Challenge

The Delaware Department of Transportation (DelDOT) observed that three section-lengths of the southbound lanes of the Korean War Veterans Memorial Highway (SR1) had settled as much as six inches. These dips or sags in the pavement were as much as 200 feet long and extended across the entire two and three lane widths of the highway. The SR1 is the main north-south thoroughfare in Delaware and the most traveled roadway in the state. Therefore, DelDOT required that the road remain open throughout the repair process and work be completed during off-peak traffic hours (6 p.m. to 6 a.m.). The cause of the roadway settlement was unknown, but suspected to be due to separations in deep storms sewers (DelDOT planned to seal any leaks) or consolidation of weak native soils beneath the roadway fill. With the depth, thickness and expansiveness of the suspected weak native soils, deep injection of polyurethane would not have been a practical or economically feasible option for soil and roadway stabilization. It was then reasoned that should the road sections continue to settle, periodic pavement re-leveling with shallow injections would still likely be more economical. Even with the suspected deep issues, DelDOT required the top several feet of the subgrade soils beneath the pavement be evaluated and stabilized as necessary. The pavement structure consisted of eight inches of concrete, eight inches of a granular drainage layer, and six inches of cement-treated base. The drainage layer could not be contaminated with polyurethane during the repair.

Solution

Dynamic Cone Penetrometer (DCP) tests were performed at locations determined by DelDOT. Representatives from AECOM were on site to observe the DCP testing as well as the polyurethane injections. The DCP tests were advanced to depths of four to five feet below the cement-treated base. After review of the DCP test results, DelDOT determined that the subgrade soils were competent and deeper subgrade stabilization was not required. The settled sections of roadway were lifted using PolyLEVEL® PL400H hydrophobic polyurethane. PolyLEVEL® is a high-density, two-part urethane that, when combined, expands into a rigid, waterproof foam that is used to fill voids, stabilize slabs and lift concrete. PL400H is often selected for roadway stabilization and lifting projects because of its ability to react and perform even in wet environments. PL400H has a typical in-place density of six to seven pounds per cubic foot, so it will not add significant weight to the underlying soils. While being light weight, PL400H also has a typical in-place compressive strength of at least 100 pounds per square inch, which provides support for heavy traffic loads. Injection ports were used to strategically place the PolyLEVEL® below the cementtreated base to prevent contamination of the drainage layer. The lift of the roadway was monitored with both surveying equipment and string lines and the road was lifted back to a level position. The work was completed during 15 night shifts where 35,575 pounds of PolyLEVEL® were injected, less than the budgeted amount of 40,000 pounds.

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Project Summary

Project Engineer: DelDOT Engineers

General Contractor: Diamond Materials

PolyLEVEL Installer: DryZone, LLC

PolyLEVEL Installed: 35,575 lbs of PolyLEVEL 400H, High Density Hydrophobic Polyurethane

Product Characteristics (PL400H): 100 psi Compressive Strength, 146 psi Tensile Strength, 69 psi Shear Strength, 19:1 Expansion Rate, 6 pcf Typical In-Place Density