Foundation Settlement - Prescott, AZ

Challenge

The Homeowners of this beautiful 14 year old, single family ranch style home reached out to us after noticing cracks in the tile flooring and gaps between the baseboards & flooring.

After examining the home and performing the manometer survey (water level), we believes this home could be experiencing foundation settlement in the Nook, Kitchen and Dining Room and in the Laundry Room as shown by the damage & topographical map. The drop off in floor elevations on the topographical map is consistent with a foundation settlement pattern.

Foundation Settlement can be caused by one - or any combination of many factors - including:

• sub-grade saturation of moisture due to poor drainage
• years of storm runoff
• plumbing leaks
• improper compaction
• lack of a proper foundation system
• and/or (in most cases) natural earth movement

We believe this central Arizona home could be experiencing minor foundation settlement at the northern portion of Bedroom 2 and at the northern portion of the Casita as shown by the lower readings (see topographical map).

There appears to be a crack in the floor slab as well. When the foundation slab cracks all the way through, the separate sections can move independently of one another. This allows for severe damage to the flooring and other signs of interior foundation stress, like:

• pinched doors
• drywall, and/or ceiling cracks
• gaps at the baseboards

Solution

The Foundation Performance Association (FPA) “Guidelines for the Evaluation of Foundation Movement for Residential and Other Low-Rise Buildings” were adopted to correlate acceptable and unacceptable distress phenomena with actual survey elevations. Deflection and Tilt calculations were performed and compared to allowable values. For this engineered analysis, the deflection of the slab (L/269) was more than the allowable deflection limit of L/360. In addition, the tilt of the slab (0.1%) was less than the allowable tilt of 1.00%.

We believe the proper way to permanently stop the perimeter foundation settlement on this home is to underpin the areas that are experiencing movement. Underpinning is the process of installing deep foundation elements called ‘piles’. Piles are engineered foundation supports that are driven down past the unstable soils and are then locked up into load bearing strata, which can support the loads that are transferred to them. Once the piles have been installed, they can be used to lift the perimeter foundation up to its Highest Practical Maximum. The piles should be spaced approximately six to eight feet on center and should start and stop near the hinge points of movement (exact spacing to be determined after load bearing calculations).

In this case, the piles would be located at the northern portion of the home and at the southern portion of the Laundry Room. The slab can then be treated by injecting a lightweight expansive polyurethane to fill existing voids and lift the floor slab. This is done by drilling small 3/8” holes in the slab after which polyurethane grout is injected directly under the slab to raise it up to its Highest Practical Maximum. Using the expansive materials will help prevent additional slab settlement by compacting the upper layer of soil as it expands.

Composite interlocking (or crack stitching) can be performed to tie the broken pieces of the concrete together. The existing crack will be cleaned, and non-parallel lines will be cut across the existing crack. Next carbon fiber laminate stitches will be inserted into the non-parallel cuts and then the gaps will be filled with a 2 part poly.

Finally, the crack should be ground smooth to minimize the differential. If done properly, this will allow the slab to function as one floating unit to help prevent the damages to flooring, ceiling and walls. If this is instead expansion joint separation, the joint should be cleaned, routed, and re-caulked with an expansive joint filler.

Project Summary

Engineer: Nestor B.