Analysis of micro-disturbance drilling pipe pre-reinforcement method for deep excavations above operating subway tunnels

Abstract

This paper uses the three-dimensional numerical simulation method to analyze the first deep foundation pit project directly above the operating subway in a certain area. The monitoring data were compared with the numerical results to verify the accuracy of the numerical model, and then a series of analyses were performed. The soil beneath the tunnel is the most direct object of tunnel deformation caused by the excavation of deep foundation pits above the tunnel. The rebound deformation of the soil beneath the tunnel forces the tunnel to produce an upward deformation cooperatively. Therefore, after comparing and analyzing the prevention criteria of traditional excavation measures, which were not sufficient for this project, a new method of fortification is proposed for the foundation pit above the tunnel, which is called the micro-disturbance drill pipe pre-reinforcement method (PRM) for the soil beneath the tunnel. The comprehensive parameter analysis of the PRM shows that the PRM can effectively reduce the uplift value of the tunnel, and the reinforcement effect is obvious.

Graphical abstract

Keywords

failure analysis / tunnel damage / deep excavation / numerical simulation / comparative analysis

1 Introduction

Nowadays, the subway has become an essential way to travel in large and medium-sized cities. The safety operation and deformation control standards of the subway are strict. However, the current prevention and control measures for excavation along the subway cannot effectively control the deformation caused by excavation [1–4]. Therefore, it is particularly vital to explore more effective prevention and control measures to ensure the safe operation of the subway [5–7].

Numerical simulations, which can simulate processes and analyze the results of different types of control measures in advance, have become an essential research method in this area [8–10]. Moreover, it has been shown that different excavation measures have different effects on the tunnel [11–14]. Chen [15] proposed a combined construction technology that had been developed for use in underground spaces. Li et al. [16,17] studied the comparison and optimization of construction methods for engineering projects in practice. Liu et al. [18] performed numerical simulations before the construction of the project and proposed to correct the deformed tunnel using perturbative grouting. In addition, on-site monitoring can intuitively and effectively observe the deformation values and displacement status of the tunnel [14,19–22].

Taking a deep foundation pit project directly above a subway tunnel in operation as an example, this paper compares and analyzes the traditional prevention and control measures of foundation pit excavation, and proposes a new micro-disturbance prevention and control measure for the substratum of the subterranean layer pre-reinforced by the advance drilling pipe. The control measure was discussed and the control effect of the measure on the deformation of the subway tunnel caused by excavation was discussed and quantified.

2 Overview of the project

2.1 Deep excavation of the basement

As shown in Fig.1, the foundation pit is divided into two construction phases. The first stage (Pit-1) has an excavation depth of −11.3 m, and two-story basements and 6 main buildings with a length of almost 100 m are planned to be built; the second stage (Pit-2) has an excavation depth of −7.05 m, it is used to build the basement, which is also the focus of this paper. The subway is located just 13 m below the excavation area.

2.2 Existing tunnels of Metro Line 3

Metro Line 3, which was completed and opened to traffic in 2016, was constructed using a mining method, with sections passing through a formation consisting mostly of silty clay and silt, with underground water buried at depths of −25 to −30 m. The length of the affected subway line is about 250 m. As shown in Fig.2, the Φ600@900 mm retaining piles are used on both sides of the tunnel with a length of 18 m. The retaining pile is about 15 m from the outermost edge of the tunnel, and the bottom of the foundation pit is about 5 m from the subway tunnel. Due to the nearly 10 mm upward deformation of the tunnel during the site formation work, Metro Group took this very seriously. At the same time, the project is significant because it is the first in the region to excavate a large area directly above an operating subway.

3 Site monitoring

3.1 Vertical displacement of the track bed

Prior to the excavation of Pit-2, which lies directly above the subway, Pit-1, a lateral area of the subway, is excavated (as shown in Fig.1). During the Pit-1 phase, the Metro Group conducted monitoring inside the subway tunnel. The aim is to monitor the displacement response of the tunnel during the excavation of Pit-1 in the lateral area of the subway. The monitoring data of the Pit-1 cannot only be used to verify the correctness of the numerical simulation of the project, but also can be used as the pre-forecast data to guide the excavation work of the Pit-2 area. Through the field monitoring data of the Pit-1, the theoretical relationship between excavation depth, excavation volume, tunnel distance and other parameters can be established under the condition of the site, according to which the tunnel buoyage during Pit-II excavation can be analyzed and predicted. This enables a comprehensive safety assessment of the subway when Pit-2, the area directly above the subway, is excavated. Fig.3 shows the vertical displacement monitoring data of the tunnel bed during the excavation of Pit-1.

