultimate strain threshold of 4000 με for key stratum failure, with pre-fracture strain measurements consistently below this threshold. The developed stress inversion formula successfully predicted pressure distribution patterns within the goaf, achieving real-time monitoring capabilities. Compared with the BPPS measurements, the deviation in the inverted data is less than 8.88%, the root mean square error (RMSE) is 0.98–1.20 in different propulsion stages, and the coefficient of determination (R²) is between 0.72 and 0.85. These findings provide a crucial theory for predicting peak stress evolution in mining areas, with implications for improving safety monitoring systems and optimizing mining operations. Full article

The rapid development of coastal cities has intensified land resource constraints and is leading to an increasing number of foundation pit projects near existing operational tunnels. This necessitates careful consideration of coastal excavation impacts on adjacent tunnels. Taking a foundation pit project in Qingdao as a case study, this paper investigates tunnel deformation through statistical analysis, numerical simulation, and field monitoring. By adjusting numerical model parameters, the research examines the influence of horizontal clearance distances, existing structure burial depths, and different retaining structure configurations on tunnel deformation, providing guidance for deformation control. Key findings include the following: (1) Statistical analysis reveals that tunnels in silty clay strata experience more significant excavation-induced deformation compared to those in silt strata, with relative positional relationships between pits and tunnels playing a critical role. (2) Numerical and monitoring results demonstrate that pit excavation induces tunnel displacement towards the excavation zone. Maximum lateral displacement reached 3.57 mm (simulated) and 4.79 mm (measured), while maximum vertical displacement was 3.11 mm (simulated) and 3.85 mm (measured), all within safety thresholds. (3) Sensitivity analysis shows that shallower tunnels exhibit more pronounced deformations. Increasing horizontal separation distance from 10 m to 25 m reduces deformation by one-third. However, adjusting diaphragm wall thickness and retaining structure embedment depth proves limited in deformation control, necessitating reinforcement measures on the tunnel side. These findings provide valuable references for protecting coastal silty clay stratum tunnels. Full article

The gob-side roadway technique is extensively utilized in coal extraction due to its capacity to enhance coal resource recovery efficiency and mitigate mining sequence conflicts. Nevertheless, increasing mining depths lead to progressively intricate stress conditions, posing challenges for maintaining gob-adjacent roadway surrounding rock stability. Taking the belt haulage roadway 1513 (BHR 1513) at Xinyi Coal Mine as an engineering case, this research investigates the application of narrow-pillar gob-side roadway construction under remote working face mining conditions. By integrating field observations, analytical modeling, and computational simulations, the cross-goaf pressure transfer phenomenon and its formation mechanism in narrow-pillar roadways under distant mining operations are systematically examined. Key findings reveal that during the alternating extraction of wide and narrow working faces, the caving angle terminates roof collapse within the narrow working face goaf at the second key stratum (KS2). The subsequent mining of the adjacent wide working face induces stress accumulation in the overlying “T”-shaped strata zone, triggering the instability of the inter-working face island pillar. This pillar failure merges the two goafs into an expanded void, initiating sequential fracture, collapse, and rotational displacement across all overlying key strata (KS). Consequently, previously intact KS above the narrow working face goaf undergo fracturing and rotation, amplifying lateral main roof block subsidence toward the goaf. This kinematic process generates substantial deformation in the narrow-pillar gob-side roadway. Full article

To the aim of this paper is to study the structural and environmental deformation characteristics caused by the excavation of a very large deep foundation pit in the sandy soil area of Beijing. This paper is based on numerical simulation and field monitoring results and these results are compared with the deformation data of a soft soil foundation pit in the Shanghai area. The results show that the influence of the environment surrounding the super-large deep foundation pit project studied in this paper is obviously too great. With the progress of construction, the deformation rate and deformation amount of the column at the side of the foundation pit are obviously higher than that of the column in the middle area. Due to the “hysteresis” of stress transfer in the sand, the settlement of the roof of the north wall is delayed and the deformation range is smaller than that of the south wall. Compared with the conventional foundation pit, the influence area of the surrounding surface is larger, reaching 4 He (He is the depth of the foundation pit). Δvmax (the maximum surface settlement) is between 0.2~2.3% He, and the relationship between δvmax = 1.43% Vwm. Through orthogonal experiments and numerical simulation, it is concluded that the deformation of foundation pit structure and its surrounding environment is more sensitive to excavation unloading, precipitation amplitude, and column spacing. It is also concluded that the strong, medium, and weak influence areas of the bottom uplift after foundation pit construction are (0~0.07) × L, (0.07~0.14) × L, and (0.14~0.5) × L, respectively (L is the width of foundation pit). When the embedment ratio is between 1.8~2.4, the displacement mode of the parapet structure is T mode; when the embedment ratio is between 2.4~3.4, the displacement mode of the parapet structure is RB mode. Full article

To explore the calculation method of settlement and deformation of existing tunnels induced by excavation, the energy method is adopted to analyze the work done by the existing tunnels with additional loads during excavation and the additional stresses caused by shield cutter thrust, shield shell, etc. The study integrates Mindlin’s stress solution and three-dimensional Loganathan’s formula to determine the friction, grouting pressure, and stratum loss. The primary objective of this approach is to identify the settlement and deformation of the existing tunnel. It is envisaged that the deformation of tunnels can be resolved by minimizing the total potential energy of the system. Relying on a new construction project, part of the Macao Sewerage Pipeline, the reasonableness and accuracy of theoretical model are verified by comparing it with the results of on-site monitoring and numerical analysis. Meanwhile, parameter sensitivity analysis is carried out to determine the sensitivity factors, including tunnel depth, diameter, and ground loss rate, on the settlement of existing tunnel, and suggestions for optimization on project are provided. The findings demonstrate the efficacy of the theoretical method in predicting the settlement and deformation of existing tunnels. Furthermore, it is evident that it can mitigate the settlement of existing tunnels by increasing the depth of new tunnels. Additionally, expanding the diameter of excavation is also a significant factor. Conversely, an increase in excavation rate will lead to an enhancement in the loss of ground layer, thereby augmenting the settlement of existing tunnels. It is noteworthy that the diameter of excavation exerts the most substantial influence on the settlement, followed by the rate of loss of ground layer, and to a lesser extent, the depth of the buried tunnel. Full article

