Reliability in the prediction of transit time through compacted clay liners
Pulapaka, Srinivas Srikanth
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All engineering designs involve uncertainties to some degree. Such uncertainties may arise due to incomplete or inconsistent input information or non-representative analysis procedures used in the design. The input information typically includes design parameters such as material properties and applied loads. Uncertainties in the estimation of material properties can result from material variability or deficiencies in the test procedures used to determine them. Similarly, uncertainties in the determination of the design loads can result from their random variability. The approach which has been traditionally used in engineering designs to incorporate such uncertainties involve the use of "Factors of Safety". In this approach, no attempt is made to quantify the variabilities or uncertainties involved. Instead, the choice of an appropriate factor of safety is made subjectively depending on the degree of uncertainties involved. In other words, the greater the uncertainties in design input information, the larger the selected factor of safety will be. An alternative and a more rational approach to incorporate uncertainties in engineering design involve the concepts of reliability. Reliability is defined as the probability that the structure will not fail during its intended service life. The concept of reliability has been widely used in the fields of aerospace engineering, industrial engineering and mechanical engineering over several decades. Its advent to the geotechnical engineering is more recent. However, it is apparent that in the last two decades geotechnical engineers have developed an interest in the use of probabilistic and statistical approach to solve problems in soil mechanics. Within geotechnical engineering the probabilistic concepts have been used to investigate a variety of problems: slope stability by Christian et al. (1992) and Vanmarcke (1977), pile foundation design and mudslope failure potential by Lee et al. (1992) and most recently to compacted soil liners for hazardous waste containing facilities by Bogardi and Kelly (1990) and Benson (1994).