Research on Pipe Jacking Construction Technology Based on Upcrossing Metro and Cable Tunnel

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IOP Conference Series: Earth and Environmental Science

PAPER • OPEN ACCESS

Research on Pipe Jacking Construction Technology Based on

Upcrossing Metro and Cable Tunnel

To cite this article: Qiang Wang et al 2021 IOP Conf. Ser.: Earth Environ. Sci. 651 042014

View the article online for updates and enhancements.

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3rd International Conference on Green Energy and Sustainable Development IOP Conf. Series: Earth and Environmental Science 651 (2021) 042014

IOP Publishing doi:10.1088/1755-1315/651/4/042014

Research on Pipe Jacking Construction Technology Based on

Upcrossing Metro and Cable Tunnel

Qiang Wang, Zong Liu, Guangwu Yang and Haoliang Wang * SINOHYDRO BUREAU 14CO.LTD, Kunming 650041, China *Corresponding author e-mail: [email protected]

Abstract. Based on the sewage pipeline defect repair project of Shizuo Road, Baiyun District, Guangzhou City, this article uses traditional technology to repair the basic pipelines of the old and new urban areas and the environmental conditions of the construction section. The pipe jacking construction in the trenchless repair is used to cross the subway and the construction pipeline. The complicated construction technology of the cable tunnel is discussed. Using the Peck empirical formula to estimate the ground settlement and its deformation pressure on the surrounding tunnels, the maximum deformation of the tunnel pipeline in the soil disturbance area during the construction process of the project is 0.80mm, and the maximum deformation of the subway tunnel is 1.42mm, which accurately reflects the roof The impact of pipe construction on the soil of surrounding tunnels. And study the disturbance influence of the two soil stabilization technologies of high pressure jet grouting pile and work well top-down construction method on the surrounding soil during the construction process, minimize the disturbance influence of the pipe jacking construction method on the surrounding soil, and ensure the construction quality and safety of the site.

1. Introduction

During the development of Chinese urban, the engineering demand for pipeline laying, renovation and restoration in new and old urban areas is increasingly strong. Compared with the traditional excavation technology, the advantage of trenchless technology includes small operational surface, fast speed, little pollution and no influence on ground construction and traffic and so on [1]. Based on the defect repair project of sewage pipeline in Shizuo Road, Baiyun District, Guangzhou city, this paper presents trenchless construction of complex underground pipelines of formed upcrossing metro and formed cable tunnel. Pipe jacking technique covers less area, greatly reduces construction cost and improves overall construction efficiency. When passing through obstacles, the demolition work along the road is reduced to save cost. The construction process is low noise, little pollution, and does not affect the ground activities [2]. According to the advantages referred above, trenchless pipe jacking technology was selected as the support project. It provides technical and engineering experience reference for the construction project of complex underground pipeline crossing in the future.

2. Support project overview

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a new pipeline should be built to connect the municipal sewage pipeline across the road. The jacking pipe, which is 120 meters long, includes one Φ 1,700 mm working well and two Φ 5,000 mm receiving wells. Each well is dug at a depth of 6.80 meters. Working well and receiving well mainly adopt up-down method for construction. The d800 Ⅲ reinforced concrete pipe with type F interface is used as pipe jacking material. The constructing way is slurry balance pipe jacking construction.

There are telecommunication, traffic signals and power pipelines on the south side of the foundation pit. The south receiving well is located above the shield tunnel of the left line of the north extension line of line 8 (construction has been completed). The vertical distance between the bottom of the foundation pit and the subway tunnel is about 8.5 meters. The receiving well in the east side is located on the pavement of Shizuo road, and there is a sewage pipe on the west side of foundation pit. Pipe jacking goes up through the 220kV Shijing to Kaixuan cable tunnel and the right tunnel of north extension line of line 8. The vertical distance between pipeline and cable tunnel is about 2.7 meters.

The stratum through which pipe jacking is carried out is mainly medium-coarse sand layer with special geological conditions, and it goes through metro tunnel and cable tunnel. The special geological conditions of soil layer and the complex underground pipeline bring great challenges to the smooth development of pipe jacking construction.

3. Analysis and corresponding measures of construction key and difficult points

3.1. Technology key

3.1.1. Analyse the degree of soil deformation. In the process of pipe jacking construction, the soil stress

state changes due to earthwork excavation above the running tunnel, which causes deformation and migration of the existing tunnel and affects the safe operation of the tunnel. When the pipe jacking construction enters into the influential range of existing tunnels, measures such as soil eating climb and the rectification of jacking force should not be used too much to adjust the pipe jacking attitude substantially. It is necessary to define the construction influenced area and investigate the deformation degree of tunnel soil during the construction process. So as to ensure the safe operation of existing tunnels and smooth construction of pipe jacking.

