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Collaborating Authors
Results
Elucidating the Anisotropic Squeezing Behavior of New Guanyin Tunnel
Huang, Tsan-Hwei (Department of Civil Engineering, National Taiwan University) | Chen, Cheng-Hsun (Department of Civil Engineering, National Taiwan University) | Wang, Tai-Tien (Department of Materials and Mineral Resources Engineering, National Taipei University of Technology)
ABSTRACT The strength and deformability anisotropy of rock masses caused by discontinuities is of difficulty in analysis and design of rock engineering. This study uses a numerical model that considers both elasto-plastic behavior and timedependent deformation of rock masses to investigate the squeezing phenomenon in the New Guanyin Tunnel, Taiwan. The influence of discontinuities on tunneling and the mobilization of squeezing phenomenon are discussed in detail. 1 INTRODUCTION Deformations of rocks surrounding the New Guanyin Tunnel exhibited asymmetric characteristics due to the influence of discontinuities. In several sections, tunneling was hindered by the need to construct reinforcements that support potential failure areas. Finally, a cave-in was induced by this asymmetrical dime-dependent deformation. 2 SQUEEZING PHENOMENON The New Guanyin Tunnel, located in eastern Taiwan, is 10,307m long. The tunnel is a typical double-lane railway tunnel 9.1m wide and 7.3m high. To shortening construction time, both portals and two adits, i.e., the south and north adits, were arranged for tunnel excavation. 2.1 Engineering geology The New Guanyin Tunnel, which is located in the eastern foothill of the Central Mountain Range, goes through the mountain at roughly 1,300m in height and is aligned parallel to the coastline bordering the Pacific Ocean. The Tananao Formation in this area is mainly composed of mica schist intercalated with chlorite schist, calcite schist and limestone. Rock strength ranges from weak to medium. However, the welldeveloped schistosity and joints and the high ground water level lead to difficulty during tunneling. United Geotech, Inc., (2001) reported that the swelling potential of surrounding rock in this area was very low, classifying the rock mass into types IV andVaccording to rock mass classification method. Based on the Geological Strength Index (GSI) proposed by Hoek and Brown (1997), the structure of rock mass can be classified as "block/disturbed", and the surface condition is from "fair smooth" to "very poor." The GSI is 10–45. 2.2 Tunnel construction and squeezing phenomenon The top heading methodwas applied in this section by machinery excavation. Drilling and blasting was also carried out occasionally to remove hard rock. The support system comprised H-125-H-200 sectional steel ribs, 0.15–0.20m thick shotcrete with steel mesh and 4–9m long rockbolts. Deformation of rock surrounding the tunnelwas significant following crown excavation, but did not have a tendency for convergence. Once the bench was excavated, the deformation prolonged several months. In many sections, the convergence, neglecting the deformation happened before the installation of monitoring instrumentation, reached approximately 2.0% compared with the tunnel diameter. The tunnel experienced the squeezing phenomenon in evidence. 3 MATHEMATICAL AND NUMERICAL MODELS Based on the concept of equivalent continuum, a threedimensional, nonlinear constitutive law, which integrates the mechanical behavior of intact rock and the discontinuities into a rock mass, has been introduced through a representative volume element. The strain-softening characteristic of intact rock is considered. Additionally, the sheared deformationrelated properties of joints, such as the shear strength and shear stiffness, were taken into account..
- Energy > Oil & Gas > Upstream (0.50)
- Transportation (0.35)
Study On Tunnel Excavation Disturbed Zone In Weak Rock With Time-dependent Behavior
Wang, Tai-Tien (Department of Materials and Mineral Resources Engineering, National Taipei University of Technology) | Lo, Wei (Department of Materials and Mineral Resources Engineering, National Taipei University of Technology) | Ding, Yung-Chin (Department of Materials and Mineral Resources Engineering, National Taipei University of Technology) | Liu, Shyh-Toung (Fourth District Maintenance Construction Office, Directorate General of Highways)
ABSTRACT Based upon the results of successive measurement on rock deformation and tunnel convergence, this study utilizes numerical simulation to investigate the effect of time-dependent behavior of surrounding rock on the excavation disturbed zone (EDZ) of a tunnel. The simulated results indicate that the time-dependent behavior of rock surrounding the tunnel may magnify the EDZ. It is also found that the variation of EDZ and the tunnel convergence are not linearly dependent. 1 INTRODUCTION The engineering properties of rocks surrounding a constructing tunnel might be notably changed, e.g. the material within the Excavation Disturbed Zone (EDZ) sometimes deteriorates more than what has been expected during the design phase. The case under studied in the present work is a double-lanes highway tunnel located in easternTaiwan. Based on rock mass rating(RMR)measurement, the rocks exposed inworking face had been rated as fair, and thus, only light supporting elements was adopted at the beginning of excavation. As expected, the deformations of rock surrounding the tunnel were limited in a few centimeters in first two months after top heading excavation. However, these rock deformations were increased up to 1.95m in portal tunnel section and 0.45m in mined tunnel section, respectively. It was then observed that the scope of tunnel EDZ increased with time noticeably. According to the successive measured results from rock deformation and tunnel convergence, the present work investigates the effect of time-dependent behavior of surrounding rock on the tunnel EDZ. Back analysis is utilized to estimate the representative mechanical properties of the rock surrounding the tunnel. The time-dependent deformation is brought into numerical simulation by reduction of engineering parameters. During the back analyses, the corresponding parameters are modified and finally determined by trial simulations and by comparing to the actual measured convergence. Finally, the characteristics of EDZ and its variation with time are discussed herein. 2 ENGINEERING GEOLOGICAL CONDITION The tunnel studied, southern one of the 3 tunnels involved in a highway improvement project, undergoes through the Coastal Range located in easternTaiwan.The strata nearby the project area include the Pliocene Fanshuliao Formation, the Pliocene to Pleistocene Paliwan Formation, and the present Alluvium. The Fanshuliao Formation, composed with mudstone and alternations of sandstone and shale, are distributed over the west of this case area. The alluvium is distributed over the coastal plain and the debouchure, which is composed of the Holocene sediment, including unconsolidated gravel, sand and mud (Fig. 1). The bedding attitude nearby is N80°W/35∼45°N, and the two sets of weak plain are N40°E/55°S and N80°W/60°S. The Fanshuliaokeng fault is located in the contacting zone between the Fanshuliao and the Paliwan Formation. In the vicinity of these tunnels, the strike of the fault strike is N10°E roughly, and the fault plain is approximately vertical. TheYenliao Syncline, located in the west of the tunnel, is parallel to the tunnel route and present as an asymmetry syncline.
- Phanerozoic > Cenozoic > Quaternary (0.54)
- Phanerozoic > Cenozoic > Neogene > Pliocene (0.45)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock (0.55)
- Geology > Structural Geology > Tectonics > Compressional Tectonics > Fold and Thrust Belt (0.46)