Rebuilding Dams in The Sand Hills: Challenges of Seepage Control and Embankment Stability-PPT Presentation

PPT Presentation

Pdf Summary

Langley Pond Dam in South Carolina is a 1,850-foot-long earthen embankment, approximately 35 feet high, with a history of seepage and internal erosion near and beneath its concrete spillway. After downstream boils were observed in 2014, the reservoir was drawn down and subsurface investigations were conducted. The dam’s challenging Sand Hills geology included loose, washed sediments and soft alluvium; cone penetration test (CPT) soundings helped characterize ground conditions.<br /><br />Remedial work carried out from 2018 to 2020 included a slag-cement cement-bentonite (SCCB) seepage-control barrier. Installed in two phases, the barrier used overlapping panels approximately 2.5 feet wide and extending to depths of about 65 feet, where they were keyed into residual soil beneath coastal plain deposits. Its specified permeability was no greater than 1 × 10⁻⁷ ft/s.<br /><br />Loose soils beneath part of the upstream slope could not be undercut because of the nearby temporary cofferdam. SCCB shear walls were therefore installed to improve slope stability. Designed to address extrusion, bearing resistance, overturning, and global stability, the walls were about 25 feet deep and spaced 20 feet apart.<br /><br />The project demonstrates how CPT-based profiling, a deep seepage barrier, and targeted shear walls can address seepage and stability challenges in difficult ground conditions.

Keywords

Langley Pond Dam

South Carolina

earthen embankment

seepage control

internal erosion

cone penetration test

slag-cement cement-bentonite

permeability barrier

shear walls

slope stability