If not properly taken care of, ground water is potentially hazardous to a basement excavattion, as it may lead to excavation failure or jeopardize the construction of basement structure. This paper discusses how dewatering is carried out for basement excavation, the basic layout is to use deep wells and sumps in conjunction. It is noted that dewatering strategy varies in accordance with in situ soil condition, in order to obtain optimal dewatering performance, issues such as the layout of dewatering system, depth and number of wells must be carefully evaluated. Two relevant subjects, including dewatering related ground subsidence and possible schemes to seal off ground water leakage, are also addressed in this paper. Dewatering itself is an art in essence, the design of an appropriate dewatering system requires engineering judgement incorporating both theory and field expenence.
This paper reviews various case histories of groundwater control schemes which were adopted at deep excavation sites of mass rapid transit systems situated in soft subsoil and high groundwater pressure conditions. The control methods comprise dewatering, underwater excavation, groundwater recharge, seepage cutoff, grout curtain, grouting mat and ground freezing. These case histories demonstrate that thorough understanding of the subsoil and the groundwater conditions is essential for selection of the proper groundwater control scheme.
Before the turn of the century the groundwater resource in the Taipei Basin was rich and the water table was even higher than the ground surface. Due to the development of Taipei City, extensive pumping to supply water for the city caused the groundwater pressure drawdown and resulted in excessive ground subsidence. The groundwater table recovered as the pumping activities were restricted in l 960's. This paper provides information on the recovery of groundwater and discusses its effects on the underground construction in the Taipei Basin. Successful dewatering in the Taipei Rapid Transit System Project provides good experience for future design.
Heavy rainfall causes the rising groundwater in slopes and is a common factor that may trigger massive landslides. Landslide correction may involve one or a combination of various subsurface drainage measures to reduce the groundwater pressure in the slope. Subsurface drainage measures also reduce the rate of groundwater rise and therefore the chance of landslide during heavy rains. This article aims at describing the subsurface drainage by catch wells ﹔it also reviews several subsurface drainage methods. An example providing the layout and the construction procedures of a subsurface drainage system is presented as a reference for similar works.
In Taiwan, most of land development projects are towards to planning and developing wet land near the shore, because the plain land development is out of limit. The key problem of the wet land development is how to accelerate settlement by the best time-saving and high-quality drainage method. This paper tries to introduce the Vertical Drainage Method and explain the principle of this method, the materials and equipment of this method. At last, it will introduce the actual application for vertical drainage method in Keelung-River Relocation and Reclamation Project.
In Taiwan most of the waste landfills are built on the hillsides. Since the size of the sites is usually less than 10 hectares，they are regulated only by”the Guide of Waste Landfills Placement” required by the Environmental Protection Agency of the Department of Health, instead of by "the Criteria for rhe Management of rhe Hillsides Development” required by the Ministry of Interior. In view of the above guide，the collection of geological data does not seem to be enough for the practical design. Thus, many environmental and geological problems, such as groundwater pollution and landsides, have occurred.
This article aims at studying topography, geology, site selection criteria for waste landfills, suitable types of slope protection, and design for pollution barrier. The data on the site of landfills related to geological investigation are synthesized. Several specific recommendations of groundwater pollution barrier design are also introduced.
Raise Boring was applied to make a pilot shaft for the penstock in Maan hydropower project，and was proved to be a successful method. The penstock is 48 degress in inclination, 6.8 meters in excavation diameter, 88.94 meters in depth ﹔its pilot shaft is 1.42 meters in diameter, 106 meters in inclined length. Its operation from beginning to finishing took only 16 working days. According to the similar projects completed, it would be about 3 months spent by the D & B. The Raise Boring method using the hydraulic drill instead of the D & B method, cuts down very much manpower ，and moreover, it is more efficient, safer and economical than others. It is also the first time that a pilot shaft of the hydopower project was completed by using Raise Boring method. This article is to report its actual operation in detail, to brief the method and merits, and to make a comparison with the traditional methods.