bluuebunny/crossref_metadata_2025 huggingface dataset:
Highway tunnel crossing fault zones with water-rich highly weathered granite
Authors: Shi Zhou , Xu Jinfeng , Xie Xiongyao , Niu Gang , Xiao Zhonglin
Published: May 2024

This study focuses on the Tianshengqiao Tunnel on the Linshuang Expressway in Lincang City, Yunnan Province, China. By combining the transient electromagnetic method, and geological radar geophysical exploration methods, joint fissures and water abundance in the surrounding rock of the tunnel were predicted. Simultaneously, combined with engineering disasters, such as water inrush and seepage in the surrounding rock during engineering practice, a numerical calculation model for the grouting reinforcement of granite mixed-rock tunnels considering the construction process was established using finite element software. The results indicated that the joint fissures in the tunnel were well-developed and exhibited a disorderly trend, showing an open shape. Accompanied by high humidity in the excavated rock mass, the overall water outflow is mainly as strands, with a large amount of water outflow, especially at the arch crown or left arch waist. The difference in the settlement values of the surrounding rocks at different depths within the grouting circle of the tunnel was relatively small, whereas that outside the grouting circle was significant. The larger the scope of the tunnel grouting circle, the smaller the overall deformation of the surrounding rock after the closure of the tunnel support structure.
Numerical Simulation of Tailings Mortar Flowing from Dam Break by Variable Concentration Two-phase Flow Algorithm
Authors: Yang Yi , Zhou Xiaowen
Published: May 2024

A dam break accident of tailings pond may result in serious loss of the residents' lives and property, and usually leads to surrounding environmental disaster. Accurately calculating the flowing distance and inundation range of discharged tailings is important but remains to be solved. The main feature of tailings mortar movement is that solid particles continue to sink and accumulate during the flow process, which makes the solid concentration in the mortar constantly change, thus altering the rheological properties of the mortar. Therefore, the advancement of tailings mortar is a kind of two-phase unsteady flow with variable solid-phase concentration. In conventional numerical calculations of tailings flow, the rheological parameters of the Bingham model used are given fixed values with no consideration of concentration change, resulting in inaccurate calculation results and difficulty reflecting the phenomenon of tailings sands accumulation along the way. In this paper, a variable concentration two-phase flow model is proposed and then applied to a typical tailings dam failure case. The flow features and inundation range of the tailings mortar are analyzed and are found to be basically consistent with the field investigation, which means the proposed two-phase flow algorithm is reasonable and reliable.
Assessment of Durability and Resilient Strain Deformation of Expansive Subgrade Treated With Nano-Slag-Based Geopolymer
Authors: Aneke Frank I. , Kalumba Denis
Published: May 2024

Nano-geopolymer binders (NGB) of 5%, 10%, 15%, and 20% concentration were used to stabilize expansive subgrade soil against strain deformation, as well as to improve its durability. The composites were subjected to a series of zero-swelling, wetting (W-D) cycles, and dynamic resilient modulus tests to determine the subgrade resilient strength against 100,000 applied repetitive loads (ARL). The results revealed that the resilient moduli of the stabilized and unstabilized subgrade soils exhibited strain-hardening responses at low cyclic stress levels. Therefore, the rate of plastic strain deformation became microscopically negligible, and the tested subgrade was considered stable at this stage. Conversely, at high cyclic stresses, the nano-geopolymer-stabilized subgrade continued to exhibit strain hardening between 80,000 and 100,000 ARL. The unstabilized subgrades exhibited strain softening at an ARL of 20,000 owing to the poor adhesion between the NGB and soil particles, leading to excessive strain deformation. The results revealed that the W-D resistance of the treated subgrade was up to 96% compared to the unstabilized subgrade, which lost over 30% of its particle mass after the 6-number cycle. This study indicates that the NGB-treated subgrade possesses the potential to sustain medium-to-high ARL loads owing to improved stiffness through polymerization reactions.
Mechanical Performance of Steel-Fiber-Incorporated Rubberized Concrete for Rigid Pavement Applications
Authors: Chusai Nutchapon , Jitsangiam Peerapong , Suwan Teewara
Published: May 2024

Sustainable solutions are required to mitigate waste tire accumulation. Using rubberized concrete (RuC) in rigid pavements is a viable and relatively environmentally friendly strategy for partially replacing fine/coarse aggregates with crumb rubber. However, crumb rubber affects the mechanical properties of concrete. Although RuC is more flexible (ideal for road pavements) than conventional concrete, its strength is lower than that of the standard concrete used in rigid pavements. Consequently, the crumb rubber generated from discarded tires cannot be used sustainably. The primary objective of this study was to characterize RuC mixed with manufactured steel fibers to improve the strength of the mixture. Fine aggregates (sand) were partially substituted with various proportions (10%, 20%, and 40%) of crumb rubber (size:1.70–2.36 mm) while incorporating 0.5% steel fibers (by volume). The compressive strength, splitting tensile strength, and flexural strength of the concrete deteriorated with increasing rubber content, consistent with the previously reported results. However, steel fiber incorporation improved the mechanical behavior of RuC, thus enhancing the compressive strength, splitting tensile strength, and flexural strength of the pavement structure. The developed steel-fiber-incorporated RuC design enhances the usability and economic value of RuC as well as minimizes the adverse environmental impact of concrete pavement technology.
Effects of pavement roughness on shakedown limits under moving traffic loadings
Authors: Lei Hao , Qian Jiangu , Dai Yuchen , Wang Yonggang
Published: May 2024

