Optimization and Impact Assessment of Excavation Sequence around Subway Stations from the Perspective of Sustainable Urban Development (2024)

1. Introduction

With the development of cities, livability has become a paramount consideration in urban planning. The growing demand for urban infrastructure projects conflicts with the development needs of urban ecological environments. Achieving a balance between engineering construction and urban ecology is one of the goals of achieving sustainable urban development.

In recent years, significant efforts have been made to develop sustainable solutions for building environments. Rogers [1] proposed three methods for evaluating the future benefits of urban infrastructure solutions put forth by civil engineers, aiding in better understanding their value and facilitating sustainable construction and development of cities. Hoornweg [2] introduced a method for assessing the balance between the evolving scale of cities and the quantity of urban infrastructure, offering a simple yet powerful tool for sustainable infrastructure planning. Building upon conventional sustainable project assessment frameworks, Zargarian [3] proposed an evaluation framework tailored to urban underground space projects, employing an innovative weighted system to effectively address sustainability concerns in underground urban projects. Berglund [4] reviewed a plethora of smart infrastructure projects in cities, discussing the roles that various professionals in the civil engineering industry can play in the sustainable development of smart cities. Hollands [5] analyzed foundational data from urban facade greening systems and created BIM objects, leveraging automated planning processes to facilitate the implementation of greening projects for sustainable urban development. Fernandez-Alvarado [6] utilized BIM technology to export urban 3D geometric data, green facility locations, and meteorological data to GIS software, promoting the visualization of urban environmental issues and aiding in reducing urban environmental risks caused by civil engineering projects.

Excavation projects are integral to urban development, presenting new challenges for the efficient utilization of underground spaces and the sustainable development of transportation systems. The construction process can cause the water table to drop, induce land subsidence, and potentially damage underground pipelines, posing a potential threat to the surrounding natural environment and soil and water resources. At the same time, environmental pollution such as noise, vibration, and dust generated during the excavation process has caused widespread concern in the community, which may have a negative long-term impact on the quality of life and health of citizens. Effectively mitigating adverse environmental impacts from excavation is crucial for urban sustainability. Niu [7] conducted research using numerical simulations and field measurements to study deformation issues of subway stations adjacent to excavations, bearing significant importance for subway system safety and urban sustainability. Shi [8] focused on a subway station project in Wuhan, investigating the influence of different excavation methods on surrounding soil and retaining structures. The results indicated that synchronous segmented excavation at the same level is conducive to controlling overall deformation. Sun [9] utilized finite element software to conduct a three-dimensional simulation analysis of groundwater-lowering processes in excavation projects, discussing the effects of dewatering sequence, well-pumping rate, and quantity on excavation projects and determining optimal dewatering rates to effectively mitigate adverse environmental impacts from excavations. Ma [10] studied the effects of different positions of isolation piles on soil settlement, building, and excavation deformation in a deep excavation project in Guangxi, proposing formulas to determine isolation pile insertion depth and a design method to determine optimal isolation pile lengths based on research findings. Ping [11] investigated the effects of different depths of dewatering wells and cutoff curtain depths on surface settlement in excavation projects in soluble rock areas, offering effective solutions for optimizing dewatering plans in gypsum-containing strata excavation projects. Tong [12] proposed a method considering the influence of shear stress distribution along the thickness direction of underground continuous walls on their lateral deformation in excavation projects, analyzing the effects of continuous wall thickness, burial depth, and lateral support type on wall stability and suggesting optimized design parameters for continuous walls. Fattah [13] used different methods to study the surface settlement caused by tunnel excavation in the environment of viscous foundation. The results show that for soft and hard clay, the prediction of settlement trough width by finite element method has a large deviation compared with Peck’s result, but has a good consistency with Rankin’s estimate. At the same time, Fattah [14] used the finite element method to analyze the settlement of soft soil roadbed, and the results showed that the settlement reached the maximum in the early stage and decreased with the passage of time.

This study, based on a group foundation pit project closely adjacent to a subway in Changzhou, conducted three-dimensional numerical simulations using the finite element software PLAXIS 3D. Various excavation sequences were simulated to systematically investigate the deformation patterns of the subway station and surrounding ground induced by different excavation sequences in group foundation pit projects. The study identified the construction scheme with the least impact and provided safety assessments and construction guidance for existing projects. The research results can serve as references for similar projects and hold significant importance for the sustainable development of urban construction.

