Tunneling with Care

by David Powell, Dir.; England Member Inst. of Mining and Metallurgy (IMM), Mott MacDonald, Croydon, England,
David Field, Tunnel Design Mgr.; Member Inst. for Civ. Engrs. (ICE), Hatch Mott MacDonald, Pleasanton, CA,
Richard Hulsen, Chartered Engr.; Mott MacDonald, Croydon, England,

Serial Information: Civil Engineering—ASCE, 2001, Vol. 71, Issue 11, Pg. 68-73

Document Type: Feature article

Abstract: The Mission Valley Light Rail East extension was to run just north of San Diego State University (SDSU), and was to be constructed using a tunnel-boring machine (TBM). But the Metropolitan Transportation Development Board decided to alter the alignment of that segment so that it would run through the center of campus, effectively shortening the segment to 330 m in length. The project's design team, Hatch Mott McDonald, of Pleasanton, California, determined that an expensive TBM was no longer cost effective for the shortened route. Instead the designers chose sequential excavation tunneling methods (commonly referred to as the new Austrian tunneling method, or NATM. The tunnel will run through a type of material known as stadium conglomerate, a dense, poorly cemented sandy gravel with cobbles. The issues they considered in determining the construction and support methods for the route included the ground conditions and the predicted ground responses to the tunneling methods chosen, the need for sequential excavation methods to control deformation, an the types of instrumentation and monitoring that would be in order.

Subject Headings: California | Construction | Tunneling | Tunnels |

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