Circle MRT Line 1 C825 Standard Tunnel Construction

Abstract Circle MRT Line 1 C825 Standard tunnel in Singapore of the most heart of the city, along the route there are many high-rise buildings, as well as the famous old buildings, tunnels using 2 sets manufactured by Herrenknecht earth pressure balance f6.6 m articulated Shield tunneling. Shield cutter through the improvement of, optimize the construction parameters, careful operation, so that shield smoothly and safely through the Y-Junction, underground garage pile groups and running south-west subway line.

Keywords Singapore Mass Rapid Transit earth pressure balance shield articulated through the building (structure) building materials

     1 Project Overview

     Circle MRT Line in Singapore a C825 marked the first phase of Metro Link project, following the North-East Line in Singapore in recent years after a major engineering projects.

     The project by the tunnel company, Wo Hop Pte Ltd, Singapore, Sweden, formed a joint venture engineering company NCC body design, construction, general contracting, the main workload, including four large-scale underground station and 2.6 km long tunnel in the upper and lower bound, temporary sections of the tunnel ( shield 600 m, cut-Law 275 m) and other ancillary structures, etc. (see Figure 1).

6 km long tunnel in the upper and lower bound, is located in the heart of Singapore's most prosperous, there are many high-rise buildings, as well as along the famous ancient buildings, such as the Pan Pacific Hotel, Raffles Hotel, municipal buildings and so on; the same time, the tunnel through the soil needed to layer of complex geological conditions, a number of underground obstacles, such as steel sheet piles, I-beam piles, boulders and so on.

     Tunnel in two German-manufactured f6.
6 m Herrenknecht earth pressure balance articulated shield tunnel outside diameter of 6.35 m, internal diameter of 5.8 m, maximum depth of 30 m. Use of precast concrete tunnel lining segment (segment width 1.4 m, thickness 275 mm), each ring by the five standard block and a cap block composition.

     Two geological conditions

     Shield through the formation along the big changes, from the mud to the composite layer, to the hardness of the hard rock up to 200MPa. Especially in the composite soil, the tunnel excavation face is often half rock, half of the soft soil; or soft soil entrained boulders, to the construction of the larger more difficult.

Mainly through the formation and old alluvium (OA), the weathered rock (S2) and weak weathered rock (S3), specific performance indicators in Table 1.

     ⑴ the cutter from five parts, the middle of the main part of the connected with the main drive; peripheral part of the 4 mosaic made of. During the construction after the end of the cutter can be removed from the tunnel, in the middle of the main parts can be reused;

     ⑵ cutter peripheral configuration of the two groups profile knife.
A group of profiling hob types of knives used to meet the needs of the rock strata; another group of scraper types, to meet the needs of soft soil layers. Of its hydraulic power supply, the operation control is divided into two kinds of manual and automatic mode;

Figure 2.
Cutter head

       ⑶ construction of the cutter can be flexible around 200 mm, to facilitate workers into Dokura removed H steel, the operator can quickly remove a continuous wall of steel, the replacement tool and more easy;

     ⑷ Cutter drive design is positive, reverse two kinds of models are divided into two block speed (stepless speed regulation);

     ⑸ cutter opening rate is 28% larger than 300 mm in diameter to prevent the boulder jammed into Dokura screw machines;

     ⑹ the scraper body mounted alloy film instead of using surfacing wear-resistant alloy, thus significantly reducing the amount of loss.

1.2 Assembled Machine

     ⑴ assembled machine before and after the use of wheel and rail travel form, travel about 2 m or so (which can be extended beyond its borders, on a ring segment);

     ⑵ damaged when the shield tail sealing brushes need to be replaced or shield the seal groove between the end of brush block filled with slurry, the assembly machine can remove brush at the end of the tube shield film;

     ⑶ assembled machines allow the head segment six degrees of freedom in the direction of rotation, so that the segment assembling more accurate and convenient.

1.3 hinged device

     Shield Shield connection with the main end use of hinged form, which makes operations more flexible shield, especially in the advance of curve segments, the effect more pronounced.

1.4 detection, control system

     ⑴ the cutter teeth on the digging of two, equipped with a tool wear detection system, when the tool wear to the required level, the system will issue a warning signal, that is, not ask for public assistance cases, to understand tool wear.

     ⑵ belt transport system in the installation of the excavated automatic weighing system, monitoring the amount of excavation to prevent surface subsidence caused by super-dug, weighing system, the accuracy within 10% deviation.

     ⑶ partial pressure system includes two pneumatic module (by decompression of compartments, the working area cabins), air pressure regulating devices, etc., may be required under conditions of pressure tool replacement, removed H steel pile foundation.

     ⑷ Siemens PLC control system, set up a chain of protective devices to prevent misuse and damage to equipment, as long as a particular problem in the system, other systems will stop functioning, and the question displayed on the screen to facilitate timely resolution of staff.