2. Engineering Description

The project is located in Changzhou City, Jiangsu Province. The total area of the foundation pit is 45,000 m², with an average excavation depth of 15 m. It is divided into two plots, north and south, with the subway station situated between them. The minimum horizontal clear distance between the northern side of the foundation pit’s retaining structure and the main retaining structure of the subway station is 8.5 m, within the range of the rail transit safety protection zone.

In the actual construction plan, the foundation pits on the north and south sides are divided into Groups 1 to 5 for excavation. Among them, Pit 3 is divided into four regions for excavation. The overall layout of the project is shown in Figure 1. The northern side of the foundation pit adopts bored pile + cutoff curtain enclosure, while the southern area adopts underground continuous wall enclosure. Pit 3 adopts anchor bolts + concrete support, Pits 1 and 2 adopt concrete support + steel support, and Pits 4 and 5 adopt concrete support. The basic information of each foundation pit is shown in Table 1, and the typical support cross-sections of the foundation pits are shown in Figure 2.

3. Materials and Methods

The present study employs numerical simulation methods to investigate the impact of different excavation sequences on the deformation of a subway station with shared walls. The accuracy of numerical simulation results is closely tied to the selection and parameterization of soil constitutive models. In this work, we adopt the HSS model [15], which is well suited for detailed analysis in deep excavation projects, and its model parameters are obtained through laboratory soil mechanics experiments. Utilizing the finite element software PLAXIS 3D, various excavation sequences are simulated, and the results are analyzed and discussed based on the computational findings.

3.1. Geotechnical Experiment

The experiment involved drilling combined with thin-walled soil samplers pressed into the ground using a probe to obtain soil samples from three typical soil layers in the Changzhou area of Jiangsu Province, as depicted in Figure 3. The basic properties of the soil samples are summarized in Table 2. Through conducting four types of soil mechanics experiments [16]—triaxial consolidation drainage tests, triaxial consolidation drainage and unloading tests, standard consolidation tests, and resonant column tests—the stiffness parameters $E_{50, r e f}$ , $E_{u r, r e f}$ , and $E_{o e d, r e f}$ and two small strain parameters $G_{0}$ and $γ_{0.7}$ of the HSS model were determined. The HSS model parameters of typical soil layers in the Changzhou area obtained by experiment are shown in Table 3.

3.2. Finite Element Model

In this study, the finite element software PLAXIS 3D was utilized for modeling. PLAXIS 3D approximates soil deformation and stress distribution by discretizing the continuous medium into finite elements and employing shape functions between nodes. The element type used is a 10-node tetrahedral element. The software addresses nonlinear material properties and large deformation problems through an incremental iterative method. Inter-element contact within the model is simulated either by node coupling or by introducing contact surfaces. The Hardening Soil Small Strain (HSS) model was selected to represent the soil behavior, as it effectively captures the nonlinear and anisotropic characteristics of soil under small strain conditions. The simulation is based on a three-dimensional excavation model for an actual engineering project, as depicted in Figure 4. The model dimensions are as follows: X = 350 m, Y = 300 m, Z = 50 m, where the X-axis represents the east–west direction, and the Y-axis represents the north–south direction. The top boundary conditions are completely free, the bottom boundary conditions are completely fixed, and the remaining boundary conditions are normally fixed. In order to compare the difference in the maximum surface deformation [17,18,19] between metro stations and their surroundings under different excavation sequences, six excavation conditions were set in this paper, and the specific excavation sequences are shown in Table 4.

4. Results and Discussion

4.1. Subway Station Envelope Deformation

The maximum displacements of the subway station enclosure structure accompanying the excavation of each pit to the bottom are presented in Table 5 for different scenarios. The variation curves of the maximum displacements are illustrated in Figure 5.

