Soil nailing in glacial till: A design guide evaluation based on Irish and American field sites

The French in-situ earth retaining system soil nailing began in 1970 and benefited greatly from that government's investment in the 1986 study 'Clouterre'. As such, French geology strongly influenced both practice and expectations world wide over the past 4 decades. Yet, recent studies in glacial till, a non-French soil type, have shown significant strength under-estimation using conventionally accepted design approaches. This paper reconsiders skin friction expectations for soil nail installations in till. Installation at 3 till sites (1 American and 2 Irish) are examined in detail. Traditional British, French, and American design methods and parameters are applied. Conventional methods under-predicted capacity by more than 50%, thereby raising serious questions as to the appropriateness of such design guidelines in tills. New correlations based on pile installation design are proposed.