Best practice for the treatment of high and steep chalk slopes over infrastructure

The infrastructure in many parts of Southern England is built upon chalk. Where excavations are required for the construction of roads, railways and other infrastructure, they often form high and steep sided cuttings. Over time, the chalk can weather and the risk presented to the infrastructure will change. It is the Engineer’s job to investigate and classify the slope condition, assessing the risk that it presents.

During this phase, the type of failure(s) within the chalk will be identified and reviewed, in conjunction with the Clients’ requirements, to prepare an options report, outlining feasible solutions. Where a risk is identified, a number of soft and hard engineering solutions are available. More often than not, superficial deposits overly the chalk and can present a further hazard requiring stabilisation. The nature of the overlying material can determine the solution for stabilising the overall cutting face; an important consideration for the Client and end user. In addition, the site constraints will determine the solution and methodology to be implemented. One of the biggest factors affecting this decision is accessibility of the site.

Over the last thirty years, considerable advances in materials and methodology have changed the way in which chalk slopes are stabilised. This paper sets out these advances and cites examples of best practice including the development of specialist plant and equipment, innovation in the materials used and how the risks associated with working at height, manual handling and protecting the infrastructure are managed. The paper will also outline other challenges that have been experienced by the Contractor in tackling unstable chalk slopes; considering ecological risks, historical mining features (deneholes) as well as discussion on how to refine the design and construction details to ensure value for money for the Client and how to ensure long-term maintenance of the asset is considered.