Research on the method of construction disturbance zoning for shield tunnel approaching to urban structures

Abstract

This paper presents a calculation method that evaluates the extent of disturbance based on structural safety limits. Additionally, it summarizes the assessment methods for construction disturbance zones in shield tunneling near pile foundations, urban ground structures, and underground structures. Furthermore, taking the construction of the Chengdu Jinxiu Tunnel under bridges and urban pipelines as the engineering background, a study on the disturbance zoning of adjacent structures was conducted. The most intense disturbance occurs within one week of the tunnel underpass process, and it has a significant impact within a range of two times the tunnel diameter along the tunnel axis. The bridge pile and bridge deck experience less disturbance from tunnel approaching construction, with a maximum disturbance zone characterized as medium disturbance. On the other hand, underground pipelines are subjected to more significant disturbances from tunnel construction, with a maximum disturbance zone classified as strong disturbance. The implementation of “bridge pile sleeve valve pipe grouting & underground pipeline ground grouting & tunnel advance grouting” in the field effectively limits the vertical settlement of bridges and pipelines, resulting in a decrease of approximately 0.1 in disturbance level for the structures. The disturbance zoning method can assess tunnel disturbance with structures, identify high-risk interference locations, and facilitate targeted design reinforcement solutions.

Graphical abstract

Keywords

shield tunnel / approaching construction / field monitoring / disturbance zoning method

1 Introduction

Tunneling in congested urban areas has become a critical issue worldwide over the past decades due to increasingly limited construction space [1]. It is inevitable for tunnel construction to close existing buildings in the urban area. However, the construction of a tunnel in close proximity will change the stress field of the surrounding rock, inducing strata displacement. This will bring additional loads and displacements to adjacent structures, and further affect the safety performance of the structure [2,3]. In this regard, numerous scholars have also conducted extensive research. According to literatures, recent advances in shield tunnel proximity construction mainly focuses on the following aspects.

1) The disturbance mechanism and theoretical analysis methods of shield tunneling. An improved empirical formula for the surface settlement curve has been proposed by Wang et al. [4], providing a means to determine the disturbance radius of tunnel excavation. Zhu and Ding [5] enhanced the Duncan-Chang constitutive model, enabling accurate prediction of soil deformation resulting from shield tunneling in coastal sandy soil environments. Huang et al. [6] and Hu et al. [7] used a two-stage analysis method, and the analytical solutions were obtained for both the tunnel induced strata displacement and the stress deformation response of adjacent piles. Zhou et al. [8] based on the peck formula, deduced a prediction formula for the ground surface deformation caused by twin-tunnel construction.

2) Analysis of the impact of shield tunnel construction on adjacent structures based on engineering cases. Engineering cases include analysis of the construction impact of shield tunneling adjacent to existing tunnels [9–12]; analysis of the construction impact of shield tunneling adjacent to existing underground buildings [13,14]; analysis of the construction impact of shield tunneling on adjacent bridges and high-rise building pile foundations [15–18]; analysis of the construction impact of shield tunneling adjacent to underground pipelines [18]. The common research methods were numerical analysis, model testing, and field monitoring [19–21]. The research covered aspects such as the load change of adjacent structures, analysis of displacement and deformation of adjacent structures, and the performance analysis of support schemes.

3) Research on the influencing factors of shield tunnel approaching construction. The impact of tunnel construction on the surrounding soil is influenced by the grouting ratio and support pressure. Excessively high or low support pressure and grout ratio can lead to significant settlement after construction [22]. A shallow tunnel depth and weaker surrounding rock properties will result in increased disturbances during tunnelling. Additionally, the construction of the second tunnel in a twin-tunnel excavation causes more severe ground settlement disturbances [23]. The impact of shield tunneling near sensitive urban areas is closely tied to the construction parameters of the shield tunnel. Inappropriate settings of parameters such as shield thrust, grouting pressure, formation friction, shield tunneling torque, and shield tunneling speed can exacerbate the disturbances caused by shield tunneling [24,25].

4) Research on disturbance zoning during approaching construction of shield tunnels. Sun et al. [26] introduced a disturbance extent calculation method based on effective stress, and used numerical simulation methods to partition the strata disturbance extent during shield tunnel construction. The stress disturbance zone can be classified into two regions with distinct disturbance characteristics: the strong disturbance zone and the weak disturbance zone. The strong disturbance zone extends approximately halfway from the tunnel boundary into the rock mass, encompassing half the tunnel diameter [27]. A new influence zone partition method which takes into account the stress disturbance and the deformation disturbance of pile foundations was put forward by Wang et al. [28]. This method defines the extent of stress and deformation disturbances experienced by individual piles during the tunneling process.

Existing research on tunnel approaching structures has primarily focused on exploring disturbance laws and analyzing settlement deformation data, limiting its scope. However, the disturbance tolerance of different structural types is different, and there is no uniform standard for the risk of the approaching construction process. Clarifying the scope and extent of disturbance in the tunnel approaching construction and dividing the construction disturbance zone are conducive to analyzing the severity of the construction disturbance of the structure from the perspective of safety. By utilizing disturbance zoning results, targeted reinforcement measures can be designed to mitigate the structural disturbances caused by tunnel approaching construction. Furthermore, the literature investigation reveals that research on disturbance zoning in tunnel construction predominantly concentrates on ground settlement and surrounding rock deformation. There is less content on the disturbance zoning of the approaching building and structures close to the tunnel construction. However, in the urban environment, buildings are more sensitive to the disturbance of approaching construction. In this condition, the existing tunnel disturbance zoning method becomes no longer applicable.

According to this, the research presents a comprehensive method for disturbance zoning in shield tunnel construction near urban buildings. This method combines the case study of Chengdu Jinxiu Tunnel, which passes beneath the Tianfu Airport Expressway Ramp Bridge, and an underground gas pipeline project. The disturbance of large-diameter shield tunnel approaching construction to high-speed bridge pile group and underground pipelines is analyzed by means of field test and numerical calculation method. The research findings can serve as valuable references for engineering design and construction purposes.

2 Disturbance zoning method of shield construction

This study draws on the calculation method of strength reserve safety factor commonly used in tunnel engineering. The key factors that control the safety of the structure are taken as the research object of the disturbance zoning, and the ratio of the disturbance quantity of the key factors after the approaching construction to the allowable disturbance quantity of the specification is taken as the disturbance extent evaluation index. The disturbance zoning of the structure is carried out by dividing the range of the disturbance extent. In this paper, the disturbance objects of shield tunnel construction will be discussed, including single pile, ground structures and underground structures. The schematic diagram of tunnel disturbance calculation is shown in Fig.1.

