Search Results (264)

This study provides evidence on the impact of a heavy rail-based suburban metro station in Fremont, California, on house prices using geographically weighted regression (GWR) and multiscale geographically weighted regression (MGWR). The dataset comprises sale price, sale date, and property and locational characteristics for single-family houses sold during the January 2000–April 2018 period within two miles of the Warm Springs Station on the San Francisco Bay Area Rapid Transit system. The results demonstrate that, relative to the referent period (2000–2001): (a) the station-led house price impacts are spatially heterogeneous—the house price increased in one pocket only, comprising less than one-tenth of the dataset, not across the entire 0–2 mile station area, (b) the price increase in that pocket began right after the project announcement period, and (c) the price impacts indicated by the MGWR model markedly differ from baseline ordinary least square regression (OLS) estimates. Overall, the study’s findings highlight the need to move beyond average estimation techniques, such as OLS, to those that account for spatially heterogeneous price impacts, such as GWR and MGWR. Full article

Circular shafts are widely used in shield launching and receiving, metro ventilation, municipal utilities, and underground energy facilities. In practical shaft construction, embedded depth design directly affects basal heave safety, material consumption, construction cost, and construction duration. However, conventional design methods for basal heave stability are mostly derived from wide pit assumptions, which may lead to conservative designs when they are directly applied to circular shafts. The scientific challenge lies in the fact that the basal heave mechanism of circular shafts is governed not only by excavation unloading and soil strength, but also by spatial confinement and circumferential arching induced by the closed annular retaining system. To address this issue, this study develops a 2D plane-strain equivalent model and a 3D full-scale numerical model using FLAC3D based on an actual circular shaft project. The spatial evolution of basal heave, retaining wall deformation, support internal force, and plastic zone development is systematically investigated. On this basis, spatial confinement and the arching effect are introduced as quantitative correction coefficients within narrow foundation pit theory, and an improved design method for basal heave resistance and critical embedded depth is proposed by combining the foundation bearing capacity failure mode and circular slip failure mode. The results show that circular shafts with width–depth ratios of 0.3–1.0 exhibit typical narrow excavation behavior. Compared with the 2D plane-strain equivalent model, the 3D model produces smaller deformation, lower support internal force, and more localized plastic zones because the closed circular structure can mobilize circumferential compression and spatial load transfer. The proposed method increases the calculated basal heave safety factor by approximately 15–40% and reduces the required embedded depth by approximately 15–30% compared with conventional code-based methods under the investigated conditions. The study provides an improved theoretical and practical approach for basal heave stability assessment and embedded depth optimization of circular shafts, contributing to safer, more economical, and more sustainable shaft construction. Full article

In earth pressure balance (EPB) shield tunneling, chamber pressure control is essential for maintaining excavation-face stability and limiting surface settlement. However, the influence mechanisms of key tunneling parameters on chamber pressure and ground response remain difficult to clarify when soil conditioning, cutterhead squeezing, muck discharge, and ground deformation are considered together. To address this issue, this study establishes a theoretical mechanical model for EPB shield tunneling and develops a calibrated three-dimensional FDM–DEM coupled numerical model based on the Jinan Metro Line 6 project. Triaxial and slump tests were used to calibrate the macro–micro parameters of unconditioned and foam-conditioned soil. The effects of tunneling speed, cutterhead speed, and screw conveyor speed on chamber pressure distribution and surface settlement were then analyzed. The results show that tunneling speed mainly affects the overall chamber pressure and face-support condition, screw conveyor speed controls muck discharge and pressure release, and cutterhead speed influences the spatial distribution of chamber pressure and settlement response. This study provides a theoretical and numerical basis for understanding chamber pressure evolution and coordinating tunneling parameters in EPB shield construction. Full article

