Bridge Approach/Departure Slab Repair

By: Michael Jaques

After four years of continued approach and departure slab settlement Caltrans looked to Uretek USA for a permanent solution to the problem.

THE LOCATION

State Route 241 runs north-south through Orange County, Calif., connecting U.S. 91 and the Oso Parkway. This four -lane highway has a bridge crossing the Tijeras Creek in Rancho Santa Margarita.

THE PROBLEM

The approach slab for the northbound lane and the departure slab for the southbound lane of this bridge began to settle almost immediately after its construction in 1998. A number of repair techniques were attempted over subsequent years to maintain the grade and profile between the bridge’s concrete slabs and the asphalt roadway. Settlement, however, continued to occur. By January 2002, the slabs had settled as much as 2 7/8 in.

THE SOLUTION

The California Department of Transportation (Caltrans) and the California Tollway Corridor Authority (CATCA) called Uretek USA to test the base soil underneath the settling slabs. Using cone penetrometer testing equipment, Uretek discovered various 2- to 4-in.-deep voids, as well as areas of weak soils down to 10 ft below the slab surfaces.

Uretek was then contracted by Caltrans to densify soils, fill voids and lift the slabs back to grade, using their patented Deep Injection process, a powerful and highly accurate polymer compaction-grouting technique. Given the bridge’s settlement history Uretek’s objective in using Deep Injection was to solve the slab settlement problem once and for all.

For this project, Uretek chose its patented Uretek 486 material, a high-density, hydro-insensitive polymer capable of expanding up to 20 times its original liquid volume. The 486 material was injected through tubes directly into the weak soil zones and was equally effective in both trapped water and wet soils environments. Within 15 minutes of injection, Uretek 486 reached 90% of its ultimate strength, giving the Uretek Deep Injection process a decided speed advantage over competing approaches.

THE APPLICATION

The Uretek 486 material was first injected over a predetermined grid pattern just below the pavement’s surface at both ends of the bridge. This first series of injections filled the voids directly beneath the pavement and assured the base materials stayed in contact with the concrete. Following the surface-level injections, Uretek’s Deep Injection process continued to densify the weak soil areas found during the cone peneterometer testing. Uretek 486 was injected at two additional elevations to increase the load-bearing capacity of the soil. The base and sub-grade materials were compressed and strengthened by the pressure of the expanding polymer. Multiple micrometers were used to carefully monitor surface movement of the pavement. By rehabilitating the base, the polymer injections halted further slab settlement. Working at night during off-peak hours, the project took only four work periods to complete and workday traffic flow was totally unaffected.

THE RESULTS

Once the work was completed, again using the cone penetrometer, Uretek measured the soil density of the injected areas and the results were excellent. The slab was raised back to its original grade and the base materials’ load bearing capabilities were significantly and sufficiently strengthened. Today, the approaches to the Tijeras Creek bridge are still on grade, ending years of problems for Caltrans, CATCA and the traveling public on Highway 241.

THE SUMMARY

Soil stabilization, pavement lifting and infrastructure rehabilitation problems can be easily controlled with Uretek’s fast, cost-effective, long-term and environmentally safe solution. Go to http://www.uretekusa.com/locations to find your nearest Uretek USA representative or simply call Uretek USA at 888/287-3835.