Gilbert, AZ Underpinning System Installation 7.2021

Monday, August 2nd, 2021 by Miguel Ramirez

Challenge

The Owners of this 1993’s single-family house got in contact with us after seeing a few signs of foundation problems.

These symptoms of stress included:

There are some cracks on the ceiling
There is a crack by the window
There is flaking paint on the stem wall
There is a horizontal crack on the stem wall

Homeowner’s Concerns/Goals:

The Homeowner is concerned about the crack on the fireplace, the columns shifting and the kitchen counter sinking.

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 are needed. The floor survey also demonstrates whether any floor slab heave or settlement exists.

A minor heave pattern is observed in the central 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.

After examining the home and performing the manometer survey, Arizona Foundation Solutions believes the home could be experiencing minor foundation settlement at the northern and southeastern portions of the home as shown by the minor damage on the topographical 2D map. AZFS also believes the home could be experiencing minor foundation settlement at the fireplace and southern columns on the back porch. 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.

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/382) was less than the allowable deflection limit of L/360. In addition, the tilt of the slab (0.17%) was less than the allowable tilt of 1.00%.

Solution

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.

The minor settlement at the fireplace and southern columns on the back porch appears to be minor at this point in time. A protection plan due to the homeowner’s concerns has been designed to stop the 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.

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.

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.

Prior to any work being accomplished, AZFS recommends that the homeowner contact a professional contractor and/or a licensed Structural Professional Engineer to look at the rear patio of the home. Carpentry and non-soil related movement are outside the scope of work of this project.

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.