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Article

Numerical Investigation on the Influence of Super-Large-Diameter Shield Tunneling on Nearby Existing Metro Tunnels and the Protection Scheme

by
Yixiang Li
1 and
Zongxing Zou
2,*
1
China Railway 14th Bureau Group Shield Engineering Co., Ltd., Nanjing 211800, China
2
Badong National Observation and Research Station of Geohazards, China University of Geosciences, Wuhan 430074, China
*
Author to whom correspondence should be addressed.
Appl. Sci. 2023, 13(24), 13179; https://doi.org/10.3390/app132413179
Submission received: 31 October 2023 / Revised: 2 December 2023 / Accepted: 8 December 2023 / Published: 12 December 2023
(This article belongs to the Special Issue Urban Underground Engineering: Excavation, Monitoring, and Control)
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Versions Notes

Abstract

:
To reduce traffic congestion and meet the demand for rail transportation, the diameters of shield tunnels are constantly expanded. The super-large diameter, deep depth and long distance of super-large-diameter shield tunnels, coupled with the limitation of existing structures on underground construction space, cause many problems in the construction of these tunnels, such as affecting existing structures. This study takes a shield project in Wuhan as the research object, uses the finite element method to simulate the influence of super-large-diameter shield tunnelling on the displacement of the existing Line 5 tunnel segments, and analyzes the influence of the isolation pile arrangement and length on the isolation effect. The analysis indicates that (1) the displacement of Line 5 decreases with an increasing horizontal center distance between the tunnels and increases with an increasing vertical center distance between the tunnels, with a maximum displacement of 17.9 mm; (2) the displacement direction and position of the maximum displacement of Line 5 vary with changes in the vertical center distance between the tunnels, but remain essentially constant with changes in the horizontal center distance; and (3) the isolation piles closer to the shield tunnel improve support, with its isolation effect on the Line 5 segment becoming limited.

1. Introduction

In recent years, with the rapid development of cities, underground space has been developed and utilized, and the construction of tunnels has greatly alleviated urban traffic congestion on the ground. Due to the imperfection of space planning in the early stage of underground space development, tunnel construction often needs to cross existing pipelines. The construction of a new shield tunnel will disturb the surrounding soil layer and endanger existing buildings (structures), which also complicates the balance between the new shield tunnel construction, the existing buildings (structures) and the subsurface environment. In particular, with the vigorous development of super-large-diameter shields in recent years, the impact of super-large-diameter shields on existing buildings (structures) and the corresponding accident prevention technology need to be studied urgently.
Shield tunneling may lead to stratum loss and changes in the internal forces of the rock and soil, resulting in the deformation and displacement of the rock, soil (Benmebarek S [1], Chen Y [2], Hasanpour R et al. [3], Mohammed J et al. [4]) and surrounding buildings (structures). Therefore, many researchers have studied the influence of rock and soil mass (Finno R.J et al. [5], Lou P et al. [6], Wang J et al. [7]), surface (Bouayad D et al. [8], Cattoni E et al. [9], Hosseini S.A.A et al. [10], Li B et al. [11], Sharghi M et al. [12], Wang X et al. [13]) and adjacent building (Katebi H et al. [14], Peng F et al. [15], Shahin H.M.d et al. [16], Sirivachiraporn A et al. [17], Wang C et al. [18]) deformation on subsurface construction (Zhang J et al. [19], Zheng G et al. [20]), based on the study of the mechanical properties of rock and soil mass (Zou Z et al. [21,22]). Similarly, when a shield tunnel passes existing tunnels, railways, and pipelines, the displacement of the surrounding rock and soil will adversely affect the existing buildings (structures). Therefore, on the basis of studying the influence of shield construction on the surrounding rock and soil, researchers have mainly used physical model experiments and finite element analysis to analyze the spacing effect of new tunnels under existing tunnels (Jin D et al. [23], Kim S.H. et al. [24], Yang F et al. [25]) and the influence of shield construction on the displacement, stress (Huang Z et al. [26], Li P et al. [27], Lin X et al. [28], Liu X et al. [29]) and deformation of existing tunnels (Fang Q et al. [30], Li X et al. [31], Zhang Z et al. [32]). With the rapid development of urbanization and the surge in demand for rail transportation, super-large-diameter shields are the mainstream direction of urban underground space development at present; most of the current research focuses on small- and medium-diameter shields (<6 m), but super-large-diameter shield research is becoming more common.
In the process of shield construction, causing disturbance to the surrounding rock and soil mass is inevitable, leading to the risk of the destruction of the original underground structures. To ensure the safety of constructing a new tunnel and the operation of the existing structures, it is necessary to implement measures for accident prevention and control. At present, the commonly used prevention and control measures are grouting reinforcement, isolation piles and diaphragm walls. According to the partitioning effect and economic considerations of these prevention and control measures, isolation piles are often selected for partitioning. During foundation pit excavation and shield construction, isolation piles are often used to protect the surface (Nie G et al. [33], Wei G et al. [34]), adjacent buildings (Yao A et al. [35,36]) and pile foundations (Tang J et al. [37]). In recent years, isolation piles have gradually been adopted in shield construction to protect existing subway lines (Lv J et al. [38], Schroeder F.C et al. [39]), but there are relatively few studies on this practice. Therefore, this paper describes the influence of super-large-diameter shield construction on existing lines and the application of isolation piles in protecting existing lines.
Taking the shield project in Wuhan as an example, this study analyzed the spatial relationship between the south extension shield tunnel of Heping Avenue and the existing Line 5, studied the influence of super-large-diameter shield excavation on the segment of the existing subway tunnel and the reinforcement effect of isolation piles, and considered the actual conditions of the project to propose a reinforcement scheme for the existing nearby line.

