February, 2015

Implications of Unstable Soil Foundations

Implications of Unstable Soil Foundations

Soil movement can cause serious problems for property owners, serious cases of subsidence have caused homes to collapse completely as the soil underneath the foundations slides lower and pulls the house with it. Less common, but still an issue, is heave whereby the soil moves upwards, which causes similar damage. Spotting an area of subsidence and acting quickly can help prevent damage to structures. Subsidence Surveys Slides from Hamilton King, a property management company, highlight the importance of completing a subsidence survey, should you think that your property is at risk of subsiding. The company is responsible for the business and residential properties for an extensive portfolio of clients and regularly carry out structural surveys as well as performing any necessary repairs. What follows is a useful guide to unstable soil foundations and what can be done about them. Natural Causes of Subsidence Various factors can contribute to the subsidence of residential properties. However, over three quarters of the subsidence claims in the UK have been attributed to soil shrinkage which can result in gradual downward movement. Soil shrinkage occurs in two ways that will depend entirely on what type of soil sits underneath the property. Non-cohesive soil is sandy or made up of other larger particles that are not susceptible to volumetric change but are liable to be washed away. This creates a natural space that will cause upper layers to fall down. Alternatively, rapid volumetric change in cohesive soil will also cause soil shrinkage. Clay is a prime example of a cohesive soil that changes its volume depending on how much water is in the ground. When clay dries out it will shrink, creating a vacuum that pulls upper levels down. Any vegetation in close proximity to houses built on clay soil can mean bad news for the property owners. The way trees draw water from the ground using their complex root network can trigger subsidence in a big way, some mature trees draw 50,000 litres from the ground per year, causing serious soil shrinkage. Artificial Subsidence Manmade factors in subsidence are slightly more predictable, however many property owners have been caught out by sudden cave-ins in long forgotten mine shafts that run under the foundations. A famous example of manmade subsidence can be seen in Staffordshire, where The Crooked House pub is four feet lower on one side than the other. The building was constructed in...

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