The Taipei Metropolitan Area Rapid Transit Systems is an important transportation project which the government has invested hundred billions NT dollars for solving urban traffic problems.The completion of the project will not only improve quality of life, but also will expedite national economic development as well as promotion of international standing.This project, which is being wholly underway at the capital area of Taiwan, has become a focus of all eyes and received eager expectations from various levels.
Based on a number of years experience on participating in the first rapid transit project in the country, the author believes that planning, design and construction of tunnel engineering for transit system are different from others. Particularily, the following items are introduced and reviewed in this paper:
(1) planning principle related to tunnel cross section, shape, alignment and ventilation,
(2) design philosophy involving tunnel linings, joints and construction environment,
(3) construction technology on mirror face excavation, curve-launching, driving control for sharp curve, building protection, settlement control, tunnel survey, etc.,
Hopefully, readers may realize that both safety and convenience have been sufficiently taken into account by Taipei rapid transit authority. In addition, considerations for strict quality requirements and safety control of construction would be good reference for future construction of underground tunnel for rapid transit system at other cities in the country.
MRT, railway, highway and lifelines are all very important to promote the living standard at Taipei metropolitan area. However the very dense population and land acquisition problem require active use of the underground space. Therefore, the tunnelling in difficult construction condition and soft ground at metropolitan area is unavoidable so that construction technique of tunnel becomes more and more important.
Tunnel at metropolitan area may meet construction difficulties, such as shallow overburden, underground water and soft ground. Also, it may encounter environmental impacts, such as ground subsidence, unpleasant noise and vibration. Though the adaptability and experience of NATM utilised in the said circumstance is limited, however, in consideration of the condition for low cost and appropriateness, NATM is still needed.
This paper aims to discuss the adaptability of NATM utilised in soft ground at Taipei metropolitan area. Also, the design and construction of NATM is included. It is expected that the experience derived from this paper would be helpful in gaining further insight into the planning of NATM at metropolitan area so that more effective design and techniques can be developed for such problem.
A statistical approach is introduced herein for obtaining representative normal distribution curves and computing ground loss and width parameters systematically from field data. Also introduced is a scheme to correct the eccentricity of settlement troughs. Surface settlement troughs over tunnels obtained for Construction Contracts CH218, CH223 and CP262 of the Taipei Rapid Transit Systems were analyzed accordingly and, based on the results obtained, empirical relationships were established for estimating the widths of settlement troughs in the T1, T2 and B2 Zones in the Taipei Basin.
Segmental Linings are widely used as lining structure for tunnels constructed by using full face tunnel boring machines. No unique methodology for the stress analysis of semental linings has been concluded in the international tunneling industry. Analytical methods widely used today are discussed and a more rigorous approach is introduced and supported by examples in this paper.
Suitable building protection measures may reduce lots of construction impact to the adjacent environment. The compensation grouting from inside bored tunnel is timely employed before ground loss develops up to ground surface. To conduct it, the grouting tube is inserted from the grout holes on segments to complete the secondary grouting into sublayer above the tunnel crown. Based on the long term instrumentation result, it indicates this method is also suitable for the soft soil condition of contract CC277 in the Taipei Mass Rapid Transit systems.
Significant ground settlement has been observed from time to time during shield tunnelling when backfill grout injection is not carried out accurately. It becomes more popular to use secondary grout injection at the proper time before the influence of ground loss to the surrounding medium extended to ground surface and to prevent/or reduce the ground settlement.
This paper will begin with explaining the relation between ground loss, backfill grout injection, and ground settlement. It also discribes the mechanism and application of secondary grout injection in reducing ground settlement. Case study focusing on the timing, area, construction management, material and effects of the secondary grout injection will also be given. It is expected that this paper can provide some valuable data for similar case in the future.
Ground settlement induced by shield tunnelling is an important issue in the tunnel construction in urban area. The ground loss and pore pressure change induced by the advance of shield machine and the unloading of excavation are the major causes for the ground settlement. To understand the mechanism of pore pressure evolution intense measurements of the pore pressure transducers are taken before and after shield machine passing through the monitoring section. An analytical model is established and verified by comparisons with the field data. Numerical analysis is performed to investigate the relationship between thrusts, excess pore pressure increments, and consolidation settlements.