Abstract:
The design and construction of large Mechanically Stabilized Earth (MSE) retaining walls over soft and variable subgrade soils can create significant settlement issues and global stability challenges. This case study summarizes the successful application of ground improvement using Rammed Aggregate Piers (RAPs) to support a tall MSE retaining wall in Fuquay-Varina, North Carolina directly adjacent to wetlands.
Subsurface conditions at the project site consisted of soft/loose alluvial soils underlain by soft to stiff residual soils, resulting in excessive predicted total and differential settlement. Traditional deep foundation options, as well as undercut and replacement options were considered. However, these options were determined to be infeasible due to economic and constructability issues.Â
RAPs were selected to improve the soil conditions beneath the reinforced zone of the proposed retaining wall. Supplemental testing which included soil borings with Standard Penetration Tests (SPT) and Cone Penetration Tests (CPT) soundings were performed, to obtain sufficient data for settlement calculations and global stability analyses. Settlement and global stability analyses following ground improvement were performed.
The poor site conditions and the proposed grading plan created several logistical difficulties with regards to providing a stable working surface for ground improvement installation. A collaborative effort between all concerned parties was required to provide the proper site conditions for installing ground improvement.
Ground improvement support for the site MSE walls was successfully designed and installed. The use of RAPs provided a cost-effective solution for constructing the site MSE walls in adherence with project plans.
This case history demonstrates the effectiveness of ground improvement with RAPs in supporting large MSE retaining walls, particularly adjacent to wetlands. This collaborative design and construction effort helped to minimize cost and construction time incurred by adverse soil conditions.