How to deal with heave, sinkholes and subsidence

We’ve all seen pictures of subsidence at its spectacular worst. The ground collapses without warning, a huge hole in the earth appears and it takes a large chunk of a building with it.

Most instances of subsidence are far less dramatic than the sinkholes described above. In areas where bedrock is either chalk or limestone, there are inevitably many cavities or caves gradually dissolved by the carbonic acid found in rainwater. Heavy rain soaks into the soil, gravity does its job until the water reaches a non-porous rock, and an acid solution slowly gets to work forming an undetected cavity.

Initially, there may be no more subsidence than a slight depression in the soil above the cavity, causing a potential drop in surface levels where cracks to brickwork may appear. But in other instances, the results can be far more severe.

Ways to deal with subsidence

In Brighton and Hove, the bedrock is primarily chalk and therefore sinkholes do appear from time to time. However, most examples of subsidence are much less severe than full blown sinkholes due to the early tell-tale signs a potential sinkhole is forming.

In most cases, remedial action can be taken which include:

  • strengthening or extending footings by reinforcing with concrete
  • piling to reach ground strong enough to support a building
  • filling the void and compacting it with ‘made up ground’

Made up ground is the term for any mix of materials used as a filler to alter the topography of a site, whether to fill, level, slope or to step a piece of land. There’s a lot of it in Brighton and Hove because buildings need horizontal bases, which is difficult to find in a city predominantly made up of hills.

In most cases, made up ground is formed by an aggregate comprising a high proportion of crushed building waste. Unless extremely well compacted, it’s almost certain to suffer a degree of subsidence over time, and therefore present building regulations require a building’s footings to reach a depth where solid rock is found. When that’s a long way down, it’s often more economical to use piles rather than conventional footings to support the building.

Subsidence in Brighton and Hove

Fortunately, very little of Brighton and Hove is built on clay, which tends to be the soil most associated with subsidence problems. One of the biggest issues with clay is that it expands (known as ‘heave’) often resulting in subsidence. During heavy rainfall it absorbs water which causes expansion, whereas through the drier months it tends to drop and contract.

The forces unleashed by these movements can cause serious structural damage, especially if extremes of wet and dry are experienced. When you combine this problem with substantial neighbouring trees or poor drainage systems, you could have a costly problem on your hands.

The whole subject of subsidence can get very technical, and here we have just touched the surface. The important thing is to be aware that a crack in a wall, a fissure appearing in the ground, or a drop in the surface level of a particular area could be a sign of subsidence. If you’re experiencing any of these problems, it’s best to contact an expert who can confirm subsidence or otherwise.

Get in touch

To discuss your subsidence problems in further detail, speak to our team today by calling 01273 031646.