A utility company applied for a permit to install a high-pressure gas pipeline
beneath the Brack Tract levee along the South Mokelumne River in San Joaquin
County. As part of their due diligence review, the Reclamation District wanted
an evaluation of the existing condition and stability of the levee. The District
retained Lowney Associates to perform a geotechnical investigation and evaluation
of the levee stability and seepage resistance capacity. Lowney determined
that the landside slope required stabilization prior to installation of the
pipeline. The pipeline was installed successfully without impacting the levee
and the District gained an improved levee section. Due to the landside slopes'
proximity to levee pump stations, levee improvement alternatives were limited.
The pipeline was installed successfully however, without impacting the District's
levee. The levee's embankment stability and seepage resistance was improved
as part of the construction for the pipeline crossing. Lowney recommended
that the annular space around the pipeline be filled with a cementitous grout
to reduce the potential for seepage along the pipeline beneath the levee.
Under-seepage during flood conditions can cause levee failure and island flooding.