This study proposes a lower-bound shakedown analysis method for pavement systems under moving traffic loadings considering pavement roughness. The effects of key variables, including moving speed, wavelength irregularity, and the modulus and thickness of pavements, on the shakedown limit are discussed. The calculation results indicate that pavement roughness has a considerable effect on shakedown limits, which can be overestimated in some cases when the pavement roughness is not considered. The effect of pavement roughness on the shakedown limit of a homogeneous subgrade layer gradually decreases with increasing speed. Additionally, the shakedown limit decreases with wavelength irregularity, particularly under high-speed traffic loadings. Furthermore, the effect of pavement roughness on the shakedown limit of a two-layered pavement system is more pronounced for a larger pavement modulus and thickness and a lower moving speed.
A numerical method for calculating the long-term settlement of three-dimensional subgrade under numerous traffic loads
Authors: Huang Da , Sun Chenfeng , Qian Jiangu
Published: May 2024

Settlement problems caused by various traffic loads significantly impact infrastructure sustainability. Accurately predicting the long-term settlement of subgrade is crucial for improving infrastructure resilience. This study determined the element strain of soil using an explicit strain model, based on the bounding surface model and associated flow rules. Using the method of generalized shear strain equivalent, a cyclic cumulative factor is proposed for determining the magnitude of cumulative strain increment. The direction of plastic strain increment was determined using the bounding surface model combined with associated flow rules. A cumulative strain calculation method integrating the bounding surface and explicit strain models under general stress states was established. This computational method, combined with equivalent finite elements, can be used for calculating the long-term settlement of three-dimensional subgrade under numerous cyclic loads at general stress states through a user-defined subroutine provided by the commercial finite element modeling (FEM) software. The reliability of the method was verified through unit tests.
Experimental study on monopile-supported offshore wind turbine subjected to long-term wind and wave cyclic loading
Authors: Zheng Hanbo , Zhang Hao , Li Gonghao , Wang Chen , Liang Fayun
Published: May 2024

Offshore wind energy has recently gained much attention. During its service life, a monopile-supported offshore wind turbine (OWT) is subjected to long-term wind and wave lateral cyclic loads with different cycle characteristics, inducing accumulated deformation of the OWT system to exceed the serviceability limit state and causing safety accidents. In this study, a 1g scaled model test with a similarity ratio of 1:100 was conducted to investigate the lateral response of a monopile-supported OWT in sand under long-term wind and wave cyclic loads. Two sets of centrifugal gear cyclic loading devices applied stable long-term wind and wave cyclic loads and different cyclic load amplitudes and directions were achieved by adjusting the input voltage and counterweight masses. Four groups of long-term cyclic loading tests were conducted for the monopile-supported OWT, considering different wind load simplification methods and various wind-wave load contribution ratios. The lateral displacement and accumulated tilt of the OWT were monitored using two laser displacement transducers installed at different heights. The results show that a simplistic treatment of wind loads as static loads results in an overestimation of the cumulative rotational deformation, and an increase in the wind-wave load contribution ratio decreases the cumulative tilts of the OWT structures.
Shear behavior of basalt fiber modified compacted red mudstone as subgrade fill material
Authors: Xu J , Liu X , Ma J , Yuan S
Published: May 2024

This study experimentally investigated the shear behavior of basalt fiber-modified compacted red mudstone as a subgrade of a high-speed railway. We examined the effects of different vertical stresses, initial water contents, and fiber contents on brittleness and dilatancy. Several direct shear tests were conducted under the aforementioned conditions. The stress displacement curve tended to vary from softening to hardening with an increase in vertical stress. In the Mohr–Coulomb mode, except for the saturated state, the residual internal friction angle was greater than the peak value, whereas the residual cohesion was lesser than the peak value. The maximum cohesion occurred at the optimal water and fiber content, whereas the friction angle exhibited a downward trend with an increase in the contents discussed above. The brittleness index (I

b
) was defined as the ratio of the peak to residual shear strengths. The magnitude of the brittleness index reduced with increase in the vertical stress. Moreover, the maximum value occurred at the optimal water and fiber content. Furthermore, the deformation mechanism was discussed based on the dilatancy angle(ψ). Based on the data, three different stages were proposed: Softening–Dilatancy (S1), the Hardening–Dilatancy (S2), and Hardening–Shrinkage (S3).
Deformation characteristics of red-mud embankment under monotonic and cyclic loads
Authors: Wu G , Chen T , Zhang G
Published: May 2024

