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ABSTRACT: Growing needs for modern transportation and utility networks have increased the demand for a more extensive and elaborate use of underground space. As a result, more underground projects have to be completed in a variety of ground conditions, including weak water bearing soils and soft rocks. Significant technological advances have rendered these projects possible, but have also given rise to new challenges as many of these projects have to be completed in difficult conditions, with very strict environmental constraints, particularly in urban areas where the potential impact of tunneling on existing structures is a major concern. This report addresses the main aspects of tunneling and underground works performed in soils and soft rocks. A summary is presented of the main features related to construction techniques, ground investigations, design methods, and instrumentation and monitoring practices, as well as of some of the more recent advances in these fields. Significant progress has been made in the area of soft ground tunneling over the past thirty years, partly because of advances in computer technologies. The scope of increasing difficult project conditions to be addressed requires that the best use be made of these technologies, as well as of lessons gained from past experience and current observational records. 1.0 INTRODUCTION Growing needs for modern transportation and utility networks have given rise to an increased demand for a more extensive and elaborate use of underground space. Some of these projects are related to urban development, which requires the construction of more metro systems, underground water mains, gas pipes, telecommunication and electric power networks, as well as underground parking facilities. Other applications of underground construction include the crossing of natural barriers such as rivers and mountains that are found across the alignment of major road, motorway or railway link projects.
- North America > United States (1.00)
- Asia (0.93)
- Europe > France (0.68)
- Europe > Germany > Baden-Württemberg (0.28)
- Overview (1.00)
- Research Report > New Finding (0.67)
- Geology > Rock Type (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Transportation > Infrastructure & Services (1.00)
- Transportation > Ground > Rail (1.00)
- Materials (1.00)
- (2 more...)
Numerical Evaluation of Surface Settlement Induced by Shield Tunneling at Rock Mass
An, Jun-Beom (Korea Advanced Institute of Science and Technology, Rep. of Korea) | Bang, Jeonguk (Korea Advanced Institute of Science and Technology, Rep. of Korea) | Seong, Joo-Hyun (Korea Advanced Institute of Science and Technology, Rep. of Korea) | Cho, Gye-Chun (Korea Advanced Institute of Science and Technology, Rep. of Korea)
ABSTRACT: There are several precedents of unintended surface settlements resulting in enormous loss of costs and time, even if for the rock medium. The expansion of shield tunneling requires controlling the shield tunneling parameters precisely to reduce the surface settlements. In this study, numerical parametric studies are conducted to evaluate the geotechnical properties, and TBM operational factors on the surface settlements during shield tunneling. The numerical model based on FLAC3D is validated by comparing the results with the literature and field data. Ground stiffness is the dominant factor in the settlement, and the groundwater inflow follows it. The face pressure and tail void grouting pressure show a relatively weak impact on surface settlements because of the higher stiffness of rock mass. The results from this study are expected to contribute to understanding the settlement behavior induced by shield tunneling through the rock mass and the prediction of surface settlement. INTRODUCTION Shield tunneling has been extensively applied in urban areas since it can achieve tunnel construction with minimized ground deformation by continuous excavation and support. However, there are several precedents of unintended surface settlements resulting in enormous loss of costs and time, even if for the rock medium. The expansion of shield tunneling requires controlling the shield TBM precisely to reduce the surface settlement. The parameters triggering the surface settlement during the shield tunneling vary; tunnel geometry factors such as the diameter and depth of the tunnel (Melis et al. 2002 and Chakeri et al. 2013), ground properties such as the elastic modulus, cohesion, and unit weight (Selby 1988 and Golpasand et al. 2018), the operational factors such as face pressures and steering gap slurry pressures (Lambrughi et al. 2012 and Comodromos et al. 2014), tail void grouting pressure, the amount of backfills and injection point (Suwansawat & Einstein 2007 and Kim et al. 2018), and other mechanical data from Tunnel Boring Machines (TBMs) (Goh & Hefney 2010 and Kim et al. 2020). All these factors are related to unavoidable gaps or stress imbalances. Among them, the operator can regulate only the support pressure on the tunnel face, along the shield skin, and along the annular between excavated surface and segmental linings. However, the surface settlements that are not directly governed by the pressure balance can be caused by direct ground loss such as the failure of achieving impermeability. As the groundwater inflows during tunneling, it causes the groundwater drawdown resulting in the reduction in pore pressure, which means the increasing effective stress, and the seepage forces occurred at the path of groundwater flow causes the ground deformation locally (Yoo 2016). In this study, several numerical parametric studies are conducted to evaluate the impact of geotechnical properties and TBM operational factors on the surface settlements during shield tunneling. The numerical model based on FLAC3D is validated by comparing the results with the literature and field data. The operational factors selected for parametric studies are face pressure, tail void grouting injection pressure, and groundwater inflow regarding the grout's setting time. It is expected that the order and amount of contribution to the surface settlement can help to understand the settlement behavior induced by shield tunneling through the rock mass in a realistic view.
