PHL Landslide Construction

The following is a brief description of the proposed scope of work. 

• Overburden (soil) Removal: Controlled stripping and removal of the overburden overlying bedrock along the face of the slope.
• Overburden (soil) Regrading: Controlled stripping and regrading of the overburden along the eastern portion of the project area. The regrading and removal of excess overburden reduces the potential of slope failure in that area, preventing damage to the facilities and equipment located at the toe.
• Scaling: Controlled rock scaling along the slope areas to remove loose and unstable rock blocks from the face. Scaling will reduce the likelihood that rockfalls will occur.
• Concrete T-walls: Pre-cast concrete T-walls should be installed at the toe of the slope and cabled together to prevent rockfall debris from reaching the powerhouse, and hence protect existing structures.

• Draped Mesh: A draped mesh should be installed along the face of the slope to prevent rockfall debris from reaching the powerhouse area, and hence to protect existing structures.
• Catchment Fence: Steel cable and wire mesh catchment fence should be erected at the toe of the slope to prevent rockfall debris from reaching the transformer yard and switchgear building, and hence to protect existing structures.

• Secant Pile Retaining Wall: Construction of a secant pile retaining wall to stabilize the upper access road during the stripping and grading of the overburden on the slope downstream of the right abutment of the dam.
• Stormwater Detention Vault: Due to the area of disturbance and VADEQ regulations the construction of a detention vault is necessary to limit the increased runoff in the project area due to the stripping and regrading of the soil. In addition to the construction of a detention vault, several new stormwater pipes will be installed, and several other drop inlets and pipes will be replaced to handle the increased runoff on the stripped portion of the slope.
• Miscellaneous Stormwater Feature Maintenance: To control and direct stormwater runoff to the detention vault and reduce the likelihood of water running along the upper access road (similar to what transpired during the 2020 slope failures), ditch maintenance and cleanout for the upper access road is incorporated into the design. Additionally, the replacement of an existing stormwater drop inlet, culvert and headwall to facilitate drainage away from the upper access road ditch is planned.
• Construction of the Switchgear Building: The building which houses the switchgear equipment was destroyed by the landslide. Once built the new switchgear equipment will be put in place for reconnection of the powerhouse.