VTA-BART Silicon Valley Phase II
The San Francisco Bay Area rapid transit system BART is expanding South into San Jose; connecting communities and supporting the region’s future growth. The next phase includes a six-mile extension of the underground train system, running from the existing train terminal at the Berryessa station, through downtown San Jose, to the proposed Santa Clara Station. The West Portal structure is located between the cities of Santa Clara and San Jose and serves as the launching point for a Tunnel Boring Machine that will excavate a five-mile-long tunnel underneath San Jose. At the heart of this effort, Kiewit Shea Traylor JV with subcontractor Malcolm Drilling was tasked to construct the West Portal Structure. The overall project included over 2,500 linear of 3ft, 4ft, and 5ft wide diaphragm walls (D-Wall) along with a network of dewatering and depressurization wells. Based on the depth of excavation, the very high-water table, variable subsoil conditions, proximity to active passenger and freight railroads, and high seismic condition, a D-Wall in the shape of a caterpillar was necessary at the launching structure. This Caterpillar Shaft structure included uniquely shaped Y-Panels which required over 1,000 cubic yards of concrete and a 270,000-pound rebar cage for each Y-Panel. At the peak of construction, Malcolm had 3 Bauer hydro cutters, 3 desanding plants running continuously for several months in order to meet the project schedule.
