Soil Stabilization for Timber Pile Repair
Challenge
The two-story, wood-frame home was built in 1999. Light loads from the first floor construction were reportedly supported by the slab-on-grade floor system with monolithic thickened edges and interior footings. The second floor and roof loads were supported by exterior timber piles founded in clean fine sand. The condition of the wood piles had deteriorated over the 15 years since construction due to the combination of high moisture conditions, high oxygen content, and fluctuating groundwater levels within the near-surface soils. Wood rot was generally observed from grade to roughly two to three feet below grade.
Another foundation repair contractor proposed to repair the timber piles and resupport the structure by severing the timber piles and installing a helical pier and retrofit, side-load bracket. This solution eliminated any remaining axial and lateral support provided by the timber pile and then left the pile in a laterally unbraced condition. The contractor gathered equipment and left the site when the homeowner questioned the repair completed on the first timber pile.
Solution
Alpha Foundation Specialists proposed to repair the deteriorated timber piles with a jacket and epoxy system. Excavations were then required around the piles to depths extending below the wood rot. However, cuts through loose, flowing sand could potentially undermine the concrete floor slab. PolyLEVEL® 100SS (PL100SS) single-part polyurethane resin was injected into the sand around the timber piles and beneath the concrete slab-on-grade. PL100SS migrates through loose soil and into voids and reacts as it comes in contact with moisture in the soil to essentially glue the soil matrix together. The low viscosity and slow reaction time of PL100SS makes it an ideal product for stabilizing sands and other loose soil strata. With the surrounding sands stabilized, clean, vertical cuts were made to allow repair of the timber piles.
Project Summary
Structural Engineer: Johnson & Milner, Inc.
PolyLEVEL® Installer: Alpha Foundation Specialists, Inc.
Products Installed: PolyLEVEL® 100SS (PL100SS) Single-Part Polyurethane Resin
