In the construction of linings for underground structures such as mines and traffic tunnels, reinforcement cages are typically assembled on concrete formwork trolleys. This practice occupies critical positions along the construction line and thereby reduces overall construction efficiency. To address this issue, the present study investigated the transformation technology of lining reinforcement cages, based on the underground project in the Xiong’an New Area of the Xiong’an-Xinzhou high-speed railway. Full-scale model tests and numerical simulations were conducted to evaluate the feasibility and effectiveness of several support schemes, which were subsequently implemented in practical engineering applications. The following conclusions were drawn: 1) A system support scheme utilizing a matrix-type lifting point system was proposed, and its feasibility was verified through implementation in actual engineering projects. 2) During the system transformation, the measured average deformation of the lining reinforcement cage was accurately maintained within 5 mm, with the maximum deformation not exceeding 10 mm. This ensured adherence to the design thickness of the structural protective layer and the installation quality of embedded components. Therefore, the proposed scheme offers a novel and effective solution for the construction of underground engineering lining.
full-scale model testnumerical simulationreinforcement system conversiontunnel liningunderground engineeringThe author(s) declared that financial support was received for this work and/or its publication. This study was supported by Hebei Province Innovation Capability Enhancement Plan Project (No.244X6102D).section-at-acceptanceStructural MaterialsIntroduction
Currently, with the continuous development of China’s mining industry and transportation industry, the quantity of mine and traffic tunnel construction is increasing. At the same time, the requirements for automation, greening and refinement of construction technology are also rising (Ji et al., 2023; Jin et al., 2024; Liu et al., 2023; Wu et al., 2025). With the rapid development of new generation information technologies such as artificial intelligence, the Internet of Things, big data, and 5G communication networks, the fourth industrial revolution centered on intelligence, digitization, and networking has brought new challenges and opportunities to various industries (Guo et al., 2023). The drilling and blasting method and TMB method are the two mainstream construction methods for tunnel construction, and researchers have conducted extensive research on intelligent construction. At present, the drill-and-blast tunnel has basically achieved fully mechanized construction and is developing towards intelligent equipment, information management, and other aspects (Cai et al., 2022; Chen et al., 2020; Li et al., 2024; Wang et al., 2024). The mechanization and informatization level are relatively high in TBM tunnel construction. Currently, relevant research mainly focuses on the digitization and intelligent empowerment of the entire process (Hou et al., 2023; Sharafat et al., 2021; Wu et al., 2024). Compared to the drilling and blasting method and shield tunneling/TBM method, the open excavation method has the advantages of simple construction technology, high efficiency, and good economy. However, there is currently limited research on the mechanization and intelligence of open cut tunnel construction.
In the mine and traffic tunnel, the lining is the key structure to protect the stability of the tunnel. Its main construction procedures include reinforcement binding, formwork installation, concrete pouring and maintenance. Trolleys are commonly used in open-cut lining construction to support these activities (Jian, 2021; Li, 2019; Wu, 2008). Traditionally, concrete is poured only after reinforcement has been bound to the formwork trolley (Liu, 2023; Zhao, 2023; Wang, 2023). However, the reinforcement binding process often occupies critical construction paths, thereby impeding overall construction efficiency.
To address this efficiency bottleneck, a construction scheme involving the transformation of the lining reinforcement cage has been proposed within the industry. Specifically, after reinforcement is pre-bound on a dedicated trolley, this trolley is repositioned to transfer the reinforcement onto a formwork trolley. This process streamlines the subsequent concrete placement.
The originally bound trolley is then moved to continue the next stage of binding operations. However, in this transformation process, down-warping may occur because of the dead weight after the removal of the bound trolley (Huang and Meng, 2020). This may prevent the concrete formwork trolley from being positioned properly due to spatial interference or affect the thickness of the protective layer.