From Figure 5, it is evident that different excavation sequences result in minimal differences in the final displacement of the subway station enclosure structure. The maximum and minimum displacements of the enclosure structures on the north and south sides differ by 19.44% and 10.94%, respectively. There are significant differences in the displacement variation curves of the enclosure structures under different scenarios. The deformation of the enclosure structure on the south side is much greater than that on the north side. This is attributed to the fact that the south-side pit shares a section of the enclosure structure with the subway station. During excavation, the displacement and stress concentration of the soil are transmitted to the subway station enclosure structure, resulting in greater deformation on the south side. Additionally, the average excavation depth of the south-side pit is deeper, leading to greater soil displacement and stress changes in deeper layers during excavation.

4.1.1. Working Condition One, Working Condition Three, and Working Condition Six

In Scenarios One to Three and Scenario six, the excavation sequence involves first excavating the pit on the north side followed by excavation of the pit on the south side. From Figure 5, it can be observed that the deformation curves of Scenarios One and Six are nearly identical. Scenario Two shows a smaller increase in the displacement of the enclosure structure at Pit 5 compared to Scenario One, but the final deformation remains close to that of Scenario One. This indicates that within a certain range, changing the excavation sequence of adjacent pits has no significant effect on the final deformation of the subway station enclosure.

Scenario Three involves the simultaneous excavation of Pits 4 and 5, resulting in a significantly greater degree of deformation of the station enclosure compared to Scenarios One and Two. This suggests that the deformation of the subway station enclosure due to excavation of the pit group is closely related to the amount of soil unloaded at once. Adopting a “divided pit, divided step” excavation method for the pit group can effectively reduce the volume of soil unloaded at once, thereby minimizing the impact of pit excavation on the nearby subway station enclosure.

4.1.2. Working Condition Four and Working Condition Five

In Scenarios Four and Five, the excavation sequence involves first excavating the pit on the south side followed by excavation of the pit on the north side. From Figure 5, it can be observed that throughout the entire excavation process of the pit group, the displacements of the enclosure structures on both sides of the station reach their maximum values after the completion of excavation of Pits 4 and 5. As the excavation progresses in steps on the north side, the displacement values decrease accordingly. The displacement of the enclosure on the south side, being further from the excavation of the north-side pit, is less affected by the excavation of the north-side pit compared to the enclosure on the north side. This indicates that the deformation of the subway station enclosure due to the excavation of the pit group is closely related to distance.

The excavation of the pit on the south side causes significant displacement and stress changes in the soil, resulting in peak displacement of the enclosure. As the excavation progresses in the north side, the stress in the soil gradually decreases with the unloading of the soil, leading to a reduction in soil pressure on the enclosure and causing a phenomenon of deformation rebound.

Based on the above analysis, it is evident that dividing large-scale pits into multiple smaller pits for excavation can effectively reduce the adverse impact of pit excavation on the subway station enclosure structure. The extent of this impact is closely related to the volume of soil unloaded at once and the distance between the pit and the enclosure structure. For the actual project on which this study is based, if the goal is to solely control the deformation of adjacent subway station enclosure structures, the excavation sequence as shown in Scenario One should be adopted. This sequence follows the principle of “start with smaller pits, then move to larger ones; begin with pits farther away, then move to closer ones; and start with shallower pits, then move to deeper ones”, ensuring the safe operation of the subway transportation system.

4.2. Shield Tunnel Deformation

The maximum displacements of the subway shield tunnel accompanying the excavation of each pit to the bottom are presented in Table 6 for different scenarios. The variation curves of the maximum displacements are illustrated in Figure 6.

From Figure 6, it can be observed that the deformation of both the shield tunnel and the station enclosure is significantly influenced by the sequence of excavation of the pits on the north and south sides. Excavating the pit on the side where the enclosure is shared first leads to a sharp increase in displacement of both the enclosure and the shield tunnel, with a corresponding increase in the final displacement. The difference between the maximum value and the minimum value of the final deformation of the shield tunnel under different working conditions is 25.85% and 18.92%, respectively. Compared with the displacement difference of the station envelope under different working conditions, the change in excavation sequence has greater influence on the shield tunnel than on the station envelope.

