Advances in the assessment of drystone retaining walls - some case studies

Drystone retaining walls have played an essential part in the infrastructure of hilly and mountainous regions around the world, and have provided platforms for building and for agricultural terraces. Research carried out in England and in France has led to a good understanding of their behaviour, but it is difficult to determine the details of the construction of individual walls without dismantling them, and so it can be hard to tell whether or not apparent defects and deformations are a threat to stability. Replacing every apparently defective or deformed wall would be a waste of resources, yet dismantling a wall would obviously be completely disruptive to its function. Invasive investigation, such as drilling, could easily cause damage to the wall structure and destabilise the wall. There is therefore a pressing need for non-disruptive methods of investigation that can reveal critical aspects of a wall's construction. Thermal imaging carried out in the right conditions can reveal important information about aspects of a wall’s construction that are critical to its stability. This paper presents case studies that have contributed to the development of this technique, and demonstrate its potential.