To address these challenges, this study investigated the application of transformation technology for the lining reinforcement cage, using the underground project in the Xiong’an New Area of the Xiong’an-Xinzhou high-speed railway as a case study. A full-scale model test was conducted to evaluate the feasibility and effectiveness of various support schemes. Based on the test results, numerical simulations were carried out to replicate and analyze the actual construction conditions. The findings were subsequently applied to practical engineering. As a result, deformation issues associated with the transformation process of the lining reinforcement cage were effectively controlled, and the overall construction duration was reduced. The research results provide an effective solution for the efficient, high-quality and refined construction of underground engineering lining.
Background of the projectOverview
Section 6 of the Xiong’an-Xinzhou high-speed railway is located within Rongcheng County, Baoding City, which falls within the starting area of the Xiong’an New Area. With a total length of 5.43 km, this section of the project is constructed via an open-cut method. The layout plan of this railway is illustrated in Figure 1. The Xiong’an Tunnel is divided into three sections, with lengths of 7,500 m for Section 1, 8,000 m for Section 2, and 4,480 m for Section 3. The maximum running speed of the train is 250 km/h. This tunnel is a single tunnel with two tracks. The effective clear cross-sectional area above the rail surface is at least 90 m2.
Plan of the Xiong’an-Xinzhou high-speed railway.
Map graphic showing a high-speed railway route with labeled stations Baiyangdian, Xiaoli, Xiong’an Intercity, and Xiong’an, as well as tunnels numbered one to three and geographical features Ping River and Baigouying River.
The hydrogeological and geological conditions of this area are as follows: This area is a North China Plain region and belongs to the alluvial-pluvial plain subregion. The primary geological formation in the project area is the Q3 stratum, which is predominantly composed of silty clay, clayey silt, and silty-fine sand. The bearing stratum consists mainly of silty clay (62.7%) and clayey silt (34.3%). The tunnel alignment extends in an east-west direction, with the groundwater recharge source located on the eastern side. Correspondingly, the groundwater level exhibits a gradual decline from east to west. In Section 1 of the tunnel, the water table ranges from 3.6 m to −8.8 m; in Section 2, it ranges from −7 m to −9 m; and in Section 3, it ranges from −8 m to −9 m. The confined groundwater level is situated at about −11 m, while the tunnel bottom elevation varies between −12 m and −19.5 m.
Construction procedures for secondary lining
The secondary lining is an inner structural layer constructed using reinforced concrete following the completion of the primary support in a tunnel. Together with the primary support, it forms a composite lining system. Its primary functions include enhancing the structural integrity of the tunnel, improving drainage performance, providing a more refined aesthetic finish, and accommodating the installation of communication, lighting, and other ancillary systems. This construction involves the following steps (Figure 2): 1. Surveying and setting out; 2. Reinforcement preparation and installation; 3. Positioning of the formwork trolley; 4. Laying of waterproof layers; 5. Concrete placement; 6. Vibration; 7. Capping; 8. Formwork removal; 9. Curing.
Schematic diagram of the construction procedures.
Five-panel illustration showing the construction stages of an arched tunnel structure. Each panel displays a different step in the structural assembly, progressing from a visible framework to a fully enclosed tunnel with support platforms and access ladders.Construction difficulties
In the process of tunnel construction via the open-cut method, the construction site is typically in open air. Construction is highly susceptible to the impact of weather changes. For example, extreme meteorological conditions (e.g., rainfall, high temperatures, and strong winds) may significantly and directly influence construction progress. Moreover, the safety and wellbeing of construction workers are significantly compromised by the unstable working environment and the risks associated with adverse weather conditions, making it difficult to ensure adequate protection. To address these challenges, this project proposed a solution grounded in the concept of a mobile factory, aiming to enhance the efficiency and quality of open-cut tunnel construction through a fully integrated, assembly-line operation. However, two major issues hinder the realization of this approach: the occupation of critical construction paths during the reinforcement process and the potential for downward deformation (down-warping) caused by dead weight following the removal of the reinforcement-bound trolley during the transformation of the reinforcement system. Addressing either of these issues is essential to ensuring an uninterrupted and effective assembly-line operation.
