Search Results (149)

With the exponential growth of engineering monitoring data, data-driven neural networks have gained widespread application in predicting retaining structure deformation in foundation pit engineering. However, existing models often overlook the spatial deflection correlations among monitoring points. Therefore, this study proposes a novel deep learning framework, CGCA (Convolutional Gated Recurrent Unit with Cross-Attention), which integrates ConvGRU and cross-attention mechanisms. The model achieves spatio-temporal feature extraction and deformation prediction via an encoder–decoder architecture. Specifically, the convolutional structure captures spatial dependencies between monitoring points, while the recurrent unit extracts time-series characteristics of deformation. A cross-attention mechanism is introduced to dynamically weight the interactions between spatial and temporal data. Additionally, the model incorporates multi-dimensional inputs, including full-depth inclinometer measurements, construction parameters, and tube burial depths. The optimization strategy combines AdamW and Lookahead to enhance training stability and generalization capability in geotechnical engineering scenarios. Case studies of foundation pit engineering demonstrate that the CGCA model exhibits superior performance and robust generalization capabilities. When validated against standard section (CX1) and complex working condition (CX2) datasets involving adjacent bridge structures, the model achieves determination coefficients (R²) of 0.996 and 0.994, respectively. The root mean square error (RMSE) remains below 0.44 mm, while the mean absolute error (MAE) is less than 0.36 mm. Comparative experiments confirm the effectiveness of the proposed model architecture and the optimization strategy. This framework offers an efficient and reliable technical solution for deformation early warning and dynamic decision-making in foundation pit engineering. 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

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

Single-lip deep-hole drilling is a key technology for the precision machining of high-temperature nickel-based alloy pore structures in aero engines. However, the intense thermo-mechanical coupling effects during machining can easily lead to surface integrity deterioration, and the correlation mechanism between microstructure and properties remains unclear. By adjusting the spindle speed and feed rate, a series of orthogonal experiments were carried out to study the integrity characteristics of the machined surface, including surface morphology, roughness, work hardening, and subsurface microstructure. The results reveal gradient structural features along radial depth: a dynamic recrystallized layer (RL) at the surface and a plastically deformed layer (PDL) containing high-density subgrains/distorted grains in the subsurface. With the increase in the spindle speed, the recrystallization phenomenon is intensified, the RL ratio of the machined-affected zone (MAZ) is increased, and the surface roughness is reduced to ~0.5 μm. However, excessive heat input will reduce the nanohardness. Low feed rates (<0.012 mm/rev) effectively suppress pit defects, whereas high feed rates (≥0.014 mm/rev) trigger pit density resurgence through shear instability. Progressive material removal rate (MRR) elevation drives concurrent PDL thickness reduction and RL proportion growth. Optimal medium MRR range (280–380 mm³/min) achieves synergistic RL/PDL optimization, reducing machining-affected zone thickness (MAZ < 35 μm) while maintaining fatigue resistance. These findings establish theoretical foundations for balancing efficiency and precision in aerospace high-temperature component manufacturing. Full article

The rational calculation of groundwater buoyancy directly impacts the safety of underground engineering. However, there is still no consensus on whether the reduction of groundwater buoyancy should be considered, and a theoretical explanation and quantification of buoyancy reduction in clayey soils is lacking. Based on laboratory engineering model tests, this study observed and analyzed the phenomenon of buoyancy reduction in saturated clayey soils. The contact area ratio of gravity water, calculated from geotechnical test data, was compared with the reduction slope. The experimental results indicated that the reduction slope of the fitted line between the static water head in the silty clay layer and the buoyancy water head was 0.8692. And theoretical analysis showed that the distribution of interparticle pore water pressure tends to attenuate from the pore center to the soil particle surface, suggesting a reduction in buoyancy head compared to the groundwater level. The reduction slope is theoretically equal to the contact area ratio of gravity water. Additionally, since limitations in current techniques for generalizing the soil–water constitutive models affect the reduction slope, this study proposes a method for determining the buoyancy reduction slope in saturated clayey soil based on the theory that interparticle pore water pressure distribution attenuates from the pore center to the soil particle surface. This method could potentially change the existing conceptual framework for buoyancy design in underground structures. Full article

