A relative elevation survey showed that a 9,300 square-foot residence settled differentially up to 9.5 inches toward the rear of house and up to six inches in the area of the attached garage. Sloping floors and cracks in the brick exterior were observed as a result of the settlement. Legacy
Engineering, Inc. conducted a geotechnical investigation and suspected the cause of settlement to be a soft layer of organic material found from a depth of approximately 5 to 25 feet below the existing home.
The home was originally built on a deep foundation system including 1.5-inch solid square shaft helical piles. However, these piles had likely failed due to the lack of lateral support and resistance within the very soft, organic soils. Solid square shaft helical products are more commonly recommended for tension applications where lateral support from the surrounding soils is less critical. Square shaft helical products also generally have less rigid coupling details and lower sectional properties than their round shaft counterparts.
Past attempts to repair the home were also discovered. These repairs included square shaft helical piers and retrofit, L-shaped brackets. The brackets consisted of a pipe sleeve, channel sections welded to the sleeve, and a bottle jack welded to the horizontal channel. The excavation around the bracket was apparently filled with a cementitious grout.
A system of hydraulically-driven push piers was chosen to permanently stabilize and attempt to lift the settled structure. A sacrificial test pier was driven and installed against the existing foundation and monitored by Legacy Engineering, Inc. to verify pier capacity. Two hundred thirty Model 350 (3.50-inch OD by 0.165-inch wall) push piers were installed along the exterior foundation and within a three-foot crawlspace. The piers were advanced to depths of approximately 30 feet to bear below the organic material and achieve a design working load of 20 kips per pier. Hydraulic lift cylinders were fitted to the installed pier assemblies and connected in series to apply uniform load to stabilize and attempt to lift settled portions of the building. The original square shaft helical piles and retrofit square shaft helical piers were detached from the structure prior to attempting a lift. As the garage foundations were lifted with the retrofit push piers, PolyLEVEL® polyurethane foam was injected under the slab to allow the foundations and slab to be lifted together. PolyLEVEL® is a two-part liquid urethane that reacts to form a rapidly setting, rigid foam with an in-place compressive strength generally greater than 75 psi. Approximately 500 pounds of PL250 were injected below the garage slab. The garage floor slab was lifted back to level and the structure was lifted to within acceptable limits.