2.1 Disturbance extent of single pile

1) The stress disturbance extent of single pile.

According to the regulations of Construction Measures for Proximity of Existing Tunnels on Japanese Railways [29]. The allowable increase of the compressive stress of the structure is 5 MPa and the allowable increase of the tensile stress is 1 MPa. Since there is no relevant regulation in China at present, the approaching construction countermeasures of existing railway tunnels in Japan are used for reference and the allowable stress value of single pile is considered as follows:

(1)[ \sigma ]=\{\begin{array}{l}5\mathrm{M}\mathrm{P}\mathrm{a},\mathrm{C}\mathrm{o}\mathrm{m}\mathrm{p}\mathrm{r}\mathrm{e}\mathrm{s}\mathrm{s}\mathrm{i}\mathrm{v}\mathrm{e}\mathrm{s}\mathrm{t}\mathrm{r}\mathrm{e}\mathrm{s}\mathrm{s},\\ 1\mathrm{M}\mathrm{P}\mathrm{a},\mathrm{T}\mathrm{e}\mathrm{n}\mathrm{s}\mathrm{i}\mathrm{l}\mathrm{e}\mathrm{s}\mathrm{t}\mathrm{r}\mathrm{e}\mathrm{s}\mathrm{s}.\end{array}

The stress disturbance extent of single pile s_1 is defined as the ratio between the stress increment of a single pile and the maximum allowable disturbance value:

(2)s_1=\frac{{\sigma }_{max}-{\sigma }_0}{[\sigma ]},

where s_1 is the stress disturbance extent of single pile, {\sigma }_{max} is the stress value of single pile after construction disturbance, {\sigma }_0 is the l stress value of single pile before construction disturbance, [\sigma ] is the allowable stress value of single pile.

2) The deformation disturbance extent of single pile.

The deformation disturbance extent of single pile s_2 is defined as the two norms of the vertical settlement disturbance extent of the pile and the lateral settlement disturbance extent. The vertical settlement disturbance of the pile is the ratio of the maximum vertical settlement of the pile to the allowable vertical settlement of the pile. Analogously, the lateral displacement disturbance of the pile is the ratio of the maximum lateral displacement of the pile to the allowable lateral displacement of the pile. The formulas are as follows:

(3)s_2=\sqrt{S_{\mathrm{V}}^2+S_{\mathrm{H}}^2},

(4)s_{\mathrm{V}}=\frac{\mathrm{\Delta }{\mathit{\text{z}}}_1^{max}}{[\mathrm{\Delta }\mathit{\text{z}}]},

(5)s_{\mathrm{H}}=\frac{\mathrm{\Delta }{H}^{max}}{[\mathrm{\Delta }H]}=\frac{max\left(\sqrt{{\left(\mathrm{\Delta }{x}_{\mathit{\text{z}}}\right)}^2+{\left(\mathrm{\Delta }{y}_{\mathit{\text{z}}}\right)}^2}\right)}{[\mathrm{\Delta }H]},

where s_2 is the deformation disturbance extent of single pile, s_{\mathrm{V}} is the vertical displacement disturbance extent of single pile, s_{\mathrm{H}} is the lateral displacement disturbance extent of single pile, \mathrm{\Delta }{\mathit{\text{z}}}_1^{max} is the maximum vertical displacement of the pile, [\mathrm{\Delta } \mathit{\text{z}}] is the allowable vertical displacement of the pile, \mathrm{\Delta }{x}_{\mathit{\text{z}}} is the x-direction displacement at each position on the axis of the pile, \mathrm{\Delta }{y}_{\mathit{\text{z}}} is the y-direction displacement at each position on the axis of the pile, \mathrm{\Delta }{H}^{max} is the maximum horizontal displacement of the pile, [\mathrm{\Delta } H] is the allowable lateral displacement of the pile.

Chinese regulations [27,28] stipulate that the threshold value of settlement at the top of the piles is 0.05 and 0.02 m respectively in the tunnel construction adjacent to the piles. This study is biased safely to take 0.02 m as the standard, meaning that the allowable vertical deformation of single pile [\mathrm{\Delta }\mathit{\text{z}}] is 20 mm. In addition, design code of architectural pile foundation [30] stipulate that the maximum value of allowable horizontal displacement of pile cap (at the top of the pile) is 10 and 6 mm for the structure sensitive to horizontal displacement. As the bridge is a horizontally sensitive structure, the allowable lateral displacement of single pile [\mathrm{\Delta }H] is taken as 6 mm in the study.

2.2 Disturbance extent of ground structures

2.2.1 Disturbance extent of bridge deck

The disturbance of the bridge deck is affected by the uneven settlement of the pile foundation, which will lead to additional flexural deflection of the bridge deck. This study introduces the concept of bridge deck disturbance extent, where the shield-bridge disturbance extent is defined as the ratio between the deflection of the bridge (single span) and the maximum allowable deflection of the bridge.

(6)s_3=\frac{\mathrm{\Delta }{\mathit{\text{z}}}_2^{\mathrm{c}\mathrm{o}\mathrm{m}\mathrm{p}}-\mathrm{\Delta }{\mathit{\text{z}}}_2^{\mathrm{p}\mathrm{r}\mathrm{e}}}{[\mathrm{\Delta }R]},

where S_3 is the bridge deck disturbance extent, \mathrm{\Delta } {\mathit{\text{z}}}_2^{\mathrm{c}\mathrm{o}\mathrm{m}\mathrm{p}} is the vertical displacement of the bridge deck after the approaching construction, \mathrm{\Delta }{\mathit{\text{z}}}_2^{\mathrm{p}\mathrm{r}\mathrm{e}} is the vertical displacement of the bridge deck before the approaching construction, [\mathrm{\Delta } R] is the allowable maximum deflection of the bridge.

According to Chinese Specifications for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts [31], the allowable vertical deflection values of the bridge are shown in Tab.1 below. Because there are many factors leading to the deflection of the bridge deck, such as traffic load, temperature-induced and structural aging [8], the tunnel construction factor only accounts for a part of the deflection deformation of the bridge. Therefore, considering the safety, the allowable deflection in the shield construction is taken as half of the allowable deflection of the specification.

