New cloverleaf design includes Maccaferri’s MacRes, ParaWeb, and “MacBox” solutions along with movement sensors
During the planning process of a new interchange near Christiana, Delaware, the Maccaferri MacRes system was selected as part of the construction. The Maccaferri MacRes system is a Mechanically Stabilized Earth (MSE) retaining wall system comprised of precast concrete facing panels and discrete high adherence polymeric soil reinforcing strips. The tensile forces in the soil are transferred to the reinforcing strips by means of friction.
The main purpose of this roads project is to relieve congestion at a highly traveled interchange by adding high speed connecting on and off ramps, 2 new lanes on the heavily traveled I-95 corridor, and 6 new bridges. Due to limited foundation locations within the existing roadway and skewed flyover alignment, new bridges required post tensioning via integral pier caps and straddle bent type piers with draped tendons.
The MacRes system consists of three structural elements designed for easy installation and flexible use:
- precast concrete facing panels either square (5’ wide x 5’ tall), or rectangular in shape (10’ wide by 5’ tall)
- high strength polyester soil reinforcing ParaWeb strips encased in a tough and durable linear low density polyethylene (LLDPE) coating available with nominal tensile strength ranging from 6,740 to 25,170 lb
- connection assembly composed of a High Density Polyethylene (HDPE) MacBox cavity insert box secured by a steel rebar cast into the precast facing panel
The ParaWeb reinforcements are planar strips manufactured from high tenacity, multifilament polyester yarns aligned and co-extruded with a LLDPE (Linear Low Density Polyethylene) sheath to form polymeric strips. The ParaWeb soil reinforcing strips are available in a wide range of tensile strengths in order to optimize the design and construction efficiency.
The HDPE MacBox is integrated with the panel by an embedded steel rebar encased in a polymeric sleeve for corrosion protection. The sleeve avoids any intrusion during the casting phase and prevents damage to the polymeric soil reinforcing strips in contact with the rebar.
DelDOT (Delaware Department of Transportation) specified that at least one section of the wall had to be instrumented to monitor the wall performances over time. The wall was instrumented and the data were collected since April 2012 up to September 2013. From the recorded data, it was shown that the design inputs and the long-term loads on the straps and on the connection were at least 4 times smaller than predicted.
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For more technical information, please download the Case Study.