Inadequate soil conditions are caused by several factors. With suitable building sites becoming more scarce, many home builders have been building houses on less than ideal lots. Due to these conditions, foundation support products must be utilized to supply support from deeper layers that are not as affected by fluctuating moisture levels. This underpinning provides a way to lift the home to an acceptable level and prevent additional settlement.
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 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.
Differential settlement causes slab on grade foundations to rise on the perimeter (dish) or fall around the perimeter (dome). 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.
In the case of homes with basements, 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. Poor drainage often causes undue pressure to build.
There are two common fixes to bowing basement walls. Plate 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. Either way, make sure to hire a professional engineer to work on your slab foundation. That is always the first step to making your home structurally sound.