2.2.2 Disturbance extent of buildings

According to the standards [32], the control factors for the disturbance of buildings are the building’s tilting and foundation settlement. Different types of buildings have varying concerns regarding disturbance factors and allowable disturbance limits, as shown in Tab.2 to Tab.5. The degree of disturbance for a building can be defined as:

(7)S_4=\frac{\mathrm{\Delta }{\mathit{\text{z}}}_3^{\mathrm{c}\mathrm{o}\mathrm{m}\mathrm{p}}-\mathrm{\Delta }{\mathit{\text{z}}}_3^{\mathrm{p}\mathrm{r}\mathrm{e}}}{[\mathrm{\Delta }Z]},

(8)s_5=\frac{\mathrm{\Delta }\theta }{[\mathrm{\Delta }\theta ]} ,

where s_4 is the building settlement disturbance extent, s_5 is the building tilt disturbance extent, \mathrm{\Delta }{\mathit{\text{z}}}_3^{\mathrm{c}\mathrm{o}\mathrm{m}\mathrm{p}} is the vertical displacement of the building basement after the approaching construction, \mathrm{\Delta }{\mathit{\text{z}}}_3^{\mathrm{p}\mathrm{r}\mathrm{e}} is the vertical displacement of the building basement before the approaching construction, \mathrm{\Delta }\theta is the building tilt after the approaching construction, [ \mathrm{\Delta }Z] is the allowable maximum building settlement, [\mathrm{\Delta }\theta ] is the allowable maximum building tilt.

2.3 Disturbance extent of urban underground structures

2.3.1 Disturbance extent of urban underground pipeline

The disturbance extent of urban underground pipeline is defined as the ratio of maximum vertical deformation to allowable deformation of pipeline.

(9)S_6=\frac{\mathrm{\Delta }{\mathit{\text{z}}}_4^{\mathrm{c}\mathrm{o}\mathrm{m}\mathrm{p}}-\mathrm{\Delta }{\mathit{\text{z}}}_4^{\mathrm{p}\mathrm{r}\mathrm{e}}}{[\mathrm{\Delta }\delta ]},

where s_6 is the deformation disturbance extent of urban underground pipeline, \mathrm{\Delta }{\mathit{\text{z}}}_4^{\mathrm{c}\mathrm{o}\mathrm{m}\mathrm{p}} is the vertical deformation of underground pipeline after approaching tunnel construction, \mathrm{\Delta }{\mathit{\text{z}}}_4^{\mathrm{p}\mathrm{r}\mathrm{e}} is the vertical deformation of the underground pipeline before approaching tunnel construction, [\mathrm{\Delta }\delta ] is the allowable maximum vertical deformation of urban underground pipelines.

Chinese Specifications for Structural design code for pipelines of water supply and waste water engineering [33] stipulate that for the flexible metal pipelines which use rigid materials such as cement mortar as anticorrosive lining, the maximum vertical deformation should not exceed 0.02D–0.03D (D is the calculated inner diameter of circular pipelines). And for the metal pipelines which are lined with anticorrosive coating with good ductility, the maximum vertical deformation should not exceed 0.03D–0.04D. For the chemical building materials pipelines, the maximum vertical deformation should not exceed 0.05D.

2.3.2 Disturbance extent of existing tunnel

The disturbance of existing tunnels includes two components: displacement disturbance and differential settlement disturbance. As shown in Tab.6, according to the standard [34], the allowable maximum vertical displacement from 10 to 20 mm, the allowable maximum horizontal displacement ranges from 5 to 10 mm, and the allowable maximum differential settlement is 0.04% L_t. (The displacement allowance is determined based on tunnel diameter and experience.)

(10)s_7=\sqrt{{\left(\frac{\mathrm{\Delta }{\mathit{\text{z}}}_5^{\mathrm{c}\mathrm{o}\mathrm{m}\mathrm{p}}-\mathrm{\Delta }{\mathit{\text{z}}}_5^{\mathrm{p}\mathrm{r}\mathrm{e}}}{[\mathrm{\Delta }\eta ]}\right)}^2+{\left(\frac{\mathrm{\Delta }{x}^{\mathrm{c}\mathrm{o}\mathrm{m}\mathrm{p}}-\mathrm{\Delta }{x}^{\mathrm{p}\mathrm{r}\mathrm{e}}}{[\mathrm{\Delta }X]}\right)}^2},

(11)s_8=\frac{\mathrm{\Delta }{\mathit{\text{z}}}_{\mathrm{t}1}-\mathrm{\Delta }{\mathit{\text{z}}}_{\mathrm{t}2}}{[\mathrm{\Delta }T]},

where s_7 is the deformation disturbance extent of existing tunnel, S_8 is the differential settlement disturbance extent of existing tunnel, \mathrm{\Delta } {\mathit{\text{z}}}_5^{\mathrm{c}\mathrm{o}\mathrm{m}\mathrm{p}} is the vertical deformation of tunnel after approaching tunnel construction, \mathrm{\Delta } {\mathit{\text{z}}}_5^{\mathrm{p}\mathrm{r}\mathrm{e}} is the vertical deformation of the tunnel before approaching tunnel construction, \mathrm{\Delta }{x}^{\mathrm{c}\mathrm{o}\mathrm{m}\mathrm{p}} is the horizontal deformation of tunnel after approaching tunnel construction, \mathrm{\Delta }{x}^{\mathrm{p}\mathrm{r}\mathrm{e}} is the horizontal deformation of the tunnel before approaching tunnel construction, [\mathrm{\Delta }\eta ] is the allowable maximum vertical deformation of tunnel, [\mathrm{\Delta } X] is the allowable maximum horizontal deformation of tunnel, [\mathrm{\Delta }T] is the allowable maximum differential settlement of tunnel.

2.4 Disturbance zone grade division

The disturbance Zoning of approaching structure:

(12)[S] =\beta \frac{\sum _{i=1,2,\dots ,N}{\alpha }_i{S}_i}{N},

where [S] is disturbance extent of approaching structure for zoning, {\alpha }_i is the disturbance weight coefficient of each factor, s_i is the approaching structure disturbance extent, N is the number of extent factors in the proximity structure, \beta is the structural importance coefficient.

In this study, it is considered that the stress disturbance of the pile and the strain disturbance of the pile reach the allowable value as the near limit state. The disturbance importance of each factor is the same, that is, the product of the disturbance threshold and the weight coefficient is 1. Hence pile load disturbance weight coefficient {\alpha }_1 = 1, the pile deformation disturbance weight coefficient {\alpha }_2 = 1/\sqrt{2}. Besides, the influence of other structures is a single factor \alpha = 1.

