Mississippi River Floodwater Opens Voids Beneath St. Louis Streets

Problem

In St. Louis, Missouri, Mississippi River flooding caused catastrophic damage to nearby sewer lines and streets. As the floodwater rose, hydrostatic ground pressure caused the collapse of a deep manhole and created voids below the street surface in one of St. Louis’ economically important tourist areas. The City of St. Louis and the Metropolitan Sewer District of St. Louis (among the largest sewer districts in the country) chose URETEK to complete this emergency repair by filling the newly opened voids and stabilizing the sub-grade soils beneath the pavement.

Analysis

When the floodwater began to rise, additional pressure was exerted on existing manholes, one of which collapsed under the load. Following the manhole failure, large voids were created below the street pavement system when sub-grade soils were washed away. With newly poured concrete around the repaired manhole, URETEK engineers understood that the voids needed to be addressed in a way that protected the pavement system while avoiding damage to the new manhole. City officials hoped that URETEK Deep Injection® (UDI) would be the answer.

Solution

Working with geotechnical data provided by the Metropolitan Sewer District of St. Louis, URETEK and its engineering team designed a solution that would eliminate the dangerous voids below the street without compromising the integrity of the newly repaired manhole within the work area.

Result

This was a project that highlighted the importance of experience. URETEK crews developed a site-specific injection plan and took advantage of many years of lessons learned while completing the job for St. Louis city officials. In just one day, URETEK deployed to the worksite and completed the UDI repair project, filling all the sub-grade voids and stabilizing the surrounding soils. Most importantly, URETEK’s repairs did nothing to compromise the new manhole installed by the city. Once the project was completed, St. Louis’ historic area was back in business.

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.

River Manhole Repair
Manhole Failure
A manhole failure led to large voids beneath a downtown street
Manhole UDI Repair
URETEK crew members perform UDI in St. Louis