Subsidence Management Ltd » Prevention


Ways of preventing further damage

In simple terms this means minimising the risk of the soil beneath the footing/foundation moving excessively. This can be achieved by addressing the cause of movement e.g. repairing drains, managing vegetation or, where movement is caused by unstable surface soils the tried and tested method is known as underpinning. This involves creating large concrete supports (or ‘pins’) under the existing foundations that extend down into the more stable soils at a greater depth. It is an expensive and disruptive process but it is known to be very effective when correctly carried-out. A modern version of underpinning is piling, or sometimes mini-piling. This involves introducing long concrete or steel columns close by the building that extend downward several metres into the subsoil, where they take their support. These are then used to carry the full weight of the building, thereby insulating it from the effects of movements within the surface soils. Alternatively, a “raft” of reinforced concrete can be used as the foundation.

Any services, i.e. drains, water pipes etc., that feed into the building must be designed to accommodate such alterations in the foundation, but this is known technology. Where the ground movement is caused by shrinkage or swelling of clay soils then the initial approach is to ensure that the soils that carry the weight of the building cannot suffer changes in their moisture content. At the design stage for a new building, this is achieved by ensuring that the foundations extend downward below the zone that may be affected by seasonal variations in moisture content, i.e. deeper than about a metre. In the case of building near to trees this will depend on the size and species of tree and their distance from the building. Where buildings are required to co-exist with trees it is prudent to maintain the trees in a way that will not allow significant changes in soil moisture content to occur. We can advise on this.

Subsidence Management Limited