3.1.2. Reduce the influence of soil disturbance. The soil in the pipe jacking section of this project is

medium-coarse sand layer with high water level and general soil strength. Due to the general strength of soil, it is easy to cause formation deformation, resulting in pipeline fracture or cracking around and road collapse. High pressure jet grouting pile technology should be used to reinforce the soil in the pipe jacking construction section. At the same time, the up-down method of working well should be used to reduce the influence of working well construction on soil disturbance. It can not only effectively avoid the construction quality problem of "popping up" and "sinking", but also reinforce foundation and cut off the water flow [3].

3.2. Technology difficult points

3.2.1. Accurate control of the process. The pipe jacking construction site is located at the T-junction of

the main road in Guangzhou City, with a large traffic flow and numerous surrounding residential areas. So it’s hard to direct the traffic under construction. There are metro tunnels and cable tunnels under foundation pits and pipelines. The soil is medium-coarse sand with general bearing capacity. How to ensure the safety of metro tunnels is the key and difficult point in this project. During the construction process, the site should be well covered and the traffic should be well directed. Site staff should be experienced and highly skilled.

3.2.2. Pipeline survey and protection. The distribution of road pipelines is complicated. In addition, the

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cable, etc., which have a great impact on the follow-up work and make the construction organization more difficult. The preparation stage should be fully connected with the relevant parts to make clear the underground pipeline direction and buried depth.

4. Theoretical analysis and construction

4.1. Calculation of construction disturbance area and soil deformation around the tunnel

The complex mechanical actions such as loading or stress release of the soil around the pipe jacking may cause deformation of the surrounding soil. The soil disturbance zoning model is shown in Figure 3. Among them, region Ⅰ, Ⅱ, Ⅲ are obviously change in soil stress, known as the construction disturbance region. While soil mass stress state in region Ⅳ basically remain unchanged [4]. Some studies have shown that the principle of pipe jacking is similar to that of shield tunneling and the disturbance deformation of soil layer [5-6].

Peck proposed the formula for estimating the lateral distribution of surface settlement in shield construction in 1969 [7]. According to the calculation formula, the soil deformation degree of adjacent pipeline and subway tunnel can be obtained by estimating the ground settlement of pipe jacking construction [8]. Ground settlement formula:

𝑆𝑆(𝑥𝑥) = 𝑉𝑉1 √2𝜋𝜋×𝑖𝑖𝑒𝑒𝑥𝑥𝑒𝑒 �− 𝑥𝑥2 2𝑖𝑖2� (1) 𝑆𝑆𝑚𝑚𝑚𝑚𝑥𝑥=_{√2𝜋𝜋×𝑖𝑖}𝑉𝑉1 ≈_2.5𝑖𝑖𝑉𝑉1 (2) 𝑖𝑖 =_{√2𝜋𝜋 𝑡𝑡𝑚𝑚𝑡𝑡(45°−}𝑧𝑧 𝜑𝜑 2) (3) 𝑉𝑉1= 𝜋𝜋(𝑟𝑟2− (𝑑𝑑₂)2) (4) 𝑊𝑊 = 2 × (𝑟𝑟 + 𝑧𝑧 tan �45° −𝜑𝜑₂� (5)

In the formula: S(x) ——Land subsidence, mm

x ——The distance between the calculative point and the center line of the hole, m V1 ——Formation loss per unit bore length, m³/m

Smax ——Maximum settlement at the axis, mm i ——Settling tank width coefficient, m d ——The casing diameter, m

z ——Overburden thickness (ground to tube wheelbase), m ψ —— Angle of internal friction, degree

r ——The hole diameter, m

W ——Total width of settling tank, m

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According to the relevant parameters of pipe jacking in Table 1 and substituting them into the above formulas (1)-(5) to get the influence of pipe jacking construction on the interval tunnel. In the working condition of metro tunnel, although there is still a certain distance between the excavation face of pipe jacking and the upper line of the tunnel, the maximum deformation of 0.80mm occurs in the pipeline tunnel, indicating that they have exerted mutual influence. In the working condition of metro tunnel, the maximum deformation of 1.42mm occurs because of the pipe jacking, which also indicates that the pipe jacking has a certain influence on the pipeline tunnel.

Table 1. Pipe jacking construction parameter table thickness of metro tunnel overburden / (Z1, m) thickness of pipeline tunnel overburden / (Z2, m)

the hole diameter

/( r, m) the casing diameter /( d, m)

15 8.3 0.8 0.98

According to the calculated data, pipe jacking has little influence on the formed metro tunnel and pipeline tunnel in this project. However, it is still necessary to control the pipe jacking so as to reduce soil disturbance and prevent soil from shear failure. Therefore, in the construction process, the following technical measures are proposed to reduce the impact on pipelines and metro tunnels [8]:

(1) Strictly control the pipe jacking speed and output. In the process of construction, the soil within the construction scope is uneven, so the compressed soil will exert pressure on the tunnel in the process of pipe jacking forward. Therefore, the information of deformation in the tunnel should be closely monitored and the advance speed should be timely fed back and adjusted. The overlying soil should be slightly uplifted above the cut so as to prevent later settlement.

