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Use of a 10.22   m diameter EPB shield: a case study in Beijing subway construction

View Article: PubMed Central - PubMed

ABSTRACT

Introduction: Beijing subway line 14 includes four stations and approximately 2.8 km of tunnels between the Dongfengbeiqiao and Jingshunlu areas of the city. Due to the surface and underground space limitations of this section, a double-track running tunnel instead of two single-track running tunnels was adopted to connect the two stations. The double-track tunnels were excavated by a 10.22 m diameter earth pressure balance (EPB) shield. It was the first time that an EPB shield more than 10 m in diameter was used in Beijing subway construction.

Case description: The shield, which passes underneath densely built-up areas of the city and is equipped with a spoke-type cutterhead, with balance between the ground pressure and the earth chamber pressure at the tunnel face, is of great importance. Referring to experiences gained in the EPB shield tunneling, attention was paid to the function of soil conditioning and simultaneous backfilling grouting of the shield, and some special designs were considered in manufacturing the machine.

Discussion and evaluation: In addition to the agitating rods welded to the cutterhead, two independently driven agitators were added to fully mix everything in the earth chamber. Independent pipelines were arranged for injecting different conditioning agents. Indoor tests in combination with field tests were conducted to find suitable additives and injection ratios of the additives, and determine the mix ratio of the two-component grout for simultaneous backfilling grouting. A scheme was employed for simultaneously injecting the bentonite slurry at 8% concentration and the foam liquid at 5% concentration to condition the excavated soil. The cement–sodium silicate grout was adopted to fill the tail void and the injection volume per ring was 14.1–15.3 m3.

Conclusions: The performance of the shield and evaluation of the corresponding tunneling technologies are introduced in terms of the shield tunneling induced ground surface settlements. The success of the project is of great significance to Beijing subway construction and underground space utilization. The findings serve as a useful reference for similar projects.

No MeSH data available.


Longitudinal section between Gaojiayuan station and Jingshunlu station
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Fig2: Longitudinal section between Gaojiayuan station and Jingshunlu station

Mentions: The soils at the job site can be divided into three groups: (1) backfill; (2) silt and silty clay and (3) fine and medium sand, as shown, taking the running tunnel between Gaojiayuan station and Jingshunlu station as an example, in Fig. 2. The soil group properties are listed in Table 1. There are four types of aquifers involved: (1) perched aquifer, (2) unconfined aquifer, (3) confined aquifer I and (4) confined aquifer II, with water tables of 2.98–6.79, 5.98–9.25, 11.70–18.40 and 21.00–27.65 m underneath the surface, respectively. The overburden depth ranges from 11.3 to 21.2 m. Two elements concerning the tunnel alignment are the minimum curve radius of 350 m and the maximum slope of 27‰. The soils of sand, rich in ground water, the shallow overburden, and the small curve radius will together contribute to high surface settlement if not properly addressed.Fig. 2


Use of a 10.22   m diameter EPB shield: a case study in Beijing subway construction
Longitudinal section between Gaojiayuan station and Jingshunlu station
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5121113&req=5

Fig2: Longitudinal section between Gaojiayuan station and Jingshunlu station
Mentions: The soils at the job site can be divided into three groups: (1) backfill; (2) silt and silty clay and (3) fine and medium sand, as shown, taking the running tunnel between Gaojiayuan station and Jingshunlu station as an example, in Fig. 2. The soil group properties are listed in Table 1. There are four types of aquifers involved: (1) perched aquifer, (2) unconfined aquifer, (3) confined aquifer I and (4) confined aquifer II, with water tables of 2.98–6.79, 5.98–9.25, 11.70–18.40 and 21.00–27.65 m underneath the surface, respectively. The overburden depth ranges from 11.3 to 21.2 m. Two elements concerning the tunnel alignment are the minimum curve radius of 350 m and the maximum slope of 27‰. The soils of sand, rich in ground water, the shallow overburden, and the small curve radius will together contribute to high surface settlement if not properly addressed.Fig. 2

View Article: PubMed Central - PubMed

ABSTRACT

Introduction: Beijing subway line 14 includes four stations and approximately 2.8 km of tunnels between the Dongfengbeiqiao and Jingshunlu areas of the city. Due to the surface and underground space limitations of this section, a double-track running tunnel instead of two single-track running tunnels was adopted to connect the two stations. The double-track tunnels were excavated by a 10.22 m diameter earth pressure balance (EPB) shield. It was the first time that an EPB shield more than 10 m in diameter was used in Beijing subway construction.

Case description: The shield, which passes underneath densely built-up areas of the city and is equipped with a spoke-type cutterhead, with balance between the ground pressure and the earth chamber pressure at the tunnel face, is of great importance. Referring to experiences gained in the EPB shield tunneling, attention was paid to the function of soil conditioning and simultaneous backfilling grouting of the shield, and some special designs were considered in manufacturing the machine.

Discussion and evaluation: In addition to the agitating rods welded to the cutterhead, two independently driven agitators were added to fully mix everything in the earth chamber. Independent pipelines were arranged for injecting different conditioning agents. Indoor tests in combination with field tests were conducted to find suitable additives and injection ratios of the additives, and determine the mix ratio of the two-component grout for simultaneous backfilling grouting. A scheme was employed for simultaneously injecting the bentonite slurry at 8% concentration and the foam liquid at 5% concentration to condition the excavated soil. The cement–sodium silicate grout was adopted to fill the tail void and the injection volume per ring was 14.1–15.3 m3.

Conclusions: The performance of the shield and evaluation of the corresponding tunneling technologies are introduced in terms of the shield tunneling induced ground surface settlements. The success of the project is of great significance to Beijing subway construction and underground space utilization. The findings serve as a useful reference for similar projects.

No MeSH data available.