2. Case Introduction

2.1. Basic Characteristics of the Shield Tunnel of South Heping Avenue and Line 5 in Wuhan

The South Extension Tunnel of Heping Avenue in Wuhan adopts a single-hole double-deck design for a two-way six-lane tunnel. The upper tunnel is 2292 m long, and the lower tunnel is 2486 m long (Figure 1). The line is composed of a ground section and a tunnel section. The tunnel shield section will be constructed by a slurry balance shield machine. The inner diameter of the shield segment is 14.20 m, the outer diameter is 15.40 m, the shield diameter is 15.96 m, the segment thickness is 600 mm, and the strength grade is C60 (the compressive strength of concrete cured for 28 days under standard conditions reaches 60 MPa) [40,41], as shown in Figure 2.
The shield will closely pass Line 5 after starting. The inner diameter of the tunnel segment of Line 5 is 5.5 m, the outer diameter is 6.2 m, and the segment thickness is 350 mm. The distance between the centers of the two tracks of Line 5 is 11.22 m. The sections of Line 5 affected by the construction of the south extension shield tunnel are mainly Simenkou Station and Tanhualin Station (Figure 1). When passing through Tanhualin Station, the shield tunnel will be relatively close to Line 5.

2.2. Spatial Relationship between the Shield Tunnel and Line 5

In some sections of Heping Avenue South Extension Tunnel in Wuhan, the shield tunneling will be nearly parallel with the existing subway Line 5, so the shield construction faces multiple challenges. Line 5, as the first fully automatic driverless subway line in Wuhan, is an important passenger transportation corridor along the Yangtze River. Metro operation has many requirements for tunnel displacement. Unmanned driving has more stringent requirements for the tunnel environment, resulting in higher requirements for the shield construction of the Heping Avenue South Extension Tunnel. In particular, at the early stage of the forward driving section of the north shield tunneling well, the distance between the tunnel to be constructed and Line 5 is very small, whether in the horizontal direction or the vertical direction. The distance between the tunnels in some sections is less than 10 m, which is less than twice the diameter of the shield tunneling tunnel. Line 5 is parallel to the planned southern extension of Heping Avenue on the east side.
As shown in Figure 1, according to the different geotechnical properties in the section, the strata through which the shield passes are divided into intensely weathered, moderately weathered and slightly weathered rock sections. Considering that the engineering geological conditions in the intensely weathered area are the worst, the shield along this section will be closest to Line 5. Compared with other sections, the excavation construction in this section will have a greater impact on the stratum and the existing Line 5. Therefore, in this study, the intensely weathered section is selected to carry out research on the impact of further construction and accident prevention measures.
The intensely weathered section is the shield starting shaft area, which is close to Tanhualin Station, with a horizontal spacing of approximately 9.4~12.9 m. The shield tunnel will be nearly parallel to Line 5 in the horizontal direction. The vertical spacing will be approximately −5.92–4.5 m (positive indicates that the shield tunnel top is below Line 5, and negative indicates that it is above Line 5). With shield tunneling, the tunnel will gradually extend downward, away from Line 5. The relationship between the cross sections of the two projects is shown in Figure 2.

