Problem:
At a Pennsylvania firehouse constructed over a former compost site, ongoing decomposition of underlying organic materials led to shifting soil conditions and progressive floor settlement. To the dismay of the firefighters, the settlement had become so severe that there were gaps in the cinderblock walls, some of which could be looked through. To further complicate the problem, the firehouse had a high voltage utility and sewer line running beneath the property, leading to safety constraints that meant excavation was not ideal and requiring a carefully controlled repair approach. Moreover, in a busy fire station that cannot be closed for repairs, finding a minimally disruptive solution was key to the success of this project. Previous repairs with cementitious grout from 1994 worked temporarily, but unfortunately did not stand the test of time due to the continued natural break down of organic waste.
Solution:
Utility Services Group, INC (USG) was contacted to use their expertise given the complicated repair situation. In order to safely move forward with any kind of repairs to the floors, the team first conducted a utility locate service, to ensure that the location of the high voltage line and sewer was known.
During the utility locate, USG conducted what’s known as a Pennsylvania One Call, where they can be connected with underground utility owners and learn more about where utilities may be located. In this case, USG was only able to locate the line up to the building, and the rest of the line was private. So, with some information missing but a solid starting point, the team decided to finish the locating process using both a utility locator and a push camera that was ran through the sewer line. The utility locator identifies conductive materials by transmitting and receiving radio frequency signals. While the camera moves through the sewer, data is collected which allows USG to have precise coordinates of where the sewer line was located.
After the utility locate, USG was able to move forward with the next part of their plan: polyurethane injection soil stabilization and floor lifting. Soil reports were reviewed and a plan was drawn up. USG then drilled holes directly into the floors of the fire house, which were carefully placed so as to avoid the high voltage utility and sewer line. Injection rods were placed into the holes, then polyurethane injections were done at 2 depths: the first depth was injected to stabilize the soils below, and the second depth was to lift the slab floor.
As the polyurethane was injected at the lower depth, it expanded to encapsulate the soils and form a dense polyurethane soil matrix, which created a solid base despite the compost decay related conditions. In the second stage of injections, the polyurethane expanded stabilizing more soils and lifting the concrete floor back to grade.
Results:
This project yielded incredible results that maintained the safety of everyone on the site and did not require the firehouse to be closed. In fact, throughout the entirety of this project, the fire station remained active. Employees were moving about the station and firetrucks were coming and going, despite the USG team being present and working. Around 600 square feet of soil and concrete floor was stabilized and lifted, with as much as 2 inches of lift in the areas most affected by settlement.
This project exemplifies the importance of utility expertise in complicated projects; careful planning, coordination around active infrastructure, and precise polyurethane injection allowed stabilization to be completed safely without disrupting critical emergency operations.