To address the problem of large deformation in deep-buried high geostress soft rock tunnels, the Yuelongmen Tunnel was selected as the research subject and adopting the methods of on-site measurements, laboratory experiments and theories, the characteristics of large deformation and its mechanism in high geostress soft rock tunnels are studied in depth, and based on the mechanism of large deformation in tunnels and the concept of active and passive synergistic control, an optimized support scheme that dynamically adapts to the deformation of the surrounding rock is put forward. The results show that (1) the deformation volume and rate of tunnel surrounding rock is large, the duration is long, and the deformation damage is serious; (2) the main factors of tunnel surrounding rock deformation damage are high geostress and stratum lithology, followed by geological structure, groundwater and support scheme; (3) the tunnel deformation hierarchical control scheme effectively controls the deformation of surrounding rock, and reduces the deformation of steel arch and the risk of sprayed concrete cracking, which verifies the applicability of this scheme to the project. It verifies its engineering applicability. The research results provide important technical reference and theoretical support for the design and construction of similar projects. Full article

Based on the Zhuyuan–Bailonggang sewage interconnection pipe project in Shanghai, the ABAQUS finite element software was used in numerical simulations to study the fine control of stratum disturbances caused by pipe jacking parameter deviation in soft soil areas. Combining the simulation results with onsite measured data, the Peck formula was used to predict surface settlement. The results indicate the following: (1) The jacking speed and face pressure are negatively correlated with surface settlement. Under the maximum positive deviation and negative deviations in the jacking speed, after the tail passes through the monitoring section D₀ 16 ring, the maximum value of settlement at point B8 increases by 21.6% and decreases by 12.8%, respectively. Increasing the jacking speed increases the area with stress change ratio R < 0 at monitoring section D₀, and the arch foot at the tail of the pipe jacking machine decreases the surface settlement. In contrast, when the face pressure deviates from its average value, the variation range is less than 1%. (2) The pipe slurry coefficient and surface subsidence are positively correlated. Under the maximum positive deviation and the maximum negative deviation, the tail passes through the monitoring section D₀ 16 ring, and the maximum settlement value at B8 decreases by 4.9% and increases by 16.5%, respectively. The increase in the coefficient reduces the area with R < 0 at D₀ and increases the surface settlement. (3) In the order of descending strength, surface settlement is affected by the jacking speed, slurry friction coefficient, and face pressure. (4) To predict the maximum surface settlement value due to deviations in the jacking parameters, the Peck formula was modified using a correction factor $\alpha$ ranging from 0.6 to 3.0 and a settlement trough width correction factor $\beta$ ranging from 1.6 to 4.0. The modified prediction curve is in closer agreement with the actual conditions. Full article

A mechanical model of a laterally loaded long pile in layered soils was established to accurately calculate the lateral load-bearing performance of the pile foundation, and attention was paid to the influence of the complete separation of the pile–soil contact surface in a certain part of the pile on its lateral load-bearing performance. Based on the modified Vlasov foundation model, the displacement equation of the laterally loaded long pile embedded in layered soils was derived by the separation variable method. Using the solution method presented in this study, the deformation and internal force of the free-fixed pile were obtained. Then, the effects of the slenderness ratio of the pile and the complete separation of the pile–soil contact surface on the lateral load-bearing performance of the long pile in layered soils were analyzed. The results show that the deformation of the pile body increases with the increase in the slenderness ratio under the lateral load. Meanwhile, the position of the maximum bending moment and the negative shear force moves upward along the pile as the slenderness ratio increases. When the contact surface of the pile–upper stratum is separated, the deformation of the pile top doubles, and the negative shear force increases by three times compared to the case without the effect of separation of the pile–soil contact surface. When the contact surface between the pile and the middle layer soil is separated, the deformation and bending moment of the pile increase by 25%, and the maximum negative shear force decreases. Full article

Investigating deformation and failure mechanisms in shafts and roadways due to rock subsidence is crucial for preventing structural failures in underground construction. This study employs FLAC^3D software (vision 5.00) to develop a mechanical coupling model representing the geological and structural configuration of a stratum–shaft–roadway system. The model sets maximum subsidence displacements (MSDs) of the horsehead roadway’s roof at 0.5 m, 1.0 m, and 1.5 m to simulate secondary soil consolidation from hydrophobic water at the shaft’s base. By analyzing Mises stress and plastic zone distributions, this study characterizes stress failure patterns and elucidates instability mechanisms through stress and displacement responses. The results indicate the following: (1) Increasing MSD intensifies tensile stress on overlying strata results in vertical displacement about one-fifth of the MSD at 100 m above the roadway. (2) As subsidence increases, the disturbance range of the overlying rock, shaft failure extent, and number of tensile failure units rise. MSD transitions expand the shaft failure range and evolve tensile failure from sporadic to large-scale uniformity. (3) Shaft failure arises from the combined effects of instability and deformation in the horsehead and connecting roadways, compounded by geological conditions. Excitation-induced disturbances cause bending of thin bedrock, affecting the bedrock–loose layer interface and leading to shaft rupture. (4) Measures including establishing protective coal pillars and enhancing support strength are recommended to prevent shaft damage from mining subsidence and water drainage. Full article