2.3. Geological Conditions

In the intensely weathered area, the shield will mainly pass through intensely weathered silty clay, heterogeneous sandstone, siliceous rock and carbonaceous shale. The design length of the shield through the strata is approximately 209.42 m. The stratigraphic layout of the I-I’ profile (Figure 1) in the strong weathering section was selected for study, and the physical and mechanical parameters of the relevant lithology are shown in Table 1.

3. Simulation of the Influence of Shield Tunneling on Existing Subway Lines

Here, the finite element theory was used for simulation. The principle and methodology of the adopted finite element methods are described in Reference [42].

3.1. Simulation Scheme

To study the spatial relationship between the proposed shield-excavated tunnel and the original Line 5 and the root of the influence of the displacement of Line 5, according to the spatial relationship between the shield tunnel and Line 5 in the intensely weathered section, the numerical simulation scheme is shown in Table 2. The spatial relationship between the shield-excavated tunnel and the existing Line 5 is expressed as follows: (1) the horizontal distances between the center of the Line 5 tunnel and the center of the shield tunnel L2; (2) the vertical distances between the center of the Line 5 tunnel and the center of the shield tunnel V2 (hereinafter referred to as the horizontal center distance between the tunnels L2 and the vertical center distance between the tunnels V2, respectively). Combined with the actual spatial relationship between the shield-excavated tunnel and Line 5, the horizontal positions of the shield and Line 5 were set in a series of simulations that changed at an interval of 2 m; four groups of simulations were considered, namely, 20 m, 22 m, 24 m, and 26 m distances. A vertical interval of 2 m was used in another series of simulations; for this, 5 groups of simulations were considered, i.e., 8 m, 10 m, 12 m, 14 m, and 16 m, for a total of 20 groups.

3.2. Model Establishment

Considering the boundary effect of the tunnel excavation stress adjustment, the boundary position of the numerical model is determined as follows: the left boundary is 32 m from the outer diameter of the west line of Line 5; the right boundary and the lower boundary are 40 m and 32 m from the outer diameter of the excavation tunnel, respectively; and the upper boundary is 15 m from the center of the Line 5 tunnel. The model size of the intensely weathered section is shown in Figure 3:
According to the determined model size and the relative spatial relationship between Line 5 and the shield tunnel, a two-dimensional model is established. The Mohr–Coulomb failure criterion is used in the simulation to evaluate the fatigue life of the material. The upper surface of the model is the surface of the earth, which can be considered to be only affected by its weight, so the top surface of the model is set as a free boundary. In practical engineering, a foundation is an elastic body in infinite space, which is reflected in the model as constraints on all surfaces except the top surface, that is, normal constraints on the surrounding sides and horizontal and vertical displacement constraints on the bottom.
Mesh size is a parameter for numerical simulation. To ensure balance between the calculating accuracy and simulation efficiency, the mesh size is set to 0.5 for division. The specific two-dimensional numerical calculation model is shown in Figure 4.