The rapid growth in the production of the red mud has led to the shortage of land for stockpiling in recent years. Although red mud has been considered as the filling material for embankments, the deformation characteristics of a red-mud embankment under traffic loads has not yet been clarified. To promote its application in embankment construction, a series of centrifuge model tests of red-mud embankment under monotonic and cyclic loads were conducted. The deformation and failure processes of red-mud embankment under normal and overproof traffic loads were analyzed. The results show that the deformation characteristics of red-mud embankment varied significantly depending on the value of the external load. The deformation induced by monotonic load was greater than that induced by the cyclic load of the normal traffic load. The monotonic and cyclic loads of normal traffic load induced similar influential areas, and their deformation processes can be divided into rapid and slow growth parts. Shear failure occurred in the red-mud embankment under overproof traffic load. The same load increment induced more deformation of red-mud embankment after failure. Under reasonable dry density and water content, the deformation of red mud was acceptable, thus meeting the engineering requirements of embankment construction.
Reusing COVID-19 personal protective equipment wastes for pavement base, subbase, and subgrade applications
Authors: Saberian M , Zhu J , Kilmartin-Lynch S , Li J
Published: May 2024

Since 2019, the coronavirus disease (COVID-19) pandemic has caused a substantial increase in personal protective equipment waste generation, resulting in significant environmental concerns. In addition, the expansive clay subgrade (ECS) must be stabilized prior to pavement construction because of its unfavorable engineering properties. The use of recycled concrete aggregates (RCA) in pavement bases/subbases offers a sustainable solution to decrease the demand for quarry materials and waste pile-up. However, RCA should be reinforced for base and subbase applications because of its low shear and dynamic properties. This study explores an innovative waste solution by recycling shredded nitrile gloves (SNG) to stabilize clay subgrades and reusing discarded shredded face masks (SFM) to treat RCA for base/subbase applications. A series of experiments including compaction, unconfined compression strength, and repeated-load triaxial tests were conducted. The test results showed that the incorporation of SNG and SFM improved the strength and stiffness of the pavement layers. The addition of 1.5% SNG to ECS resulted in the highest unconfined compressive strength (UCS) value (315.50 kPa) and highest resilient modulus (Mr) (79.98 MPa). Furthermore, introducing 1% SFM into RCA increased the UCS and Mr to peak values of 216 kPa and 314.35 MPa, respectively.
Hydrodynamic and bearing behaviors of two typical deepwater dynamically installed anchors: torpedo anchor and fish anchor
Authors: Zhang B , Fu Y , Zhang M H , Wang H
Published: May 2024

Dynamically installed anchors, such as torpedo and fish anchors, are innovative and cost-effective anchorage foundations. In this study, the advantages and disadvantages of these two types of dynamically installed anchors are discussed by comparing the hydrodynamic and bearing characteristics of torpedo and fish anchors commonly used in practical engineering. First, based on OpenFOAM, 3D numerical models were established to investigate the directional stability and simulate the underwater free-fall process of anchors using static and dynamic model analysis methods. Using the validated model, the hydrodynamic performances (i.e., inclination angle, installation offset distance, penetration velocity, and drag coefficient) of torpedo and fish anchors were explored and compared. Based on these findings, the installation height of each anchor was recommended. Finally, the bearing performances of the torpedo and fish anchors were investigated using ABAQUS, and the selection principles of these two types of dynamically installed anchors were presented based on their hydrodynamic and bearing behaviors.
Reliability-based evaluation of ultimate embedment depths of torpedo anchors in spatially variable clay
Authors: Liu Chaofan , Chen Bao
Published: May 2024

In this study, a large deformation random finite element (LDRFE) method was used to investigate the dynamic penetration of anchor piles in spatially variable clay. Validation of the rationality of the proposed methodology using data from published studies. The randomness of the undrained shear strength of the soil in the system is considered by three-dimensional random fields to investigate the anchor penetration mechanism and quantitatively assess the ultimate embedment depths (Hran
) of the anchor in spatially variable clay. The strain softening and strain rate effects of the soft clayey soil were considered. The findings indicate that the variability in soil strength significantly affects the flow pattern and failure mechanism of the soil, consequently influencing the Hran
of the anchor. Furthermore, according to the computed Hran
results, a coefficient of variation of soil shear strength φ can be used to connect the deterministic (Hdet
) and random analysis results. This correlation may facilitate further development of reliability-based designs.
FAGSO-BP neural network model for settlement prediction of soft soil foundation
Authors: Ma Binhui , Zhao Zijing , Deng Xu , Lan Tian , Du Bicheng , Xiao Yarui
Published: May 2024

