Risk Reduction, Management, and Mitigation from Experience-Based Learning During Construction of Cross Passages, Seattle, Washington

摘要

Cross passages are critical elements in transit and highway tunnels, providing a means of safe emergency egress between adjacent running tunnels. Although usually short in length, they are often technically challenging and can pose significant construction risks. Two recent projects in Seattle-Sound Transit's University Link Light Rail Contract U230 and Northgate Link Extension Contract N125-involved cross-passage construction between twin single-track Metrorail tunnels. This paper describes risk reduction, mitigation and management experience gained from the U230 and N125 contracts during construction of cross passages. Specific emphasis is given to challenges associated with excavation in glacial deposits under high ground water pressure and the ground improvement measures implemented, which included dewatering, grouting and ground freezing.