Foundation Stabilization Repair Options

SLAB-ON-GRADE FOUNDATION STABILIZATION TECHNIQUES

Many building owners elect to ‘repair’ or ‘stabilize’ their ground supported slab-on-grade foundation system without the
guidance and expertise of a licensed professional engineer. The results can be devastating. Under the direction of an
unqualified foundation repair contractor, building owners often conclude they have structural foundation problems based
solely upon the distress they see, rather than taking the extra step to engage a licensed professional engineer to accurately
diagnose the signs and symptoms of an authentic structural foundation problem. And unfortunately, when the building
owner bypasses the engineer and hires an unqualified foundation guru, what they actually get is a high risk, low benefit, and
often irrevocably damaging foundation disaster masquerading as a budget friendly foundation ‘repair’. In the current
structural engineering lexicon, this pervasive yet destructive attempt by incompetent contractors to ‘stabilize’ ground
supported concrete slab-on-grade foundation systems has come to be known as ‘fractional underpinning’.

WHAT IS FRACTIONAL UNDERPINNING? Fractional underpinning is the partial underpinning of a slab-on-grade
foundation system. It is the fractional support of a structure that requires 100% uniform support to remain structurally
sound over its serviceable life. Fractional underpinning often attempts to lift or level part of the foundation system, while
leaving its remaining parts unsupported. Fractional underpinning has long been blacklisted by competent professional
engineers as a principal cause of irrevocable foundation structural damage and cosmetic finish distress. Here’s why:

(i.) Slab-on-grade foundation systems (ground supported and steel reinforced concrete slab-on-grade) depend
principally upon uniform bearing material support across their entire bottom bearing surfaces to remain
structurally sound and reasonably serviceable.

(ii.) The design premise of slab-on-grade foundations are based upon uniform and equivalent support over
their entire bottom bearing surfaces in contact with the ground. Uniform foundation bearing support
minimizes foundation movement while preserving and protecting their structural performance and
foundation structural strength.

(iii.)Fractional underpinning, or putting piers or underpins under only part of the foundation system disrupts
foundation bearing uniformity by restraining and stiffening its isolated parts which bear directly atop the
new underpins. The remaining unrestrained, non-underpinned parts of the foundation system remain
relatively flexible. Non-Uniform foundation bearing support increases the risk of abnormal foundation
displacement and often emasculates foundation structural performance and structural strength.

(iv.) Fractional underpinning restrains foundation vertical movement near its underpinned areas (perimeter
areas) while simultaneously allowing its non-underpinned areas (interior areas) to displace vertically with
ongoing changes in its supporting material moisture content. Over time, this forced restraint imbalance
weakens and emasculates the foundation system resulting in its non-uniform and unpredictable vertical
displacement.

(v.) Any remedial underpinning method applied to ground supported foundation systems must include
sufficient quantities of appropriately spaced underpins uniformly distributed beneath it to assure its
uniform support and to preserve and protect its ongoing structural integrity and structural serviceability.

(vi.) The following foundation stabilization methods (Options #1, #2, and #3) below attempt to restore the
structural integrity and improve the serviceability of a Slab-on-grade foundation system which requires
structural “repair” or “stabilization”. Foundation Stabilization “Cost” is evaluated on a scale of 1 to 5
with 1 being the least costly and 5 being the most costly. Foundation Stabilization “Potential Benefit” is
evaluated on a scale of 1 to 5 with 1 being the least beneficial with the most risk and lowest reliability, and
5 being the most beneficial with the least amount of risk and the greatest reliability.
Option #1: NON-INVASIVE TECHNIQUES. Cost: 1-2. Potential Benefit: 3. Implement “Steps To
Improving Foundation Performance” found here: http://anyflip.com/ajix/qnqy/. Note: Excessive
foundation cracking and excessive foundation floor surface deflection may be consistent with
foundation loss of section and its corresponding diminished structural integrity. Customer may

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consider crack repair to restore stiffness across multiple crack areas when their widths equal or
exceed 1/16 inch width. Cracks with widths as narrow as 1/32 inch may be candidates for repair
using epoxy injection methods. Follow the epoxy makers instructions.
Option #2: MUDJACKING (STRUCTURALLY INVASIVE). Cost: 2-5. Potential Benefit: 2.
Remove any existing underpins/repair systems from beneath the foundation system which may
improperly restrain it. Attempt to stabilize and level the foundation system by filling any existing
voids between the foundation fill materials and the slab panel bottom surfaces with an approved
flowable material. Fill any cracks or foundation penetrations > 1/16” width or diameter with an
approved construction adhesive (Low or medium viscosity Epoxy Resin). Cracks with widths as
narrow as 1/32 inch may be candidates for repair using epoxy injection methods. These procedures
must be done under the guidance of a competent and experienced professional engineer licensed in
the State of Texas.
Option #3: SUSPENDED SLAB CONVERSION (STRUCTURALLY INVASIVE). Cost: 5+.
Potential Benefit: 3-4. Remove any existing underpins from beneath the foundation system which
may improperly restrain it. Attempt to stabilize the existing shallow bearing ground supported slab by
converting into a suspended slab bearing atop deep drilled underpins. The underpin system must be
specified and designed by a competent and experienced professional engineer licensed in the State of
Texas. Underpins will typically be placed beneath the interior/exterior slab stiffening beams and will
bear to depths below the ground surface in excess of 20 feet. Underpins will normally be drilled and
steel reinforced bell bottomed piers. Fill any cracks or foundation penetrations > 1/16” width or
diameter with an approved construction adhesive (Low or medium viscosity Epoxy Resin). Note:
Cracks with widths as narrow as 1/32 inch may be candidates for repair using epoxy injection
methods.

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