Foundation Settlement in Mesa, Arizona
Challenge
The owners of this mid 70’s Mesa, Arizona single family ranch home reach out to us after noticing symptoms of a foundation issue. Unlevel floors, doors and windows that are out of square along with wall cracks were among the list of symptoms. Cracks in the home’s concrete patio were also observed.
A visual, level A, inspection determined that a Forensic Foundation Inspection is needed. A Forensic Foundation Inspection, or level B foundation inspection, is much more comprehensive than the level a, or visual, foundation inspection.
Solution
After examining the home and performing the manometer survey, Arizona Foundation Solutions believes the home could be experiencing foundation settlement at the northwest, west, and southwest portions of the home as shown by the damage and lower readings. The drop off in floor elevations on the topographical map is consistent with a foundation settlement pattern. 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, the lack of a proper foundation system, and/or (in most cases) natural earth movement.
Arizona Foundation Solutions believes that the proper way to permanently stop the perimeter foundation settlement 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 northwestern, western, and southwestern portions of the home. 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 5/8” 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.
AZFS believes the home could be experiencing minor foundation settlement at the northeast portion of the home as shown by the signs of stress. The home could also be experiencing minor foundation settlement at the eastern portion of the home and around the perimeter of the Arizona Room addition as shown by the lower readings.
The settlement at the east and northeast portions of the home and around the Arizona Room addition perimeter appears to be minor at this point in time. A protection plan has been designed to stop these areas from any additional settlement and further damages. AZFS can permanently stabilize this area to protect the foundation from future settlement at the homeowner’s discretion.
A minor heave pattern is observed in the southcentral portion of the home, and western portion of the garage as indicated by the higher elevation readings. This phenomenon usually occurs in areas where structures are built on expansive clays. Moisture from one or any combination of the following: storm runoff, poor drainage around the foundation, plumbing leaks and/or underground moisture sources will allow the moisture/ vapor to accumulate underneath the foundation. The moisture then interacts with the clayey soils, causing them to swell. The clay soils take the path of least resistance and expand upwards and lift the foundation.
The rebar in the stem wall along certain sides of the home has begun to rust. This has caused the rebar to deteriorate and the iron oxide to expand. The expansion from the iron oxide generates enough pressure to crack the stem wall. The corrosion of the bar has typically exceeded 20% before there is enough pressure to crack the stem wall. This issue should be dealt with properly to prevent the corrosion from spreading down the perimeter of the rebar and to return the original strength and span capacity to the stem wall.
Arizona Foundation Solutions believes that the rusting rebar in the foundation stem wall needs repair. The stem wall must be chipped back to expose the corroded rebar. The rebar should then be cut out and replaced with a composite bar and dowelled to bridge the separation between the bars. The stem wall should then be patched and finished smooth. This will prevent the treated area from future rust and restore the ability of the stem wall to span small voids and support the load. It is recommended to wait at least one week before painting the surface of the stem wall.
There appears to be a crack in the garage floor slab. When the slab cracks all the way through, the separate sections can move independently of one another. This allows for severe damage to flooring and other signs of interior stress like pinched doors, drywall, and/or ceiling cracks. A protection plan has been designed to repair the cracks in the garage slab. AZFS can repair the cracks in the garage slab at the homeowner’s discretion.
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.
The stem wall in certain areas around the home appears to be spalling. Spalling is when the concrete face of the stem wall is deteriorating. Spalling can occur when there is excess moisture near the foundation, minerals in the soil, and/ or when the concrete was not mixed correctly. This is most often a cosmetic issue but if deterioration has occurred underneath the loads of the structure, it is no longer considered cosmetic.
The spalling stem wall can be cosmetically repaired. First, the face of the stem wall needs to be chipped back to fractured rock. Then a cementitious patch can be applied and finished smooth. Please wait at least one week before painting the surface.
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. Data from our first visit showed the foundation failed on overall deflection of L/308 from an allowable L/360 and passed on overall tilt with an actual percentage of 0.04% from an allowable 1.00%. For this engineered analysis, which is a comparison of the prior slab data and the most recent measurements, the deflection of the slab (L/896) was less than the allowable deflection limit of L/360, and therefore is acceptable in tilt and deflection.
While the home passes in tilt and deflection, this is a general guide and the home is showing distress at areas indicating heave and areas indicating settlement.
Maintaining proper drainage is critical to the performance of every home’s foundation. It is important to get the roof and other drainage to empty at least 20’ away from the house and keep ponding to a minimum along with any watering of plants.
We recommend that drainage be improved with gutters and or drain lines.
Project Summary
Engineer: Nestor B.