Among them, Pit-1-stage I and Pit-1-stage III are the excavations outside the subway protection red line (50 m), and Pit-1-stage II and Pit-1-stage IV are the excavations inside the subway protection red line (35–50 m). The response degrees of the subway vary depending on the proximity degree of the lateral excavation. Fig.3(a) and Fig.3(b) demonstrate that during the initial excavation stage of Pit-1-stage I, the down-track and up-track tunnels experienced minor settlement. The Pit-1-stage II excavation, which is closer to the tunnel, results in a more dramatic subway response. The data within the red circle in Fig.3 shows a significant difference in the displacement of the track bed at each monitoring section of the subway at this time. During the excavation of Pit-1-stage III and Pit-1-stage IV, the subway experienced continuous floating, with a maximum displacement value of 2 mm. Analysis of the excavation monitoring data from Pit-1 suggests that the displacement of the subway track bed will be more significant during the excavation of Pit-2.

3.2 Vertical convergence

The continuous excavation in the Pit-1 area may result in uneven deformation of the subway. To ensure the safe operation of the subway, it is necessary to analyze the vertical convergence of the subway. As shown in Fig.4, the red circle is the excavation data of Pit-1-stage II area, which leads to large fluctuation of vertical tunnel convergence. Regarding the excavation of the entire Pit-1 area, the convergence rate shows that the down-track subway as a whole is in vertical compression. The up-track tunnel has undergone a convergence state transition, which increases the likelihood of cracks in the subway lining.

3.3 Investigation on the service status of the subway

Before excavating Pit-2, an investigation was conducted to better understand the safety of the subway lining, as depicted in Fig.5. The investigation aimed to assess the service state of the subway lining. Fig.6 displays the scanning profile of a typical section of the down-track tunnel. The horizontal clearance of the subway increases progressively due to lateral excavation. Fig.6 displays the distribution of the mean structural strength of the subway tunnels. It is evident that the structural strength of the up-track tunnels is slightly higher than that of the down-track tunnels. This also indicates that more attention should be paid to the structural safety of the down-track tunnel during the excavation of Pit-2. The statistical diagram of subway lining cracks in the affected area before and after Pit-1 excavation is presented in Fig.7. The data indicate that lateral excavation results in a notable expansion of both the width and quantity of cracks in the subway lining. Local cracks and water leakage in the tunnel are visible in Fig.8.

According to the investigation and statistics, the main diseases of subway tunnels are cracks and water seepage, accompanied by local concrete crushing and falling blocks, as shown in Fig.9. Among them, the annular cracks in the up-track tunnel are more significant, and most of them are newly added cracks (short and numerous cracks, without leakage). The lateral deformation of the tunnel is caused by the initial close-range lateral excavation, which results in the formation of new cracks. The down-track tunnel is mainly characterized by water leakage, which is a historical disease with fewer cracks, indicating better safety and service performance. Based on the monitoring data and investigation of the lining service condition, it is evident that the excavation of the lateral area of the tunnel, Pit-1, has caused irreversible damage to the tunnel. To ensure the safety of the operating subway, it is necessary to conduct a comprehensive and accurate analysis of the construction method before officially excavating Pit-2 in the area directly above it.

4 Numerical modeling and validation

4.1 Numerical modeling

To accurately simulate the deformation state of the tunnel under different prevention and control measures, the analysis was performed using the finite element software ABAQUS 2021 [23–27]. The model size is 700 m × 450 m × 50 m and consists of 360806 solid elements. The transverse and bottom boundaries are set with the corresponding constraints, respectively, without considering the effect of groundwater. The model includes engineering piles, retaining piles, prestressed anchor cables, and down and up track tunnels, the exact arrangement of which is shown in Fig.10 [28–30]. This paper adopts the modified Cambridge constitutive model. As most of the soil at the project site is silty clay, the modified Cambridge constitutive model is the most typical critical state soil mechanical constitutive relation, which better describes the mechanical properties of the clay during unloading and loading. Meanwhile, its corresponding mechanical parameters are also relatively easy to obtain. The constitutive parameters used in this model were obtained through a series of experiments such as the indoor triaxial compression tests, but this is not the focus of this paper, therefore the relevant experiments are not included in this paper. The physical parameters used in the model are given in Tab.1. As shown in Fig.2, the tunnel is buried at a depth of about 14 m underground. According to previous geological survey data, the groundwater level in this area is at a depth of 30 m below the surface. Therefore, the model does not consider the factor of groundwater.

