Reactive soils are clay-type soils that swell on wetting and shrink on drying. The soil type is classified by a testing procedure as part of the building planning/approval process. Drains laid below ground in reactive soils will need to provide for ground movement. Failure to provide for this movement may result in drain failures such as shearing, leakages and blockages of the drain and further building problems such as structural cracking which may be very costly to remedy.
Where the type of soil can have a significant impact upon building structural issues, it is advisable to seek the advice of a structural engineer and have the soil professionally tested.