(2) Synchronous grouting and secondary back-wall grouting. Checking and controlling synchronous grouting quantity and slurry quality on site to reduce soil deformation during construction. The interval between the secondary grouting and synchronous grouting should be kept a certain distance that is about 20cm. At the same time, the space in the soil body is further filled to maintain synchronization and the late subsidence of the ground is controlled.

4.2. Construction procedure and effect

The main procedures of pipe jacking construction in this project are listed as follows: construction preparation, pipeline detection, measurement and setting out → construction of working well and receiving well → equipment installation and commissioning → tunneling and pipe jacking → grouting → pipeline connection → closed water test → earthwork backfilling.

According to the geological survey report, the soil was from top to bottom filled with miscellaneous soil, silty clay, medium-coarse sand, silty clay. The floor of the working well and receiving well is located in the middle coarse sand and silty clay layer. According to the design requirements, in order to consider the impact of pipe jacking on the surrounding soil, high-pressure jet grouting piles are arranged around the pipe jacking and outside the working well protection wall during the implementation of pipe jacking project. Pile spacing is 350mm, a total of 2,288 pieces, and the pile length should not go deep within the metro protection line (5 meters outside the tunnel). Portland cement is 42.5R and water-cement ratio is 1:1. The water-cement content is greater than 0.3 t /m, the shotcrete pressure is greater than 20MPa and the pile lifting rate is controlled at 0.2m/min. Strengthening the soil at the pipe jacking hole in advance can effectively avoid the soil "popping" and "sinking" and reduce the deformation pressure of the pipe jacking on the tunnel.

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grade is C30, impermeability grade is P6. The floor thickness of the net protective layer of reinforcement is 40mm, and the rest 35mm.

During the on-site construction, due to the theoretical model calculation in the early stage, as well as the rigorous attitude of on-site construction technicians and rich experience in pipe jacking, the entire construction was completed as planned, without any impact on the cable tunnel and metro tunnel below. 5. Epilogue

In the actual construction process, fundamental pipeline laying and defective pipeline repair engineering may run into special construction sections and environment [10]. This paper relies on the pipeline restoration project in “villages” in city of Baiyun District, Guangzhou City, which is faced with the construction situation of the coarse sand layer pipe jacking in the subway and cable tunnel of the pipeline crossing and forming. The Peck empirical formula was used to analyze the soil disturbance area and soil deformation during pipe jacking and quantitatively reflect the influence of pipe jacking on formed metro tunnel and cable tunnel. At the same time, in order to solve the problem of poor geological condition of medium-coarse sand layer and the limitation of construction site, the high pressure jet grouting pile technology and up-down method are adopted to reduce the influence of working well construction on the tunnel in the region. They ensure construction safety and smooth and effectively solve the problem of construction site restriction. It avoids the hindrance to citizens' travel during the construction process and greatly reduces the disturbance to the surrounding structures and soil.

References

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[2] Feng Haining. Environmental effects and countermeasures of pipe jacking construction [D]. Zhejiang University, 2003.

[3] Lin Fankang. Application of pipe jacking construction in municipal water supply and drainage construction[J]. Housing and Real Estate, 2016(06): 158.

[4] Lin Jindun. Application of pipe jacking construction technology for municipal water supply pipelines[J]. Jiangxi Building Materials, 2018 (04): 109+111.

[5] Shi Chenghua, Huang Linchong. Calculation of soil deformation in disturbance zone of pipe jacking construction[J]. Journal of Central South University (Natural Science Edition), 2005(02): 323-328.

[6] Song Wenxin, Zheng Bin, Luo Weijin, Yang Lanqiang. Study on the influence of foundation pit excavation in soft soil area on adjacent power pipe jacking tunnel[J]. Bulletin of Science and Technology, 2018, 34(11): 197-203+208.

[7] Pan Jianli. Calculation method and application of soil deformation caused by pipe jacking construction [J]. Journal of Jilin University (Earth Science Edition), 2016, 46(05): 1458-1465. [8] Chen Hailong, Liu Huajun, Xu Lei. Discussion on the application of high-pressure jet grouting in the construction of pipe jacking in soft soil [J]. Heilongjiang Science and Technology Information, 2009(15): 221.

[9] Song Pengfei, Cao Xiaokang, Wang Feiteng. Application of double-pipe high-pressure jet grouting pile in pipe jacking of urban roads [J]. Architecture, 2013(04): 74-75.