3.3. Analysis of Influence Numerical Simulation Results

According to the above simulation scheme, the displacement of the Line 5 segment under different shield positions is obtained, as shown in Figure 5.
As shown in Figure 5, when the horizontal center distance between the tunnels L2 is the same, the overall displacement trend of the Line 5 segment increases with the vertical center distance between the tunnels V2, and the displacement direction of the Line 5 segment gradually shifts to the lower right. Even if the vertical center distance between the tunnels V2 increases, the Line 5 segment is still in the range of stress disturbance caused by shield excavation due to the large diameter of the shield tunnel excavation. The missing stratum caused by shield excavation causes the redistribution of stress in the stratum. The soil near the segment tends to slide toward the inner part of the tunnel, and the sliding direction generally points to the center of the shield tunnel. As the vertical center distance between the tunnels V2 increases, the segment displacement direction gradually shifts downward and to the right.
Figure 5 shows that, when the vertical center distance between the tunnels V2 is the same, with the increase in the horizontal center distance between the tunnels L2, the overall displacement trend of the Line 5 segment decreases. The position of the maximum displacement is basically unchanged, and the maximum displacement shows a decreasing trend. However, the displacement direction of the Line 5 segment does not change significantly. This indicates that with the increase in the horizontal center distance between the tunnels L2 (the shield tunnel moves to the right horizontally), the stress disturbance range formed by the shield excavation shifts to the right, and the influence on Line 5 is reduced. Moreover, the change in the horizontal center distance between the tunnels L2 does not cause a large deflection in the displacement direction of the segment, but the deflection in the displacement direction is highly sensitive to the change in the vertical center distance between the tunnels V2.
As shown in Figure 6, with the increase in the vertical center distance between the tunnels V2, the maximum point of the displacement of the east line of Line 5 gradually moves upward, and the maximum displacement of the Line 5 segment shows an increasing trend. Thus, with the increase in the vertical center distance between the tunnels, the stress disturbance range caused by shield excavation shifts downward, and the influence effect on the displacement disturbance range of Line 5 decreases. Therefore, the disturbance of the soil mass under the Line 5 segment decreases, and the influence factor of the maximum displacement point becomes the self-weight extrusion of the soil mass above the segment.
Figure 7 shows the contour map of the change in the maximum displacement of the Line 5 segment with the change in the spatial relationship between Line 5 and the shield tunnel. The smaller the horizontal center distance between the tunnels L2 and the greater the vertical center distance between the tunnels V2, the greater the overall displacement of the Line 5 segment. The maximum value occurs at the lower left corner of L2 = 20 m, V2 = 16 m, and the displacement is 17.9 mm. The greater the horizontal center distance between the tunnels L2, the smaller the vertical center distance between the tunnels V2, and the smaller the displacement of the Line 5 segment. The minimum displacement appears in the upper right corner of L2 = 26 m, V2 = 8 m, and this displacement is only 2.8 mm.
According to the above numerical simulation results, it can be concluded that the displacement of large-diameter shield tunneling has the following characteristics.
(1)
The overall displacement trend of adjacent segments is affected by the vertical center distance between the tunnels V2, which is greater than the horizontal center distance between the tunnels L2.
(2)
The position of the maximum displacement of the adjacent segment moves up toward the vault with the increase in the vertical center distance between the tunnels V2 and is basically not affected by the horizontal center distance between the tunnels L2.
(3)
The vertical center distance between the tunnels V2 is an important factor affecting the displacement direction and deflection of adjacent segments, and the horizontal center distance between the tunnels L2 has little influence on it.
(4)
As the vertical center distance between the tunnels V2 increases, the overall displacement of adjacent segments increases; as the horizontal center distance between the tunnels L2 increases, the overall displacement of adjacent segments decreases.

4. Simulation of the Reinforcement Effect of Isolation Piles

4.1. Simulation Scheme

In the simulation of isolation piles, four rows of Φ180 composite bolt piles are arranged in the plum blossom type with a horizontal and longitudinal spacing of 250 mm × 250 mm, a pile diameter of 180 mm, and a steel cage welded with Φ20 steel bars built in. The top of the composite bolt pile is connected with a 500 × 1200 mm crown beam made of C30 concrete (the compressive strength of concrete cured for 28 days under standard conditions reaches 30 MPa) [1,37]. See Figure 8 for details.
According to the numerical simulation results of the influence of shield tunnel excavation on Line 5, when the horizontal center distance between the tunnels L2 is 20 m and the vertical center distance between the tunnels V2 is 16 m, the excavation of the shield tunnel has the greatest impact on the existing Line 5, and the maximum displacement of the Line 5 segment reaches 17.92 mm. Therefore, this working condition is selected for numerical simulation to analyze the supporting effect of an isolation pile.
The simulation scheme in this section mainly analyzes the influence of the length of the isolation pile and the distance between the isolation pile and the outer diameter of the east line of Line 5 on the displacement and reinforcement of Line 5, and the simulation scheme is shown in Table 3.
According to the above simulation scheme, a schematic diagram of the spatial distribution of the isolation pile position is shown in Figure 9.

