The Cooper River Bridge, the longest cable-stayed bridge in North America,
replaces two existing bridges along U.S. Highway 17 and connects the City of
Charleston and the town of Mount Pleasant, South Carolina. Two diamond
shaped towers support the 1, 546 ft long main span over Cooper River and allows
for a 1000 ft wide navigation channel. The Charleston high-level approach is
4351 ft long and provides a 250 ft wide navigation channel for Town Creek, while
the Mount Pleasant high-level approach is 2, 090 ft long. Due to the high
seismicity in the region, potential vessel impact, and hurricanes, large lateral
loads are expected. From various types of foundations, 10-foot diameter drilled
shafts were selected for their high capacity against vertical and lateral loadings.
The shafts are founded on a stiff to very stiff lightly cemented calcareous sandy
clay or sandy silt layer, called Cooper Marl, which underlies the coastal
sediments of the interbedded clays and sands. A group of 11 shafts supports
each main tower, while a rock island protects it from vessel collision. A group of
4 to 8 shafts foundations support the other piers of the main span unit. A pair of
shafts supports the High Level Approach piers. The shaft tip elevations vary from
120 ft to 230 ft below water line. An elaborate geotechnical investigation was
conducted on the site, including a load test program on full-scale shafts under
axial and lateral loads. The results of the tests were used to calibrate the lateral
and axial soil resistance. The objective of this paper is to present the different
aspects of the bridge foundation design.
Author: Liang Shen, Osama Safaqah & Robert B. Bittner, Ben C. Gerwick, Inc.
Publisher: DFI