4.2 Numerical results and validation

Field monitoring can be used to learn the health of the tunnel promptly [31–34]. Before the official excavation of Pit-2, Pit-1 was monitored in the subway tunnel. To verify the accuracy of the numerical simulations, monitoring data of 4–5 typical sections of the down-track and up-track tunnels were selected as model validation data [35]. Fig.11 shows the excavation process and results of Pit-1. When using on-site monitoring data to validate the numerical model, corresponding to the specific analysis steps in implicit analysis based on the actual time nodes at different stages of on-site construction, the reliability and accuracy of the numerical model are verified by comparing the numerical results at the corresponding locations at different analysis steps with the monitoring data at the same locations at the corresponding time nodes. As shown in Fig.12, by comparing the actual monitoring results with the numerical simulations, it can be seen that the deformation law is consistent with the displacement values and the accuracy of the model has been verified, providing excellent high-level conditions for the Pit-2 excavation simulation.

5 Traditional prevention and control measures

5.1 Direct excavation

As a result of the site formation work, the tunnel has generated an upward displacement of approximately 10 mm. At the request of the Metro Group, a control value of 10 mm was used for the deformation of the subway in this section. It analyzes the direct excavation (DE) of a large area without any prevention and control measures [36,37], as shown in Fig.13, which shows the maximum displacement and deformation curves of the up-track tunnel vault and arch base for different excavation analysis steps. It can be seen that the tunnel responds violently when excavated directly above it, with a maximum displacement value of about 25 mm, and this prevention and control measure does not meet the requirements of metro protection.

5.2 Different excavation sequences

Excavation is a complex process of mechanical changes, and different sequences of excavations directly affect the mechanical response of the foundation pit. To this end, several prevention and control measures commonly used in foundation pit excavation are analyzed. As shown in Fig.14, DE, Block Continuous Excavation (BCE, dividing the excavation area into equally sized blocks, and then excavating the divided blocks in a certain order) [38,39], Block Skip Excavation (BSE, dividing the excavation area into equally sized blocks and then using a staggered excavation sequence) [16,40], and Reserved Core Soil Excavation (RCE, dividing the excavation area into equally sized blocks, first excavating the blocks at both ends and finally excavating the soil in the middle area) [41] were simulated respectively. It can be seen that the DE method has the largest shift and the reserved core soil method has the smallest shift. However, considering only different sequences of excavations, the maximum displacement of the tunnel is between 20 and 25 mm, which does not meet the deformation control requirements of the project.

The displacement state of the tunnel shifts with time at different excavation stages [42,43]. As shown in Fig.15, these are the time-history curves of the tunnel displacement at different excavation stages when the RCE method is employed. In the RCE method, the soil within 70 m of the two ends is first excavated in blocks, and then the soil within 100 m of the reserved middle core is excavated. It can be seen that the tunnel responds sharply as the excavation process continues to advance, that is, once the area directly above the excavation is reached, the tunnel immediately produces a large deformation, which poses a great challenge for the deformation control measures of the tunnel.

5.3 Application of uplift piles

Uplift piles are characterized by large bearing capacity and excellent deformation control [44–46]. The main mechanism of the uplift pile is to resist axial tension by relying on the frictional force between the pile body and the soil layer. The uplift piles can effectively reinforce the soil above the tunnel and reduce the uplift value of the tunnel. At the same time, the barrier effect of the uplift piles reduces the span of the excavation area to a certain extent, which is favorable for tunnel protection [47]. As shown in Fig.16, a single row of uplift piles in the middle of the down-track and up-track tunnels and three rows of uplift piles in the middle and sides of the down-track and up-track tunnels are simulated separately. The pile body parameter is Φ600 mm@1800 mm, the pile length is 12 m, and the distance between the uplift piles and the outermost edge of the tunnel is about 3.5 m. The tops of the uplift piles are secured with structural bottom plates to jointly resist the upward movement of the soil.

