Alternative retaining wall solution


    For many years the Erickson Avenue/Stone Spring Road Project has been identified as a top priority to improve street system connectivity, provide better east to west mobility, and address deficient capacity and critical safety concerns in the southern portion of the City of Harrisonburg, Penn. Initial conceptual planning for this project began in the late 1980s. In the mid 1990s, the city entered into contract with Mattern & Craig, Inc. to perform design and engineering services. (

    The project is divided into four phases. Funds for the construction project are from a combination of local funds, plus state and federal urban transportation funds. On Thursday, Dec. 13, 2012 the second phase of the Erickson Avenue—Stone Spring Connector Project was officially completed.

    Phase II of the project involves improving existing Stone Spring Road between S. Main Street (Route 11 and the location of the structure evaluated with the RECo/Menard VE Proposal) to east city limits (near Peach Grove Avenue).

    The original contract plans specified three small mechanically stabilized earth (MSE) walls. Designs were submitted in in the fall of 2010 and fabrication of materials began in the winter of 2010. Due to site issues, one of the MSE walls was eliminated in early 2011. In February 2011 construction began on the Gilco wall and new bridge over I-81.

    Elevation of Gilco Wall

    The Reinforced Earth Company (RECo) and Menard coordinated a value engineering proposal for the use of conventional Reinforced Earth Mechanically Stabilized Earth Walls with Menard Controlled Modulus Columns (CMC’s) as foundation support in lieu of the retaining wall system shown in the plans. Due to the variable foundation soils and the geotechnical engineer’s concerns for foundation bearing capacity and settlement, the original structural plans indicated that the retaining wall consist full height concrete panels, backfilled with light-weight expanded polystyrene (EPS) fill to minimize the loading on the foundation soils. Due to the use of EPS fill, grade beams are required for panel support at the base of wall and a structural slab is required near the top of wall to anchor the full height panels and provide protection and load distribution of roadway sub-grade and traffic loads to the EPS fill below.

    By eliminating the grade beams, structural slab and using conventional backfill, the value engineering (VE) proposal provided considerable cost savings to the contractor and owner. The use of CMC’s for ground improvement allowed for conventional weight backfill to be used and supported applied bearing pressures of nearly 7,000 psf (pounds, square-foot), while minimizing construction and post construction wall/embankment settlements. The VE proposal allowed for the original bridge and abutment substructure design to remain un-changed, thus saving valuable time in the design and construction schedule.

    In addition to design and supply of Reinforced Earth wall materials, RECo designed and supplied precast “half-connector” top out pieces for the coping section of the moment slab/parapet system. This project was also RECo’s first project to utilize the VDOT specified “corrosion resistant reinforcement” or CRR rebar. Rather than conventional corrosion protection of rebar by using epoxy coating or galvanization, VDOT now specifies the use use CRR rebar (which consists of either low-carbon/chromium, solid stainless or stainless clad reinforcement) for certain concrete elements.

    Installation of CMC’s at Abutment ‘B’
    Installation of CMC’s at Abutment ‘B’

    The CMC’s installation by Menard was performed over a two-week period in November 2011. The CMC’s are augured to refusal or until 100,000 pounds of torque is reached. A 2000 psi (pounds, square-inch) grout is pumped into the void left by the laterally displaced soil as the auger is extracted. The CMC’s achieve a compressive strength of 3500 to 4000 psi in approximately seven days. A layer of dense graded aggregate material was placed and compacted to provide a working platform for the CMC drill rig and an additional layer of dense graded aggregate material was placed and compacted after CMC installation to provide a load transfer platform for the MSE walls.

    VE Abutment ‘B’
    VE Abutment ‘A’

    The original contract for this project was for three plain finish MSE walls with coping and total design quantities of 11,046 square feet of Reinforced Earth MSE Walls and 1,138 linear feet of coping. The cancellation of one of the original walls and the addition of the VE walls resulted in final quantities of about 41,670 square feet of Reinforced Earth Walls, 1,138 linear feet of coping and about 900 linear feet of half connector.