Full-scale model test
In actual construction, the tunnel lining reinforcement cage is divided into standard segments measuring 9 m in length. For the purposes of this study, the plane size of the reinforcement cage in this test was completely consistent with the design size. The lateral support and vertical support were located in the vertical plane, and were evenly arranged along the longitudinal spacing of the reinforcement cage. The deformation of each longitudinal section of the reinforcement cage was similar, so it can be considered that the length of the reinforcement cage had little effect on the test results. In order to reduce the test site and workload, a 3 m-long full-scale cross-sectional reinforcement cage was selected for testing to examine the effects of lateral support, vertical support, and their combined application on reinforcement cage deformation. The objective was to assess the feasibility and effectiveness of various support schemes for the lining reinforcement cage and to provide experimental data to inform subsequent numerical simulation analyses.
Test methodLayout of test points
Three cross-sections were selected to measure the deformation of the reinforcement cage. Eleven deformation measurement points were symmetrically arranged on each cross-section (Figure 3). The average values of the measurements obtained from these three cross-sections were used for analysis. The deformation of reinforcement cage was measured by Leica tz08 total station with a measurement accuracy of 1 mm. The measurement targets were set at the monitoring point.
Layout of deformation measurement points. (a) Cross-sectional layout. (b) Measurement point layout.
Figure (a) shows an overhead view of a construction structure divided into three labeled monitoring sections with red lines and yellow text. Figure (b) shows a frontal view of the same or similar structure with several monitoring points labeled in yellow text distributed along the arch and sides, each designated by codes such as HE0-1, 2, 3 and HW1-1, 2, 3.Boundary conditions
In the test, both lateral and vertical support systems were employed. The lateral support consisted of elastic support applied using a proving ring with a stiffness of 3.19 t/mm. For vertical support, two types of rigid supports were used for comparative analysis: a screw jack and a gantry lifting point. All support positions were aligned with the locations of the stiffened frameworks (Figure 4).
Positions of support points.
Structural diagram of an arched frame showing seven red circled Xs marking measurement points along the arch and four green arrows identifying support points at the base and sides, with accompanying legend explaining each symbol.Test conditions
The test conditions are listed in Table 1. Test 1, which involved reinforcement cage deformation without any support, was used as a control to facilitate comparison and analysis of the effectiveness of various system support schemes in mitigating reinforcement cage deformation.
Test conditions.
S/N
Lateral support
Vertical support
1
-
-
2
√
-
3
-
√ (jack)
4
-
√ (gantry lifting point)
5
√
√ (jack)
6
√
√ (gantry lifting point)
Test resultsComparison of single support schemes
The results of tests 1, 2, 3, and 4 (Figure 5) were chosen to compare the deformation magnitude of the reinforcement cage in each single support scheme.
Deformation results of the reinforcement cage in single support schemes. (a) Without support. (b) Lateral support. (c) Vertical support (jack). (d) Vertical support (gantry lifting point).
Four labeled engineering diagrams of a steel arch structure display measured deformations at various points, indicated by arrows and color-coded annotations for expansion, shrinkage, rise, or decrease in millimeters; panels are labeled (a) through (d).
As illustrated in Figure 5, in the absence of any support, the reinforcement cage exhibited a maximum vertical deformation of 104.33 mm and a maximum horizontal deformation of 162 mm due to its self-weight. Such deformation could potentially hinder the correct positioning of the concrete formwork trolley due to spatial constraints, or affect the appropriate thickness of the structural protective layer. The provision of lateral or vertical support led to a notable reduction in both vertical and horizontal deformations of the reinforcement cage. To further assess the merits and limitations of the different support schemes, a comparative analysis was conducted on the vertical and horizontal displacements at various locations along the reinforcement cage. The corresponding results are presented in Figure 6.
Displacements at different measurement points. (a) Vertical displacement. (b) Horizontal displacement.
Two grouped bar charts compare support types at different measurement points. Chart (a) displays vertical displacement and chart (b) shows horizontal displacement, each with without support, lateral support, and two types of vertical support.