This study investigates the deformation characteristics and base stability of a circular diaphragm wall support system (external diameter: 90 m, wall thickness: 1.5 m) with pit bottom reinforcement for the South Anchorage deep foundation pit of the Zhangjinggao Yangtze River Bridge, which uses layered and partitioned top-down excavation combined with lining construction. Through field monitoring (deep horizontal displacement of the diaphragm wall, vertical displacement at the wall top, and earth pressure) and numerical simulations (PLAXIS Strength Reduction Method), we systematically analyzed the deformation evolution and failure mechanisms during construction. The results indicate the following: (1) Under the synergistic effect of the circular diaphragm wall, lining, and pit bottom reinforcement, the maximum horizontal displacement at the wall top was less than 30 mm and the vertical displacement was 0.04%H, both significantly below code-specified thresholds, verifying the effectiveness of the support system and pit bottom reinforcement. (2) Earth pressure exhibited a “decrease-then-increase” trend during the excavation proceeds. High-pressure jet grouting pile reinforcement at the pit base significantly enhanced basal constraints, leading to earth pressure below the Rankine active limit during intermediate stages and converging toward theoretical values as deformation progressed. (3) Without reinforcement, hydraulic uplift failure manifested as sand layer suspension and soil shear. After reinforcement, failure modes shifted to basal uplift and wall-external soil sliding, demonstrating that high-pressure jet grouting pile reinforcement had positive contribution basal heave stability by improving soil shear strength. (4) Improved stability verification methods for anti-heave and anti-hydraulic-uplift were proposed, incorporating soil shear strength contributions to overcome the underestimation of reinforcement effects in traditional pressure equilibrium and Terzaghi bearing capacity models. This study provides theoretical and practical references for similar deep foundation pit projects and offers systematic solutions for the safety design and deformation characteristics of circular diaphragm walls with pit bottom reinforcement. 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

In water-rich strata, a traditional vertical barrier exhibits certain limitations when applied to deep foundation pit construction under complex geological conditions, such as it is difficult to completely cut off deep and thick aquifer, which may pose potential risks during pit dewatering. To address the above challenge, this study introduced a mixed barrier system in which the horizontal barrier (HB) was set at the bottom of the foundation pit and was combined with the enclosure wall to collectively retard groundwater seepage into the pit. Based on an actual project in Tianjin, this study established HB models with varying numbers of its layers using ABAQUS 6.14 software. It systematically investigated the effect of HB on groundwater drawdown, ground surface settlement, and enclosure deflection during foundation pit dewatering. The research shows that HB can significantly reduce the magnitude of external water level drawdown by altering groundwater seepage paths while effectively controlling soil settlement. Furthermore, it exhibits favorable overall restraining effects on wall deformation. Varying the number of horizontal barrier layers (L) exhibits an insignificant effect on water-blocking and subsidence-control performance. However, the constraint effect on the enclosure shows a correlation with L. Full article

In order to analyse the changes in pit stability caused by the removal of steel support and solid casting of a variable section pit, this paper carried out the whole process of numerical simulation of the selected section pit construction using ABAQUS, introduced a redundancy evaluation method based on the growth rate of deformation, calculated the stable state of the supporting structure, assessed the de-supporting state under two de-supporting design schemes—laminar and stepped—and carried out the stability analysis of the two schemes. Finally, the characteristics of pit stability changes under the state of de-supporting in the variable cross-section area were obtained. The results show that the stepped backfill and de-propping scheme provides better stability control than the laminated scheme, the minimum redundancy R_min in the key variable section area increases by 0.03 on average, the minimum relative deformation P_min decreases by 5% on average, and the maximum local improvement is 10.52%. The stepped scheme shows the most significant improvement in redundancy at the distal end of the reduced section, and the overall deformation response is more homogeneous. The study verifies the applicability of the redundancy analysis method in evaluating variable cross-section pit bracing, which is of great engineering significance for the optimisation of pit bracing design under similar structural conditions. Full article

Accurate determination of constitutive model parameters is crucial for reliable numerical simulation in deep foundation pit engineering. This study presents an inverse analysis method using Multioutput Least-Squares Support Vector Regression (MLSSVR) optimized by the Gray Wolf Optimization (GWO) algorithm to invert key parameters of the Hardening Soil (HS) model. A case study on a foundation pit in the dredger fill stratum of Xiamen Railway integrates finite element simulation with machine learning. The proposed GWO-MLSSVR model demonstrates high predictive accuracy, with lateral displacement predictions closely matching field monitoring data and relative errors within 5% at various depths of measurement point. Compared to traditional inversion methods and MLSSVR models optimized by other algorithms, this approach significantly reduces prediction errors. Additionally, the influence of construction stages, input layer nodes, and training sample size on inversion performance is investigated. This method provides a practical and efficient solution for accurately obtaining soil parameters under complex soil conditions, thereby enhancing the reliability of geotechnical numerical simulations and offering valuable guidance for foundation pit design and safety assessment. 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

