Foundation repair is defined as the art of underpinning or stabilizing a structure that has moved from its originally constructed design. To underpin a home or structure one must extend the current foundation into a soil stratum or layer that is deeper and more stable than the current soil that the foundation is resting upon. This is accomplished by providing additional support from the current footing or wall via piers, piles, or anchors. Methods of foundation repairs include push piers, wall plate anchors, helical anchors or piers, and concrete piles.
Concrete slab on grade or pier and beam foundations are the most susceptible to weak or expanding clay soils. Due to the nature of having a large surface area resting on the uppermost soil layers these foundations have a tendency to move as the soil moves. Most concrete slab on grade homes are monolithically poured with the slab and beams cast together creating a rigid foundation. This rigid foundation becomes susceptible to differential settlement when moisture levels under the slab do not remain consistent. This can result from broken water lines, poor drainage, or even inadequate guttering. Trees can also affect soils with their roots. They will dry out areas under these slabs while the rest of the slab has normal moisture levels.
Differential soil or foundation settlement causes slab on grade foundations to rise or fall around the perimeter. Steel push piers and helical piers are generally an engineer’s recommended solution for these conditions. These piers penetrate through unstable soils down to a more consistent soil layer that has adequate strength to support the structure. These piering systems provide a deep foundation that can now be used to lift the foundation and to regain lost elevation levels.
Expansive clay soils that have been over-saturated with water can cause hydrostatic pressure on walls. This newly imposed pressure can cause wall bowing and concrete cracking. In extreme cases, catastrophic failure can occur from these wall stresses. When basement homes are originally designed it is with normal moisture content. Poor drainage often causes undue pressure to build behind basement walls exerting forces on the basement foundation. This is often the source of concrete cracking and water to infiltrate the space. Once again it is generally the differential movement that causes the foundation repair problem.
There are two common methods of fixing bowed basement walls. Plate Anchors (wall anchors) are an effective solution for many homes. These wall anchors are embedded into competent soils beyond a zone of influence surrounding the structure. Threaded rods are then connected to these anchors on one end with the opposite end being attached to a wall plate inside the basement. With this system, total excavation is not required and because of this additional soil load, wall recovery is accomplished over time with continued tightening of the anchor rods.
Next, there are helical tiebacks. This system of basement or retaining wall anchoring involves the complete excavation of the affected area. Helical anchors are screwed into the soil hydraulically and then attached with a wall plate situated inside the basement wall. With the full excavation, the wall can be instantaneously pulled back to plumb. The helical anchors can resist very heavy loads due to their design and the fact of their installation force equates to their resisting force.
The art of underpinning or stabilizing a structure that has moved from its originally constructed design must be performed by a foundation repair expert under the guidance of professional engineers.