In San Jose, California, portions of a sheet metal bridge abutment wall were removed by occupants of a homeless camp living under the bridge. Over time, a combination of slope failure, erosion, and lateral failure under and around the bridge approach slab and abutment wall contributed to the development of a six-foot by 12-foot sinkhole underneath the roadway above. The threat of collapse under heavy traffic loads led city officials and Graniterock Construction personnel to contact URETEK.
Geotechnical investigation revealed the presence of a large sinkhole under the roadway. In this emergency situation, four project goals were identified: sinkhole repair, abutment wall stabilization, hillside stabilization, and bridge approach and departure stabilization. All parties agreed that the job required a custom application of URETEK Deep Injection® (UDI) to properly address the complex circumstances at the bridge.
Coordination was required between multiple parties on this project. State Homeless Abatement officials had to coordinate the relocation of people who had been living below the bridge, and temporary shoring had to be installed to replace the original abutment wall facing. After much discussion about methods and materials, URETEK’s in-house engineering staff recommended URETEK 486 Star® polymer for the sinkhole repair, in conjunction with gravel backfill. A multi-phase, multi-level 10-foot by 15-foot injection plan was laid out for the site to encompass the entire sinkhole and surrounding areas. The surface pavement system was removed, and URETEK crews began placing injection rods at multiple depths. Targeted UDI was performed initially in a row closest to the failed abutment wall, followed by injections at the opposite end of the project area. With the sinkhole fully encapsulated, gravel was added to the sinkhole and UDI commenced within the main project area. Upon completion, Graniterock crews finished backfilling the sinkhole, compacted the work area and overlaid it with a new asphalt surface. Once the southbound lanes were completed, URETEK crews conducted a standard UDI injection on the northbound lanes as well to increase the overall bridge bearing capacity.
Working together with San Jose city officials and Graniterock Construction, URETEK successfully completed the project in just two days. City officials were thrilled with the outcome. TempShoring was removed from the abutment wall upon completion of injections, and it was confirmed that the soil-gravel-polymer combination behind the abutment wall was a singular mass. The sloughing problem at the bridge ceased, the sinkhole was filled, the abutment wall was stabilized, and the entire bridge approach / departure ramp was strengthened to provide years of reliable service. The project was completed on-budget, saving the city over 30 days of production time, at less than one third of the cost associated with full excavation and replacement repair options.
URETEK Deep Injection® (UDI)
Widely referenced throughout our industry, UDI involves the injection of structural polymer into base and subgrade soils to increase the load bearing capacity. This is achieved by injecting the polymer through small holes drilled directly through the pavement structure to depths determined by site-specific analysis. Our URETEK 486 Star® material flows easily into voids and weak zones within the soil mass below. Through a controlled chemical reaction, the expanding polymer compacts surrounding soils and applies a controlled pressure on targeted areas of the affected pavement above. If needed, a multi-injection design plan is utilized to gently return the pavement to its original grade. The composite material quickly cures into a strong, dimensionally stable, and water-resistant geo-material, providing years of reliable service.
URETEK 486 Star®
URETEK 486 Star® polymer is a two-component, high-density, expanding thermoset polyurethane system. It was developed to be the ideal solution for under-sealing, void filling, lifting of settled pavement, stabilization and stiffening of weak soils, and for encapsulating and sealing buried infrastructure. URETEK 486 Star® is environmentally inert, non-toxic, and resists underground water erosion or weakening due to its industry-leading hydrophobic properties.