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

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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.


Recorded cutterhead torque
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Fig13: Recorded cutterhead torque

Mentions: In general, the well-controlled shield operation could be achieved when the slumps of the muck were more than 160 mm, with shield tunneling parameters remaining almost stable, as given in Figs. 13, 14 and 15. However, when the slumps reached 180 mm, the construction efficiency was significantly affected due to the difficulty in muck transport by the belt conveyor. Thus, the overly large slumps of the muck were not suitable. Higher earth chamber pressure and lower ground surface settlement were obtained when using the No. 1 and 2 formulations to condition the soil, as shown in Figs. 12 and 15. The surface settlement profiles in Fig. 15 were measured after grouting. When shield driving passing the test sections, the key shield operational parameter including grout injection volume were controlled at almost the same level to understand the conditioning effects using foam. The test sections were arranged with a spacing of more than 20 m, resulting the same influence of the test section locations on the measured settlements. Considering the ease of the operation, the conditioning scheme using the No. 1 formulation was suggested; however, the scheme using the No. 2 formulation was used, when more sand in the soils, with the increased injection ratio of the foam liquid. Variations of the total thrust and cutterhead torque with different formulations, as shown in Figs. 13 and 14, may have led to friction changes caused by different additives between the cutterhead, shield skin and soils.Fig. 13


Use of a 10.22   m diameter EPB shield: a case study in Beijing subway construction
Recorded cutterhead torque
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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

Fig13: Recorded cutterhead torque
Mentions: In general, the well-controlled shield operation could be achieved when the slumps of the muck were more than 160 mm, with shield tunneling parameters remaining almost stable, as given in Figs. 13, 14 and 15. However, when the slumps reached 180 mm, the construction efficiency was significantly affected due to the difficulty in muck transport by the belt conveyor. Thus, the overly large slumps of the muck were not suitable. Higher earth chamber pressure and lower ground surface settlement were obtained when using the No. 1 and 2 formulations to condition the soil, as shown in Figs. 12 and 15. The surface settlement profiles in Fig. 15 were measured after grouting. When shield driving passing the test sections, the key shield operational parameter including grout injection volume were controlled at almost the same level to understand the conditioning effects using foam. The test sections were arranged with a spacing of more than 20 m, resulting the same influence of the test section locations on the measured settlements. Considering the ease of the operation, the conditioning scheme using the No. 1 formulation was suggested; however, the scheme using the No. 2 formulation was used, when more sand in the soils, with the increased injection ratio of the foam liquid. Variations of the total thrust and cutterhead torque with different formulations, as shown in Figs. 13 and 14, may have led to friction changes caused by different additives between the cutterhead, shield skin and soils.Fig. 13

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.