The entire stability of any building is dependent on its foundations. Every year in the UK, millions of pounds are spent repairing damage to buildings caused by foundation failures. Preventing these problems early is far less expensive than rectifying them afterwards. The most common factors to consider are rapid changes in soil moisture, soft ground, drainage or lack of design consideration:
Clay shrinkage: Fluctuations in moisture content don’t cause significant variations in the volume of sandy soils. However, clay soils expand when they are wet & shrink when they are dry. If a structure is supported on clay that is moving in this way, the building will move with it causing damage. Trees can cause shrinkage down to 4m.
Clay heave: As tree roots pull moisture out of the clay, the soil shrinks and ground level drops. If a tree stops extracting moisture, then the clay rehydrates & swells. The forces generated by swelling clay are large enough to lift up any structure. A common cause is when trees are removed from a site. Ground heave can start immediately and continue for months & years afterwards.
Soft ground: Some soil types are weaker than others and not strong enough to support building structures. These include river alluvial deposits, peat & man-made soils. When foundations are dug into these soils, the building’s weight can cause movement in the soil’s structure.
What steps can be put in place to prevent foundation problems occurring? Below are 4 practical steps to consider:
- Don’t accept a ‘one size fits all’ foundation
- Take reasonable precautions to mitigate against the effects of nearby trees and soft soils
- Choose the right kind of foundation for your building
- Consider access requirements & restrictions. Ask for advice if needed
The foundations are one of the most important parts of your building investment. Often more time is spent considering the type of floor tiles than the foundation type. Foundations are often specified as a standard design ‘to be confirmed on site’. This can lead to inappropriate foundations being constructed. It is essential that adequate thought is given to the foundation type and depth before work starts on site.
At Shire we design foundation systems for a wide range of project types. We have developed patented systems like QuickBase giving deep piled foundations that can be taken down to depths below the zone of influence of any tree roots or down to 20m in soft soils to find ‘good ground’. QuickBase has also been designed to be installed in areas where parking & access is restricted. Foundations are installed quickly, often leading to cost reductions in the overall schedule.
Where there are unknown ground conditions, our geotechnical team can investigate and give advice on the appropriate solution.