Production rate of self-drilling soil nails in a coastal slope stabilisation project in Scotland

The aim of this study is to establish the production rate of self-drilling soil nails through different soil strata. To achieve
this aim, the production rate of more than 800 self-drilling soil nails was monitored and recorded during a coastal slope stabilisation project in North-East Scotland. The recorded data was then analysed against the expected geology in order to establish the production rate in the varied soil types encountered on site which included: raised beach deposits of sands and silts, various cohesive strata comprising clays, and deeper granular deposits of gravel. The depth of installation of the soil nails ranged between 3 m and 22 m which allowed a determination of average production rate and standard deviation from the mean. The results showed that the production rate was the highest in the raised beach deposits, while most obstacles and refusals occurred in the deeper gravel deposits. The limitations of the production approach are discussed in light of the installation plant choice, the availability of skilled labour, as well as the site constraints such as perched ground water table, soil erosion, and vegetation protection. The need of relevant monitoring and quality control is highlighted from construction management point of view. The results of this study will help designers, construction supervisors, and quantity surveyors in the planning, design, construction and monitoring of similar works in the future.