During deep excavation construction, deformation impacts on adjacent structures are inevitably induced, and field monitoring data are often contaminated by noise that degrades prediction accuracy. To address these issues, this study develops a joint denoising strategy combining CEEMDAN, sample entropy-based adaptive IMF screening, and an improved wavelet threshold (IWT) function, followed by a Bayesian optimization-based extreme gradient boosting (BO-XGBoost) model for surface settlement prediction. The developed method automatically identifies high-noise IMF components via sample entropy and processes them using an improved threshold function that overcomes the discontinuity of hard thresholding and the constant bias of soft thresholding, thereby preserving useful information while suppressing noise. Experimental results on a Wuhan metro deep excavation project demonstrate that the CEEMDAN-IWT method improves SNR by up to 4.09% and reduces RMSE by up to 8.00% compared with conventional CEEMDAN-wavelet threshold denoising. The BO-XGBoost model trained on denoised data achieves an RMSE of 0.09 mm and a MAPE of 3.54%, outperforming BP, LSTM, standard XGBoost, GRU, CNN-LSTM, TCN, and simple regression baselines. Feature importance analysis confirms that the denoised data retain physical interpretability consistent with soil deformation continuity. This framework provides a practical solution with promising accuracy for deformation monitoring and early warning in deep excavation engineering. Full article

The construction of deep foundation pits for urban metro systems, particularly when in close proximity to existing sensitive structures, can easily induce unacceptable settlement and deformation. When shield tunneling and the top-down method are superimposed in both space and time, the resulting disturbance to the surrounding environment is more complex. A metro station project in Shenzhen was selected as the case study. Field monitoring and numerical simulation were combined to analyze the deformation of nearby bridge piers during different construction stages. The settlement-control effects of different reinforcement measures were also compared. The results indicate that the maximum settlement of the bridge piers throughout the monitored construction period reaches 31.81 mm. In the third stage, the cumulative settlement exceeded 10 mm. After the left-line shield passed through the station, the differential settlement between adjacent piers exceeded 5 mm. In the fourth stage, upon completion of the south section of the negative third floor, the differential settlement within the same pair of piers exceeded 4 mm. The maximum differential settlement between adjacent piers on the side closer to the foundation pit is 8.92 mm, whereas that on the side farther from the pit is 12.53 mm. The maximum values of both the differential settlement between adjacent piers and that within the same pair of piers occur during stages where multiple construction processes overlap. The connections between successive construction procedures are thus identified as weak links in deformation control. The discrepancy in cumulative settlement between symmetrically located piers arises primarily from the different reinforcement methods adopted. Supplementary pile reinforcement provides better performance than sleeve-valve-pipe grouting reinforcement. Because its reinforcement depth is insufficient to extend below the foundation pit excavation surface, the latter method fails to effectively restrain deformation in deep soils. The results describe the spatio-temporal development of pier deformation under combined construction disturbances. They also help identify critical construction stages and compare the settlement-control effects of different reinforcement measures. In addition, the numerical results provide a possible interpretation of pile load-transfer behavior under the combined effects of shield tunneling and top-down excavation. These findings serve as a practical reference for the design, construction sequencing, and risk management of similar metro station projects adjacent to bridges. Full article

Fiscal shocks in post-land-finance China are weakening the funding basis of capital-intensive metro public-private partnership (PPP) projects, but the system-level mechanism through which public fiscal stress becomes subcontractor-level financial viability pressure remains underexplained. This study examines a section-level metro PPP project ecosystem in a sub-provincial Chinese city to trace this transmission mechanism and its financial implications. The analysis combines de-identified audit evidence and interviews with a scenario-based structural NPV model and 800,000 model-generated Monte Carlo realizations under calibrated institutional scenarios. The evidence indicates that quasi-bureaucratic SPV internal capital-market arrangements convert fiscal shortfalls into vertical and horizontal cross-subsidization practices, preserving short-term project continuity while shifting cash-flow pressure downstream. This condition is defined as a strategic resilience trap: practices that preserve short-term project continuity while potentially eroding the project ecosystem’s long-term adaptive capacity. Under calibrated assumptions, improving the contract-payment channel reduces model-generated losses by approximately 4%, suggesting that payment punctuality addresses only one part of the wider internal capital-market mechanism. Full article