It can be seen that the maximum displacement value of the tunnel is controlled from 20–25 mm to 15–20 mm, but it still does not meet the tunnel control requirements. However, the mechanism of the uplift piles is worth referring to. According to the above analysis, conventional prevention and control measures can reduce the maximum displacement value of the tunnel to some extent, regardless of whether auxiliary reinforcement is employed. However, due to the specificity and extreme rigor of this project, the aforementioned traditional prevention and control measures can hardly meet the requirements of this project. Therefore, it is necessary to seek new reinforcement measures.

The traditional reinforcement methods for the excavation of foundation pits are mostly lagging behind, and reinforcement is carried out after the excavation of the foundation pit is completed. Most of the deformation of the foundation pit has already occurred, resulting in an unsatisfactory reinforcement effect. With the continuous emergence of new technologies and equipment in the construction field, advanced pre-reinforcement has become possible. Therefore, this article proposes a micro-reinforcement drilling pipe pre-reinforcement method (PRM).

6 Micro-disturbance drilling pipe pre-reinforcement method

6.1 Introduction to the construction method of pre-reinforcement method

The construction diagram of the micro-disturbance drilling pipe PRM is shown in Fig.17. The specific construction process is as follows. a) After the completion of the Pit-1 construction in the first stage, the excavation site on both sides of the pit is used for micro-disturbance drilling pipe construction, and then heavy concrete composed of the iron sand mixture is poured inside the drilling pipe. b) After the construction of the micro-disturbance drilling pipe is completed, the soil in the area directly above the tunnel is excavated in blocks. c) After excavation of each area, the concrete structure bottom plate shall be constructed in time and fixed with the retaining piles on both sides. d) Cyclic reciprocating operation.

In the “General, Static” analysis step of ABAQUS/Standard, the “Model change” is used for the construction and assembly of components. After the excavation of the soil in the Pit-1 area is completed, the structural components of the drill pipe section are activated using “Model change” to represent the construction process of the drill pipe. The drilling pipe components adopt solid elements, and their material properties are converted into steel pipe concrete material properties.

6.2 Parametric studies of pre-reinforcement method

6.2.1 Analysis of single-row pre-reinforced drilling pipes (SRP)

6.2.1.1 Single-row drilling pipes diameter analysis

Parameter attribute analysis is an important method to recognize new things [48]. The diameter of the drilling pipe plays an essential role in the prevention and control effect. This section will analyze the conventional pipe diameters that can be performed by current state-of-the-art drilling pipe technology. Fig.18 shows the prevention and control effect of pipe diameter Φ200 mm@1000 mm–Φ600 mm@1000 mm. It can be seen that as the pipe diameter continues to increase, the maximum uplift value of the tunneling gradually decreases. According to the displacement reduction rate R (R = \mathrm{\nabla }/0.5, \mathrm{\nabla } is the displacement reduction value and 0.5 is the normalized reference value of 0.5 mm), the inhibition effect becomes more obvious with the gradual increase of pipe diameter.

6.2.1.2 Analysis of the spacing of the single-row drilling pipe

To thoroughly grasp the performance of the PRM parameters, we analyze the drilling pipe spacing parameters in this section. As shown in Fig.19, the final deformation state of the tunnel under different drilling pipe spacing Φ600 mm@1000 mm–Φ600 mm@3000 mm is analyzed. It can be seen that when Φ600 mm pipe diameter is used, the final uplift value of the tunnel is about 10 mm, which gradually meets the displacement control requirements of this project. The displacement reduction rate R indicates that the strengthening effect becomes more pronounced as the drilling pipe spacing is gradually reduced and the drilling pipe density is increased.

With the decrease of drilling pipe spacing, the density of the drilling pipe increases, and the effect of gravity backpressure of heavy concrete is gradually prominent. At the same time, the drilling pipe and heavy concrete form the horizontal large rigidity of the concrete-filled steel tube structure, linking the two sides of the foundation pit retaining wall to form a backpressure system. Therefore, the bulge of the land under the tunnel was fundamentally effectively inhibited, and then the tunnel’s bulge value decreased significantly. In addition, since the drilling pipe is already in place before the unloading of the soil, it has the advantage of being pre-positioned and pre-reinforced in comparison to the protection of the soil after rebound deformation occurs during or after the unloading.