Figure 6 demonstrates that the adoption of vertical support—whether through a jack or a gantry lifting point—resulted in smaller vertical deformations across all measured points compared to those observed with lateral support alone. Furthermore, the horizontal displacements under vertical support were also lower than those recorded with the horizontal support scheme. This suggests that the primary cause of the reinforcement cage deformation was its self-weight, and that applying constraints aligned with the gravitational direction is effective in controlling the overall deformation. Among the two vertical support methods, the gantry lifting point was more effective in limiting deformation.
Subsequently, experimental analysis was conducted on combined support schemes, and the deformation results were compared to validate whether the gantry lifting point support represented the optimal solution.
Comparison of combined support schemes
The results of tests 5 and 6 (Figure 7) were considered to compare the deformation magnitudes of the reinforcement cage when combined support schemes were employed.
Deformation results of the reinforcement cage in combined support schemes. (a) Lateral support + jack. (b) Lateral support + gantry lifting point.
Side-by-side photographs labeled (a) and (b) show a large blue steel frame arch structure with measurement annotations in red, yellow, and blue identifying dimensional changes such as rises, decreases, expansions, and shrinkages in millimeters at specific locations across the structure.
As shown in Figure 7, the combination of lateral support and jack resulted in a maximum vertical deformation of 15.33 mm and a maximum horizontal deformation of 17 mm. In contrast, the combined lateral support and gantry lifting point scheme exhibited a maximum vertical deformation of 10 mm and a maximum horizontal deformation of 13 mm. Among the two combined support configurations, this scheme demonstrated better performance in controlling the deformation of the reinforcement cage.
To identify the optimal scheme, a further comparison was made between the most effective single support scheme and the most effective combined support scheme. The outcomes of this comparison are depicted in Figure 8.
Comparison between the best schemes. (a) Vertical displacement. (b) Horizontal displacement.
Bar chart comparison with two panels. Panel (a) on the left shows vertical displacement in millimeters at five measurement points for two conditions: gantry lifting point and lateral support plus gantry lifting point. Panel (b) on the right shows horizontal displacement in millimeters for the same measurement points and conditions. Each panel uses distinct colors to differentiate between the two test conditions.
As observed in Figure 8, when these two types of schemes are implemented, the vertical displacements of the reinforcement cage at the measurement points do not exhibit regular changes. When the combined support scheme was adopted, the horizontal displacement of the reinforcement cage did not decrease notably compared with that when the gantry lifting point support scheme was used. This further confirmed that applying a constraint in the vertical direction of the reinforcement cage was a better support scheme and that providing support at the gantry lifting points was the optimal scheme for controlling reinforcement cage deformation.
Analysis of the segment length of the reinforcement system
Based on the model test, numerical analysis was further conducted to evaluate the actual construction effectiveness of the support scheme in a 9-m standard segment reinforcement cage, thus guiding on-site construction.
Numerical modeling
Midas Civil was used for modeling. The structural reinforcement, spreader beams, and sling chains were simulated based on beam elements, and the computational model is illustrated in Figure 9.
Schematic diagram of the calculation model.
Finite element mesh illustration of an arched bridge structure features a curved arch, vertical suspender cables, and rectangular supports at each end, with color differentiation for elements and support zones.
In this model, the elastic constitutive model of the Q235B material was adopted for the steel components, whereas the elastic constitutive model of the HRB400 material was employed for the reinforcement. The material parameters are shown in Table 2. The boundary conditions of the model were set as follows: (1) consolidation at the lower edge of the structural reinforcement; (2) alignment of sling chains and lifting points at shared nodes; (3) constrained vertical displacements at the connection points between spreader beams and chain blocks; and (4) elastic connection constraints at the contact points of the reinforcement.
Material parameters.
