Arizona Foundation Solutions Case Studies: Foundation Investigation of a 2006 Prescott, AZ Area Home 12.2021
Challenge
This 2006 single family home is on a conventional slab with the top of the footing at 14” below grade. A number of symptoms prompted the current owner to have the foundation evaluated.
An initial Level A Foundation Inspection noted interior wall cracks, exterior wall cracks, and interior concrete slab cracks.
Based on the symptoms noted, a Level B Foundation Investigation was recommended and completed.
Homeowner’s Concerns/Goals: The homeowner is primarily concerned with the signs of stress in bedroom 2. The homeowner would like to address any foundation issues and sell the home.
Purpose of the Investigation: The purpose of this report is to evaluate the foundation and the foundation conditions of this property, and to perform a manometer and foundation survey on the interior of the property.
Scope of Services: The extent and scope of this manometer and foundation survey and assessment is detailed as follows:
• Perform a manometer survey.
• Locate the areas of foundation and floor slab failure, if any.
• Visually inspect and record the interior and the exterior of the location.
• Determine the extent of the foundation failure, if any.
• Prepare a documented repair plan if needed.
Limitations: The purpose of this report is limited to documenting and addressing the areas of concern indicated by the customer related to potential foundation movements. Arizona Foundation Solutions uses a variety of tools such as manometer survey, observations by technicians with notes and photographs, and industry standards such as the Foundation Performance Association (FPA) “Guidelines for the Evaluation of Foundation Movement for Residential and Other Low-Rise Buildings” to determine if foundation movement has impacted the serviceability of the home. The term serviceability relates to items such as pinched doors and windows, cracks in drywall and slabs, cracks in exterior stucco and walls and the like. Recommendations in this report are made to address and limit future issues related to serviceability and the customer’s concern.
Unless expressly stated in the Safety and Structural Concerns section of this report, nothing in this report should be interpreted as: a determination of structural inadequacy, an occupancy issue or a safety issue.
This report offers no opinions as to the adequacy of the work of previous designers or contractors. This report is based on our observations and may not be indicative of all factors contributing to foundation and floor slab movement. Only a comprehensive geotechnical investigation and structural engineering investigation by licensed engineers would be able to determine all of the factors contributing to the failure of a foundation.
Foundation Footprint: A drawing of the footprint of the first floor was created and is included in this report.
Exterior Inspection: The exterior of the location was visually inspected. Items such as foundation cracks, exterior wall cracks, improper grading, type of structure, poor drainage, gutters or no gutters, bowed retaining walls, large trees close to the foundation and any type of obstructions that may or may not influence the repair process were noted and recorded.
Interior Inspection: The interior of the location was visually inspected. Items such as floor cracks, wall cracks, ceiling cracks, sloping floors, uneven counter tops, doors and windows that are out of alignment, cracked window glass and bowed walls were noted and recorded.
Manometer Survey: The manometer survey, also known as a floor survey, is a measurement of the differences of interior floor elevations. The flatness of the interior floor was measured using a highly accurate survey device known as a Manometer. The entire interior floor area was surveyed and the elevations were recorded. These data points were then entered into a computer program that provides a topographical map showing the high and low elevation contours of the floor surface. This topographical map shows where the foundation is no longer level and shows where support and stabilization is needed. The floor survey also demonstrates whether any floor slab heave or settlement exists.
After examining the home and performing the manometer survey, Arizona Foundation Solutions believes the home could be experiencing foundation settlement at the east, northeast and southeastern portions of the home and at the northeast portion of the garage as shown by the damage (also known as Signs of Stress) and lower readings on the Topographical 2D Map. 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.
AZFS believes the home could be experiencing minor foundation settlement at the northwestern portion of the home as shown by the minor damage (Signs of Stress) and lower readings on the Topographical 2D Map.
There may be a crack in the floor slab. The flooring will need to be removed by others to verify the slab cracks. 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.
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 to typically exceed 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.
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/641) was less than the allowable deflection limit of L/360. In addition, the tilt of the slab (0.12%) was less than the allowable tilt of 1.00%.
While the tilt and deflection was less than the allowable limit, this is a general guide and the home is showing distress at areas indicating settlement.
Solution
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 it’s Highest Practical Maximum. The piles should be spaced approximately 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 east, northeast and southeastern portions of the home and at the northeast portion of the garage. The slab can then be treated by injecting a light weight 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 it’s Highest Practical Maximum. Using the expansive materials will help prevent additional slab settlement by compacting the upper layer of soil as it expands.
A protection plan has been designed to stop the northwestern portion of the home from any possible future settlement and further damages. AZFS can permanently stabilize this area at the homeowner’s discretion.
Composite interlocking 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 two-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 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. A determination as to which repair is needed will be made on site once the crack is exposed. The homeowner may want to contact a flooring expert and consider floating the flooring after the repair has been made.
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.
It is also beneficial to manage the moisture around your home using conventional means as outlined below:
-Hire a reputable plumbing leak detector and repair service to check both pressure and sewer lines, this is usually done for less than $500. If repairs are needed, they are usually not expensive.
-Make sure the grading of the terrain is sloped downwards at 5% slope from the home at all areas of the perimeter.
-Stop irrigating plants that are near the foundation and make sure there is nothing -trapping the moisture from flowing away from the home.
-When permanently stabilizing, lifting and/or mitigating a foundation movement problem, AZFS recommends waiting AT LEAST 6 months before investing in cosmetic repairs.
Safety or Structural Concerns: None
