As a recipient of the ACEC of North Carolina’s 2020 Engineering Excellence Award, we spoke with Principal Engineer Marc Plotkin, PE, D.GE about our work for the Tumbling Creek Road Repair.
Tell us about the project.
Tumbling Creek Road provides access to the Clinch Mountain Wildlife Management Area (WMA) which is a 25,477- acre mountain forest managed by the Virginia Department of Game and Inland Fisheries for recreational activities. The road was originally constructed as a rail bed with 1.3 horizontal to 1 vertical natural side slopes. In February of 2018, a landslide occurred within the road, closing the main access route to the WMA. ECS designed a Shored Mechanically Stabilized Earth (SMSE) Wall with various contingencies allowing for procurement of the landslide repair in a Design-Bid- Build contracting approach resulting in an under budget on-time construction completion.
What were some of the unique construction and design challenges faced?
The project had several unique construction and design challenges. These challenges included site access, difficult terrain for access, and remote site location. Due to limited access and the active landslide, only limited subsurface information could be collected during the project design phase. This resulted in many unknown issues that could have slowed construction and resulted in delays and costly change orders to the owner. Although the available subsurface information was limited, the information gathered was sufficient to define that the landslide occurred along the interface between bedrock and residual soil.
Of utmost importance during any landslide repair is the protection of the remaining slope and more importantly protection of the health and safety of the workers performing the repair. All movement of earth, either by person or outside influences, runs the risk of destabilizing the earth mass. This safety concern was at the forefront of the design teams evaluation of all repair options.
One unique concern with the project was the remote location which is nearly two hours from the nearest concrete batch plant, which had to be considered when specifying and developing a repair method.
What were the original or innovative applications used for this project?
A Shored Mechanically Stabilized Earth (SMSE) Wall is a relatively new earth retention system and is a combination of a Mechanically Stabilized Earth (MSE) Wall and a Soil Nail Wall. Where each of these systems individually could not meet the overall design and safety requirements of the project, their combination into an SMSE Wall did.
What were the social/economic considerations?
The use of various design contingencies enabled ECS to not only protect both the Virginia Department of Game and Inland Fisheries (VDGIF) and the Commonwealth of Virginia from change orders throughout the project, but also allowed the construction to be completed on-time and under budget. The selection of a Shored Mechanically Stabilized Earth (SMSE) Wall enabled ECS to not only widen the road, but reopen access to the Wildlife Management Area (WMA) prior to the time limit issued by the VDGIF.
How did we meet or exceed our client’s needs?
The use of Shored Mechanically Stabilized Earth (SMSE) Wall combined soil nail wall allowed the Virginia Department of Game and Inland Fisheries (VDGIF) to procure the landslide repair in a Design-Bid-Build contracting approach. The implementation of various design contingencies resulted in a construction plan that allowed for the necessary construction variations required while working in mountainous terrain. The final project was completed with zero construction change orders, ahead of schedule and under budget.