Fix up methods that don’t fix slab heave
Tyning the soil before construction
This is strictly a slab give fixup method. It is meant to be a sad he preventative method however tyning of the soil before construction of a slab offers limited success in preventing slab heave. The intention of timing is to create a layer of soil that will consolidate away from the underside of the slab. When soil expansion heave does occur for, the expansion of the soil will not bring the soil into contact with the underside of the slob, hence preventing movement in the slab. The slab therefore essentially designed as a suspended slab with no support from the ground immediately under it.
The problem with this method is the inherent difficulties in obtaining a uniform level of looseness in the soil.
Irrigating around the outside of a slab
Sometimes irrigation around the outside of Slaby specified to undo the effects of differential soil moisture that has resulted in slab heave. My problem with irrigation is the fact that it needs to be maintained for the life of the building. It needs to be adjusted during the wet weather. Sometimes the amount of moisture introduced to the soil by wet weather will exceed the level of moisture being inserted by the irrigation. The change in soil moisture content will still create uneven soil moisture conditions and result in slab heave,
Furthermore the danger exists that moisture transfer under the house will not be consistent and that might still result in slab heave.
Directional boring under a house and controlled flooding
Similar difficulties with maintaining soil moisture content for the life of the building by the use of directional boring and underground flooding occur as for perimeter irrigation. The system. Yet be maintained by present and future owners, it must be adjusted for seasonal moisture influences and the trench must be level under the building to prevent abnormal soil moisture conditions under the middle of the building compare to the perimeter.
Chemical treatment of clays
Clay is a particularly impervious material. It resists transfer of moisture so well that it is used to line dams. Therefore the treatment of clay soil by injecting chemical treatments under a slab is a recipe for disaster. Distribution of the stabilisation chemicals into the soil matrix is severely limited. Pockets of stabilise clay will still be surrounded by regions of reactive clay. The foundation will be similar to having rock floaters with in a deep clay matrix. Movement will still occur on an overall scale under the building unless the pockets of stabilise clay outnumber the regions of reactive clay. This is incredibly difficult to achieve under an existing building.
Soil stabilisation may improve the serviceability of the building if it is applied to the construction site before the construction of the footings and slabs. However the chemical will need to be thoroughly mixed and then the soil compacted back to 95 standard compaction. This method of stabilisation is only likely to be economically feasible on the worst of sites. The cost of the treatment may significantly outweigh the cost of removal and replacement of the highly reactive clay with granular material, which is my preferred treatment for a site containing poor soil conditions.