Type
Material
Elastic modulus
Poisson’s ratio
Yield strength
Yield strain
Steel
Q235B
206 GPa
0.3
235 MPa
0.001
Reinforcement
HRB400
206 GPa
0.3
400 MPa
0.002
Numerical model verificationAnalysis of deformation of the inner-layer reinforcement cage
To reflect the real effect of wire-type connections in the reinforcement cage, computational analysis was carried out on the connection methods between the circumferential reinforcement and longitudinal reinforcement of the inner-layer reinforcement cage. There are two types of connection methods, namely, hinged connections and rigid connections.
Hinged connection
Figure 10 presents the displacement of the inner-layer reinforcement cage assuming hinged wire-tying connections. Under gravity, the inner-layer mesh exhibited a maximum vertical deformation of 226 mm and a maximum lateral deformation of 153 mm.
Cloud map for the displacement of inner-layer reinforcement cage during hinged connection (unit: m). (a) Vertical displacement. (b) Lateral displacement.
Two ANSYS simulation results displaying color contour plots of mechanical deformation on a curved structural component, each with a different deformation pattern and color distribution. Image (a) shows a wide range of deformation indicated by diverse color bands from blue through red, while image (b) depicts a different pattern with more uniform colors and less variation in deformation. Both include legends labeling deformation values and coordinate axes for orientation.Rigid connection
Figure 11 illustrates the displacement of the inner-layer reinforcement cage assuming rigid connections. When the wire-tying connections were modeled as rigid, the inner-layer mesh experienced a maximum vertical deformation of 225 mm and a maximum lateral deformation of 152 mm under the action of gravity.
Cloud map for the displacement of inner-layer reinforcement cage during rigid connection (unit: m). (a) Vertical displacement. (b) Lateral displacement.
Two ANSYS simulation results display color contour plots of stress or displacement on a curved structural component, with figure (a) showing a sharper gradient and more pronounced deformation than figure (b), both annotated with legends and numerical ranges.
The displacements of the inner-layer reinforcement cage with hinged connections and rigid connections were compared, with the results illustrated in Figure 12.
Comparison of the vertical displacements.
Bar chart comparing vertical deformation in millimeters for three configurations: single reinforcement at 168 millimeters, hinged connection at 226 millimeters, and rigid connection at 225 millimeters.
As revealed in Figure 12, only a 1 mm difference was observed in the vertical deformation of the reinforcement cage between the hinged and rigid connection states. This finding indicated that the connection methods between the longitudinal and circumferential reinforcements had almost no impact on the overall deformation of the reinforcement cage.
In addition, Figure 12 compares the vertical deformation of individual reinforcements. The inner-layer mesh showed a vertical displacement 57 mm greater than that of a single reinforcement. This indicates that longitudinal reinforcement did not significantly enhance the stiffness of the reinforcement cage; rather, it functioned primarily as a load-transferring element. The contribution of longitudinal reinforcement to the rigidity of the circumferential reinforcement cage was minimal, effectively serving as an additional load. Consequently, the method of connecting the circumferential and longitudinal reinforcement had negligible impact on the overall structural performance, provided that the connection nodes could transfer the dead weight of the longitudinal reinforcement.
Comparison between the numerical simulation results and test results
Based on the above simulations, an analysis was conducted under the condition of lateral support combined with lifting point support. The obtained results were then compared with those from the full-scale model test to verify the accuracy of the numerical model. The reinforcement cage deformation under these conditions is shown in Figure 13.
Cloud map of reinforcement cage deformation (unit: m). (a) Vertical displacement. (b) Lateral displacement.
Side-by-side ANSYS finite element analysis results show color-mapped deformation of a curved structure under load, with diagram (a) on the left and diagram (b) on the right, each using a blue-to-red displacement scale.
Figure 14 compares the deformation results obtained from simulation and experimental measurements at different points. Here, positive and negative values simply denote direction. The maximum discrepancy between simulation and test results was 3.43 mm, indicating that the parameters used in the numerical model accurately reflected the actual reinforcement cage deformation.
Comparison between the simulation results and test results. (a) Vertical displacement. (b) Lateral displacement.
