Abstract:
Slope stability issues upslope of a substation in the Appalachian Plateau Region during its construction required the construction of several soil nail walls upslope of the station. Post construction, a deep-seated landslide occurred on a section of hillside above the corner of the station and caused considerable damage to a powerline structure and the corner of a pile and lagging wall. The location and direction of the slide also threatened a drainage ravine and railroad tracks.
Instrumentation, geotechnical exploration, and survey monitoring were implemented to support the landslide remediation design. Geotechnical exploration revealed the site is covered with colluvium (including large boulders) and the top of bedrock varies significantly across the site and is up to 100 feet below ground surface. Instrumentation revealed the slide plane to be 20-30 feet deep. Several remediation methods were considered with a ground anchor remediation system, utilizing strand anchors and reinforced concrete block, being selected. Â Each anchor is attached to a concrete block at the surface and the anchors are tensioned to provide an active resisting force. The system was selected as the most cost-effective method due to the depth to bedrock.Â
Key aspects of the design included: determining the direction of sliding, avoiding anchor interference due to convex slope shape, designing around existing retaining walls, and determining the required bond zone in the underlying broken bedrock. Installing the anchors and placing the blocks required cutting slopes on the hillside in the landslide to provide the working benches. Factors effecting the construction included: the standup time of excavation, the strength and stiffness of subgrade, and loss of grout in the anchor bond zones. The selected contractor brought experience with this type of remediation construction. Several lessons learned are provided regarding the concrete block design and strand anchor design and construction.