According to the requirements of the code [35], the structural importance coefficient is 1.1 for buildings with a service life of 100 years, 1.0 for buildings with a service life of 50 years, and 0.9 for buildings with a service life of 5 years. The design service life of bridge and bridge pile is 100 years, and the design service life of underground pipeline is 50 years.

3 Field monitoring test of tunnel approaching construction

3.1 Engineering background

This study takes the Jinxiu tunnel of Chengdu–Zigong high-speed railway line as the engineering background. The tunnel is situated in the urban area of Chengdu, traversing various urban risk sources including railway bridges, municipal tunnels, overpasses, underground pipelines, and high-rise buildings. The buried depth of the tunnel is 7–51 m, and the strata through which the tunnel mainly passes are fully weathered mudstone, strongly weathered mudstone and weakly weathered mudstone. The outer diameter of the tunnel is 12.4 m, the inner diameter is 11.3 m, the thickness of the segment is 0.55 m, and the width of the segment is 1.8 m. The lining ring is composed of 9 segments (6 + 2 + 1), which are assembled by staggered joints. The concrete grade of the segment is C50. The basic information of the tunnel is shown in Fig.2.

3.2 Overview of information on approaching construction zones

Jinxiu Tunnel laterally crosses Tianfu Airport Expressway Ramp Bridge in the range of (DK3 + 527.94)−(DK3 + 671.94), and the schematic plan of the approaching construction interval can be seen in Fig.3. The superstructure of the ramp bridge is a continuous simply supported box beam with a standard span of 30 m. The bridge deck is 14 m wide, and the pile foundation is a bored pile with a diameter of 1.5 m. The tunnel underneath passes two urban gas pipelines (DN160) at mileage DK3 + 599.94 and mileage DK3 + 614.44, respectively, of which the inner diameter is 160 mm, the outer diameter is 170 mm, and the wall thickness is 5 mm. The urban pipelines are roughly parallel to the ramp bridge in the horizontal plane, forming an angle of approximately 70° with the new tunnel.

Fig.4 is the section diagram of the tunnel at the location of DK3 + 599.94 which is in the approaching construction section. The buried depth of the tunnel is about 12.8 m, and the tunnel is covered with 2.96 m thick fill and 9.84 m thick silty mudstone layer. The bridge pile cap is buried 0.5 m below the ground surface while the buried depth of underground pipelines is about 2.8 m. The length of the bridge pile on the left side of the tunnel is 21 m, and the length of the bridge pile on the right side is 17 m. The horizontal distance between the left bridge pile and the outer boundary of the tunnel segment is about 6.57 m, while the horizontal distance between the right bridge pile and the outer boundary of the tunnel segment is about 5.38 m.

To reduce the influence of tunnel approaching, sleeve valve pipeline grouting reinforcement is carried out in the 2.25 m circular range around the bridge pile during construction. The soil grouting reinforcement is carried out at 1m below the gas pipelines, of which the range is 3 m thick, 3 m wide, and the length is three times the outer diameter of the tunnel (37.2 m). In addition, advanced tunnel grouting reinforcement is carried out in the (DK3 + 563.94)−(DK3 + 635.94) interval of the tunnel, whose range includes 150 cm grouting ring in the upper part of the tunnel and 50 cm grouting ring in the lower part of the tunnel.

The shield jacking parameters and grouting pressure parameters in the approaching construction interval are shown in Fig.5. In the shield approaching construction interval, the grouting pressure after the wall is set in the range of 0.2–0.8 MPa with an average value of about 0.465 MPa, while the jacking force of shield construction is set in the range of 25000–48000 kN with an average value of 38320 kN.

3.3 Analysis of field monitoring data

3.3.1 Field monitoring scheme

In the field construction, the ground surface settlement monitoring and the vertical displacement monitoring of the bridge pile were carried out in the tunnel underpass section. The layout scheme of surface subsidence monitoring points in the approaching interval is shown in Fig.6. As shown in Fig.6(a), the ground surface monitoring sections are arranged at 10 m intervals, with a total of 6 monitoring sections numbered GM1 to GM6 along the tunnel excavation direction. A total of nine settlement monitoring points is set up in each monitoring section, with the measurement points arranged at 10 m intervals on both sides of the tunnel axis. Fig.6(b) is the schematic diagram of the layout of the ground surface settlement monitoring points. The ground surface settlement test adopts the standard burial method. First, drill holes on the ground surface and place the steel casing, then insert the steel bar in the center, and finally fill the isolation layer between the steel casing and the steel bar while ensuring that the top of the steel bar is 5 cm lower than the ground surface. During the monitoring, the electronic level is used to monitor the surface subsidence.

The bridge pile number is shown in Fig.7(a). The measuring points are set on the bridge pile 3 to pile 6 on both sides of the tunnel to monitor bridge pile settlement. Fig.7(b) is a schematic diagram for monitoring the vertical displacement of the bridge piles. The monitoring equipment utilizes a fully automatic total station that is operated by automatic deformation monitoring software. The automatic total station is powered by cables and has the capability to control, collect, and store measurement data in real-time. Simultaneously, the real-time data are transmitted to an office server through a data transmission module for calculation and settlement data output.

3.3.2 Analysis of ground settlement

The surface subsidence in the approaching construction section is collected during the construction within one month, and the time-varying curve of the surface subsidence is drawn as shown in Fig.8. On the whole, temporally, the peak of surface subsidence occurs approximately one week before and after the shield excavation face passes. Spatially, the disturbance caused by tunnel construction is concentrated within a two-dimensional (2D) range around the tunnel’s central axis.

In terms of tunnel cross-section, the surface subsidence on the monitoring section follows a ‘W’ type distribution. The subsidence measured by the surface monitoring point at ±10 m from the tunnel axis is the largest, and the surface subsidence at the tunnel axis is smaller than the peak subsidence. This may be due to the advance grouting reinforcement of the shield, which makes the upper stratum of the tunnel more stable than the surrounding stratum, thus inhibiting the ground settlement above the tunnel. With the further increase of the distance between the measuring point and the tunnel axis, the measured surface subsidence gradually decreases.

