Design, Testing and Construction of Rock Socket for Tower Foundations of the New Carquinez Bridge

The new Carquinez Bridge is a suspension bridge with spans of 147 m, 728 m, and 181 m. It consists of the south anchorage, a transition pier, two towers (South and North towers), and the north anchorage. This paper describes the rock conditions and available rock strength data beneath each tower foundation and the design considerations and procedure used for estimating the axial capacity of the rock sockets for the piles for the tower foundations. The towers are each founded on two footings, which are each supported by six vertical, 3-m-diameter steel shells infilled with reinforced concrete, followed by 2.7-m-diameter drilled shafts in rock (i.e., cast-in-drilled hole, or CIDH, piles). The total length of the CIDH pile at the South Tower is approximately 89 m, with about 43 m of drilled shaft in rock. The total length of the CIDH pile at the North Tower ranges from 49 to 64 m, with about 16 to 26 m of drilled shaft in rock. The design parameters used for the South Tower piles were later confirmed by a pile load test. Additional field investigations during construction revealed significant variations in rock conditions at the North Tower, resulting in the redesign of the length of the piles. Major construction challenges encountered during construction of the South Tower piles are described, and the revised construction procedure (i.e., under-reaming) used by the constructor to mitigate caving is presented.