Pressure Balance Tunnel Boring Machines Research Articles

A study on large volume losses induced by EBPM tunnelling in sandy soils

Tunnelling-induced ground surface settlements can be described by a Gaussian distribution curve with two key factors; the displacement trough width and the volume loss. In most cases the volume losses are well-controlled with maximum settlements less than the allowable limits. However, there have been reports showing abnormally large ground surface settlement, in sandy soil, induced by Earth Pressure Balance Tunnel Boring Machines (EPB TBMs). This research reports field data obtained during the construction of the Metro Line 1 Ben Thanh – Suoi Tien Tunnels in Ho Chi Minh city, Vietnam. Data include ground settlement measurements, the geotechnical conditions and TBM operation parameters. The results show that in locations where large settlements had occurred there were common characteristics of high liquefaction index, large excess pore pressure and abnormally large tail void grouting. A novel equation is suggested to describe the relationship between the volume loss and the liquefaction potential index. This has been calculated using simple and commonly available geotechnical parameters for use in practice as an indicator for potentially large settlements caused by EBP TBM tunnelling in sandy soils.

Stability analysis when tunnelling in soft soil condition in Hochiminh city

The rapid development in the economy and the urban population in cities in Vietnam in recent years leads to dramatic growth in traffic congestion, noise and air pollution, and environmental degradation. Urban underground infrastructure thus becomes an inevitable solution since the surface space becomes too expensive and restricted in spite of the high cost of tunnel construction. However, tunnelling in deltaic urban areas, in particular in the cases of Mekong Delta and Red River Delta areas, often faces to difficulties of soft soil conditions and the existence of important historical buildings on the surface. The first metro line constructed in Vietnam from Ben Thanh to Suoi Tien, which is located under crowded areas of Hochiminh city, was tunnelled in such conditions. This paper presents a back analysis for the stability of the tunnelling process in the project. The minimum support pressures is estimated by using the wedge model proposed by Jancsecz, S., & Steiner, W. (1994). Meanwhile, the maximum support pressure is estimated by the blow-out model proposed by Vu et al. (2016). Based on these results, the range of support pressures recommended for the Earth Pressure Balance Tunnel Boring Machine in the Hochiminh Metro Line No.1 project soft soil conditions is derived and compared to in situ support pressures obtained from the monitoring data in this tunnelling project. The study result shows a good agreement between the support pressures obtained from stability analysis models and the monitoring data from the construction site. Based on this back analysis, some recommendations are proposed with the purpose of successful construction in the next tunnelling projects in Hochiminh city.

Performance analysis of tunnel-boring machine by probabilistic systems approach

In this paper, the performance of an earth pressure balance tunnel-boring machine (EPB-TBM) during tunnel construction is analysed. A case study with data from the east–west part of the Tehran metro line 7 is employed to develop a methodology. Several parameters of different types that influence TBM operations in soft ground are identified and analysed, and the probabilistic systems approach is utilised to interpret the interactions between pairs of parameters. For this purpose, the probabilistic expert semi-quantitative and Monte Carlo simulation techniques have been employed. An index is developed to calculate the utilisation along the studied tunnel path. The results have been compared with real utilisation factor values from the project, showing an excellent agreement between estimations and observations.

Safe excavation of large section tunnels with Earth Pressure Balance Tunnel Boring Machine in gassy rock masses: The Sparvo tunnel case study

In the last decades mechanized tunnelling with Tunnel Boring Machines (TBMs) has spread, due to the sensible technological developments, allowing for higher advancement rates, huge excavation diameters (up to 17m) and lower excavation costs.Methane inflows from gassy rock masses may represent a serious hazard in underground excavations and could cause expensive delays and, at worst, tragic accidents to workers. Consequently, if methane-air mixtures may be present, a safety engineering system should be designed and set up before starting the excavation works in order to prevent fires or explosions.Due to the impossibility to prevent the contemporary presence of explosive gas-air mixtures and ignition sources, TBMs have never been adopted for tunnelling in gassy rock masses until 2011 (excluding the tunnels excavated with TBM, where methane gas hazard was underestimated, consequently producing delays and unpredicted expenses).The paper describes the safety engineering system developed for the excavation of the Sparvo twin tunnels (Italy) with EPB–TBM. The machine (Herrenknecht S-574) was specifically designed to prevent the risk of having explosive gas-air mixtures and ignition sources in the same place and at the same time, hydraulically confining the volumes inside the machine. After a brief description of the case study, the paper illustrates the design criteria, the technological solutions adopted for the construction of the Herrenknecht S-574 and the operating procedures. Then, the paper focuses on examining and interpreting the methane monitoring results during Sparvo tunnel construction, that highlight the presence of huge volumes of methane. The developed safety engineering system allowed tunnelling without interruptions even with sensible gas flows. Current limits and possible improvements to the safety system described are also discussed.

Environmental effects of tunnel excavation in soft and shallow ground with EPBM: the case of Istanbul

In metro tunnel excavations, it is important to control surface settlements observed before and after excavation, which may cause damage to surface structures. Otherwise, the metro tunnel cannot perform the task expected, and the advantages of the tunnel are lost. In this study, short-term surface settlements and their effect on buildings are examined in three zones for twin tunnels, which have been excavated between the Otogar and Kirazli 1 stations of the Istanbul Metro line, and are 5.8 km in length. Geology in the study area is composed of fill, stiff clay, dense sand, very dense sand, and hard clay, respectively, starting from the surface. Tunnels are excavated by using two Earth Pressure Balance Tunnel Boring Machines (EPBMs) with a 6.5 m diameter as twin tubes with 14 m distance from center to center. The EPBM in the right tube is followed about 100 m behind the other tube. Segmental lining with 1.4 m of length is currently employed as final support. The results of this study indicate that, with EPBM excavation method in shallow depths and soft grounds, the damage done to the environment prolonged project costs up to 15.8% more. In addition, tunnel conditions prolonged the project schedule to 29.3%.

Ground conditioning for earth pressure balance machine tunneling

Abstract The objective of this paper is to provide insight to the application of state-of-the-art ground modification technology for Earth Pressure Balance (EPB) soft ground tunneling. The paper reflects data from a wide array of sources including conference proceedings, trade journal articles, manufacturer publications, books and personal experience. The paper first introduces the concept of soft ground tunneling and then discusses the Earth Pressure Balance Tunnel Boring Machine method. The bulk of the paper is spent discussing ground-conditioning agents, particularly foam. Use of, quantities, theory behind them, environmental impact, lab testing, and effects of foams are described. The paper concludes with a brief case study of the Sheppard Subway Twin Tunnels in Toronto, Canada. Attached to the paper is a comprehensive literature search on EPB tunneling, particularly with regards to foam use.

Denmark’s First Metro System

A new mass transit system, the Copenhagen Metro, has been planned to connect the central part of Copenhagen and ∅restad. The contract for the detailed design and construction of the first phase of the Copenhagen Metro was signed in October 1996. The construction of the tunnels and underground stations could affect the stability of buildings and lead to formations of cracks resulting in structural damage unless adequate precautions are taken during the design and execution of the works. The key element in the control of risk of settlement damage is to adopt construction methods that minimise the likelihood of significant ground movement. The requirements led to a design based on tunnelling with earth pressure balance tunnel-boring machines and underground station excavations within retaining walls of secant piles, protected by grout curtains and grout blankets.