Abstract
Forepiling has found wider application recently for restraining the tunnel crown settlements. However, the working mechanism of forepiles have not yet been well understood. In the construction of a diversion channel of the Katabira River, we placed forepiles as auxiliary means in the tunneling practice by the NATM with side drifts, and evaluated their displacement-restraning effect by measurements. The bedrock of this site is characterized by the fact that almost no displacement occurred ahead of the face. This paper poses a problem about the stress relief ratio to be included in two dimensional analysis for predicting the behavior of grounds presenting such displacement characteristics.