The maximum subsidence of each monitoring section GM1−GM6 is −9.65, −10.86, −11.03, −10.91, −10.92, and −10.51 mm, respectively. Among them, the surface subsidence measured at GM3−GM6 measuring point is the largest, which is in the surface monitoring section 3, 10 m to the right side of the tunnel axis and located near the bridge pile 5. In addition, the surface subsidence measured at the surface monitoring sections (GM3−GM5) located in the range of pipelines and bridge pile is larger than that of other monitoring sections. It is not difficult to find that the existence of the building above the tunnel will increase the surface subsidence near the building.

3.3.3 Bridge pile settlement analysis

The variation law of pile foundation settlement of bridge pile 3 to pile 6 with time is monitored, and the monitoring results are shown in Fig.9. The increase of settlement is mainly concentrated in the 6 to 12 d when the shield passed through tunnel grouting reinforcement area. On the 16 d, the change of subsidence quantity tends to be stable, and the monitoring amount has only a small amount of data fluctuation due to the error caused by the external environment. The settlement values of pile 3 and pile 4 are similar, about 10 mm. The settlement values of pile 5 and pile 6 are similar, and because the distance from the tunnel is closer, it is more disturbed by the shield construction, with the value reaching about 11 mm. In general, the difference of settlement values measured at different positions in a single pile foundation is small, and the pile foundation is in the state of overall settlement.

4 Numerical analysis and structural disturbance zoning

4.1 Model establishment

The three-dimensional numerical analysis model composed of tunnel, stratum and adjacent structure is established by simulation computing software FLAC3D, as shown in Fig.10. The model is 144 m long (along the Y-axis), 140 m wide (along the X-axis), and 50 m high (along the Z-axis). The model is built according to the positional relationship between the adjacent structure and the tunnel described in Subection 3.2. The bridge deck is simplified as a plate structure with a thickness of 0.5 m. On the one hand, the Mohr−Coulomb (M−C) constitutive model is more suitable for the simulation of rock-soil mass and as the tunnel passes through the silty mudstone stratum, the surrounding rock adopts the M-C model in the numerical calculation. On the other hand, the adjacent structure (the bridge) is regarded as an elastomer using Hooke’s elastic constitutive. The material parameters set in the numerical simulation can be seen in Tab.7. The buried depth of the tunnel is small, and there is almost no groundwater in the approaching section, so the influence of groundwater is ignored in the numerical calculation. For the boundary conditions of the model, the bottom of the model is completely constrained, the front and back and left and right sides are constrained to the normal direction displacement, and the top surface of the model is the free surface.

The shield shell of the shield machine in Jinxiu Tunnel is 15 cm thick. In addition, considering that the taper of the shield machine will affect the settlement in the numerical analysis [36], over-excavation at shield tunneling with the radius of 4 cm is adopted in the numerical simulation. The numerical analysis takes into consideration the actual construction process of the tunnel, including four steps: rock excavation, advancing the shield body and synchronous excavation grouting, and segment assembly, as shown in Fig.11(a). The calculation process is illustrated in Fig.11(b), while the construction process can be described in detail as follows.

1) The area of 1 ring at the tunnel excavation surface is assigned null to simulate the tunnel excavation. Gradually activate the shield shell units within a 4-ring range behind the excavation face (activating one ring per excavation step). Additionally, apply a jacking pressure of 0.308 MPa on the excavation face (calculated based on on-site construction parameters in Subection 4.2).

2) After reaching the third ring, each excavation step activates one ring segment, simulating the assembly of tunnel segments.

3) After reaching the 5th ring during excavation, the over-excavation area and shield shell are designated as null, activating this area and specifying the grouting material parameters. Furthermore, a circumferential pressure of 0.465 MPa is applied to the interface between the grouting area and the surrounding rock in the two rings of the shield tail, simulating the impact of grouting pressure on the surrounding strata.

4) After reaching the 20th ring, during the subsequent excavation of 40 rings, the advance grouting area is cyclically activated in the leading ring of the excavation face.

4.2 Numerical calculation results

4.2.1 Comparison between numerical calculation results and on-site monitoring results

The surface subsidence in the numerical calculation results is extracted, and the polynomial difference surface fitting of the data points is carried out by using MATLAB software, and the surface map of the surface subsidence in the approaching construction interval is obtained as shown in Fig.12. It can be concluded that the distribution of surface subsidence in the approaching interval after tunnel construction generally shows the following characteristics. 1) The surface settlement on the section perpendicular to the tunnel is roughly ‘W’ type distribution, and the maximum surface subsidence is at about ±10 m from the tunnel axis. 2) Along the advancing direction, surface subsidence increases at the center of the construction section being approached and gradually decreases with increasing distance from the center. 3) The existence of bridge piles will lead to an increase in local surface subsidence, and the closer the bridge piles are to the tunnel, the greater the disturbance.

The subsidence law obtained by the numerical calculation results is consistent with the field monitoring results. In addition, in the numerical calculation, the surface subsidence of the center is −10.84 mm, the surface subsidence of the left bridge pile is −10.5 mm, and the surface subsidence of the right bridge pile is −11.15 mm, which fits well with the subsidence data measured by field monitoring. Based on this, it can be considered that the numerical calculation results have great reliability for the simulation of the actual approaching construction process.

4.2.2 Bridge disturbance analysis

The stress and displacement changes of the bridge pile after the tunnel passes through the bridge can be seen in Fig.13. As shown in Fig.13(a), the bridge pile foundation is in a compressive state after the approaching tunnel construction, and the maximum compressive stress increment of the bridge pile is between 1.27 and 0.45 MPa. The increment of compressive stress of single pile is related to the distance from bridge pile to disturbance source, that is, the closer to the tunnel excavation surface, the greater the stress change. However, considering the allowable compressive stress increment in the specification, the approaching construction leads to less stress disturbance of the bridge pile. For the vertical displacement of bridge piles, the vertical settlement of pile 3 to pile 6 near the tunnel is significantly greater than that of pile 1, pile 2, pile 7, and pile 8 far away from the tunnel. The vertical displacement of pile 3 to pile 6 is similar, among which the vertical displacement of pile 5 is the largest, with a value of −11.52 mm, and that of pile 1 is the smallest, with a value of −10.83 mm.

