City Creek Center is an up-scale shopping mall in downtown Salt Lake City. While under construction a five-foot-wide trench, located between two underground parking garages, was back-filled with pea gravel, and then a sidewalk was built on top of it. About ten years later the gravel began to settle enough to cause underground power lines to stretch and finally tear, knocking the power out for many of the local businesses. Engineers determined that the trench could be stabilized with the installation of polyurethane grout at depths of 30 feet below the surface. PolyFoam Solutions, a local geotechnical services contractor, was called in to perform the work.
AP Fill 700 is a single component, water-activated, hydrophobic, low viscosity, closed-cell polyurethane injection resin. This polyurethane material was selected because it is ideal for both permeating soil and filling voids. It also provides excellent strength and stability.
An Alchemy-Spetec technical consultant worked closely with the geotech contractor to develop the injection plan, detailing exactly where each of the injection points would be located. The plan was then communicated to the engineer and approval was given to move forward with the project. The geotech crew installed 10 injection tubes 30 feet deep into the soil. They then pumped approximately 1 gallon per vertical foot of AP Fill 700, as they pulled the tubes up 1 foot at a time. The injection points were spaced about 36” apart.
After only two days the site work was completed, and the general contractor was able to move forward with filling the trench and repairing the sidewalk.