DESCRIPTION

Four MSE abutment walls totaling 12,000 square feet were designed for a two-phase construction project.

CHALLENGE

New bridge abutments for widening of I-395 for the new HOT Lanes project were founded atop very low shear strength marine clays which are locally a concern since they are prone to landslides. To mitigate the instability and to provide adequate bearing for the abutments, Cement Treated Aggregate (CTA) Densified Aggregate Piers (DAP’s) were specified by VDOT. The CTA piers served to increase the shear strength and capacity of the DAPs while providing and low permeable pier which would not be a conduit for moisture to penetrate the highly plastic marine clays. Challenges included working in a tight location adjacent to the highway and the use of CTA had special construction requirements. All CTA materials needed to be used with 8 hours of delivery to the site.

SOLUTION

A total of 193, 24-inch diameter, 26-foot long CTA Geopier elements were installed for support of Wall 4RW5 on the I-495 portion of the HOT Lanes. The high friction angle of the CTA Geopier elements, combined with the very low, 10-degree friction angle for the highly plastic marine clay soils, resulted in a composite friction angle for the DAP zone of well over the 34 degrees required per the project specification.