Fig.14 is the fitting surface of the vertical displacement of the bridge deck after polynomial difference processing. The vertical displacement of the bridge deck is roughly ‘W’ type along the length direction, and the peak value on the right side of the bridge deck is larger than that on the left side. The vertical displacement of the bridge deck changes little in the width direction. The vertical displacement change of the bridge deck is mainly concentrated in the position of the pile foundation, and the displacement change of the bridge deck between the bridge piles is approximately linear. It can be considered that the bridge deck deforms at the position of the bridge pile and does not deform between the bridge spans. The maximum vertical displacement of the bridge deck is at the position of (15, −7), with a value of −11.6 mm.

4.2.3 Settlement analysis of underground pipelines

The displacement data in the Z direction of the underground pipelines are extracted to draw the curve, as shown in Fig.15. The variation pattern of the Z-displacement curve for pipeline 1 is similar to that of the surface subsidence curve observed in the previous section. The deformation reaches the peak at about ±10 m from the tunnel axis, and the maximum displacement is about −3.68 mm at −10 m from the tunnel axis. Pipeline 2 is located directly below the bridge. Due to the influence of the bridge, the displacement of pipeline 2 is unevenly distributed and increases. The Z-displacement of Pipeline 2 is the largest at 5 m from the tunnel axis, about −3.77 mm. In addition, the pipeline at the position of the bridge pile foundation is uplifted relative to the surrounding area, which may be caused by the large settlement of the pile and the upward displacement of the surrounding soil. In the grouting reinforcement interval of underground pipeline, the Z-displacement of pipeline changes little, which shows that grouting reinforcement can effectively limit the occurrence of vertical displacement of pipeline.

4.3 Disturbance zoning of approaching structure

The specific values of the parameters involved in the disturbance zoning method in the second section are shown in Tab.8. In this study, the disturbance of shield approaching construction is divided into five levels: extremely strong disturbance (A), strong disturbance (B), moderate disturbance (C), weak disturbance (D), and extremely weak disturbance (E). The disturbance extent interval corresponding to each level is shown in Tab.9 Using the shield tunnel construction disturbance zoning method proposed above, the disturbance zoning analysis of the adjacent structure is carried out.

The disturbance zoning of the single pile can be seen in Fig.16. The bridge pile is less disturbed by the tunnel approaching construction, and the disturbance extent of pile 1, pile 2, pile 7, and pile 8 far from the tunnel axis is less than 0.2, which is an extremely weak disturbance. The disturbance zone of pile 3 and pile 4 are weak disturbance, and the disturbance zone of pile 5 and pile 6 are medium disturbance. The disturbance extent of pile 5 is the largest among all bridge piles, only 0.42. The disturbance extent of single pile is composed of displacement disturbance and stress disturbance. The influence of approaching construction on the displacement disturbance of bridge pile is significantly higher than that of stress disturbance. It is not hard to see that more attention should be paid to the displacement and deformation of pile foundation when the tunnel construction is in proximity to the pile foundation, and the design of supporting measures should also pay attention to the control of pile foundation displacement.

The disturbance zoning of the bridge deck can be seen in Fig.17. The fact that the settlement of bridge pile foundation on both sides of the tunnel leads to the uneven settlement of the bridge deck and the deflection is the main reason for the disturbance of the bridge deck. The settlement of the bridge deck on both sides of the pile foundation near the tunnel is the largest and the disturbance is greater. The bridge deck disturbance between the bridge pile foundations on both sides near the tunnel axis is medium disturbance. In a word, the bridge deck structure is less disturbed by the tunnel approaching construction, and the maximum disturbance extent under the normal support condition is 0.42.

Fig.18(a) shows the disturbance zoning of pipeline 1, and Fig.18(b) shows the disturbance zoning of pipeline 2. The influence of tunnel approaching construction on underground pipelines is relatively large, and the range of ±20 m above the tunnel axis belongs to the strong disturbance range. pipeline No. 1 is strongly disturbed in the range of −19.5 to 17.3 m (tunnel axis is 0 m), and the maximum disturbance extent is 0.72. Pipeline 2 passes through the bridge piles, and the disturbance extent of the pipeline affected by the bridge piles is larger than that of pipeline 1. The pipeline is strongly disturbed in the range of –22 to 20.6 m, and the maximum disturbance extent is 0.74.

4.4 Comparison of structural disturbance zoning without reinforcement measures

To explore the performance of the ‘bridge pile sleeve valve pipe grouting and underground pipeline ground grouting and tunnel advance grouting’ close reinforcement measures adopted in the background project, the numerical simulation that removed the reinforcement measures (only 50 mm synchronous grouting ring) was carried out and recalculated, and the same method was used to analyze the disturbance zoning of the structure under the condition of no reinforcement measures.

The disturbance extent and disturbance zoning of bridge piles without reinforcement measures can be seen in Fig.19. Compared with Fig.16, the disturbance of compressive stress of single pile without reinforcement measures changes little. Although the compressive stress increases slightly, the overall disturbance extent is still less than 0.3. For the displacement disturbance, the displacement disturbance of pile 3 to pile 6 in the unsupported working condition is obviously improved. The disturbance extent of pile 5 is the largest, changing from 0.51 to 0.62, and the displacement disturbance extent of four piles increases by about 20%. For the single pile disturbance zoning, the disturbance zone of pile 3 to pile 6 without reinforcement is medium disturbance, and other bridge piles are still in extremely weak disturbance. From the optimization of reinforcement measures, the sleeve valve pipeline grouting reinforcement used in bridge piles can be used to reduce the displacement disturbance of bridge piles, but the reinforcement effect is not significant. In addition, the reinforcement measures of bridge piles far away from the center of the approaching construction section have no obvious effect and can be removed from the economic point of view.

The disturbance of the bridge deck structure is directly affected by the uneven settlement between the bridge piles. From the analysis of bridge piles, it can be seen that the settlement of bridge piles increases in unsupported working condition, but changes evenly. Therefore, the law of bridge deck disturbance zoning remains unchanged, and only the extent value increases. As illustrated in Fig.20, the bridge deck experiences maximum disturbance at the location of the bridge pile on the right side, but it is still considered medium disturbance. The extent of the maximum disturbance is 0.506.

The disturbance zoning of underground pipelines under the condition of no reinforcement measures can be seen in Fig.21. Pipeline 1 is in the extremely strong disturbance zone between −13.3–−8.2 m and 6.3–11.7 m, and the maximum disturbance extent reaches 0.813, while Pipeline 2 is in the extremely strong disturbance zone between −13.3–−7.8m and 5.8–17m, and the maximum disturbance extent is 0.824. Compared with the working conditions of the reinforcement measures, the peak value of the disturbance extent increased by about 0.9. During the tunnel excavation construction, the disturbance is also greater due to the closer distance between the pipelines and the excavation surface, and the pipelines are also the structure with the greatest risk of the approaching construction project.

