Remediation of Slope Instability in Presumpscot Marine Clay using Steel H-Piles Mile Brook Bridge over Outlet Stream, Winslow, Maine

摘要

The new, two-lane, 325-ft long replacement bridge required the approach embankments to be raised by 2 to 4 ft to improve the vertical profile of the roadway. As a result, engineering evaluations were conducted to assess the potential for global stability issues associated with a 40-ft thick layer of soft, marine clay located below the west embankment. The results of these evaluations showed that an approximately 100-ft long portion of the slope had a lower factor of safety than the minimum required by AASHTO LRFD. Several remedial alternatives were considered, including use of lightweight fill to raise embankment grades, construction of embankment retaining walls, installation of slope reinforcing elements, conducting ground improvement and constructing a stabilization berm at the toe of the slope. Alternatives were evaluated based on technical feasibility, cost, environmental impacts and schedule impacts. Slope stabilization piles were determined to be the most cost-effective alternative, in part since pile driving equipment would already be on site to install the west abutment foundation piles. Equally as important, this alternative had the shortest installation time, which was another critical factor as the design-build project schedule developed by Maine Department of Transportation (MaineDOT) was aggressive. Slope stabilization using reinforcement piles had not previously been used by MaineDOT, but the technique has been successfully used on projects outside the State. A total of 32, HP 12×53 piles were installed using a vibratory hammer in four days to stabilize the west approach. This cost-effective and innovative approach played a part in the successful award of this $5.4 million project to the design-build team.