Past techniques for repair of sunken concrete has varied. Wood, concrete, cement and steel have been poured, pushed, turned or somehow forced into the ground trying to salvage these foundations and slabs, while early on, anyone and everyone, trained or untrained, became “experts” at this type of repair. Often as not, the repairs proved to be futile.
Other, more successful, methods of remediation involve extensive disruption of the family or business using the building. Usually, it is desirable that settlement of building slabs and monolithic foundations in residential areas be corrected without having to move all furniture, appliances, and possibly the whole family, or in commercial areas, without disrupting business.
However, with todays technology and trained experts, there are a number of very successful solutions to the problem of sunken concrete that involve little or no disruption to normal living or business routine.
The two most common methods of this type of repair are slabjacking and hydraulic jacking (also known as piering).
In a slabjacking operation, grout is pumped beneath a slab or beam to produce a lifting force that restores the member to its original elevation.
In piering, steel posts are driven through unstable soil and hydraulic jacks are used to raise or stabilize concrete slabs affected by changes in the underlying soil. The repair method used depends on the type of distress being treated.
Choosing the Correct Method for Concrete Foundation Repair
Before deciding on a repair method, you must determine what is causing the distress. Examine moldings and trim boards, mortar joints in brick veneer, and windows in low areas for clues. Also take note of recent weather. Unusually dry or wet weather can cause problems in the underlying soil.
The most commonly used method of correcting smaller slabs of sunken concrete, such as residential slabs, driveways, sidewalks, swimming pool decks, etc. is slabjacking.
Slabjacking is done by pumping a cement grout through small, strategically-located holes in the concrete slab. Once in place, the grout solidifies into a dense concrete mass and provides a competent bearing for the concrete slab.
If a soil-cement-lime grout is used, the lime content of the slurry will impart the benefits of lime stabilization to the base or sub-base. This combined treatment not only restores the slab to proper grade but also stabilizes the sub-soil to prevent re-occurrence of the problem.
For larger problems, especially those found in house and commercial building foundation shifting, piering is typically used to lift and stabilize the foundation.
Piering involves the use of strategically placed mechanical jacks to lift the settled beam to grade. The beam must be raised carefully to avoid further or unnecessary damage. Once raised, the beam is held to elevation by a specially designed spread footing and pier.
The footing is set deep enough so that it will be independent of variations in soil moisture. It is also designed to adequately distribute the load without creating unnecessary bulk or mass. The pier is tied into the footing with steel and supports the foundation beam.