Using reliability theory to assess the stability and prolong the design life of existing engineered slopes

Modern engineered slopes are designed to exceed certain safety targets set out in design codes. This is in stark contrast to earthen infrastructure inherited from the 18th century which typically was constructed in a haphazard manner without design. This infrastructure seldom meets modern deterministic guidelines yet clearly exhibits some degree of safety, as a failure has not occurred in the intervening years. This paper highlights the use of reliability theory for evaluating the stability of existing engineered slopes. A comprehensive review of geotechnical uncertainty and existing reliability based techniques are outlined. Furthermore, the paper highlights the issue of finding the critical slip surface and gives a brief summary of the current state of the art. Finally a case study of an Irish railway embankment is presented and both a deterministic and reliability analysis is performed on it highlighting the benefits of probabilistic methods over traditional techniques