To address the problem of difficulty in theoretical formulas and numerical analysis methods to consider the prediction of foundation settlement in the case of multiparameter coupling, the fireworks algorithm (FWA) with a gravity search operator (FAGSO) is introduced into the back propagation (BP) neural network model, and the weight and threshold processes in the neural network are improved by the FAGSO algorithm. A soft soil foundation settlement prediction model based on a FWA optimized BP neural network (FAGSO-BP) with a gravity search operator is proposed. Based on the second phase of the soft foundation treatment project of the Shatian Port Area, Humen City, and Dongguan City, the parameters of pile load height, pore water pressure, and groundwater level were collected and tested. The results indicate that the average relative error of the predicted cumulative settlement value of the soft soil foundation was 0.06%, root mean square error was 7.68, mean absolute error was 4.30, mean absolute percentage error was 1.40%, and mean square error was 59.98. Compared with the BP neural network, GA-BP neural network, and FWA-BP neural network, the error was smaller and the model stability was higher.
Self-healing analysis of steel slag asphalt mixture under microwave heating through laboratory fatigue-healing test and microscopic characterization method
Authors: Chen X , Zhang J , Liu Z , Wan B , Dong Q
Published: May 2024

Steel slag is an eco-friendly low-carbon building material that has been widely used for pavement construction in recent years. In this study, the steel slag aggregate (SSA) is used to replace a part of the basalt aggregate in the porous asphalt mixture to improve its microwave absorption ability. Microwave heating promotes the self-healing capability of steel-slag asphalt mixture. We designed and conducted 16 groups of fatigue-healing tests based on an orthogonal experimental design to analyze the influence of various factors, including the degree of damage, healing temperature, and rest time, on the self-healing ability of the steel slag asphalt mixture. The ratio of the number of cyclic loads after healing (N1) to the number of cyclic loads before healing (N0) is defined as the healing index. The results of the range analysis demonstrate that the healing temperature presents the greatest impact on the healing rate of fatigue damage, followed by the degree of fatigue damage; the rest time has the least impact. The fatigue damage healing rate gradually decreases with the increase in the degree of damage. It first increases and then decreases with the increase in the healing temperature. It increases with the rest time. The optimal healing state of the steel slag porous asphalt mixture involves heating to 80℃ with 60 % degree of damage followed by resting for 8 hours. CT scanning technology is used to observe the crack distribution before and after healing. The CT images and a 3D reconstruction of the asphalt mixture demonstrate that obvious healing of cracks can be observed after microwave heating, and microwave heating does not significantly affect the porosity of the asphalt mixture. The nano-indentation indicates that the Young’s modulus and hardness of the asphalt mortar in the cracking area increased by 16.8 % and 22 %, respectively, after healing due to microwave heating, which can be attributed to the ageing of the asphalt.
Rig test of light railway transport ballast vibration
Authors: Petriaev A , Konon A , Saidaliev A
Published: May 2024

This article presents findings from rig tests focusing on the oscillatory behavior of ballast in light rail transportation. Tests were carried out using an Amsler HB-250 pulsator, applying a load of 50 kN and operating at a frequency of 8 Hz. Accelerometers were positioned at depths of 10, 30, and 50 cm beneath the sleeper within the ballast shoulder to record vibrations of the crushed stone particles. The study determined the amplitudes of particle vibration accelerations in three directions: vertically, perpendicular to the track axis, and along the track axis. Results indicate that the lowest vibration accelerations were consistently observed across the track axis (Y-axis) at all sensor locations. At a depth of 10 cm beneath the sleeper, contiguous values of vibration accelerations were recorded in the vertical plane (Z-axis) and horizontal accelerations perpendicular to the track (X-axis). However, at depths of 30 and 50 cm below the sleeper, vertical vibrations registered the highest accelerations, while horizontal vibrations along the X-axis were 30-36% lower.
Settlement control in large span tunnels under shallow over burden: a case study of the Arash-Esfandiar-Niayesh tunnel
Authors: Yasrebi S , Salehi B
Published: May 2024

Settlement control is pivotal in the construction of large span tunnels, particularly when situated under shallow overburden. The importance of settlement control in the context of the Arash-Esfandiar-Niayesh tunnel project, a multi section tunnel designed to facilitate two-way traffic in Municipality of Tehran District 3, is studied. The tunnel, which possesses an overburden of 4–15 m, faces unique challenges such as low overburden, urban location, and proximity to tall structures. By integrating the New Austrian Tunneling Method (NATM), this paper examines the effects of various support systems on construction of the tunnel project. Two critical sections are analyzed, and the settlement control strategies are examined according to a combination of various support elements. Analysis and numerical modeling based on PLAXIS 2D finite element code revealed the impact of these support systems on ground settlements on the structural and geotechnical stability. They had a substantial impact of tunnel geometric shape on sustainability and stress distribution. The inadequacy of common support systems, especially in tunnels with a horseshoe section, is highlighted. The impact of removing temporary lattice girderson surface settlements emphasizes the importance of settlement monitoring. Field data, including a maximum vertical displacement of 2.6 cm on the ground and in the tunnel, validate the numerical analysis results. Despite the challenges, the consistency between numerical and instrument data underscores the effectiveness of settlement control strategies.
New indices of the recovery effect of the large deformation shield tunnel based on a light-disturbance grouting model test
Authors: Ye Z W , Zhang D M , Zhang J Z , Chu W
Published: May 2024