4.5 Discussion

Based on the zoning results of the Liucun Tunnel approaching construction section, it is evident that underground pipelines are subjected to the most severe construction disturbance caused by tunneling activities. Consequently, the reinforcement scheme should focus on minimizing the disturbance to the pipelines. First, the distance between the ground grouting reinforcement area and the pipelines is 1 m, which will weaken the effect of the reinforcement scheme. Accordingly, the ground grouting range should be increased and the distance between the grouting reinforcement area and the pipeline should be reduced. Either reinforce the surrounding areas of the underground pipelines with circumferential grouting to enhance the soil’s resistance to settlement, or directly control the deformation of the pipelines by strengthening their stiffness. The peak value of underground pipeline disturbance is roughly in the position of 5m outside the left and right excavation boundary of the tunnel. Accordingly, in order to reduce the influence of tunnel excavation, the range of advance grouting reinforcement can be increased by 5 m, covering the range of strong disturbance zone of pipelines caused by tunnel construction.

The stress and deformation of structures in the extremely weak disturbance zone (E) are minimally affected by tunnel construction, and generally do not require special engineering measures. Structures in the weak disturbance zone (D) are subject to minor effects, with slight disturbances in stress and deformation of the structures. Structures within this disturbance zone should undergo corresponding deformation monitoring to ensure structural safety in exceptional circumstances. For structures in the medium disturbance zone (C), the structural disturbances are still within the normal range. It is possible to reinforce the heavily disturbed formation in specific areas, such as using tunnel advance grouting for reinforcement, to reduce disturbances. Additionally, it is important to strengthen disturbance monitoring and implement preventive engineering measures. For structures in the strong disturbance zone (B), tunnel construction disturbances will have a significant impact on the performance of existing structures. Prior to construction, targeted strengthening design should be implemented to reinforce the formation and structures in close proximity. For structures in the extremely strong disturbance zone (A), tunnel construction disturbances pose significant safety risks to existing structures and can cause structural damage. In addition to implementing reinforcement measures, it is necessary to consider engineering risk mitigation strategies such as tunnel route changes, personnel evacuation plans, and relocation of affected individuals or properties.

The proposed disturbance zoning method in this study enables the analysis of tunnel construction disturbances on urban structures prior to construction design. It can assess for the evaluation of the degree of disturbance to nearby structures and identifies high-risk locations for disturbances. During the design and construction phases, specific reinforcement measures can be implemented for areas with significant disturbances. Furthermore, a comparative analysis of support effects under different reinforcement schemes can be conducted to identify effective approaches for reducing tunnel construction disturbances.

5 Conclusions

To investigate the impact of tunnel construction on nearby buildings, this paper introduces a calculation method for assessing the extent of disturbance based on the allowable limit of structural safety. Additionally, a method for assessing construction disturbance zones near tunnel approaching piles, urban ground structures, and underground structures was also summarized. Combined with the engineering example of Chengdu Jinxiu Tunnel undercrossing existing bridges and underground pipelines, the method of field test and numerical analysis is used to analyze the influence of tunnel construction on adjacent buildings and divide the disturbance zone of adjacent structures. The following conclusions are obtained.

1) According to the field monitoring test, the increase of surface subsidence in the approaching construction interval mainly occurs within one week before and after the tunnel excavation surface passed. The surface subsidence on the tunnel cross section is ‘W’ type distribution, and the ground settlement is the largest in the position of 5 m outside the boundary of the excavation surface, and the maximum settlement is −11.03 mm. In addition, the ground settlement at the position of the bridge pile is increased by the influence of the bridge pile foundation.

2) Through the analysis of disturbance zoning for structures affected by approaching construction, it is observed that tunnel construction results in minimal disturbance to individual piles, and the maximum disturbance zone falls within the range of medium disturbance. The single pile is mainly disturbed by displacement, while the stress disturbance extent is small. The deflection disturbance of the bridge deck is influenced by the settlement of bridge piers. The peak of the bridge deck disturbance is at the position of bridge pile, and the maximum disturbance zone is also medium disturbance. Underground pipelines are most severely affected by tunnel construction disturbances. Within the 2D range of the tunnel axis, underground pipelines belong to high disturbance zones.

3) Through comparative analysis of numerical calculations with and without grouting reinforcement measures, it has been determined that the “bridge pile sleeve valve pipe grouting & underground pipeline ground grouting & tunnel advance grouting” scheme can effectively reduce the vertical settlement of bridges and pipelines. Moreover, this scheme can decrease the settlement disturbance extent of structures by approximately 0.1. In view of the shortcomings of reinforcement measures, it is suggested that the protection of underground pipelines should be appropriately enhanced in construction design.

4) The disturbance zoning method proposed in this study allows for the assessment of the level of interference caused by tunnels to nearby structures before construction design and identifies high-risk locations of interference. It can be applied to targeted design reinforcement solutions in the design process.

References

[1] Liu C, Zhang Z X, Kwok C Y, Jiang H Q, Teng L. Ground responses to tunneling in soft soil using the URUP method. Journal of Geotechnical and Geoenvironmental Engineering, 2017, 143(7): 04017023

[2] Huang Z, Zhang C, Fu H, Deng H, Ma S, Fu J. Numerical study on the disturbance effect of short-distance parallel shield tunnelling undercrossing existing tunnels. Advances in Civil Engineering, 2020, 2020: 8810658

[3] Liang R, Xia T, Hong Y, Yu F. Effects of above-crossing tunnelling on the existing shield tunnels. Tunnelling and Underground Space Technology, 2016, 58: 159–176

[4] Wang J, Zhou P, Song Z, Li S, Zhang Q. A new calculation method for tunneling-caused stratum settlement. KSCE Journal of Civil Engineering, 2022, 26(6): 2624–2640

[5] Zhu Q, Ding Y. Impact of new undercrossing tunnel excavation on the stability of the existing tunnel. Frontiers of Earth Science, 2022, 10(6): 1–12

[6] Huang M, Zhang C, Li Z. A simplified analysis method for the influence of tunneling on grouped piles. Tunnelling and Underground Space Technology, 2009, 24(4): 410–422