Pair of grouped bar charts comparing simulation results, test results, and their differences for deformation value in millimeters at multiple measurement points. Chart (a) displays five points with notable differences, particularly at HW1-1.2.3, while chart (b) shows four points with smaller differences annotated above each red line. Legends and axis labels are present.Simulation of actual conditions
With the numerical simulation validated, further analysis was conducted to simulate site-specific conditions and identify a force application scheme at the lifting points that minimized reinforcement cage deformation. A key consideration was ensuring the lifting point positions matched the on-site layout.
The lifting points were arranged per the actual layout positions of the erection reinforcement bars, with spacings of 2.4 m, 3.6 m, and 2.4 m between adjacent lifting points. A total of 16 lifting points were arranged, forming four rows. The positions and numbering of the lifting points are illustrated in Figure 15.
Distribution of lifting points. (a) Layout of lifting points. (b) Numbering of lifting points.
Technical diagram with two panels: Panel (a) shows a front view of a load lifting assembly, including electric hoists, a distribution beam, and sling chains with detailed measurements labeled in millimeters. Panel (b) presents a grid layout for tunnel segments labeled by rows and columns, with an arrow indicating tunnel direction.No force at the lifting points
When no lifting force was applied at the lifting points (i.e., the vertical displacements of the lifting points remained fixed), the inner-layer reinforcement cage exhibited a down-warping deformation of 16 mm, a bulging deformation of 1.1 mm, and a maximum lateral deformation of 18 mm. The calculation results are shown in Figure 16.
Cloud map for the displacement of inner-layer reinforcement cage without forces applied at the lifting points (unit: m). (a) Vertical displacement. (b) Lateral displacement.
Two ANSYS simulation graphics compare deformation results for an arched structure. Panel (a) displays a range of deformation values with more pronounced red and blue areas, while panel (b) shows mainly green with smaller high-stress zones. Both panels include color bars to indicate displacement values and axes for orientation.
The extracted counter forces at lifting points 1 to 8 were 13289 N, 28638 N, 28638 N, 13289 N, 9606 N, 21668 N, 21668 N, and 9606 N, respectively. The total force borne by the 16 lifting points reached 29.3 t, accounting for 54% of the weight of the entire reinforcement cage (53.9 t).
Applying forces at the lifting points
To minimize the reinforcement cage deformation, the forces applied at the lifting points were adjusted and optimized many times, with the deformation results illustrated in Figure 17. When the minimum deformation state was achieved, the inner-layer reinforcement cage experienced a down-warping deformation of 7.2 mm, a bulging deformation of 7.8 mm, and a maximum lateral deformation of 8.6 mm.
Cloud map for the displacement of inner-layer reinforcement cage with forces applied at the lifting points (unit: m). (a) Vertical displacement. (b) Lateral displacement.
Finite element analysis results from ANSYS software show two color-mapped contour plots of structural deformation on a curved surface, labeled (a) and (b), with different stress distributions indicated by blue, green, yellow, and red gradients.
At this moment, the tensile forces applied at lifting points 1 to 8 were 12625 N, 34611 N, 34611 N, 12625 N, 9204 N, 24834 N, 24834 N, and 9204 N, respectively. A total tensile force of 32.5 t was applied at the 16 lifting points, accounting for 60.3% of the weight of the entire reinforcement cage.
The results showed reduced overall deformation when force was applied at the lifting points. Notably, forces applied at the edge columns were greater than those at the middle columns, while forces in the two middle rows surpassed those in the front and rear rows. About 70% of the total force was borne by the eight lifting points located in the two middle rows. This distribution offers valuable guidance for practical construction.