The sudden surface surcharge is a key disturbance that causes excess transverse deformation of the existing shield tunnel underneath. The light-disturbance grouting technique, which is applied on two sides of a tunnel spring-line, is an effective way to control or even recover the large tunnel structural deformation. Based on the 1g model test of grouting for the shield tunnel in the sand layer using the Shanghai Metro shield tunnel as a prototype, a numerical model is established based on the FLAC3D software. Meanwhile, the numerical simulation method of simulating grouting involves the application of the virtual expansion stress. The grouting transfer efficiency and recovery bias are proposed in this paper and used as the evaluation indexes of the recovery effect of light-disturbance grouting on the shield tunnel. The findings indicate that irrespective of various overloading modes and symmetrical single-row grouting, the transfer efficiency remains approximately 12%, which may potentially serve as a optimization index for determining the number of grouting rows. Moreover, the observed disparity in recovery bias within tunnels experiencing asymmetric deformation underscores the significance of joint behavior, emphasizing the necessity for closer monitoring during grouting procedures.
Cluster analysis of underground space in the core area of new districts from the perspective of urban morphology
Authors: Zhang T Z , Wang W X , Dong Y H , Peng F L
Published: May 2024

Extensive underground space development worldwide has significantly contributed to the sustainability of social, ecological, and economic growth. In view of the tendency towards haphazard urban sprawling during the development of new areas in China, underground spaces have been increasingly utilized to create sustainable and resilient urban built environments. However, insufficient attention has been paid to their morphological characteristics, resulting in a lack of sustainable and resilient underground space morphological planning and design techniques. To bridge this gap, we established a computational morphology indicator system pertaining to underground spaces, considering land use, spatial distribution, and street networks. We selected 20 underground spaces in well-developed core areas of new districts in China. Hierarchical cluster analysis was adopted to investigate the morphological features of underground spaces. Additionally, the typology of underground space morphology and the corresponding characteristics were systematically summarized to facilitate decision-making for different patterns of underground space planning.
Centrifugal modeling on influence of superstructure construction of high-rise building on adjacent subway tunnel
Authors: Hong Y , Xu Y , Zhang Z , Ye G , Ge J
Published: May 2024

With the urban development in China, high-rise buildings must be constructed adjacent to subway tunnels. The superstructure construction process directly affects adjacent tunnels. However, only a few studies have focused on this topic. In this study, a series of centrifugal model tests were conducted to investigate the impact of the superstructure construction process of high-rise buildings on the deformation of adjacent tunnels in soft soil. Three model tests were designed, considering the buried depth of the tunnel. A loading system was implemented to simulate the superstructure construction process with a centrifugal acceleration of 100 g. The results showed that the superstructure construction caused the adjacent tunnel to deform vertically and laterally owing to its downward dragging effect. The vertical deformation of the tunnel was approximately thrice the lateral displacement. As the buried depth increased, the superstructure construction changed the transverse deformation of the tunnel section from vertical to horizontal tension. The outcomes of the study will provide guidelines for the safe operation of subways.
Firefighters’ behavior via vertical shafts in natural-ventilated tunnels
Authors: Zhang Y , Rui Y , Zhu H , Yan Z
Published: May 2024

Tunnel load traffic flows day and night, and is highly susceptible to catching tunnel fires. When a tunnel is on fire, occupants are endangered by the rapid deterioration of the tunnel environment during burning, and their self-evacuation is limited by their unfamiliarity with tunnels. Therefore, efficient and effective firefighting and rescue methods are urgently required to guarantee the safety of occupants during tunnel fires. During firefighting, one of the most important issues is that a fire brigade may encounter difficulties identifying the fire source. They have to deal with congestion and navigate cars piling into the tunnel, which wastes significant time. Therefore, this study provides an alternative approach for firefighters to access fire sources in naturally ventilated tunnels equipped with vertical shafts. This study explored three routes for firefighters from the ground to a fire source in a tunnel. The duration and speed of taking the three routes, along with the use of facilities, firefighters’ communication, and emotions, were presented and analyzed. This indicates that firefighting and rescue via vertical shafts is a feasible and optimized method for naturally ventilated tunnels because the estimated duration decreased by 56.2% (without smoke) and 60.0% (with smoke) compared to traditional routes when the minimum distance from the fire to the nearest exit is 2000 m. In addition, the study provides field experimental data on vertical firefighting in tunnels, which are expected to be used to build and calibrate models for firefighters in future studies.
A data-informed assessment method for the urban underground complex vitality
Authors: Pan Q , Dong Y H , Peng F L
Published: May 2024