Deep excavation in soft soil readily induces lateral displacement of retaining structures and basal heave, posing serious threats to adjacent underground structures and the surrounding environment. Basal reinforcement is a key measure for improving excavation stability and controlling deformation; however, systematic comparative studies on multiple reinforcement methods and their spatial parameters in complex asymmetric shared-wall excavations remain scarce. Based on the Tianjin Binhai International Airport Integrated Transportation Hub project, a three-dimensional coupled numerical model of the “soil–Z2 excavation–existing M2 metro station” interaction was established using PLAXIS 3D. The effects of reinforcement depth, width, and area replacement ratio on diaphragm wall deformation, ground settlement, and base slab vertical deformation were quantified for four methods: strip, grid, full-area, and skirt reinforcement. All methods exhibit a pronounced critical depth threshold: the effective depth limits are 0.4H for strip, grid, and skirt reinforcement and 0.5H for full-area reinforcement, beyond which engineering benefit decreases substantially. Reinforcement width shows a marginal diminishing effect and should not be treated as the primary controlling parameter. Under the same area replacement ratio, skirt reinforcement leads to significant conical heave in the central excavation base, whereas strip reinforcement provides the best full-profile deformation control. Under the same total reinforcement volume, full-area reinforcement achieves the best performance across all deformation indices through uniform full-coverage constraint of the excavation base soil. This study elucidates the asymmetric deformation control mechanisms of shared-wall excavations and provides theoretical guidance for reinforcement scheme optimization in similar soft soil projects. Full article

Three-dimensional numerical investigations into the synergistic mechanism of composite pile retaining systems consisting of large-diameter bored cast-in-place piles and small-diameter micro-grouted steel pipe piles remain limited. To address this gap, a refined three-dimensional finite element model was established using ABAQUS based on the Hutan Park Station excavation project of Dalian Metro Line 5. Five design cases were analyzed by varying pile diameter, pile spacing, and the presence or absence of micro piles. The main findings are as follows: (1) The maximum horizontal soil displacement in all cases remained below 8 mm, indicating satisfactory excavation stability. (2) The inclusion of micro piles promoted stress redistribution within the inter-pile soil and was associated with a more pronounced soil arching tendency, as indicated by the displacement contour patterns. (3) Based on the comparison between Case 3 and Case 5, where the spacing between bored cast-in-place piles increased from 2.0 m to 3.0 m while maintaining the composite support configuration, the maximum horizontal displacement and maximum bending moment decreased by approximately 12% and 9%, respectively. The inserted micro-grouted steel pipe piles participated in lateral load transfer, enhanced stress redistribution, and reduced local stress concentrations acting on the primary bored piles. Under the investigated geological and support conditions, the numerical results suggest that the introduction of micro steel pipe piles may improve deformation control and load-sharing performance in composite pile-supported excavations. The proposed support configuration shows potential for reducing the number of large-diameter bored piles while maintaining acceptable excavation performance and overall support stability. Full article

Deep excavations in soft soil present a significant threat to adjacent operational metro tunnels. Based on an actual engineering project, field displacement monitoring and analysis were first conducted to establish a validated three-dimensional FLAC3D numerical model. This calibrated model is adopted to carry out systematic single-factor sensitivity analysis encompassing three core design indicators, and further quantifies the influences of groundwater seepage and uncertainties in soil parameters, thereby filling the research gap of integrated multi-index quantitative control criteria for pit–tunnel projects in Nanjing soft soil strata. The sensitivity analysis clarifies tunnel deformation responses concerning pit–tunnel clearance, the number of internal struts, and the retaining pile embedment ratio. Results indicate that tunnel deformation exhibits a ‘middle-large, ends-small’ pattern, with an optimal safe clearance of 8 m, a minimum requirement of three inner struts, and a critical embedment ratio of 0.34. Groundwater seepage increased tunnel deformation by 13.84% horizontally and 11.64% vertically; however, all critical thresholds remained valid. The proposed thresholds also demonstrated robustness under ±20% variation in key soil parameters. These quantitative findings are derived from Nanjing soft soil conditions and provide localized design references for similar metro-adjacent excavations in the region. Full article

