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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.


Layout and makeup of the simultaneous backfilling grouting system
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Fig10: Layout and makeup of the simultaneous backfilling grouting system

Mentions: In view of the efficacy of confining the ground movements of backfilling using the two-component grouts, two-component system injection is progressively substituting the traditional use of cementitious mortars (Peila et al. 2011). The equipment for the two-component system was required for the 10.22 m diameter shield. Five sets of simultaneous backfilling grouting systems were arranged at five positions along the circumference of the 10.22 m diameter shield, as shown in Fig. 10. The system consisted of injection pipelines for A-liquid and/or B-liquid, injection jacks, oil-pressure pipes for the injection jack, water injection pipelines, a front switch, a back switch, a ball valve, oil-pressure pipes and injection ports. Additionally, three pumps for the A-liquid, three pumps for the B-liquid, two water pumps, and corresponding storage tanks, pipelines were provided.Fig. 10


Use of a 10.22   m diameter EPB shield: a case study in Beijing subway construction
Layout and makeup of the simultaneous backfilling grouting system
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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

Fig10: Layout and makeup of the simultaneous backfilling grouting system
Mentions: In view of the efficacy of confining the ground movements of backfilling using the two-component grouts, two-component system injection is progressively substituting the traditional use of cementitious mortars (Peila et al. 2011). The equipment for the two-component system was required for the 10.22 m diameter shield. Five sets of simultaneous backfilling grouting systems were arranged at five positions along the circumference of the 10.22 m diameter shield, as shown in Fig. 10. The system consisted of injection pipelines for A-liquid and/or B-liquid, injection jacks, oil-pressure pipes for the injection jack, water injection pipelines, a front switch, a back switch, a ball valve, oil-pressure pipes and injection ports. Additionally, three pumps for the A-liquid, three pumps for the B-liquid, two water pumps, and corresponding storage tanks, pipelines were provided.Fig. 10

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.