The urgent need for urban renewal and the rapid expansion of underground spaces has spurred the construction of urban underground complexes (UUCs). Vibrant UUCs are crucial for the efficient utilization of underground spaces and urban sustainability. Previous research on urban underground complex vitality (UUCV) has been primarily theoretical with limited reusability. In this study, we aimed to address this gap by focusing on underground functional facilities and spatial distribution characteristics to establish a UUCV indicator system based on walkability theory. We introduced a method based on exponential weighted mean for weight allocation to facilitate vitality calculations. Using the Wujiaochang UUC in Shanghai as a case study, we explored the spatial distribution mechanism of vitality and validated the feasibility of this research framework. The proposed assessment method and results obtained in this study offer valuable insights into underground space planning and design, particularly in the context of urban renewal.
Development and verification of shield thrust vector self-adaptive control technology in soft soil strata
Authors: Zhu Y T , Bi X L , Zhu Y F , Wu H M , Wang X Z , Zhang Z X , Chen J , Qin Y
Published: May 2024

To solve the difficulty in automatically obtaining an effective total thrust vector relative to the shield posture adjustment requirements during self-driving in soft soil strata, a shield thrust vector self-adaptive control technology for shield machines was proposed. Subsequently, a large-scale model platform was established to simulate the straight-line advancement of the testing shield machine under dynamic loads, and the feasibility of steady shield driving was verified. The test results showed that: the actual total thrust force exhibited the same variation characteristics according to load force, while a relatively fixed difference of 1000 kN between the two caused by the system friction was observed. A quick recovery after an abrupt jump of the shield speed was discovered once there was a sudden, significant change in the load. The actual resultant moment of total thrust force effectively responded to the load force, and the shield postures were maintained well. Further, the driving speed and the horizontal stroke difference were controlled in the ranges of ±3 mm/min and ±5 mm of each set values, respectively. Subsequently, this technology was applied to the Wusongkou Yangtze River Tunnel project in Shanghai, and the on-site test results verified its feasibility in actual soft soil strata. The shield speed remained stable as the actual thrust forces shared the same changing low of the target values, and a fixed difference between the two was maintained to ensure the movement of the shield machine. The variation curves of the actual steering angles in both the horizontal and vertical directions coincided with those of the target steering angles because the resultant horizontal and vertical moments of the thrust force effectively responded to each steering requirement, which was executed with high quality.
Impact of extreme rainfall on metro network resilience: Shanghai metro as an example
Authors: Feng Q K , Zhang D M , Huang Z K
Published: May 2024

Extreme rainfall results in urban floods that are known to occur frequently and worldwide. In particular, a metro system faces a high risk of inundation owing to its special geographical location. Consequently, metro network flood resilience has attracted increased attention. This study considered Shanghai as an example to assess the resilience of metro network under extreme rainfall. First, a resilience assessment method of metro networks under extreme rainfall conditions was proposed. This method comprised comprehensive urban waterlogging analysis, construction of a topological structure of metro networks, and resilience assessment of metro networks. Subsequently, the resilience analysis of the Shanghai metro network under extreme rainfall was conducted as a case study based on the above method. The results showed that the disruption of stations and corresponding intervals caused greater damage to network performance. Finally, based on the analysis results, suggestions were provided to improve the flood resilience of the metro network under extreme rainfall conditions.
Experimental study on the triaxial mechanical properties of hybrid steel fiber–reinforced self-compacting concrete
Authors: Gong Chenjie , Kang Lei , Ding Wenqi
Published: May 2024

In this study, the triaxial mechanical properties of hybrid steel fiber–reinforced self-compacting concrete (HSFRSCC) were investigated. Based on previous research, a mixture of HSFRSCC that satisfies the requirements of compression and workability performance was determined. Conventional triaxial compression tests were performed at confining pressures of 0, 4, 8, 12, and 16 MPa. The results showed that all the specimens had excellent deformation ability, and both the steel fibers and confining pressure improved the ductility of HSFRSCC. With an increase in the confining pressure, the triaxial peak stress and strain of concrete were increased. The differences in the damage characteristics of HSFRSCC and plain concrete were compared based on scanning electron microscopy test results. Finally, the applicability of the Mohr–Coulomb criterion with that of the Willam–Warnke (W–W) criteria to HSFRSCC was compared. the results showed that the nonlinear W–W criterion had a better fitting effect. Hence, the relationship between triaxial peak stress, peak strain, and confining pressure was established, and the triaxial compression meridian formula for HSFRSCC was obtained.
Deformation caused by T-shape expansion of existing metro station: complex challenges and strategies
Authors: Lin Jiangyuan , Tong Liyuan , Li Hongjiang , Qiu Tao , Wen Yingwen , Liu Songyu
Published: May 2024

