As well as man-made hazards such as mine shafts, shallow mine workings, and poorly constructed slopes, there are other geohazards that can potentially pose a risk to both people and property. Some of these are naturally occurring while some are man-made, or at least made worse by human activity.

These geohazards include:

• Sinkholes caused by the collapse of soils or weak rock covering or filling dissolution features in rocks like chalk, limestone, salt and gypsum. These features can occur in may areas of the UK but a particularly notable in the Chiltern Hills area and parts of Dorset and Hampshire (all underlain by chalk), the Peak District, North and South Wales, the Mendip Hills and the Yorkshire Dales (all underlain by limestone), areas of north-east England (underlain by Gypsum), and Cheshire (underlain by salt deposits).

• Natural slopes that become unstable (e.g. landslides and debris flows) due to factors such as unusually heavy or prolonged rainfall increasing porewater pressure and/or erosion, removal of the slopes toe by for example river erosion or human activity, and increased loading at the crest such as new landscaping or development works.

• Shrinking or swelling clays that can cause significant damage to foundations and floor slabs, especially where trees are (or were!) present nearby.

• Soft or compressible natural deposits such as peat, soft clays and silts, and very loose sands that can lead to excessive settlement of structures or earthworks, or even their complete failure/collapse..

• Collapsible soils such as non-engineered fill and loess.

• Collapse of man-made substructures (often unrecorded) such as drains, wells and other features, often associated with the 'washout' of surrounding soils. These are often initially reported as 'sinkholes'.

• Soils rich in water soluble sulphates that can attack buried concrete. This risk is best assessed by carrying out appropriate soil or groundwater testing, but the potential for such a risk existing in a site is often apparent at desk study stage.

• Variable geology within relatively small areas such as localised sand and gravel deposits within a predominantly cohesive glacial or periglacial deposit, or a highly variable depth to rockhead in area of karst (e.g. limestone dissolution) resulting in variable soil thicknesses possibly leading to a risk of differential settlement or variable foundation requirements.

• Ground gases such as methane, carbon dioxide and radon.

 

G&J are experienced in dealing with these hazards, and others, in a cost-effective and practical manner. A preliminary assessment of the of the risk of these geohazards affecting a site, even if not currently apparent, is typically included in our Phase I Desk Studies where there is a geotechnical component.

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