Have you ever wondered whether you should involve a Structural Engineer when planning a new building, an extension or supporting slab? It is quite common to assume that the underlying ground is strong enough to support the proposed building or loads, however there is much more to consider than you might think, particularly when the soil is 'cohesive' (like clay).


Being located in East Anglia we are well versed in dealing with different soil types as this region has one of the most variable throughout the U.K. It is quite common for the underlying soil to consist of granular material (such as gravel or sand), as well as cohesive material (such as clay or silt). There are even soil types that don't necessary fall within these categories, such as chalk or peat! These different soil types can occur alongside each other within a project site, above or below each other, or even both. It's therefore very important to ensure that the type, extent and properties of the supporting soil are identified before consideration is given to actually excavating the foundations.

The nature of the soil investigations can be tailored to suit the scheme, with simple 'trial pits' being carried out at one end of the scale, through to involving specialist site investigation companies at the other end of the scale. We are more than happy to provide a consultant service role to our clients to assist them in determining what approach is most suitable, and also to help them minimise the potentials risks to the project that might otherwise occur and result in significant costs and delays at construction stage.

Many people have heard the term 'subsidence' related to building movement. You might even have heard the term 'heave' too. These terms refer to the tendency for buildings to lose foundation support or to be lifted by the underlying ground, most commonly as a result of changes in the moisture content of cohesive soils like clay. These changes usually occur as a result of nearby vegetation roots extracting moisture from the soil, resulting in the soil shrinking in volume. If this volume change occurs once the building is supported by the soil, the building will subside. If the soil volume increases whilst the building is supported on the soil, as can be the case if a tree is removed or dies, this can result in the building being lifted by 'heave'.

All clay soils have a potential for this volume change, however, some have a greater potential than others. This means that the recommended site investigation should include more than simply confirming the soil type, but it should also determine the soil properties to ascertain the degree of 'volume change potential' as this will directly inform what a suitable foundation depth would be related to any vegetation type, height and distance from the proposal.

Only after determining what impact the soil type in conjunction with any current or recently removed vegetation can the most suitable and appropriate foundation solution be determined. This decision also needs to include consideration of buildability, health and safety, cost, timescales, site access, loads to be supported, etc.

Our extensive experience allows us to provide professional guidance and assistance to our clients and help them to fulfill their project intentions efficiently, effectively and in a cost-effective way. Although site investigation costs and Structural Engineer fees are seen by some as optional, this initial outlay can save far more expensive construction costs or unexpected remediation costs in the long term!

Should you have a scheme that involves the need for foundations, please feel free to give us a call or drop us an email for outline advice and guidance. We'd be happy to assist.

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Article Author
R Ponter
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