This case study presents an investigation on existing metro station deformation characteristics during T-type expansion in Nanjing, China. A three-dimensional elastic-plastic finite element model is adopted to consider the interaction of soil, retaining structure, horizontal support system and existing station structure. The results indicate that coupling deformation of asymmetric uplift deflection and existing structure rotation occurs on existing structure. Moreover, the sensitivity of influencing factors is analyzed, including the dimension of retaining structure, the support spacing, the excavation method, the soil reinforcement depth in passive area, the width of retaining soil during excavation, the relative position between foundation pit and existing structure, the excavation depth, the existing structure rigidity. Furthermore, based on the analysis of difficulties in the T-shape expansion projects, the controlling measures for the deformation of existing metro station are proposed. The achievements of this case study can be used as a reference for similar underground expansion projects.
Optimized identification for critical metro stations from urban resilience perspective
Authors: Liu S C , Qiao Y K , Peng F L
Published: May 2024

Urban rail transit systems and metro-led underground space contribute to urban resilience. The critical level of metro-led underground space in a metro network demands different resilience requirements, thereby rendering the identification of critical metro stations before the evaluation of the resilience contribution essential. This study optimized the identification of critical metro stations in terms of network model construction and evaluation methods to suit urban resilience perspective. The optimized metro network model considered the influence of transfers, difference between above-ground and underground routes, and cost between adjacent stations, to construct an undirected weighted graph of a metro network. Three evaluation metrics: node betweenness, network efficiency loss, and route redundancy, were adopted for a comprehensive identification method of critical stations. The optimized identification method was applied to the Shanghai Metro network (402 stations and 481 links by 2023). The betweenness identified the downtown stations to be more critical, whereas the network efficiency loss and route redundancy identified the critical stations at downtown-suburban connections. Moreover, the vulnerability and distribution of above-ground stations influenced the identification result of critical stations. The identification results are expected to facilitate the resilience evaluation of metro-led underground space, to examine whether the contribution is balanced with the demand.
Experimental investigation of tail void grouting pressure evolution for super-large diameter shield tunnels
Authors: Zhao C , He H , Lin C , Chen Y , Lavasan A
Published: May 2024

The shield tunneling method is widely used in underground construction. Factors such as the variations in grouting pressure and stiffness/strength evolution over space and time directly affect ground deformation and system stability. To investigate the effect of grouting pressure variation, grouting influence zone, and hydromechanical properties on the model responses (e.g., surface settlement and lining forces), an innovative model test setup was developed to simulate the tunneling process wherein the lining could settle or float during grout injection. This setup included tunnel shrinking, loading-unloading, grout injection, and sample preparation systems. The experimental results show that the grouting pressure evolution law may be significantly affected by the tunnel translation. When the tunnel centerline was fixed in the traditional model tests, the resulting grouting pressure in the tail void was lower than that when the tunnel was free to move. This is because the tunnel translation changed the shape of the annular gap and contributed to the measured grouting pressure. The proposed setup is capable of revealing a more realistic law of grouting pressure evolution, and the subsequent spatio-temporal grouting-induced soil/lining behavior is currently being investigated.
Influence of frost heave with confining pressure under seepage on compressive strength of frozen silt in artificial ground freezing
Authors: Li Z , Zhou J , Wang J
Published: May 2024

Artificial ground freezing (AGF) is used for constructing subway cross passages in coastal areas. The continuous construction of complex projects (cross-sea or cross-river tunnels) has resulted in freezing environments with high groundwater seepage velocities. Seepage cannot provide an open system in soil freezing for moisture migration, resulting in large amount of frost heave owing to segregated ice compared to close freezing system. The influence of frost heave under seepage on the compressive strength of frozen silt during artificial ground freezing must be studied to ensure AGF construction safety. Thus, a unidirectional freezing device that can control seepage and confining pressure conditions during freezing was designed to prepare frozen silt samples under different seepage velocities with confining pressures and to measure the relevant segregation frost heave. Subsequently, uniaxial compression tests were performed. The compressive strength of frozen silt under the influence of frost heave and seepage conditions was analyzed. The frost heave rate, uniaxial compressive strength, and elastic modulus of frozen silt in an open freezing system were measured. The seepage velocity during freezing increased the frost heave rate of the silt; the uniaxial compressive strength and elastic modulus of the frozen silt increased subsequently. The effective confining pressure suppressed frost heave of silt and reduced the uniaxial compressive strength and elastic modulus of the frozen silt. The test results were analyzed considering the segregation frost heave formation mechanism, and a theoretical improvement model of the uniaxial compressive strength and elastic modulus of frozen silt related to the content of segregated ice was proposed. This research is significant for ensuring the AGF construction safety in cross-river or ocean tunnel engineering under seepage conditions.
Study on microscopic mechanisms of slurry infiltration in calcareous sand based on CT scanning
Authors: Yuan H , Zhang Z , Huang X
Published: May 2024

