Many of the properties built on shallow foundations over shrinkable clay are susceptible to heave and subsidence. Foundations of all properties undergo various degrees of settlement which is a downward movement of foundations as a result of the soil being compressed by the weight of the buildings. This usually takes place immediately after construction and could continue over ten years of construction. However, if cracking is observed later in the life of a building, this could be a sign of subsidence, heave or landslip. Subsidence is the downward movement of the ground beneath the buildings other than by settlement. Heave is the upward movement of the ground beneath the buildings as a result of the soil expanding. Landslip is the downward movement of sloping ground.
As Beta Structural Engineers is based in West London, where most properties are founded on shallow foundations over shrinkable London Clay, we are heavily involved in assessing properites for damage related to ground movement. We provide a comprehensive service that includes the following:
A a detailed visual inspection. This includes an assessment of any cracks or structural defects. This inspection is in most cases limited to an external inspection from street level and internal inspection at all levels (including the loft if accessible but excluding cellar or ground floor voids). It also excludes any intrusive inspection.
A desk study and a review of the history of structural alterations. We follow the industry standard practice adopted by the Institution of Structural Engineers, the Insurance Industry and the Royal Institute of Chartered Surveyors. This means that all cracks according to their scale using BRE Digest 251 for the Assessment of Cracks in Low Rise Building.
We usually aim to establish a diagnosis for the damage. If a reason can't be established, further investigation or monitoring is usually prescribed.
In some cases, we specify some measures to manage the issue and avoid sub-ground intervention. Such measures would include for example dealing with moisture changes caused by rainwater/dry weather cycles or caused by major vegetation/mature trees.
If underpinning is required, we advise clients on the cost, appropriate underpinning method, and any other super structure repairs required such as the crack repair of masonry or the repair of any damaged lintels.
We could also offer a project management service where we actively work with the client to prepare the works specification, prepare tender documents, approach contractors and supervise the works until a completion certificate is obtained. We work with contractors who are members of the Association of Underpinning Contractors and are able to provide a quality repair with a 10-12 year defects warranty backed up by the ASUC.