4.2. Influence of Different Factors on the Control Effect of Isolation Piles

4.2.1. Analysis of the Control Effect on Isolation Piles under Different Pile Lengths

It can be seen from Figure 10 that under the same pile length condition, the farther the isolation pile is from the east line of Line 5 and the closer it is to the shield tunnel, the smaller the maximum displacement of the Line 5 segment, and the better the support effect. Due to the application of the isolation pile, the overall displacement direction of the Line 5 segment is deflected, and its deflection angle is related to the distance between the isolation pile and the east line of Line 5. This shows that the isolation pile can effectively reduce the sinking of Line 5.

4.2.2. Analysis of the Control Effect of Isolation Piles under Different Horizontal Distances between the Isolation Pile and the Outer Diameter of the East Line of Line 5

As shown in Figure 11, with the same horizontal distance between the isolation pile and the outer diameter of the east line of Line 5, the maximum displacement of the Line 5 segment decreases as the pile length increases. However, when the pile reaches a certain length, the maximum displacement of the Line 5 segment gradually increases, and the pile length at the inflection point is 52 m. The simulation results show that when the pile length is 52 m, the maximum displacement of the Line 5 segment is the smallest, which is 5.75 mm. Moreover, the displacement direction of Line 5 is deflected counterclockwise, and the longer the pile length is, the more obvious the deflection angle, indicating that the segment displacement of Line 5 can be reasonably controlled according to the length of the isolated pile within the effective pile length of the isolation pile.
Comparing the supporting situation and unsupported conditions in Figure 10 and Figure 11 shows that the displacement of the Line 5 segment is significantly reduced after the application of the isolation pile, indicating that the isolation pile is very effective in the isolation of the shield excavation from the existing Line 5.

5. Discussion

To reduce the impact on Line 5 during the construction of the Heping Avenue Shield Tunnel, the isolation pile construction scheme was designed based on the simulation analysis of the control effect of an isolation pile, the ground space conditions and the cost of an isolation pile.
Due to the densely distributed aboveground buildings around the Heping Avenue South Shield Tunnel and Line 5, the space for the implementation of isolation piles from the ground is limited, and there is no site available for large-scale bored pile construction; however, the microcomposite bolt pile requires a small construction site, has a convenient construction scheme, and uses a multirow plum blossom pile arrangement, which can ensure the isolation stiffness requirements. Therefore, the project adopted microcomposite bolt piles, and the pile layout is the same as that used in the simulation, as shown in Figure 8.
In the isolation pile area shown in Figure 12, microcomposite bolt piles with a diameter of Φ180 and lengths of 25 m, 26 m, and 28 m are adopted. The bolt piles are arranged in four rows of plum blossom patterns, the spacing is 0.25 m × 0.25 m, and the top of the pile is applied with a 0.5 m × 1.2 m crown beam. To monitor the impact of the construction of the backing structure after the isolation piles were applied, some monitoring points were arranged on the surface and buildings near the isolation pile, and the monitoring data are shown in Figure 13.
As can be seen from Figure 13, the displacement of each monitoring point is not large, and the surface displacement has changed greatly from 10 to 13 December 2021, but the order of magnitude is small, and the overall impact is not great.
According to the monitoring data, after the application of the isolation piles, the settlement of the surrounding surface and buildings was within a reasonable range, so the effectiveness of the method is proven, and the installation of the isolation piles can ensure the safe and smooth passage of the shield tunnel.
In this paper, the impact of super-large-diameter shield construction on the existing Line 5 is studied by means of numerical simulation, and the reinforcement effect of different protection schemes on the existing line is studied, but there are still some problems in this study, which need to be further studied. In this paper, only the pile length and the horizontal position of the single pile are considered when simulating the influence of different isolation schemes on the isolation effect of the existing lines, and the pile spacing and pile diameter of multiple piles should be considered in further research. In this study, a two-dimensional finite element numerical simulation method is adopted; however, in the simulation of the shield construction process, three-dimensional numerical simulation can fully take the shielding process into account, and therefore, it will make the calculation results more accurate. Thus, it is recommended that the three-dimensional numerical simulation is conducted in further research work.

