CONSTRUCTION OF A PIPEROOFED UNDERPASS BELOW GROUNDWATER TABLE.

An underpass constructed under a busy road of Taipei city is studied herein with emphasis on the geotechnical engineering aspect. A watertight piperoof structure which was formed by several interlocked, horizontally jacked pipes was adopted as the temporary retaining structure for the underpass excavation. To facilitate the pipe jacking process and the subsequent underpasss excavation in the sandy layer below the groundwater table, an intensive soil grouting programme was carried out prior to the construction of the piperoof. Meanwhile, the ground settlement was constantly monitored throughout the entire construction process. In general, this project was completed successfully without causing any ground loss problem around the underpass. Problems encountered and experience gained from this project are discussed in this paper. (A)