[7] Hu H, Zhu Y, Zhang G, Zhang H, Tu P. The environmental effects induced by a metro shield tunnel side-crossing on adjacent pile foundations and its impact partition. Advances in Civil Engineering, 2021, 2021: 8216724

[8] Zhou J, Sun Z, Wei B, Zhang L, Zeng P. Deflection-based multilevel structural condition assessment of long-span prestressed concrete girder bridges using a connected pipe system. Measurement, 2021, 169(4): 108352

[9] Li J, Fang Q, Liu X, Du J, Wang G, Wang J. Mechanical behaviors of existing large-diameter tunnel induced by horseshoe-shaped undercrossing twin tunnels in gravel. Applied Sciences, 2022, 12(14): 7344

[10] Ou X, Liu Y, Li C, Zhou X, Chen Q, Zhou Y, Zhang Q. Analysis of the interaction effects of shield structure oblique passing under an existing tunnel. Applied Sciences, 2022, 12(11): 5569

[11] Lan X, Zhang X, Li X, Li Z, Liu Y, Xia M. Model experiment on surface subsidence induced by excavation of shallow small-spacing tunnels. Environmental Earth Sciences, 2022, 81(4): 133

[12] Zhang D, Liu B, Qin Y. Construction of a large-section long pedestrian underpass using pipe jacking in muddy silty clay: A case study. Tunnelling and Underground Space Technology, 2016, 60: 151–164

[13] Boonyarak T, Phisitkul K W W, Ng C, Teparaksa W, Aye Z Z. Observed ground and pile group responses due to tunneling in Bangkok stiff clay. Canadian Geotechnical Journal, 2014, 51(5): 479–495

[14] Yang Z, Wang X. Influence of metro tunnel excavation on deformation of existing pedestrian underpass in Changzhou railway station platform. IEEE Access: Practical Innovations, Open Solutions, 2020, 8: 55860–55871

[15] Song G, Marshall A M. Centrifuge study on the influence of tunnel excavation on piles in sand. Journal of Geotechnical and Geoenvironmental Engineering, 2020, 146(12): 04020129

[16] Lee C J. Three-dimensional numerical analyses of the response of a single pile and pile groups to tunnelling in weak weathered rock. Tunnelling and Underground Space Technology, 2012, 32: 132–142

[17] Chen L T, Poulos H G, Loganathan N. Pile responses caused by tunneling. Journal of Geotechnical and Geoenvironmental Engineering, 1999, 125(3): 207–215

[18] Zhang Z, Zhang M, Zhao Q. A simplified analysis for deformation behavior of buried pipelines considering disturbance effects of underground excavation in soft clays. Arabian Journal of Geosciences, 2015, 8(10): 7771–7785

[19] Yan X, Sun Z, Li S, Liu R, Zhang Q, Zhang Y. Quantitatively assessing the pre-grouting effect on the stability of tunnels excavated in fault zones with discontinuity layout optimization: A case study. Frontiers of Structural and Civil Engineering, 2019, 13(6): 1393–1404

[20] Yu H, Chen X, Sun Y. A generalized bond-based peridynamic model for quasi-brittle materials enriched with bond tension–rotation–shear coupling effects. Computer Methods in Applied Mechanics and Engineering, 2020, 372: 113405

[21] Jing L, Kwok C Y, Leung Y F. Micromechanical origin of particle size segregation. Physical Review Letters, 2017, 118(11): 1–5

[22] Meng F, Chen R, Kang X. Effects of tunneling-induced soil disturbance on the post-construction settlement in structured soft soils. Tunnelling and Underground Space Technology, 2018, 80: 53–63

[23] Mahmutoǧlu Y. Surface subsidence induced by twin subway tunnelling in soft ground conditions in Istanbul. Bulletin of Engineering Geology and the Environment, 2011, 70(1): 115–131

[24] Liu D, Liu X, Zhong Z, Han Y, Xiong F, Zhou X. Realization of super-large-diameter slurry shield passing through settlement-sensitive area based on unreinforced disturbance control technology. Computational Intelligence and Neuroscience, 2022, 2022: 6299645

[25] Ren T, Zhang H, Guo Y, Tang Y, Li Q. Numerical simulation of ground surface settlement of underpass building in tunnel boring machine double-line tunnels. Frontiers of Earth Science, 2022, 10: 1–11

[26] Sun F, Jin Z, Wang C, Gou C, Li X, Liu C, Yu Z. Case study on tunnel settlement calculations during construction considering shield disturbance. KSCE Journal of Civil Engineering, 2023, 27(5): 2202–2216

[27] Zhu Z, Sheng Q, Zhang Y, Liu S. Numerical modeling of stress disturbance characteristics during tunnel excavation. Advances in Materials Science and Engineering, 2020, 2020: 4508905

[28] WangCPeng ZGouCFengKWuW LinH. Study on the influence zone partition method of shield tunnel-pile foundations approaching construction. China Civil Engineering Journal, 2017, 50: 174–181 (in Chinese)

[29] Japan Railway Joint Technology Research Institute. Manual for Construction Work of Existing Tunnel, 1995

[30] JGJ94-2008. Technical Code for Building Pile Foundations. Beijing: Ministry of Housing and Urban-Rural Development of the People’s Republic of China, 2008 (in Chinese)

[31] JTG3362-2018. Specifications for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts. Beijing: Ministry of Transport of the People’s Republic of China, 2018 (in Chinese)

[32] GB/50007-2011. Code for Design of Building Foundation. Beijing: Ministry of Housing and Urban-Rural Development of the People’s Republic of China, 2011 (in Chinese)

[33] GB50332-2002. Structural Design Code for Pipelines of Water Supply and Waste Water Engineering. Beijing: Ministry of Housing and Urban-Rural Development of the People’s Republic of China, 2002 (in Chinese)

[34] GB/T51438-2021. Design Standards for Shield Tunnel Engineering. Beijing: Ministry of Housing and Urban-Rural Development of the People’s Republic of China, 2021 (in Chinese)

[35] GB50068-2018. Unified Standard for Reliability Design of Building Structures. Beijing: Ministry of Housing and Urban-Rural Development of the People’s Republic of China, 2018 (in Chinese)

[36] Liu C, Zhang Z, Regueiro R A. Pile and pile group response to tunnelling using a large diameter slurry shield—Case study in Shanghai. Computers and Geotechnics, 2014, 2014(59): 21–43

RIGHTS & PERMISSIONS

Higher Education Press