Case Studies

Foundation Inspection Case Studies: Foundation Settlement in Tucson, AZ 9.2021

Monday, September 20th, 2021 by Jessica LaFlesch

Challenge

Homeowner’s Concerns/Goals: The homeowner’s main concern is the addition, specifically the slab crack and also the addition being constructed without a footing.

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 southern portion of the home (addition) as shown by the 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.

A minor heave pattern is observed in the central portion of the home 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.

There are cracks in the floor slab in the addition. 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/762) was less than the allowable deflection limit of L/360. In addition, the tilt of the slab (0.14%) 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 five 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 south, southeast and southwestern 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. If the addition was not properly permitted, then the recommended repairs may have to wait until the city issues a permit.

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.

Composite interlocking can be performed to tie the broken pieces of the concrete together. The existing cracks will be cleaned, and non-parallel lines will be cut across the existing cracks. 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. 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.

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.

Project Summary

Engineer: Néstor J. Brea

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Arizona Foundation Solutions of Tucson
5151 E Broadway Blvd Ste 1600
Tucson, AZ 85711
1-520-399-7726
Arizona Foundation Solutions of Tucson service area