6.2.1.3 Analysis of the distance between drilling pipes and tunnels

According to the specification, the minimum distance between the pile and the tunnel is 3 m. To analyze the effect of the spacing parameter D between the drilling pipe and the tunnel, the spacing between the drilling pipe and the bottom of the tunnel was simulated at 3.0, 3.5, 4.0, 4.5, and 5.0 m, respectively. Fig.20 shows that the maximum displacement value of the tunnel varies in a straight line for different spacings, indicating that this parameter has a minor effect on the prevention and control effect. Drill pipes are mainly used to significantly reduce the uplift of tunnels through their advanced preloading characteristics. However, this parameter is of great significance for engineering construction, and for excavation projects, the cost per 1 m of downward excavation is extremely considerable. Therefore, suitable drilling depths can be selected to optimize the construction costs for the foundation pit with different excavation depths.

6.2.2 Analysis of double-row pre-reinforced drilling pipes (DRP)

6.2.2.1 Double-row drilling pipes diameter analysis

For deep foundation pits with different excavation depths or higher deformation control criteria, it is necessary to analyze the control effect of multiple rows of drilling pipe when a single-row of drilling pipe cannot meet the engineering control requirements. This section mainly studies the influence of different pipe diameter parameters on the tunnel uplift under double-row drilling pipe protection. Fig.21 shows the tunnel displacement states under different drilling pipe diameter parameters Φ200, Φ300, Φ400, Φ500, and Φ600 mm, respectively. Compared to the single-row drilling pipe, the double-row drilling pipe has an obvious effect on suppressing the tunnel uplift, and the overall displacement of the tunnel is reduced by about 5–6 mm. For this project with displacement control criteria of 10 mm, the double-row drilling pipe with a diameter of Φ200 mm can meet the requirement. It is further demonstrated that directly strengthening the soil beneath the tunnel is a powerful method to solve the deformation problem of the foundation pit above the tunnel.

In addition, while the displacement reduction rate R still shows an increasing trend concerning the single-row pipe, there is a clear anti-bend point where the suppression effect gradually decreases as the diameter of the double-row pipe increases. The reverse bending point is focused on Φ400 mm pipe diameter. Construction costs should also be considered under the same suppression effect for practical projects.

6.2.2.2 Double-row drilling pipes spacing analysis

As shown in Fig.22, the tunnel deformation law is analyzed using a double-row of drilling pipes at different pipe spacings of @1.0, @1.5, @2.0, @2.5, and @3.0 m, respectively. When the pipe diameter of the tunnel is Φ600 mm, the maximum displacement of the tunnel is still less than 10 mm even if the pipe spacing is 3 m, and the inhibition effect is significant. With a pipe spacing of @1 m, the maximum tunnel displacement is even less than 5 mm. This approach can give full play to its advantages when the conventional means of control do not meet the requirements of some higher standard excavation pit.

6.2.2.3 Pipe-to-pipe spacing analysis

Similar to Subsection 6.2.1.3, for the multi-row drilling pipe structures, in addition to focusing on the effect of the spacing parameter D between the drilling pipe and the tunnel, the effect of the spacing L between the vertical double-row drilling pipe should also be analyzed. As shown in Fig.23, the variation characteristics of the maximum deformation value of the tunnel at different spacing of 3.0, 3.5, 4.0, 4.5, and 5.0 m are analyzed for drilling pipes of Φ200, Φ300, and Φ400 specifications. The results show that the tunnel maximum displacement decreases slightly with increasing the spacing L of the double-row drilling pipes, and the overall effect is not significant. This indicates that the change in the distance between the rows of the drilling pipe does not change the self-gravity of the drilling pipe or the backpressure system, so the effect is not obvious. However, this parameter has important implications for the construction cost.