4.2.1. Working Condition One, Working Condition Three, and Working Condition Six

Comparing Figure 5 and Figure 6, it is evident that except for Scenario Three, the deformation response of the shield tunnel to different scenarios aligns with that of the subway enclosure. The interchange of excavation sequences for Pits 4 and 5 did not lead to significant changes in the final deformation of the shield tunnel, except in Scenario Three. When Pits 4 and 5 are excavated simultaneously, the displacement of the shield tunnel does not increase noticeably; instead, it slightly decreases. This is primarily because, unlike the subway enclosure, the shield tunnel does not have direct contact with the soil, and the stress generated by soil unloading does not directly act on the shield tunnel. This indicates that the deformation of the shield tunnel is minimally affected by the volume of soil unloaded at once.

4.2.2. Working Condition Four and Working Condition Five

In the scenario where the excavation of the south-side pit occurs first, the deformation response of the shield tunnel aligns with that of the subway enclosure. As Pits 4 and 5 are successively excavated, the deformation increases rapidly. The final displacement values of the shield tunnel under these two scenarios are relatively close and greater than those under other scenarios. When excavating the north-side pit, as depicted in Figure 6, the excavation method of Pit 3 in segmented zones has no significant impact on tunnel deformation. However, when Pits 1 and 2 are excavated, there is a noticeable decrease in tunnel displacement. For this project, the distance of Pit 3 from the subway perimeter line is about 40 m, indicating that when the shield tunnel is located outside the affected area of the foundation pit excavation, its excavation has almost no influence on the displacement of the shield tunnel.

From the above analysis, it can be inferred that the impact of pit excavation on the deformation of the shield tunnel is greater than its impact on the deformation of the subway enclosure. The distance between the pit and the shield tunnel is the primary controlling factor influencing its deformation. For the practical engineering project under consideration in this paper, if the focus is solely on controlling the deformation of the adjacent subway station’s shield tunnel, the excavation sequence indicated by Scenario Two should be adopted.

4.3. Ground Subsidence around the Station

In the actual engineering practice, a total of six sets of surface settlement monitoring points were arranged to monitor the surface settlement between the north-side pit and the subway station in real time. In the finite element model, the calculation points for surface settlement were selected according to the actual monitoring points. The specific locations of these calculation points are illustrated in Figure 7.

The comparison of surface settlement around the subway station under different scenarios is illustrated in Figure 8.

As can be seen from Figure 8, under six different working conditions, the variation amplitude of land surface settlement is significantly greater than that of subway enclosure and shield tunnel. The surrounding surface settlement induced by Scenario Four and Scenario Five is relatively small, while the surface settlement caused by Scenario Three is relatively the largest. The surface settlement values closer to the pit side are greater than those farther away from the pit side, consistent with the pattern of surface settlement around pit excavation.

For Scenarios One and Two, where the north-side pit is excavated first followed by the south-side pit, the surface settlement curves almost overlap, indicating that simply swapping the excavation order of equidistant pits on the same side does not substantially affect surface settlement. While Scenarios Four and Five yield similar final surface settlement values, the slight differences can be attributed to variations in the distances between Pit 3 and Pits 1 and 2, respectively, and the monitoring points. In Scenario Six, where the excavation order of Pit 3 and Pits 1 and 2 is reversed compared to Scenarios One and Two, the final surface settlement values near the north-side pit’s retaining boundary decrease. This demonstrates that, within a certain range, the distance between the pit and the surface directly influences surface settlement values, but altering the excavation order of equidistant pits has minimal impact on the final surface settlement.

The final ground settlement value for Scenario Three is the highest among all scenarios, indicating that the single excavation volume is also one of the factors affecting ground settlement, and its impact is greater than the distance factor.

The response pattern of surface settlement to different excavation sequences of the group foundation pits exhibits similarities with that of the subway retaining structures. It is closely associated with factors such as the volume of earthwork excavation and the distance between the foundation pits and the surface. For the actual engineering project under consideration, focusing solely on controlling the adjacent surface settlement, the excavation sequence suggested by Scenario Five would be recommended.

5. Comprehensive Deformation Evaluation Method for Group Foundation Pit Engineering

In complex group foundation pit projects, ensuring the overall safety of the construction cannot be solely achieved by controlling a single deformation indicator. It requires a comprehensive consideration of multiple deformation indicators, including surface settlement, structural deformation, and building settlement. By integrating and controlling these deformations within safe limits, the impact of group foundation pit projects on the surrounding environment can be minimized.

