Gilbert Foundation Investigation 2.2022
Challenge
The owners of this 1994 single family home reached out to Arizona Foundation Solutions after noticing a few signs of a potential foundation problem.
These signs included:
-Interior wall cracks
-Gaps at the baseboards
-Exterior wall cracks
Home Details: 1994 single family, 2 story, wood framed home on a conventional slab. Concrete stem wall with top of footers 14” below grade.
An initial, Level A Foundation Inspection was completed. Based on the observations, a more in depth, Level B Foundation Investigation was recommended.
Homeowner’s Concerns/Goals: The homeowner is primarily concerned with the damages in the dining area
Level B Foundation Investigation
Introduction: Thank you for allowing Arizona Foundation Solutions to present this foundation survey and assessment for the proposed foundation repairs on your property.
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.
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.
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.
The extent and scope of this manometer and foundation survey and assessment is detailed as follows:
• Perform a manometer survey.
• Locate areas of potential foundation and floor movement, if any.
• Visually inspect and record the interior and the exterior of the location.
• Evaluate any noted movement using industry consensus methods, if any.
• Prepare a documented repair plan if needed.
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 northern and western portions of the home as shown by the damage (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 eastern portion of the home and northeastern portion of the garage as shown by the minor damage (also known as Signs of Stress) and lower readings on the Topographical 2D Map. The drop off in floor elevations, at the eastern portion of the home, on the topographical map is consistent with a minor foundation settlement pattern.
A minor foundation heave pattern is observed in the southern portion of the garage as indicated by the higher elevation readings on the Topographical 3D Map. 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 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/205) exceeds the allowable deflection limit of L/360. In addition, the tilt of the slab (0.16%) was less than the allowable tilt of 1.00%.
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 northern and western portions of the home. 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 eastern portion of the home and northeastern portion of the garage from any possible future settlement and further damages. AZFS can permanently stabilize this area at the Homeowners discretion.
AZFS does not suggest a foundation heave repair plan at this time as there is no significant damage to correspond with the high elevation readings. The home should be monitored and should damage arise in the future, AZFS should be contacted to perform a comparative manometer survey at a discounted price.
Since storm runoff is responsible for the majority of the moisture that pools next to the foundation, gutters need to be installed to prevent the storm runoff from increasing the amount of foundation movement. A proper gutter system should be installed to discharge the storm runoff a minimum of 10 feet, preferably 20 feet away from the foundation. We do not recommend installing gutters that discharge next to the foundation as this will only increase the probability of a foundation problem.
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
Project Summary
Engineer: Néstor J. Brea
