Locks & Dam Guidewall Stabilization
Challenge & Solution
The current configuration of the upper and lower guidewalls of the locks and dam, downstream on the Ohio River from Pittsburgh, were constructed between 1927 and 1934.
In 1990, survey pins were installed along the length of the guidewalls and initial readings were taken. The survey results collected over the years at both the upper guidewall and the lower guidewall indicated progressive riverward movement.
Rhea was retained by the federal government to perform an expedited geotechnical exploration and laboratory testing program, in the winter of 2010/2011, to collect additional information on the stratigraphy of the soil and bedrock behind the guidewalls.
Project Description & Highlights
Eight borings were drilled at each guidewall; three of the borings at each wall were drilled through the wall and into the underlying bedrock.
Analyses were performed of the soil and bedrock to estimate the index properties of the soil and some strength parameters of the bedrock. Sample strength was evaluated using unconfined compressive strength tests on concrete and bedrock samples. Shear testing was performed to estimate the interface peak and residual friction between faces of existing fractures in the bedrock samples. Additional shear tests were performed on intact samples of the bedrock to provide an estimate of the internal angle of friction of a specified bedrock layer.
Rhea completed a Summary Report following field activities and laboratory examination of soil and rock. This report noted that rotation, rather than sliding, of the gravity guidewalls was the likely mode of failure. Rhea’s analysis of the survey data indicated that wall movement had occurred both towards and away from the river, likely from barge impacts.
Rhea performed a geotechnical evaluation of an operating locks and dam structure on an expedited schedule.
A laboratory testing program of soil and rock was performed to remediate movement of the guidewalls at the site. An analysis was performed to demonstrate that the likely mode of movement for the walls had been rotational, rather than sliding, in nature.