5.1. Calculation Method

For the practical engineering discussed in this paper, to minimize the deformation impact of group foundation pit projects on the subway station, it is necessary to comprehensively consider three deformation indicators: “subway station structural deformation”, “shield tunnel deformation”, and “surface settlement around the subway”. By using Equation (1), different structural deformations can be comprehensively evaluated. Based on the warning values and calculated values of deformations for different structures, the deformations can be quantified and normalized, allowing for an objective comparison of different deformations.

$γ = η_{1} \cdot λ_{1} \cdot \frac{α_{1}}{β_{1}} + η_{2} \cdot λ_{2} \cdot \frac{α_{2}}{β_{2}} + \dots \dots + η_{n} \cdot λ_{n} \cdot \frac{α_{n}}{β_{n}}$

(1)

where $η$ represents the calculated weight, $λ$ represents the balance coefficient, $α$ represents the calculated deformation value, and $β$ represents the monitoring and early warning value.

5.2. Calculation Result

The monitoring warning values for subway station structural deformation, shield tunnel deformation, and surface settlement in practical engineering are shown in Table 7.

The maximum deformations of various structures under different conditions according to the calculation results are shown in Table 8.

The comprehensive deformation values under different operating conditions can be calculated using Equation (1), as shown in Table 9.

From Table 9, it can be observed that considering the three deformation indicators of “subway retaining structure deformation”, “shield tunnel deformation”, and “ground settlement around the subway”, after quantification and normalization for objective comparison, Condition 6 results in the least impact on the actual engineering subway and its surrounding environment. Compared with the original project, the comprehensive deformation is reduced by 3.8%. Therefore, for the practical engineering case relied upon in this paper, it is recommended to adopt the excavation scheme of “Pit 2 → Pit 1 → Pit 3 (Zone I → Zone II → Zone III → Zone IV) → Pit 4 → Pit 5”.

6. Conclusions

This study systematically investigated the impact of different excavation sequences on subway station deformations in group foundation pit projects. Multiple numerical simulations under various conditions were conducted using the finite element software PLAXIS 3D. Based on the calculation results, a comparison and comprehensive evaluation of the “subway retaining structure deformation”, “shield tunnel deformation”, and “surrounding ground settlement” were performed, leading to the following conclusions:

(1) During the excavation process of group foundation pits, there is a noticeable “stacking effect” in the deformation response of the surrounding soil and existing subway stations. Adopting a “sub-pit, step-by-step” excavation method can effectively reduce the impact of group foundation pit projects on the surrounding environment.

Author Contributions

Conceptualization, X.L.; methodology, X.L.; software, S.J.; formal analysis, Y.G.; investigation, Y.G.; resources, X.L.; data curation, T.L.; writing—original draft preparation, T.L.; writing—review and editing, T.L.; visualization, S.J.; supervision, S.J. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Xiongwei Li, (2023–2025) Master Teacher (master craftsman) training object project; Jiangsu Province vocational education “double teacher type” famous teacher studio project.

Data Availability Statement

The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1.General plan of the project.

Figure 2.Typical support profile of foundation pit.

Figure 3.Experimental soil samples.

Figure 4.Finite element model.

Figure 5.Maximum displacements in different stages of subway enclosure under different working conditions.

Figure 6.Maximum displacement of shield tunnel at different stages under different working conditions.

Figure 7.Land surface settlement calculation point layout.

Figure 8.Comparison of final surface settlement under different working conditions.

Table 1.Basic information of each foundation pit.

Foundation Pit	Area	Excavation Depth	Enclosure Form	Containment Depth	Internal Support Form
Pit 1	2300 m²	−8.25~−11.65 m	Bored pile + Water curtain	−14.3~−21.8 m	Concrete support + steel support
Pit 2	2400 m²	−11.7 m		−16.3~−20.3 m	Concrete support + steel support
Pit 3	9100 m²	−9.85~−11.65 m		−20.3~−21.8 m	Bolt + concrete support
Pit 4	4300 m²	−15.65~−18.65 m	Diaphragm wall	−41.5 m	Three concrete supports
Pit 5	4100 m²	−15.65~−18.65 m	Diaphragm wall	−41.5 m	Three concrete supports

Table 2.Basic index of experimental soil samples.