6. Conclusions

Based on the analysis of engineering geological conditions, this paper carries out a finite element simulation study of shield excavation, analyzes the influence of future super-large-diameter shield tunneling on the existing Line 5, and proposes an optimization method for installing isolation piles in the key areas that will be affected by shield construction. The main conclusions are as follows:
(1)
The overall displacement trend of the Line 5 segment decreases with an increasing horizontal center distance between the tunnels and increases with an increasing vertical center distance between the tunnels. The maximum value occurs at the lower left corner of L2 = 20 m, V2 = 16 m, and the displacement is 17.9 mm.
(2)
The displacement direction and the position of the maximum displacement of the Line 5 segment will continue to change with the change in the vertical center distance between the tunnels, but basically will not change with the change in the horizontal center distance between the tunnels.
(3)
When the lengths of the isolation piles are the same, the closer an isolation pile between the two tunnels is to the shield tunnel and the farther it is from the east line of Line 5, the smaller the maximum displacement of the Line 5 segment, and the better the support effect. When the distance between an isolation pile and the two tunnels remains unchanged, when the length of the isolation pile reaches a certain length (52 m), the isolation effect of the isolation pile on the Line 5 segment becomes limited.
(4)
The surface monitoring data show that the isolation pile support effectively controls the displacement of the surrounding soil and buildings, and is an effective means to protect the existing structures.

Author Contributions

Conceptualization, Y.L.; Software, Y.L.; Formal analysis, Z.Z.; Investigation, Y.L.; Resources, Y.L.; Writing—original draft, Z.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Scientific and technological innovation projects of China Railway 14th Bureau Group Shield Engineering Co., Ltd. (No. 2021306687).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within the article.

Acknowledgments

The authors wish to thank Luoxia Li and Haojie Duan of China University of Geosciences (Wuhan) for their assistance in the preparation of this article.

Conflicts of Interest

Author Yixiang Li was employed by China Railway 14th Bureau Group Shield Engineering Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The authors declare that this study received funding from Scientific and technological innovation projects of China Railway 14th Bureau Group Shield Engineering Co., Ltd. (No. 2021306687). The funder was not involved in the study design, collection, analysis, interpretation of data, the writing of this article or the decision to submit it for publication.