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     ⑸ SLS-T tunnel axis-oriented system that will shield the attitude information, timely and accurate feedback to the shield operators, after adjustment, so that the axis of advance is consistent with the design of the axis. The system also has a "pre-ring" feature, engineers enter the shield tail as long as the gap value, the system will be under the jack, hinged itinerary, automatically calculate the next location of a few ring segment for the operations officers.

2 Shield to promote

2.1 through the Y-Junction

     In the shield through the Y-Junction ago, has completed the underground continuous wall construction, and the reserve position in the shield through the 7 m diameter hole circle, the hole loop at a continuous wall of glass fiber instead of steel in order to shield across.

     Shield in the temporary segment promoting the 120 m, the southern route shield for a 3% slope down forward, the north line of shield upward slope of 4% of the advance. Into the Y-Junction in the area, the shield radius of 250 m along the tunnel axis to promote a left turn; in Y-Junction area (length 45 m), the formation of cross-stacked from top to bottom (intervals 3 m); a Y-Junction, the Also along the radius of 250 m turn right at the tunnel axis of advance, and then connected with a permanent tunnel (see Figure 3).

2.2 Pile groups through the underground garage

     Pan Pacific Hotels and Xi 1000 is Singapore's famous Plaza hotel and commercial center, its share has a huge traffic flow underground garage, and many hotel's water supply pipes, power lines are built on both sides of the underground garage. At the top of the garage with heavy traffic, Temasek Avenue, the hotel liaison channel between the ground and viewing is also supported by pillars in the underground garage on the pile foundation.

     Pile group by the bored piles, steel pipe piles (Raymond Pile) and micro-pile form.
Steel pipe piles and bored piles which is deeper than the tunnel depth 3 m, there are two steel pipe pile is located in the tunnel area, the need to shield forward during the process of pile replacement and removed (see Figure 4).

     In the garage of the column, beams, floor of the settlement control point, pre-installed on the stress meter, inclinometer, in advancing the process of shield, so that regular measurement, and timely feedback and, based on results of the monitoring and timely adjustment of the construction parameters to ensure that the entire underground garage security. Maximum settlement of pile group of 3 mm, pile replacement did not have any impact on the entire building complex.

2.3 through the operation of the Southwest line of Subway

     ⑴ Metro Southwest line of the 20th century 80 years the introduction of new Austrian law and shield the construction of two kinds of construction methods, and its junction is located just across the tunnel area, separated by a distance of only 3 m. Therefore, through the process is likely to result in differential settlement affecting the south-west subway line running.

     ⑵ across the region, formation of S2, is in the weathering rock, the intensity greater self-reliance is good, but easy to encounter boulders. Strength, help control the settlement, but the increase in tool wear, improving the frequency of the Open Position Tool Changer; strength does not help the settlement control, if you encounter boulders, knives plate can not be cutting them effectively, so that the whole excavation of the cutting surface uneven, leading to localized subsidence caused by super-dug.

     ⑶ repeated by calculating and expert proof shield two times through the tunnel after the final settlement must be controlled at 5 mm or less, otherwise, the operation of the subway will slow down or outage. Therefore taken the following measures:

     ① based on risk rating will be across the region is divided into three regions, respectively, ± 10 m, ± 20 m, ± 30 m, Figure 5.

     Shield before crossing through the region need to fully understand the actual situation of the soil to predict cutter cutting ability and tool change cycle, adjust the construction parameters.

     ② In the region near the third guard, the right shield annual maintenance, elimination of hidden faults and strive through the danger zone when the shield in the zero failure rate, to avoid the shield in the region caused by the settlement of long-term stay.

     ③ Shield reaches second warning zone must be carried out through the last one before the cutter repair, replace all the wear and tear

More than 5 mm of the hob; will be replaced by two new knife around the hob to ensure that the cutting radius of the cutter.
Ensure that the shield in the first and second guard unlocked the cells within the region without tool change.

     ④ In the shield through the period, must pay close attention to changes in soil surface excavation; the project team set up by the earth pressure, cutting speed and other parameters of the construction works; strictly controlling the amount of excavated (not super-digging, not less digging) to ensure that pressure pulp quality.

     ⑤ in accordance with design requirements, through the shield before the tunnel to monitor the running dispatched (see Figure 6).

     Shield 2 times through the tunnel, run the final settlement value of the tunnel 4 mm, to ensure the safety of running the tunnel.

     4 Conclusion

     March 8, 2005 Circle MRT Line 1 C825 Standard Tunnel Completed.
Singapore's Land Transport Authority, Metro Link, a project inspector (Project Director) Guy Taylor told Singapore's Straits Times interview, said: city center in Singapore to promote the C825 tunnel, is Singapore's history, the most complex and one of the most difficult projects, face enormous challenges, through our common efforts to make this tunnel to become one of Singapore's most successful projects. Reposted elsewhere in the paper for free download

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