Serial Number	Name	Physical Properties	Moisture Content/%	Natural Unit Weight /(kN·m⁻³)	Initial Porosity Ratio	Depth of Excavation/m
①	Silty clay	Dense	22.0	19.5	0.677	2.6~6.4
②	Silt	Loose	25.0	18.9	0.779	6.6~9.4
③	Silty soil	Loose	19.8	20.4	0.577	10.1~12.9

Table 3.HSS model parameters of typical soil layers in Changzhou.

Serial Number	Name	$E_{oed, ref} / M p a$	$E_{50, ref} / M p a$	$E_{ur, ref} / M p a$	$G_{0, ref} / M p a$	$γ_{0.7} / 10^{- 4}$
①	Silty clay	4.8	5.5	32.0	25.7	4.0
②	Silt	7.1	8.7	48.0	61.8	1.9
③	Silty soil	12.9	14.2	88.9	69.1	2.2

Table 4.Excavation sequence of foundation pit groups under different working conditions.

Working Condition	Excavation Sequence
1	Pit 3 (Zone I → Zone II → Zone III → Zone IV) → Pit 2 → Pit 1 → Pit 4 → Pit 5
2	Pit 3 (Zone I → Zone II → Zone III → Zone IV) → Pit 2 → Pit 1 → Pit 5 → Pit 4
3	Pit 3 (Zone I → Zone II → Zone III → Zone IV) → Pit 2 → Pit 1 → Pit 4 and Pit 5
4	Pit 4 → Pit 5 → Pit 3 (Zone I → Zone II → Zone III → Zone IV) → Pit 2 → Pit 1
5	Pit 4 → Pit 5 → Pit 2 → Pit 1 → Pit 3 (Zone I → Zone II → Zone III → Zone IV)
6	Pit 2 → Pit 1 → Pit 3 (Zone I → Zone II → Zone III → Zone IV) → Pit 4 → Pit 5

Table 5.Maximum displacement of the south and north side of the subway station at different stages (unit: mm).

Working Condition	Structure	Construction Phase
Working Condition	Structure	1	2	3	4	5	6	7	8
1		Zone I	Zone Ⅱ	Zone Ⅲ	Zone Ⅳ	Pit 2	Pit 1	Pit 4	Pit 5
	north	3.43	3.44	3.45	3.26	3.28	3.37	6.73	8.59
	south	3.7	3.71	3.72	3.68	3.74	3.97	16.83	23.77
2		Zone I	Zone Ⅱ	Zone Ⅲ	Zone Ⅳ	Pit 2	Pit 1	Pit 5	Pit 4
	north	3.43	3.44	3.45	3.26	3.28	3.37	4.1	9.04
	south	3.7	3.71	3.72	3.68	3.74	3.97	13.32	24.6
3		Zone I	Zone Ⅱ	Zone Ⅲ	Zone Ⅳ	Pit 2	Pit 1	Pit 4 and Pit 5
	north	3.43	3.44	3.45	3.26	3.28	3.37	10.26
	south	3.7	3.71	3.72	3.68	3.74	3.97	26.37
4		Pit 4	Pit 5	Zone I	Zone Ⅱ	Zone Ⅲ	Zone Ⅳ	Pit 2	Pit 1
	north	9.02	10.58	10.05	10.07	10.09	10.13	9.83	9.62
	south	18.39	24.99	24.95	24.96	24.97	24.97	24.67	24.47
5		Pit 4	Pit 5	Pit 2	Pit 1	Zone I	Zone Ⅱ	Zone Ⅲ	Zone Ⅳ
	north	9.02	10.58	10.2	10.21	9.68	9.68	9.65	9.6
	south	18.39	24.99	24.87	24.75	24.51	24.52	24.5	24.48
6		Pit 2	Pit 1	Zone I	Zone Ⅱ	Zone Ⅲ	Zone Ⅳ	Pit 4	Pit 5
	north	3.05	2.78	3.11	3.14	3.55	3.54	6.91	8.81
	south	3.61	3.6	3.85	3.87	3.87	3.97	16.98	23.92

Table 6.Maximum displacements at different stages of the upper and lower running lines of shield tunnel (unit: mm).

