Development of a Design Technology for Ground Support for Tunnels in Soil. Volume III. Observed Behavior of an Earth Pressure Balance Shield in San Francisco Bay Mud

摘要

This report is a study of one of the most successful and economic new gereration soil tunneling machines--earth pressure balance (EPB) shield. The EPB machine was used for the first time in the United States in 1981 to construct a 12-foot diameter tunnel for the San Francisco Clean Water Program. The tunnel alignment is under a busy city street in a soft soil deposit with a high groundwater table. An extensive instrumentation of the San Francisco tunnel was undertaken to monitor the behavior. This report presents the data obtained and an analysis of the observed behavior. The results showed the EPB shield to have successfully controlled ground movements with a unique face support mechanism. No dewatering was required, and the shield was able to cut through 90 wooden piles during the tunneling. The EPB technology appears to have considerable potential for future use in the U.S.