6.3 Comparison of reinforcement effects for different construction methods

As shown in Fig.24, the uplift displacement of the tunnel is compared and analyzed for different methods of excavation control. Considering the excavation control methods of the foundation pit directly above the tunnel, it can be concluded that: for excavating a foundation pit with general deformation control standards using partition and block or selecting a reasonable excavation sequence, the traditional non-reinforced method (TNRM) can reduce the tunnel deformation caused by excavation to a certain extent, but the control effect is limited. The traditional reinforced method (TRM), which partially strengthens the structure using tensile piles and structural floor, can control the uplift deformation of the tunnel to a certain extent. However, the control effect is limited since the TRM is mainly performed during or after the excavation when the soil unloading has been completed.

The advanced PRM has the following advantages: 1) the micro-disturbance drilling pipe method before excavation has the effect of pre-reinforcement; 2) the pre-made drilling pipe is perfused with heavy concrete and forms a backpressure system with the retaining wall of the foundation pit; 3) this method focuses on strengthening the soil beneath the tunnel, effectively blocking the tunnel from floating at the source, which is different from the passive measures of the traditional method to strengthen the soil above the tunnel. The PRM can significantly reduce the upward deformation of the tunnel, which reflects the superiority and advancement of the PRM.

7 Discussion and conclusions

Although PRM can effectively control tunnel uplift and deformation, the method is currently rarely used in large-scale excavation prevention and control measures and is only applied in modest-scale excavation projects that cross major urban transportation roads or railway lines. Moreover, the supporting mechanized construction equipment is incomplete, which poses certain difficulties for the implementation of this method. However, it is foreseeable that with the continuous expansion of the city scale and the continuous improvement of the density of urban buildings, the requirements for the deformation control of the foundation pit will be higher and higher, and the rough and open construction will gradually be transformed into fine construction with micro-disturbance.

As an example of a concrete project, this paper presents a multi-angle analysis of the deep foundation pit excavation above the cross-operation subway tunnel; moreover, it adopts a numerical simulation method to compare and analyze the reinforcement effect of this project with the TRM and the advanced PRM. The following conclusions may be drawn.

1) Foundation pit excavation is the fundamental cause of tunnel buoyancy, but the direct cause of tunnel buoyancy is more due to the rebound of soil under the tunnel, so prevention and control measures should focus on the soil under the tunnel.

2) Most of the traditional prevention and control methods are soil excavation followed by reinforcement. Although space-time effects are taken into account, the effect due to the excavation cannot be ignored. PRM can mitigate this effect to a greater extent.

3) PRM focuses on strengthening the soil beneath the tunnel, effectively blocking the tunnel from floating at the source, which is different from the passive measures of the traditional method to strengthen the soil above the tunnel.

References

[1] Brown D C. Novel method of excavation. Journal of Construction Engineering and Management, 2003, 129(2): 222–225

[2] Zhang L, Wu X, Liu H. Strategies to reduce ground settlement from shallow tunnel excavation: A case study in China. Journal of Construction Engineering and Management, 2016, 142(5): 1–8

[3] Xiao X, Li M G, Wang J H, Chen J J. Numerical evaluation of control measures for tunnel deformation induced by an oversized deep excavation. Journal of Aerospace Engineering, 2018, 31(6): 1–11

[4] Li M G, Xiao X, Wang J H, Chen J J. Numerical study on responses of an existing metro line to staged deep excavations. Tunnelling and Underground Space Technology, 2019, 85: 268–281

[5] Chen J J, Zhu Y F, Li M G, Wen S L. Novel excavation and construction method of an underground highway tunnel above operating metro tunnels. Journal of Aerospace Engineering, 2015, 28(6): 1–7

[6] Liang R, Wu W, Yu F, Jiang G, Liu J. Simplified method for evaluating shield tunnel deformation due to adjacent excavation. Tunnelling and Underground Space Technology, 2018, 71: 94–105

[7] Lin P Y, Lim A, Ho S, Ho S P. Application of the novel composite earth retaining structure method to urban excavations: A constructability analysis. Journal of the Chinese Institute of Engineers, 2018, 41(7): 603–611

[8] Bose S K, Som N N. Parametric study of a braced cut by finite element method. Computers and Geotechnics, 1998, 22(2): 91–107

[9] Ng C W W, Sun H S, Lei G H, Shi J W, Mašín D. Ability of three different soil constitutive models to predict a tunnel’s response to basement excavation. Canadian Geotechnical Journal, 2015, 52(11): 1685–1698

