Manhole Stabilization in Knoxville, Tennessee

Problem

In Knoxville, Tennessee, the Knoxville Utility Board (KUB) discovered a broken eight-inch pipe near a 54-year old manhole. The broken pipe was weakening the soils around the manhole and creating voids in the soil as large as 33-inches. Left unchecked, the voids and ever-weakening soils would eventually have caused the street to collapse. This would have been catastrophic as the pipe was situated in a busy riverfront avenue adjacent to Neyland Stadium.

Analysis

URETEK performed soil density tests and identified weak soils and voids as far down as 25 feet. The KUB chose to use URETEK’s Deep Injection® (UDI) method because it offered a fast, inexpensive solution without the need to excavate. URETEK crews placed a grid pattern over the area where UDI would take place.

Solution

The KUB wanted traffic to remain uninterrupted during the manhole repair, so URETEK crews completed the work at night to avoid peak traffic hours. UDI was applied at several elevations to fill large voids and densify the soils around the manhole. This deep stabilization was designed to prevent the street from what seemed its inevitable collapse. As a final touch, URETEK sealed off the entry of the eight-inch pipe to the brick manhole to ensure no further leakage into the manhole.

Result

URETEK crews completed the work in just five nights with full traffic flow during the daytime, fulfilling the KUB’s requirement of minimizing traffic disruption. URETEK found and filled massive voids and stopped all inflow. URETEK saved the KUB the monetary- and time-cost of a 25-foot excavation and ensured many years of safe driving for the citizens of Knoxville.

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.

The manhole is located on a busy street near Neyland Stadium
URETEK crews worked at night to minimize traffic disruptions