A novel detachable microslurry infiltration device tailored for computed tomography (CT) scanning was developed. Using this device, a series of slurry infiltration tests was conducted on calcareous and Fujian sand columns with various bentonite slurry concentrations. CT scanning technology nondestructively captured the cross-sectional image slices of each specimen for analysis. A comprehensive image processing methodology was deployed to precisely differentiate the three phases—calcareous sand, slurry, and air—enabling 3D reconstruction of the infiltrated sand column. This approach combines three techniques: threshold segmentation, the watershed algorithm, and deep learning. Distinctive particle morphologies inherent to the calcareous and Fujian sands were observed. Notably, CT scans revealed a markedly greater angularity and irregularity of the calcareous sand compared with the Fujian sand, leading to different pore characteristics. Given an identical permeability coefficient, the calcareous sand porosity exceeded that of the Fujian sands. Furthermore, image analyses revealed distinct features of filter cake formation in these two soil columns. In calcareous sands with finer grain sizes, the slurry particles were more prone to clogging because of constricted and irregular seepage pathways. Conversely, with increasing particle size, the internal pores of the calcareous sand particles augmented channels for slurry infiltration, hindering filter cake formation.
Simulation-based approach for the optimization of ground freezing in tunneling
Authors: Williams M Rodolfo J , Cao Ba-Trung , Alsahly Abdullah , Meschke Günther
Published: May 2024

Artificial ground freezing is used in tunnelling for temporary ground improvement primarily to control groundwater flow and provide excavation support. The principle of ground freezing is based on freeze pipes bored into the ground where a coolant flows through the freeze pipes. Eventually, the ground freezing process converts pore water into ice by withdrawing the heat from the soil. In tunneling, artificial ground freezing is applied to form a closed arch frozen ground around the tunnel. Under the presence of high seepage flow, the formation time of the frozen arch is delayed. In some cases, it cannot be formed, leading to high construction costs or unsafe temporary frozen ground support. This study proposes a strategy for systematically reducing the freezing time through an optimal design arrangement of the freeze pipes. The strategy is based on the combination of the numerical modeling of the ground freezing process using a multifield finite element model in conjunction with a surrogate model to enable real-time prediction.
Construction control technology for cutting historical anchor cables along the path of shield tunnels crossing existing tunnels at close proximity
Authors: Mu Yilong , Zhou Xiaowen , Liu Huaiyu
Published: May 2024

In Dongguan Metro Line 1, the new shield tunnel crosses above the existing metro tunnel at a close proximity, necessitating strict control over the displacement of the existing tunnel caused by shield construction. In addition, on the left route of the new shield tunnel, anchor cables used to strengthen the stratum during the construction of the existing tunnel remain embedded in the soil. These anchor cables must be cut off to avoid damaging the shield machine. However, cutting these anchor cables may influence the stress states of the soil and existing tunnel, resulting in additional displacements. To address these challenges, an innovative cutting method for anchor cables was employed in this project. To strictly control the induced settlements of the existing tunnel during shield tunneling, the following measures were implemented: pregrouting reinforcement of the soil above the new tunnel, numerical simulation, and displacement monitoring. The construction of the new tunnel through shield tunneling was successfully completed. The monitoring data indicated minimal displacement of the existing tunnel, demonstrating effective construction control. The control technologies introduced in this study for constructing new shield tunnels crossing an existing tunnel serve as valuable reference for similar projects in the future.
Analytical model for calculating the soil pressure on inclined shield tunnels during construction phase
Authors: Wang Z , Li H , Zhu Y , Huang J , Xie J , Huang X
Published: May 2024

As a new tunneling technology for shallowly buried tunnels, ground penetration shield tunneling (GPST) penetrates the ground directly without launching or receiving shafts, thereby improving the construction efficiency and land-occupation economics. Unlike traditional shield tunnels, which have a leveled or approximately leveled route, the entrance and exit sections of GPST tunnels are inclined, and the external soil and water pressures acting on the latter vary along the route. This study proposes a new loading calculation model for the GPST during the construction phase, considering the dynamically varying stress state along the route. First, a comparison was conducted to delineate the advantages of the proposed model in contrast to the modified conventional method, followed by an analysis of the potential underlying reasons. Subsequently, a parametric study is conducted to evaluate the influence of the excavation slope on the soil pressures acting on the tunnel. The results indicate that the proposed method is better suited for calculating loads at shallow burial depths in GPST.