Major infrastructure investments alter accessibility and urban development patterns, yet their impact on housing prices varies significantly across regions. The prevailing interpretation attributes this heterogeneity to supply differences or regulatory constraints, treating land use regulations as exogenous variables. Nevertheless, even two regions with a nominally similar regulatory framework may produce substantially different outcomes in the housing market, depending on the effectiveness of rule implementation. This paper argues that this approach overlooks a critical variable: the ability of regional authorities to coordinate, regulate, permit, and implement spatial development in a predictable and timely manner. In line with this, a conceptual framework is developed, grounded in the literature on spatial and multi-level governance, in which regional institutional capacity is proposed as a potential mediator of capitalization around project milestones (announcement, funding, construction, operation), rather than as a backdrop. This capacity shapes outcomes through three interrelated dimensions: the responsiveness of supply, which depends on administrative capacity and regulatory consistency; the coherence of governance across jurisdictions within functional urban areas; and the management of land value through land value capture instruments. From this framework, testable propositions are derived regarding the intensity, timing, and spatial distribution of price effects. The study does not empirically estimate changes in housing prices, nor does it test the propositions put forward. Instead, it develops the conceptual framework and organizes the spatial and institutional units of observation required for a subsequent empirical test. The framework is specified spatially through Section A, Line 4 of the Athens Metro to organize the project’s spatial units, administrative jurisdictions, land uses, and milestones for future analysis. The contribution is threefold: conceptual, as it elevates regional institutional capacity from a contextual to an explanatory variable; theoretical, in that it bridges urban economics with the governance literature; and policy-relevant, since it repositions the reform of regional governance as a constituent element of housing policy and as a factor that may shape sustainable spatial development outcomes. Full article

Taking the over-track development project of a metro depot in Chongqing as the engineering background, this study investigates the socket-type disc-lock full-hall scaffold system beneath the long-span transfer beam of Tower 9. A finite element model was established using MIDAS Civil to analyze the stress distribution and deformation characteristics of the scaffold system under construction loads, and the model was validated through field monitoring. On this basis, a parametric analysis was conducted to investigate the effects of erection height, step spacing of vertical standards, spacing between vertical standards, sweeping rod height, and joint stiffness on the overall stability of the scaffold system. A fitted analytical model for the buckling eigenvalue was further established. The results show that the scaffold system was mainly subjected to compression during construction. The measured maximum compressive stress of the vertical standards was 90.92 MPa, with an error of 12.50% compared with the finite element result of 80.82 MPa. The measured maximum tensile stress was 22.37 MPa, which was close to the calculated value of 21.96 MPa. The measured maximum average cumulative vertical displacement of the scaffold was 1.69 mm, which did not exceed the allowable deformation range during construction. The parametric analysis indicates that increases in erection height, step spacing of vertical standards, spacing between vertical standards, and sweeping rod height reduce the overall stability of the scaffold system, among which the step spacing of vertical standards has the most significant influence. In contrast, increasing joint stiffness is beneficial for enhancing the stability reserve. In this study, the overall stability of the scaffold system is characterized by the buckling eigenvalue obtained from linear eigenvalue buckling analysis. These findings can provide a reference for parameter selection, scheme comparison, and construction control of similar disc-lock high-formwork support systems for heavily loaded transfer beams. However, the conclusions of this study are mainly based on linear eigenvalue buckling analysis and single-factor parametric investigation, without further consideration of material nonlinearity and multi-parameter interaction effects. Full article

With the increasing development in urban underground spaces towards greater depth, scale, and complexity, the prediction and control of deformations in deep excavation engineering have become critical challenges in geotechnical engineering. This study investigates the ultra-deep excavation of the Tianjin Metro Line 8 Liulitai Station, analyzing the deformation characteristics of the retaining structure during top-down construction in soft soil based on field monitoring data. The results reveal a typical “bulging” pattern in the horizontal displacement of the diaphragm wall, which accumulates progressively with excavation depth. To enhance deformation prediction accuracy, a self-developed beam-plate finite element method (BPFEM) platform, implemented in Python (version 3.11.9), is introduced. The platform integrates code-specified analytical methods and the incremental approach to simulate the internal forces and deformations of the support system with high precision. By incorporating a dual-parameter back-analysis technique—adjusting both the horizontal subgrade reaction modulus and active earth pressure—the numerical model achieves significantly improved agreement with monitoring data. The proposed method demonstrates strong predictive capability, with a maximum error of only 4.4% in subsequent construction stages, confirming its feasibility and reliability for deformation forecasting in top-down deep excavations. The BPFEM framework and parameter inversion strategy presented herein provide an effective technical basis for intelligent prediction and dynamic control in deep excavation projects under complex geological conditions. Full article

