Long tunnels with high rock cover have become one of the important infrastructures in recent transportation projects in Taiwan and have been considered as a key factor controlling the over all construction schedule. Cases in this island and around the world indicated that difficult ground conditions can not be avoided in any underground construction and should not be overlooked during planning stage, design stage and construction stage. This paper introduces several cases regarding the unfavorable ground conditions encountered in long tunnels with high rock cover and is followed by a brief discussion on the future geological exploration of long tunnel.
With the detailed geologic investigation during the route selection、basic design and detail design stages, the owner and client of the San-I No.1 tunnel have a good understanding of the geological conditions along the tunnel and make the best choice of the alignment and the proper design. All the difficulties among the San-I no.1 tunnel had been overcome. The difficulties include the passage under the No.1 freeway and passing through of San-I Fault and other geological defects.
Based on the consideration of water head and geology, the powerhouse of Shihlin Hydropower Project was located in the underground of the right bank of Chin San Creek at Chin San. However, bad geological conditions including gushing groundwater and shear zone were encountered during excavation of the access tunnel and powerhouse. It took one month and half a year separately to treat the above said geologic hazards. In considering the safety of powerhouse structure, a design change of relocation of powerhouse cavern was made. At present, the construction is going on smoothly.
The Li-Shan Landslip located on the central crossisland highway in Taiwan happened in April 19, 1990. The occurrence of the landslip endangered the safety of the highway and several buildings.
The study area of 230 ha is divided into west, southeast and northeast slip-areas. Each slip-area is composed of several connected sliding blocks. The depth of slip plane ranges from 15m to 60m. The mechanism of landslip was triggered by the groundwater.
The remediation measures including surface drainage, horizontal drainage, drainage well, drainage tunnel, sabo dam and steel pipe were planned. Up to now, the supplementary investigation for detailed design was carried out.
Landsliding mapping is always the first step in the process of slopeland development. This paper presents a landslide mapping case in the South-western Taiwan. Investigation process, site geology, and landslide mapping are briefly described. Geological data reliability is discussed to avoid misleading and misusing.
A special type of landslide is recognized in a gentle dip solpe (only 10 degree in dip angle) , but can not be discerned from the available airphotographs (with scale of about 1/20,000). These special landslides are quite active. A special type of landslide is recognized in a gentle dipslope (only 10 degree in dip angel). These special landslides are quite active, but can not be discerned from the available airphotographs (with scale of about 1/20,000). It is important to identify their distributions before any slopeland development.
In the following paper, the result of the in-situ investigation of a rockfall event in the Lien-Tung area of Northeastern Taiwan is used to describe the simulation approach of rockfall trajectories using mathmatical models and computer program. The in-situ investigation was conducted in order to obtain parameters for the simulation.They include source locations and failure type of boulders,rockfall path and footprints,shape and size of boulders,slope inclination and length, slope surface roughness,and slope geomaterial properties.The trajectories of rockfall were back-analysed by using mathmatical models and Colorado Rockfall Simulation Program.This analysis can be used as a tool to study the rockfall trajectories needed for rockfall mitigations
Peitou depot is the most important maintenance works of Taipei Rapid Transit Systems with an area of forty acres. A clay layer of low strength and high compressibility with a thickness of 15~50 meters is beneath the ground surface. To raise its ground level, an earthfill with a thickness of 1.5~5.2 meters was placed over the clay layer. Vertical drains were installed in the same period of time. After completion of the earthfill in November 1990, the largest settlement within the area has reached 1.9 meters and continues to increase at acurrent rate of 1.0~2.7 mm/month.
The Taipei Fault trending NE-SW and passing through southeastern part of the Taipei Basin has attracted much attention recently due to the rapidly eastward development of the Taipei metropolis. However, the trace and activity of the fault has long been the controversy among the geologists who have worked in this area due to the overlying hundreds meters thick of Quaternary basin deposits.
Benefiting from the deep drilling project of the Taipei Basin conducted by the Central Geological Survey, the trace of eastern segment of the Taipei Fault in the basin is gradually raveled, while the western segment still remains inferred. Correlation of a series of deep boreholes which cross the trace of the Taipei Fault along several Taipei Rapid Transit lines shows that the contact between the Chingmei Gravel and the Sungshan Formation has not been offset by the Taipei Fault. This means that the Taipei Fault may have not been active since the beginning of the deposition of the Sungshan Formation, which has been dated to around 10,000 years before present.
If the Taipei Fault has not moved since the recent 10,000 years, the activity of the fault is not longer the major threat to the construction and development of the metropolis. However, the wide fracture zone along the fault can be the disadvantage for the foundation of high-rise buildings and underground constructions while the fault passing through the shallow part of the Taipei Basin. The bearing capacity of the Chingmei Gravel in the eastern part of the Taipei Basin is apparently insufficient for high-rise buildings mainly because it is composed of fine, matrix-supported gravel with thickness less than 10 meters. Furthermore, the Chingmei Gravel fades out in the easternmost part of the basin, the Hsin-Yi District. The foundations of high-rise buildings have to be put on the basement rocks of the basin. The width and the properties of the fault zone should be accurately investigated during the site investigation for constructions.
Shallow seismic reflection is used to map the surface location of the Nankan fault in the Taoyuan-Nankan area. Based on the Seismic profiles of field survey, it can be concluded that:
1. The Nankan fault is a thrust fault located at the northern shore of Nankan His, which extends from the Sanchiao Junior High School toward the north-west. The strike of the fault is about N25°W with a very large dip angle of about 85°NE. The fault is a strike-slip fault but with a dip-slip component. The stratum in the northeast side of the fault toward the Linkou Terrace is uplifted ,while the stratum in the southwest side of the fault directed to Taoyuan Terrace is dropped down. The vertical displacement of the Nankan fault is about 20 meters.
2. The vertical displacement of the Nankan fault is very smaller than the difference in height between the LinKou Terrace and the Taoyuan Terrace. It implies that the Nankan fault is not the main factor to cause the height difference of the two terraces.