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Applsci 13 13179 g001
Figure 1. Spatial relationship between the South Extension Tunnel Project of Heping Avenue and Line 5. (a) Profile view of the spatial relationship between the two tunnels; (b) plane view of the spatial relationship between two tunnels.
Figure 1. Spatial relationship between the South Extension Tunnel Project of Heping Avenue and Line 5. (a) Profile view of the spatial relationship between the two tunnels; (b) plane view of the spatial relationship between two tunnels.
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Figure 2. Cross-sectional spatial relationship between the shield section of the South Extension Tunnel and Line 5 (unit: mm).
Figure 2. Cross-sectional spatial relationship between the shield section of the South Extension Tunnel and Line 5 (unit: mm).
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Figure 3. Schematic diagram of the model size in the intensely weathered section.
Figure 3. Schematic diagram of the model size in the intensely weathered section.
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Figure 4. Model meshing diagram (horizontal displacement constraints on the left and right sides, horizontal and vertical displacement constraints on the bottom).
Figure 4. Model meshing diagram (horizontal displacement constraints on the left and right sides, horizontal and vertical displacement constraints on the bottom).
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Figure 5. Line 5 displacement change diagram.
Figure 5. Line 5 displacement change diagram.
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Figure 6. Variation in the position of the maximum segment displacement of Line 5 with excavation depth. (a), (b), (c), (d) display the maximum displacement with L2 of 20 m, 22 m, 24 m, and 26 m, respectively.
Figure 6. Variation in the position of the maximum segment displacement of Line 5 with excavation depth. (a), (b), (c), (d) display the maximum displacement with L2 of 20 m, 22 m, 24 m, and 26 m, respectively.
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Figure 7. Contour map of the maximum segment displacement of Line 5.
Figure 7. Contour map of the maximum segment displacement of Line 5.
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Figure 8. Schematic diagram of the pile section. (a) Layout of isolation piles; (b) spatial relationship between the South Extension Tunnel Project of Heping Avenue and Line 5; (c) size of the isolation pipe.
Figure 8. Schematic diagram of the pile section. (a) Layout of isolation piles; (b) spatial relationship between the South Extension Tunnel Project of Heping Avenue and Line 5; (c) size of the isolation pipe.
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Figure 9. Schematic diagram of the spatial distribution of the isolation pile position.
Figure 9. Schematic diagram of the spatial distribution of the isolation pile position.
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Figure 10. Change in the maximum displacement of Line 5, with a horizontal distance between the isolation pile and the outer diameter of the east line of Line 5 under different pile lengths.
Figure 10. Change in the maximum displacement of Line 5, with a horizontal distance between the isolation pile and the outer diameter of the east line of Line 5 under different pile lengths.
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Figure 11. Variation in the maximum displacement of the Line 5 segment, with the pile length at a different horizontal distance between the isolation pile and the outer diameter of the east line of Line 5.
Figure 11. Variation in the maximum displacement of the Line 5 segment, with the pile length at a different horizontal distance between the isolation pile and the outer diameter of the east line of Line 5.
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Figure 12. Plan view of the layout of the isolation piles and the location of the monitoring points.
Figure 12. Plan view of the layout of the isolation piles and the location of the monitoring points.
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Figure 13. (a) Monitoring data of surface monitoring points; (b) monitoring data of building monitoring points.
Figure 13. (a) Monitoring data of surface monitoring points; (b) monitoring data of building monitoring points.
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Table 1. Physical and mechanical parameters of the soil and rock in the intensely weathered areas.
Table 1. Physical and mechanical parameters of the soil and rock in the intensely weathered areas.
LithologyThickness/mModulus of Elasticity/kPaPoisson’s RatioUnit Weight kN/m3Cohesive Force kN/m2Friction Angle/°
Miscellaneous fill, plain fill512,0000.3519.51015
Silty clay712,0000.3519.92312
Clay mixed with gravelly soil320,0000.3018.83915
Intensely weathered chert-bearing graywacke10.5180,0000.2821.01235
Intensely weathered siliceous rock11200,0000.2821.51035
Intensely weathered carbonaceous shale13.5150,0000.2822.01235
Moderately weathered marl24400,0000.2427.02528
Table 2. Numerical simulation scheme.
Table 2. Numerical simulation scheme.
Numerical Simulation GroupThe Shield Mainly Crosses the StrataLine 5 Mainly Crosses the StrataLine 5 Depth/mHorizontal Distance/mBurial Depth of Shield/mVertical Distance between the Two Tunnel Centers V2/m
Line 5 Outer Diameter Top Distance from the Surface h1/mLine 5 Center Distance from the Surface h2/mHorizontal Distance between the Two Tunnel Centers L2/mDistance between the Outer Diameters of the Two Tunnel Segments L1/mDistance from the Top of the Outer Diameter of the Shield Tunnel to the Surface H1/mBurial Depth of the Shield Tunnel Center H2/m
NS1-1Intensely weathered argillaceous sandstone, carbonaceous shale, siliceous rockclay11.915201015238
182510
212712
242914
273116
NS1-2221215238
182510
212712
242914
273116
NS1-3241415238
182510
212712
242914
273116
NS1-4261615238
182510
212712
242914
273116
Table 3. Isolation pile simulation scheme.
Table 3. Isolation pile simulation scheme.
Model NamePile Length H/mThe Distance between the Isolation Pile and the Outer Diameter of the East Line of Line 5 S/m
NS2-1281234
567
NS2-2361234
567
NS2-3441234
567
NS2-4521234
567
NS2-5601234
567
NS2-6681234
567
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Li, Y.; Zou, Z. Numerical Investigation on the Influence of Super-Large-Diameter Shield Tunneling on Nearby Existing Metro Tunnels and the Protection Scheme. Appl. Sci. 2023, 13, 13179. https://doi.org/10.3390/app132413179

AMA Style

Li Y, Zou Z. Numerical Investigation on the Influence of Super-Large-Diameter Shield Tunneling on Nearby Existing Metro Tunnels and the Protection Scheme. Applied Sciences. 2023; 13(24):13179. https://doi.org/10.3390/app132413179

Chicago/Turabian Style

Li, Yixiang, and Zongxing Zou. 2023. "Numerical Investigation on the Influence of Super-Large-Diameter Shield Tunneling on Nearby Existing Metro Tunnels and the Protection Scheme" Applied Sciences 13, no. 24: 13179. https://doi.org/10.3390/app132413179

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