Considerations for Very Shallow Conventional (SEM) Tunneling in Urban Settings

Synopsis:

Construction of shallow mined tunnels is frequently undertaken by use of conventional tunneling known as the Sequential Excavation Method (SEM) and sometimes called NATM. In soft ground at shallow cover the method relies on the use of presupport methods and ground improvement to satisfy permissible deformations of affected facilities. A recent project involved tunneling for twin single-track Metrorail guideway tunnels at Tysons Corner, Virginia at depths as shallow as 7–8 feet overburden over the crown. The paper addresses the range of considerations, including ground conditions, insurer’s requirements, utilities, and existing structures, that prompted design and construction refinements. These led to a robust design and successful execution nowadays called for in urban environments.

Considerations for Very Shallow Conventional (SEM) Tunneling in Urban Settings
2011 RETC Conference Proceedings
June 19-22, 2011
San Francisco, California