Prescott Foundation Investigation 10.2021
Challenge
The owners of this Prescott, AZ Home reached out to us after noticing several symptoms of a potential foundation problem.
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.
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.
Findings: An edge heave pattern is observed in the northeastern, eastern and southern portions of the home as indicated by the higher elevation readings on page 10 (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.
After examining the home and performing the manometer survey, Arizona Foundation Solutions believes the home could be experiencing minor foundation settlement at the central portion of the home as shown by the lower readings on the Topographical 2D 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, the lack of a proper foundation system, and/or (in most cases) natural earth movement.
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 heave and areas indicating settlement.
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/372) was less than the allowable deflection limit of L/360. In addition, the tilt of the slab (0.39%) was less than the allowable tilt of 1.00%.
Solution
Arizona Foundation Solutions believes that the proper way to deal with edge heave is to first install piers to support the perimeter walls of the area that is experiencing edge heave. Under excavation will be performed in this area. This is where some of the heaving soils will be removed to create voids for future expansion. If possible, the perimeter can be lowered to practical recovery. This will be determined by field conditions.
AZFS does not suggest a settlement repair plan at this time as there is no significant damage to correspond with the low 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.
Arizona Foundation Solutions believes that the proper way to deal with foundation heave is by lowering and managing the moisture content of expansive clays that cause heaving. It is our recommendation to manage the moisture underneath the foundation through active soil depressurization. This process will remove existing moisture from the soil as well as new moisture from the expansive clays and will help bring the moisture content down to an optimal level using both convection and evaporation. This will mitigate future heaving of the clay soil and possibly allow existing heaving to subside. This process can take six months to several years to reach equilibrium. Minor movement may still occur, as the Moisture Level® System is intended to prevent significant and continual upward movement caused by moisture.
The Moisture Level® System is designed to control the moisture of expansive clays that cause heaving under the home. If optimal results are not achieved with the Moisture Level® System including additional measures described below, more aggressive measures may be required. The manometer and foundation survey will act as a baseline to measure performance over time.
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: Michael R. Simpson