Shield tunneling in urban areas can generate ground vibrations that may threaten adjacent buildings, especially in hard rock strata. However, the effect of foundation type on the vibration response of multi-story buildings is not yet fully understood. This study investigates this issue through a combined approach of field monitoring and three-dimensional numerical simulation based on the Jinan Metro Line 4 project. Five-story frame buildings with pile, raft, and isolated footing foundations were analyzed, and the numerical model was validated against measured data to ensure reliability. The results show that vibration waves attenuate in an approximately symmetric elliptical pattern and are amplified by the presence of buildings. A significant vertical amplification effect is observed, with peak particle velocity at the top floor reaching up to 2.11 times that at the ground surface. Foundation type exerts a significant influence on vibration transmission. Raft foundations exhibit a more uniform vibration distribution, whereas isolated footings demonstrate a weaker attenuation capacity, with only 23.6% attenuation and a first-floor response approximately 3.3 times greater than that of pile foundations. Although the structural safety requirements are satisfied, the vibration levels at upper floors may still exceed the human comfort limit of 75 dB, with the pile-founded building reaching 85.38 dB. These findings improve the understanding of vibration transmission mechanisms under symmetric disturbance conditions and provide a scientific basis for foundation selection and vibration mitigation in urban tunneling projects. Full article

This paper examines the evolution of urban transport policy in Saudi Arabia from a car-dependent paradigm toward sustainability-oriented planning and early implementation between 2000 and 2025. Using a longitudinal qualitative analysis of national strategies, municipal plans, and giga-project documents, this study traces shifts in policy discourse, governance arrangements, and delivery evidence across three phases: an expansionist phase (2000–2015), a vision transition phase (2016–2020), and a sustainability implementation phase (2021–2025). These phases were selected to capture the transition from pre-Vision 2030 automobile-oriented planning to the early implementation of sustainability-oriented transportation reforms. The findings reveal a clear transition from road-expansion-oriented planning—characterized by highway development, fuel subsidies, and limited public transport—toward system performance, decarbonization, and multimodal integration. Recent years have seen the rollout of metro and bus networks, expansion of rail systems, early electrification of vehicles and public transport, and fuel price rationalization. However, persistent behavioral lock-in, low-density urban forms, climatic constraints, and complex multi-level governance arrangements continue to limit modal shift and equitable mobility outcomes. The findings suggest that infrastructure investment alone cannot achieve substantial modal shift without integrated land-use planning, feeder systems, and demand-management measures. By linking policy ambition to implementation pathways over time, this study provides transferable insights for sustainable mobility transitions in oil-dependent and arid urban contexts. Full article

Urban rail transit projects situated in Quaternary deposits are progressively influenced by ultra-shallow gas. During the investigation and construction phases, this gas may instigate gas outbursts, combustion, explosions, stratum disturbances, and secondary ground deformations. To transparently and applicably identify the most crucial disaster-inducing factors in engineering practice, this research constructs a hierarchical risk factor evaluation framework for shallow gas hazards during the investigation stage of rail transit engineering. Initially, candidate indicators were screened via a literature review of shallow gas hazard studies and metro engineering reports. Subsequently, by employing the AHP, four first-level indicators and fifteen second-level indicators were compared and weighted. The findings indicate that shallow gas pressure, methane content per ton of soil, and the occurrence form of shallow gas are the three most influential factors, with comprehensive weights of 0.2735, 0.2319, and 0.1113 respectively. A metro tunnel case in Guangdong Province was then utilized to illustrate how the ranked indicators can guide the verification of suspected zones, section-based hazard discrimination, and the planning of controlled gas release. In comparison with existing studies that concentrate on descriptive disaster phenomena or single-factor analyses, the contributions of this study are threefold. Firstly, it offers a structured indicator system specifically tailored to Quaternary shallow gas in rail transit engineering. Secondly, it makes the expert-based weighting process explicit. Thirdly, it links the ranking results to practical investigation and prevention decisions. This framework is intended as a preliminary engineering decision support tool rather than a substitute for detailed predictive modeling or large-sample statistical validation. Full article