Foundation Repair Q & A

1. Is it true that, by keeping the moisture content of the soil under my house constant, foundation movement can be stopped?
2. Is piering a permanent fix to water damage, or is it an ongoing job?
3. What are the different types of repairing—I am particularly interested in piering, but I am not sure how piering compares to other types of repair.

Q. Is it true that, by keeping the moisture content of the soil under my house constant, foundation movement can be stopped?

A. This is often true, but movement can be caused by other factors, such as increased load, vibration, or subsurface changes such as plant or animal activity, frost action, or hydrological changes. Maintaining constant soil moisture is always beneficial, but this can be a major engineering challenge itself.

Q. Is piering a permanent fix to water damage, or is it an ongoing job?

A. Piering is a repair to provide vertical load support, and it permanence is determined by the design and installation approach. Shallow underpinning may provide success, but permanent load bearing strata may require deeper penetration, which can be provided at an affordable cost by hydraulically driven structural, steel tubing. This is a major repair project that can encounter subsurface complications, so an experienced contractor with the financial resources to manage these issues is important. The need for future piering for other parts of the building will vary from site to site, but proper installation methods should provide permanent vertical stability to the portion of a foundation that is supported by piers.

Q. What are the different types of repairing—I am particularly interested in piering, but I am not sure how piering compares to other types of repair.

A. Here is an overview of the various methods of foundation repair:.

For sinking foundations (Differential Vertical Movement):

MUD JACKING - Injecting grout to fill voids or raise a slab
PROS: Good for leveling sidewalks, driveways, patios
CONS: Will settle again as soil settles; not recommended for foundation walls or footings

ADJUSTABLE JACK POSTS - Steel posts placed in basement under first floor with screw adjustments to allow for height adjustment
PROS: Allows adjustment as movement occurs; cheaper than underpinning or piering
CONS: Does not stop soil or foundation movement; when movement of soil or cracking damage occurs, this is the sign indicating need for adjustment

UNDERPINNING - Excavating unstable soil beneath a footing and filling the void with more, stable material
PROS: If soil properties are known, unstable soil is shallow and firm soil is within a few feet, this can be a low cost, successful repair
CONS: If soil properties are unknown, weak soil depth may go beyond the repair depth, and future settlement may occur

PIERING - Bridging through weaker soil to construct a support capable of carrying the requiring load
PROS: Drilling or driving piers is less expensive than deep excavations to build foundations on solid soil
CONS: Obstructions below the soil's surface may prevent successful installation; can cause damage to existing structures

FRICTION PIERS - Carry load by soil friction of material driven or drilled in place
PROS: Cheaper than driving to solid strata
CONS: If there is vibration in the soil or changes in the soil load, they will compromise this method; unstable soil below pier may move and undermine the pier

HELICAL PIERS - Helical plate welded to steel shaft, screwed into soil by hydraulic drill
PROS: Cheaper than full-depth piering; can be installed quickly; increased depth improves tension resistance
CONS: Soil disturbed by auger action may move over time; water may weaken soil resistance; soil below helical plate may move; not the strongest repair method available because the strength of the system is in the helical plate and the surrounding soil

STEEL RESISTANCE PIERS - Structural Steel Shaft driven hydraulically to supporting strata
PROS: Driven full depth through weak soil, resting on stable strata; not subject to settlement
CONS: Must be spaced properly to balance and support the required load

CRACK INJECTION - A common and popular method to quickly stop water leaks and improve the appearance
PROS: It is much less expensive than structural repairs that reinforce or add load capacity; it can be effective in correcting minor leakage if damaging water pressure or active movement is not present
CONS: Rarely does crack repair  add structural strength to the concrete; if the stress that caused the crack is not removed, a new crack will form after the repair is made; it is very unlikely that a crack repair can reverse the damage from differential foundation movement, or prevent further movement

For buckling or bowed foundation / basement walls (Horizontal or Lateral Wall Movement)

WALL BRACE BEAMS - Anchored at top and bottom
PROS: Quick to install; requires no excavation
CONS: Puts the entire load of your basement wall on the weaker floor joists; can cause major problems with your floor joists, upstairs walls, carpentry, etc.; can cause movement on opposite wall if earth load is unbalanced; structural integrity will likely be lost.

WALL PLATE TIED TO ANCHOR ROD - With helical plate screwed into outside soil or steel plate anchor buried outside of wall
PROS: Anchor is independent of floor joist system
CONS: Must bore large hole in basement wall to insert helix; will let water into the basement and further weaken the basement wall; obstructions may prevent proper installation; anchor strength limited by plate area and soil properties; site or soil conditions may allow plate to move

STEEL WALL BRACE SYSTEM - Structural Steel Wall Brace anchored to Reinforced Concrete Earth Anchor
PROS: Anchor is independent of floor joist system; concrete anchor combines mass and soil friction for increased stability; can be sized to fit soil properies
CONS: Outside excavation required; structural integrity of wall must be sound after straightening

WALL STRAIGHTENING
PROS: Cheaper than replacing wall; improves structural stability if wall misalignment is excessive
CONS: Outside excavation required; structural integrity of wall must be sound after straightening

HIGH STRENGTH FIBER STRAPPING - Thin, fiber / epoxy strap bonded to inside face of wall
PROS: Thing strap material has smaller profile than structural steel; anchor is independent of floor joist system; requires no excavation
CONS: Structural integrity of wall must be sound; if wall has excessive misalignment, excavation may be needed to straighten wall; bond between strap and wall material may fail from moisture and weathering

WALL REPLACEMENT
PROS: Can address walls that have failed or are too unstable to repair
CONS: High cost; may not change conditions that damaged wall

CRACK INJECTION
(see above)