The development trend of urban underground space towards deep and large three-dimensional foundation pit projects in complex environments faces the challenges of deformation and instability of supporting structures, strong sensitivity of the surrounding environment, and significant limitations of the traditional design theory. Based on the ultra-long/deep foundation pit project at the Shenzhen Airport East Station, a refined three-dimensional finite element simulation is used to systematically study the deformation mechanism of the supporting structures of deep and large foundation pits under a complex environment and investigate the influence on the neighbouring buildings. In this study, a three-dimensional finite element model is constructed considering the soil–structure coupling effect, and the mechanical response law of the foundation pit under the compliant–inverse combination method is revealed. Based on ABAQUS 6.14, a 10 m wide strip-shaped model of the central island area and an environmental risk source model including an underground station and group pile foundation are established. The analysis shows the following: the lateral shift in the ground wall is distributed in a ‘convex belly’ shape, with a maximum displacement of 29.98 mm; the pit bottom is raised in the shape of the bottom of a rebutted pot, and the settlement behind the wall has an effect ranging up to 3.8 times the depth of the excavation; the lateral shift in the side wall of the neighbouring underground station and the differential settlement of the group piles validate the predictive ability of the model on the complex-environment coupling effect. The research results can provide guidance for the design and construction of support structure projects and similar projects. Full article

To ensure the stability of deep foundation pits in confined aquifers, dewatering is often required. However, pumping from confined aquifers in large deep foundation pit groups may lead to significant environmental deformations. Therefore, field pumping and recharge tests are required to guide design of groundwater and environmental deformation control scheme. Focusing on a super-large deep foundation pit group in Shanghai, single-well pumping, multi-well pumping, and recharge tests were conducted in distinct geological zones (normally consolidated area and paleochannel zone). The hydraulic connectivity and spatiotemporal patterns of groundwater drawdown and soil settlement were systematically analyzed. The results show that: (1) There exists a certain hydraulic connection between the first and second confined aquifers. In the paleochannel area, the aquitard between the micro-confined and the first confined aquifer is insufficient to completely block hydraulic connectivity. (2) The ratio of ground surface settlement to groundwater drawdown is about 3.4 mm/m, and the deep soil settlement is significantly or even greater than the surface settlement, so it is necessary to strengthen the monitoring of deep settlement. (3) Recharge can elevate the groundwater and reduce settlement; however, it is difficult to eliminate the variation in settlement along the vertical direction. Full article

Deformation monitoring of deep foundation pits is critical for ensuring construction safety. However, traditional methods (e.g., inclinometers) face inherent challenges such as limited spatial coverage (<30% in large-scale projects), low operational efficiency (requiring 2–3 times longer data acquisition than 3D scanning), and spatiotemporal discontinuity (single-point measurements fail to capture 3D dynamic deformation fields, leading to incomplete mechanical interpretations of soil–structure interactions). In contrast, 3D laser scanning provides rapid, non-contact, and high-resolution data acquisition that can capture comprehensive deformation fields over large areas. Therefore, this study proposes a novel deformation monitoring framework, aiming to expand the monitoring range and enhance the measurement accuracy. The proposed framework combines the extensive spatial coverage of 3D laser scanning with the corrective capability of a backpropagation neural network (BPNN) model. The proposed approach leverages sparse yet high-precision traditional monitoring data to train the BPNN, effectively correcting systematic deviations in laser scanning measurements caused by external disturbances and instrument errors. Validation at an active deep foundation pit site in Hangzhou reveals that the method reduces the mean absolute error (MAE) from 5.2 mm to 1.8 mm, with corrected scanning data consistency exceeding 80 percent compared to conventional monitoring measurements. This work establishes a scalable framework for deformation analysis and sets a technical benchmark for monitoring in large-scale deep foundation pit projects. Full article

Under the adverse geological conditions of silty soft soil in coastal, lakeside, and river areas of countries worldwide, safety and quality during deep foundation pit construction are research challenges that researchers must overcome. Through 3D simulation, micro-finite element coupling modeling and construction site monitoring tests, this paper comprehensively analyzes the formation mechanism and causes of deep foundation pit foundation quality defects and diseases under the most unfavorable environment and multi-factor interference and puts forward scientific treatment suggestions. The research process accurately applies multidisciplinary coupling model research such as computer science, instrument science and technology, and material mechanics to solve the impact of multi-factor and uncertain environments on construction. The final research results provide sufficient theoretical and physical cases for improving the safety and stability of deep foundation pits under soft foundation conditions and provide rich practical specifications for the testing, monitoring and construction of similar projects; it provides a strong guarantee for the global deep foundation pit monitoring and early warning system under soft foundation conditions. Full article