[10] Liu Z, Xue J, Ye J, Qian J. A simplified two-stage method to estimate the settlement and bending moment of upper tunnel considering the interaction of undercrossing twin tunnels. Transportation Geotechnics, 2021, 29: 100558

[11] Ou C Y, Hsieh P G, Chiou D C. Characteristics of ground surface settlement during excavation. Canadian Geotechnical Journal, 1993, 30(5): 758–767

[12] Shi J W, Fu Z Z, Guo W L. Investigation of geometric effects on three-dimensional tunnel deformation mechanisms due to basement excavation. Computers and Geotechnics, 2019, 106: 108–116

[13] Sun H S, Chen Y D, Zhang J H, Kuang T S. Analytical investigation of tunnel deformation caused by circular foundation pit excavation. Computers and Geotechnics, 2019, 106: 193–198

[14] Zhang P, Du X, Lu D, Jin L, Qi J. Study on the excavation disturbed zone during tunneling in sandy cobble stratum considering the material meso-structure. Transportation Geotechnics, 2021, 29: 100590

[15] Chen X. Research on combined construction technology for cross-subway tunnels in underground spaces. Engineering, 2018, 4(1): 103–111

[16] Li M G, Zhang Z J, Chen J J, Wang J H, Xu A J. Zoned and staged construction of an underground complex in Shanghai soft clay. Tunnelling and Underground Space Technology, 2017, 67(1): 187–200

[17] Li M G, Chen J J, Wang J H, Zhu Y F. Comparative study of construction methods for deep excavations above shield tunnels. Tunnelling and Underground Space Technology, 2018, 71: 329–339

[18] Liu B, Zhang D W, Yang C, Zhang Q B. Long-term performance of metro tunnels induced by adjacent large deep excavation and protective measures in Nanjing silty clay. Tunnelling and Underground Space Technology, 2020, 95: 103147

[19] Tang W, Tang L, Ling X, Kong X, Zhang Y. Long-term performance of subway tunnels induced by the symmetrical excavation of semicircular deep foundation pits in the Northeast Region hard silty clay. Tunnelling and Underground Space Technology, 2024, 154: 106052

[20] Zhao X, Wang H, Li Z, Dai G, Yin Z, Cao S, Zhou J. Numerical study on the deformation of tunnels by excavation of foundation pit adjacent to the subway. Applied Sciences, 2022, 12(9): 4752

[21] Ling X Z, Kong X X, Tang L, Zhao Y Z, Tang W C, Zhang Y F. Predicting earth pressure balance (EPB) shield tunneling-induced ground settlement in compound strata using random forest. Transportation Geotechnics, 2022, 35: 100771

[22] Zheng G, Pan J, Li Y, Cheng X, Tan F, Du Y, Li X. Deformation and protection of existing tunnels at an oblique intersection angle to an excavation. International Journal of Geomechanics, 2020, 20(8): 05020004

[23] Kung G T, Juang C H, Hsiao E C, Hashash Y M. Simplified model for wall deflection and ground-surface settlement caused by braced excavation in clays. Journal of Geotechnical and Geoenvironmental Engineering, 2007, 133(6): 731–747

[24] Zheng G, Wei S. Numerical analyses of influence of overlying pit excavation on existing tunnels. Journal of Central South University of Technology, 2008, 15(S2): 69–75

[25] Ng C W W, Shi J, Hong Y. Three-dimensional centrifuge modelling of basement excavation effects on an existing tunnel in dry sand. Canadian Geotechnical Journal, 2013, 50(8): 874–888

[26] Ximena Ferrada A S. Selection of construction methods for construction projects: A knowledge problem. Journal of Construction Engineering and Management, 2014, 140(4): 1–7

[27] Lu D, Li X, Du X, Lin Q, Gong Q. Numerical simulation and analysis on the mechanical responses of the urban existing subway tunnel during the rising groundwater. Tunnelling and Underground Space Technology, 2020, 98: 103297

[28] Dong Y P, Burd H J, Houlsby G T. Finite-element analysis of a deep excavation case history. Geotechnique, 2016, 66(1): 1–15

[29] Liu B, Yu Z, Han Y, Wang Z, Zhang R, Wang S. Analytical solution for the response of an existing tunnel induced by above-crossing shield tunneling. Computers and Geotechnics, 2020, 124: 103624