Field application and the effect
The lifting point system was subsequently designed based on the simulation results. For a 9-m standard segment, 16 lifting points were evenly distributed in four rows, with four lifting points per row. The main components of the lifting point system included sling chains, spreader beams, and electric hoists arranged from bottom to top. The lower ends of the sling chains were connected to reinforcement N3 via shackles, while the upper ends were linked to the spreader beams through lifting lugs. Four single-row sling chains were vertically aligned along the tunnel direction, spaced at 2.4 m, 3.6 m, and 2.4 m, respectively, and positioned centrally. Four spreader beams, each 9 m in length, were aligned with the tunnel direction. Each spreader beam’s upper end was connected to two electric hoists, while the lower end was attached to four sling chains. The hoists were also vertically arranged, with an 8-m spacing between them. Their lower ends were connected to the spreader beams via lifting lugs, and the upper ends were secured to girders on the side spans of the mobile factory building. The structural layout and dimensions of the lifting point system are provided in Figure 18.
Arrangement of the lifting point system along the sectional direction of the tunnel (unit: mm).
Technical diagram illustrating the lifting setup for a large curved structure using an electric hoist, distribution beam, and sling chains. The structure spans 9401 millimeters in total, with central and side segments measured at 2807 millimeters and 3297 millimeters respectively.Construction equipment for system transformation
The primary construction equipment for the system transformation was a modified factory building for the lining reinforcement cage, illustrated in Figure 19. This facility provided an industrialized and enclosed environment with lifting capabilities, facilitating the shift from outdoor to indoor construction. As a result, the working environment improved, and the impact of external construction conditions was minimized. In addition, the sidewall could open and close and was equipped with a cantilever truss crane, facilitating the timely transfer of reinforcement and other materials inside and outside the pit. The lifting process was safe and reliable.
Transformation factory building for the lining reinforcement cage.
Large industrial building structure with Chinese signage, an overhead crane marked with a number four, safety railings, and a worker wearing a helmet and high-visibility vest observing the site.
The factory building was integrated with the distributed lifting system, which was equipped with eight proving rings and eight electric hoists, as shown in Figure 20. The proving rings enabled real-time measurement of the warping degree within the lifting system, while the electric hoists facilitated coordinated stress distribution and pre-camber adjustments, thereby controlling system deformation. By utilizing the proving rings on the lifting system in conjunction with the stress gauge installed on the reinforcement trolley, the system transformation was executed without inducing load differentials.
Distributed lifting system. (a) Proving rings. (b) Electric hoists.
Panel (a) shows a close-up of an industrial lifting system with metal chains, a hook, and a load cell attached to a white overhead beam. Panel (b) displays a wider view of two similar lifting setups, including chains, straps, hooks, and a surrounding metal structure in an industrial environment.Construction process for the system transformation
The main implementation steps of the lining steel reinforcement system conversion technology are as follows: (1) Installation of distributed lifting system; (2) Steel bar trolley in place; (3) Binding of lining steel bars; (4) Connection between lining steel bars and lifting system; (5) System transformation; (6) Remove the steel bar trolley and move in the formwork trolley. The specific implementation situation is as follows.
Connection between the distributed lifting system and the factory building: The distributed lifting system, from top to bottom, consists of proving rings, electric hoists, sling chains, and spreader beams. There were four spreader beams (lengths of 9 m each) arranged along the tunnel direction. Each spreader beam was connected at its upper end to two electric hoists, spaced 8 m apart along the same beam. The lower ends of the hoists were attached to the spreader beam via lifting lugs, while the upper ends were connected to proving rings and affixed to the girders on the side spans of the mobile factory building, also through lifting lugs. The completed connection between the distributed lifting system and the factory building is shown in Figure 21.
Connection Between the Distributed Lifting System and Reinforcement: Upon completion of reinforcement binding, the weight of the reinforcement was monitored in real time using a stress gauge installed on the reinforcement trolley. This measurement facilitated the precise application of force at the lifting points. The distributed lifting system was connected to the lining reinforcement cage via sling chains on the spreader beams and turnbuckles. The turnbuckles were configured as depicted in Figure 22. The reinforcement was secured to the four sling chains at the lower ends of each spreader beam using these turnbuckles. The spacings between adjacent sling chains along the tunnel direction were 2.4 m, 3.6 m, and 2.4 m, maintaining the lifting points near the erection reinforcement bars and generally centered.