Working Condition	Structure	Construction Phase
Working Condition	Structure	1	2	3	4	5	6	7	8
1		Zone I	Zone Ⅱ	Zone Ⅲ	Zone Ⅳ	Pit 2	Pit 1	Pit 4	Pit 5
	uplink	6.471	6.455	6.490	6.447	6.531	7.133	6.247	6.841
	downlink	5.876	5.881	5.851	5.852	5.801	5.676	6.751	7.729
2		Zone I	Zone Ⅱ	Zone Ⅲ	Zone Ⅳ	Pit 2	Pit 1	Pit 5	Pit 4
	uplink	6.471	6.455	6.490	6.447	6.531	7.133	6.676	6.329
	downlink	5.876	5.881	5.851	5.852	5.801	5.676	5.691	7.292
3		Zone I	Zone Ⅱ	Zone Ⅲ	Zone Ⅳ	Pit 2	Pit 1	Pit 4 and Pit 5
	uplink	6.471	6.455	6.490	6.447	6.531	7.133	6.709
	downlink	5.876	5.881	5.851	5.852	5.801	5.676	7.431
4		Pit 4	Pit 5	Zone I	Zone Ⅱ	Zone Ⅲ	Zone Ⅳ	Pit 2	Pit 1
	uplink	5.009	7.036	7.856	7.863	7.870	7.871	7.882	7.965
	downlink	3.165	4.401	9.189	9.202	9.190	9.204	9.123	8.649
5		Pit 4	Pit 5	Pit 2	Pit 1	Zone I	Zone Ⅱ	Zone Ⅲ	Zone Ⅳ
	uplink	5.009	7.036	7.858	7.996	7.941	7.949	7.930	7.953
	downlink	3.165	4.401	9.241	8.994	8.758	8.765	8.727	8.672
6		Pit 2	Pit 1	Zone I	Zone Ⅱ	Zone Ⅲ	Zone Ⅳ	Pit 4	Pit 5
	uplink	6.045	6.329	6.649	6.643	6.719	6.776	6.263	6.857
	downlink	5.901	5.671	5.490	5.652	5.654	5.671	6.695	7.675

Table 7.Early warning values of different deformation indices.

Deformation Index	Prewarning Value (mm)
The subway envelope is deformed	15
Shield tunnel deformation	10
Surface settlement	15

Table 8.Maximum deformation of different structures under different working conditions (unit: mm).

		Condition 1	Condition 2	Condition 3	Condition 4	Condition 5	Condition 6
Subway enclosure	North	8.59	9.04	10.26	9.62	9.6	8.81
Subway enclosure	South	23.77	24.6	26.37	24.47	24.48	23.92
Shield tunnel	Uplink	7.133	7.133	7.133	7.965	7.996	6.857
Shield tunnel	Downlink	7.729	7.292	7.431	9.204	9.241	7.675
Surface settlement	DB1	8.82	8.74	8.93	7.75	7.3	8.2
	DB2	16	16	16	12	9.41	12
	DB3	21	22	24	16	15	20
	DB4	14	15	17	9.52	10	14
	DB5	22	22	24	15	9.7	15
	DB6	11	11	12	7.66	7.94	10

Table 9.Maximum deformation of the south and north enclosures under different working conditions.

		Condition 1	Condition 2	Condition 3	Condition 4	Condition 5	Condition 6
Subway enclosure	North	0.086	0.090	0.103	0.096	0.096	0.088
Subway enclosure	South	0.238	0.246	0.264	0.245	0.245	0.239
Shield tunnel	Uplink	0.178	0.178	0.178	0.199	0.200	0.171
Shield tunnel	Downlink	0.193	0.182	0.186	0.230	0.231	0.192
Surface settlement	DB1	0.020	0.019	0.020	0.017	0.016	0.018
	DB2	0.036	0.036	0.036	0.027	0.021	0.027
	DB3	0.047	0.049	0.053	0.036	0.033	0.044
	DB4	0.031	0.033	0.038	0.021	0.022	0.031
	DB5	0.049	0.049	0.053	0.033	0.022	0.033
	DB6	0.024	0.024	0.027	0.017	0.018	0.022
Composite deformation		0.901	0.908	0.957	0.921	0.904	0.867

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