Retaining Walls: A students perspective from a Building Survey

When inspecting a property/site, we sometimes encounter retaining walls. On a recent building survey seven retaining walls were noted within the property boundary, this gives some indication as to the topographic nature of the land where the property was situated! Retaining walls can be problematic when left unmaintained, consequently defining ownership of the walls is one of the main issues as this ultimately determines who is responsible for maintenance of the wall.

Defining ownership of a retaining wall is often difficult as retaining walls regularly make up the boundary of a site, therefore there can be confusion between the property owner, the local authority or Management Company as to who is responsible. When determining ownership of retaining walls other issues can also come into play, such as; road adoption and shared ownership with neighbouring properties. These issues will all need to be clarified by legal advisors before determining who has to inevitably pay for maintenance of said retaining wall.

If a retaining wall situated close to a building was to collapse it could cause structural defects to the building in question and potentially others nearby through ground movement. Retaining walls often support many tonnes of weight, consequently ground movement could negatively influence the buildings foundations causing issues such as structural failure, highlighting the importance of retaining wall stability. It is therefore crucial to keep an eye out for structural defects regarding the retaining wall.

There are several tell-tale signs that a retaining wall is beginning to destabilise and fail, the obvious being bulging, cracking and tilting of the wall. When these defects are visible immediate action is recommended to remediate the wall to avoid a full-scale collapse. It is also important to consider the surrounding area of the retaining wall; does it overlook a road or somebody else’s property? If it does then the wall owner may be liable for damage caused to another person’s property.

Sometimes, in areas of steep topography, retaining walls may support other retaining walls at higher ground, consequently if the wall at the bottom (supporting the most weight) was to collapse, then a domino effect may occur and retaining walls situated higher may also collapse potentially causing structural defects to buildings some distance away from the original wall collapse.

Causes of retaining wall failure can vary, one of the main is the weight the wall supports. In most cases this weight can be exacerbated due to poor drainage, poor drainage can result in the soil becoming more saturated and therefore concentrating more weight onto the retaining wall. Other causes of failure include poor building practice i.e. insufficient footing depth, wall thickness and the use of sub-standard materials.

John Blackmore

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