Record of Forces Applied at the Lifting Points: Once the distributed lifting system was connected to the reinforcement, forces were applied at the lifting points using the electric hoists. The magnitude of the applied forces was determined based on both the real-time weight measurements obtained from the stress gauge and the simulated force distribution across the lifting points, as illustrated in Figure 23. Following the application of force, the initial readings from the proving rings were recorded to monitor the resulting deformation of the lining reinforcement.
Trolley Transition Process: After force application, the reinforcement trolley beneath the lining reinforcement cage was maneuvered to shift out of position. Subsequently, the formwork trolley was brought in, completing the transformation phase of the lining reinforcement cage.
Application results of the system transformation
Through the implementation of this measurement-enabled distributed lifting system, in combination with the factory building infrastructure, a load-balanced transformation process was achieved using electrically controlled lifting equipment, calibrated according to the load-bearing capacity of the reinforcement trolley. This approach effectively minimized reinforcement deformation. While the design allowance for deformation in the lining reinforcement cage was 2 cm, the application of the transformation technology resulted in a measured average deformation of 5 mm and a maximum deformation of 10 mm, thereby ensuring both the required thickness of the concrete protective layer and the installation accuracy of embedded components.
Connection between the distributed lifting system and the factory building.
Steel structure construction site with a large white gantry and red Chinese characters on a sign, flanked by stairs and equipment, with construction workers and blue barriers visible in the background.
Layout of turnbuckles.
Aerial view of construction workers in safety gear assembling a dense curved steel reinforcement structure within a concrete enclosure, indicating preparation for pouring concrete in a large-scale infrastructure project.
Stress gauges on the reinforcement trolley.
Close-up view of a metallic device with a cylindrical sensor attached to a blue painted steel structure using bolts, featuring Japanese text printed on the sensor’s label.Conclusion
A microstrain differential control technology was developed for transforming the lining reinforcement cage, based on the underground engineering practices of the Xiong’an-Xinzhou high-speed railway in Xiong’an New Area. Numerical simulations and full-scale model tests were conducted to evaluate the feasibility and performance of various support schemes. The optimal scheme was identified and subsequently applied in practice. Together with the matrix-type lifting point system of the mobile factory, this solution effectively resolved the construction challenges in the transition from reinforcement binding to concrete placement. The following conclusions were drawn:
Reinforcement cage deformation can be controlled by both lateral support and vertical support. Among the support schemes, providing vertical support at gantry lifting points achieved the best results.
It was observed that the forces applied at the lifting points were higher at the edge columns compared to the middle columns, and greater in the two central rows than in the front and rear rows. The resultant force at the eight lifting points located in the two central rows constituted about 70% of the total applied force. Optimal control of reinforcement cage deformation was achieved when the total applied force at the lifting points equaled 60.3% of the reinforcement cage’s weight.
By using micro-strain difference control technology, the average deformation of lining reinforcement cage was controlled within 5 mm, and the maximum deformation was controlled within 10 mm during the transformation process. This outcome ensured both the required thickness of the protective concrete layer and the installation quality of embedded components.
The conversion technology of steel reinforcement system has realized the assembly line operation of tunnel lining, significantly improving construction efficiency. In addition, technology can effectively reduce the deformation of lining steel cages, ensure construction quality, and have high promotion and application value.
Data availability statement
The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author.
Author contributions
XS: Conceptualization, Project administration, Writing – original draft. WT: Formal Analysis, Methodology, Supervision, Writing – review and editing. HY: Data curation, Investigation, Writing – original draft. XF: Data curation, Investigation, Writing – original draft. HZ: Resources, Validation, Writing – review and editing. HL: Data curation, Writing – original draft.
Conflict of interest
Authors XS, WT, HY, XF, and HL were employed by CCCC Second Harbor Engineering Co., Ltd.
The remaining author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Generative AI statement
The author(s) declared that generative AI was not used in the creation of this manuscript.
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Edited by:Jiangyu Wu, China University of Mining and Technology, China
Reviewed by:Chao Kong, Southwest University of Science and Technology, China