Comparing with other transportation infrastructures such as freeway and MRT, the geotechnical engineering design for high-speed rail project adopts similar principles except different loading conditions, higher safety factor, and more stringent allowable displacement of foundation structure. However, from operational safety point of view, minimizing the impact from natural geological hazards along the railway alignment becomes a critical issue. This paper will first review the natural geotechnical hazard along the HSR alignment. It has been identified that slope instability associated with heavy rainfall, earthquake and active fault movement, and ground subsidence are the three key natural geotechnical hazards. The actions including monitoring, inspection by professional geotechnical engineer and geologist, engineering assessment, and building up the early warning system have been taken to ensure the railway operational safety.
The northern section of Taiwan HSR is located in the frontier of western foothills. Quaternary strata including Cholan Formation, Toukoshan Formation, and lateritic terrace deposits are predominantly distributed over this region. The nature of these formations is younger, poorly cemented, frangible, and strongly effected by weathering. Along this section there are so many cut-slopes and tunnels across foothills and tablelands, joined with embankments and bridges. Many existing problems of those slopes about geotechnique are associated with such geomaterials. This paper outlines the engineering geological characters with some accidents, and reviews related issues on slope stability.
Hueilung tunnel is the first tunnel in south bound of Taiwan High Speed Rail, about 2,149m in length. This tunnel passes through the strata of the Mu-Shan formation with coal seam. The geological conditions along Hueilung tunnel are tectonically disturbed, highly fractured sandstone with shear and fault zone. The south portal of this tunnel adjoins a residential area and factories. The restrictions due to environmental impact are one of our concerns in the design. The main topics introduced in this design include the results of numerical analysis of rock supports and inner lining. Besides the traditional support design, many special considerations are introduced in this design, such as the flexible options of the support and auxiliary construction method for the contractor, potential natural gases assessment and precautions, cleanable drainage system design, noise isolation and safety protection, and cut and cover portal section design, etc.
The Taiwan High Speed Rail (THSR) runs through several hilly areas in the northwestern island of Taiwan and there are therefore quite many tunnels constructed along the alignment. Special considerations are required for the design of these tunnels due to the soil-like rock strata, low overburden and underpassing the existing freeway with cover as thin as 9 m. Various monitoring systems were then adopted to verify the initial design parameters and assumptions. The results reveal that the deformation and convergence of tunnel linings are significantly affected by the asymmetrical loads due to inclined topography, unfavorable bedding conditions and the poor strength of rocks. A case history of a tunnel underpassing an existing freeway embankment will be demonstrated to explain the overall slope stablity design concept for a portal which located in an old landslide area.
The alignment of Taiwan High Speed Rail (THSR) passes through the southwestern coast plain in southern Taiwan. The geological condition in the region consists of soft compressible alluvial deposits in the upper soil strata. Over twenty thousands of 1.5 to 2.5m large diameter bored piles with lengths of 50 to 60 m were constructed to support the viaducts and bridges of the rail. The foundation engineering practices through this significant project in Taiwan are discussed in details. An overview of the THSR Project will first be provided, and then important design requirements and considerations are discussed. This is followed by discussions of load test programs implemented in this infrastructure project. Finally, several issues related to design and analysis of foundation systems were discussed from a retrospective perspective.
Because of the unique compositional characteristics of the gravel formation, the designed bearing capacity and the construction are very distinctive from those of general soils. However, due to the lack of systematic organization of experiences encountered, the design and construction of pile foundation in gravel formation usually conflict great difficulties. Henceforth, in this article, it is the hope of the authors to share the valuable experiences obtained from the High Speed Rail construction to provide references for future pile foundation construction in similar gravel formations. More importantly, with the analysis of in-situ pile loading tests, this article explores the characteristics of pile foundation in the gravel formations, and consequently suggests the bearing capacities of the pile foundations for future references.
It has been noticed that the existing viaduct structure with pile foundation has been suffered settlement due to adjacent construction activities such fill and piling work. Extensive studies with field tests and monitoring have been carried out to identify the cause and mechanism inducing settlement. It was concluded in this paper that adjacent construction effects to the existing viaduct structure with pile foundation is significant. Regulations to minimize the impact are crucial to protect the railway due to its sensitivity to the differential settlement.
Real time Automatic monitoring system has been widely applied to various infrastructure construction projects and environmental control works due to its cost-effective, reliable, and efficiency. For the same reasons, Taiwan High Speed Rail Project has adopted the real time monitoring system during the construction and revenue operational stages. This paper will brief the system adopted and followed by the descriptions of monitoring work carried out in two construction projects. The first case is the tunnel construction underneath the existing freeway. The allowable settlement on the freeway pavement is 20 mm. The second case is the embankment remedial work by grouting. The uplift of the embankment during grouting should not cause adverse impact to the operational high-speed rail. The automated real time monitoring system introduced in this paper has been successfully demonstrated its superiorities in these two projects.