ABSTRACT Several approaches have been developed to analyze the face stability for TBM tunneling in soft ground. The face stability for TBM is a three-dimensional (3D) problem. Three characteristic zones can be identified during the tunnel advance in a lined tunnel: a) an undisturbed zone where the soil mass is not yet affected by the passage of the face, b) a tunnel face or transition zone corresponding to the radius of influence of the face, c) a stabilized zone where the face no longer has any influence and the situation tends to stabilize. It is important to observe that in passing from the undisturbed zone to the stabilized zone, the medium undergoes from a triaxial to a plane stress state and that the face zone is where this transition takes place. Consequently, the face area is the most important zone from a design point of view. It is in the face that the action of the excavation disturbs the medium and design considerations must be focused on. The TBM-face interaction is a 3D problem by nature. With regard to the problem boundary conditions 3D analyses are the most realistic especially for the modeling of face stability. In this study, a comprehensive simulation of the EPB shield-driven tunnel advance to be employed in the Mashhad metro line 2 project was performed. The FLAC-3D code was employed to construct a 3D model of the TBM-ground interaction. The main objective of the analysis was to determine the optimum face pressure required to prevent the soil collapse/blow-out processes at the face. Moreover, since the tunnel passes underneath the city center some buildings are located along the tunnel path. The appropriate face pressures to avoid ground subsidence were also calculated numerically at critical building locations. The loads acting on the tunnel face were estimated according to the active and passive earth pressure principles. The optimal face pressures for EPB shield was analyzed as a function of, soil cover to tunnel diameter ratio, lateral earth pressure coefficient and soil mechanical and strength parameters. The analyses provided valuable information regarding the ground deformation mechanisms, the cross sectional lining stresses due to soil loading, and loading of the tunnel lining at the Mashhad metro line 2 project. INTRODUCTION Shallow tunnels in urban areas are often excavated near existing structures such as buildings, roads, railways, and so forth. It is probable that the ground movements induced by such tunneling works affect these existing structures. Therefore, builders should pay close attention to ground movements so as to minimize the effects of tunneling on nearby structures. In many cases, large ground movements bring about a failure in the stability of the tunnel. This is one of the biggest reasons why caution is strongly recommended. In general, tunnel stability can be maintained by installing appropriate supports and reinforcements such as liners and rock bolts. Since shallow ground often consists of soft rock, clay, or sand, their levels of strength are normally quite low. This makes it almost impossible for a structure built in shallow ground to stand alone.
The Trans-Tokyo Bay Highway project is the first phase of an ambitious plan to connect Kawasaki and Chiba by a 15-km crossing of Tokyo Bay. The crossing involves a 5-km bridge, a 10-km undersea tunnel, and two manmade islands in the middle of the bay. The construction method for the undersea tunnel must take into account the large external diameter of the primary lining (approx. 14 m); the extremely soft ground under the sea; the extremely high water pressure to which the tunnel will be subjected; and active seismic conditions in the Tokyo Bay area. This paper discusses the state-of-the-art in planning, engineering and construction of the tunnel. INTRODUCTION The Tokyo metropolitan region, inclusive of the three neighboring prefectures (Kanagawa, Chiba and Saitama), has the highest concentration of population and industry in Japan; with an area of 13,500 km-" or only 3.6 percent of the national land, but a population of 31.8 million or 26 percent of the national total, and a Gross Regional Product (GRP) of 146 trillion yen (US$1.33 trillion) or 36 percent of the overall GDP of Japan as of 1990. Tokyo Bay, embraced by the metropolitan region as shown in Fig. 1 (a), (b),(refer to the full paper) is open to the Pacific Ocean as a marine gateway and is tinged by large cities and coastal industrial zones together with port facilities, all constituting a concentration of prime importance for socio-economic activities. The Trans-Tokyo Bay Highway (TTB highway), which crosses Tokyo Bay and provides a direct transportation link between the west and east sides of the bay, has long been a sort of "dream-come-true" project in Japan. As shown in Fig. 2(refer to the full paper), linked to the Tokyo Bay Shore Highway, Metropolitan Inter-city Expressway, Tokyo Outer Ring Road, Tateyama Expressway, and others, it will play an important role as an integral part of the regional highway network to help promote spatial redistribution and multipolarization of urban functions, thus strengthening cooperation between cities and restructuring the metropolitan region.
- Construction & Engineering (1.00)
- Transportation > Ground > Road (0.88)
- Energy > Oil & Gas > Upstream (0.68)
- Transportation > Infrastructure & Services (0.67)
ABSTRACT: Excavation of a tunnel provides an opening into which the soil can deform and gives rise to "ground loss". The ground loss is generally defined as the volume of soil that has been excavated in excess of the theoretical design volume of tunnel excavation. In practice, the ground loss values are estimated from empirical correlations based on past experiences. Rowe et al (1992) presented a theoretically-based method for the estimation of ground loss from first principles. This method considers the parameters related to tunnel boring method and soil conditions. In this paper, design charts are presented to estimate ground loss by performing a detailed parametric study via the theoretical method presented by Rowe et al (1993). These design charts include; a stability parameter which considers tunnel depth from the ground surface, tunnel diameter, earth pressure coefficient, vertical effective stress at the tunnel springline, tunnel face supporting pressure and pore pressure at the tunnel springline, average soil strength above the tunnel, and physical gap parameters involved with the tunnel boring machine, including the effects of thickness of tail piece, clearance for the erection of lining, length of shield, maximum allowable excess pitch and thickness of the cutter bead. The design charts have then used to estimate the ground loss values in the soft ground tunnelling operations for the new Sydney airport link tunnel. These ground loss values have then been used to estimate the surface settlement troughs, and to compare the estimated settlements with those measured. In total, six sections in soft soil have been analysed, and the agreement between theoretical estimates and the measurements has been found to be encouraging. INTRODUCTION Rapid growth in urban development has resulted in increased demand for the construction of transportation systems, water supply, and sewage disposal systems.