[30] DongXMeiLYangS YHeL. Deformation response research of the existing subway tunnel impacted by adjacent foundation pit excavation, advances in materials science and engineering. Advances in Materials Science and Engineering, 2021, 2021: 1–11

[31] Chang C T, Sun C W, Duann S W, Richard N. Response of a Taipei Rapid Transit System (TRTS) tunnel to adjacent excavation. Tunnelling and Underground Space Technology, 2001, 16(3): 151–158

[32] Liu G B, Jiang R J, Ng C W W, Hong Y. Deformation characteristics of a 38 m deep excavation in soft clay. Canadian Geotechnical Journal, 2011, 48(12): 1817–1828

[33] Zhang H B, Chen J J, Fan F, Wang J H. Deformation monitoring and performance analysis on the shield tunnel influenced by adjacent deep excavations. Journal of Aerospace Engineering, 2017, 30(2): B4015002

[34] Ahmed N Z, El-Shourbagy M, Akl A, Metwally K. Field monitoring and numerical analysis of ground deformation induced by tunnelling beneath an existing tunnel. Cogent Engineering, 2021, 8(1): 1861731

[35] Zhang Z, Xu R, Wu X, Wang J. ANN-based dynamic prediction of daily ground settlement of foundation pit considering time-dependent influence factors. Applied Sciences, 2022, 12(13): 6324

[36] Shi J, Ng C W W, Chen Y. Three-dimensional numerical parametric study of the influence of basement excavation on existing tunnel. Computers and Geotechnics, 2015, 63: 146–158

[37] Moeinossadat S R, Ahangari K. Estimating maximum surface settlement due to EPBM tunneling by Numerical-Intelligent approach—A case study: Tehran subway line 7. Transportation Geotechnics, 2019, 18: 92–102

[38] Tan Y, Li X, Kang Z, Liu J, Zhu Y. Zoned excavation of an oversized pit close to an existing metro line in stiff clay: Case study. Journal of Performance of Constructed Facilities, 2015, 29(6): 1–19

[39] Liu B, Li H, Li L, Zhao Q, Gao J. Construction technique of vertical shafts excavation above subway tunnel. Geotechnical and Geological Engineering, 2021, 39(6): 4225–4235

[40] Hu Z F, Yue Z Q, Zhou J, Tham L G. Design and construction of a deep excavation in soft soils adjacent to the Shanghai Metro tunnels. Canadian Geotechnical Journal, 2003, 40(5): 933–948

[41] Zhang Z J, Li M G, Chen J J, Wang J H, Zeng F Y. Innovative construction method for oversized excavations with bipartition walls. Journal of Construction Engineering and Management, 2017, 143(8): 04017056

[42] Shen S L, Wu H N, Cui Y J, Yin Z Y. Long-term settlement behaviour of metro tunnels in the soft deposits of Shanghai. Tunnelling and Underground Space Technology, 2014, 40: 309–323

[43] Harahap S E, Ou C Y. Finite element analysis of time-dependent behavior in deep excavations. Computers and Geotechnics, 2020, 119: 103300

[44] Chen J J, Zhang L, Zhang J F, Zhu Y F, Wang J H. Field tests, modification, and application of deep soil mixing method in soft clay. Journal of Geotechnical and Geoenvironmental Engineering, 2013, 139(1): 24–34

[45] Li M G, Chen J J, Xu A J, Xia X H, Wang J H. Case study of innovative top-down construction method with channel-type excavation. Journal of Construction Engineering and Management, 2014, 140(5): 05014003

[46] Liu G B, Huang P, Shi J W, Ng C W W. Performance of a deep excavation and its effect on adjacent tunnels in shanghai soft clay. Journal of Performance of Constructed Facilities, 2016, 30(6): 1–14

[47] Peng H, Tang Q, Zhu L, Li Z, Li H, Wang G. Deformation control of subway stations under the influence of the construction of deep and large foundation pits with composite support systems. Applied Sciences, 2022, 12(6): 3026

[48] Huang X, Schweiger H F, Huang H. Influence of deep excavations on nearby existing tunnels. International Journal of Geomechanics, 2013, 13(2): 170–180

RIGHTS & PERMISSIONS

Higher Education Press