Analyzing Uncertainty in Civil Engineering





Assessment of characteristic shear strength

parameters of soil and its implication in

geotechnical design


Wolfgang Fellin

Institut f¨ur Geotechnik und Tunnelbau, Universit¨at Innsbruck

Summary. The characteristic shear strength parameters of soil are obviously decisive

for the geotechnical design. Characteristic parameters are defined as cautious

estimates of the soil parameters affecting the limit state. It is shown how geotechnical

engineers interpret this cautious estimate. Due to the inherent lack of data in

geotechnical investigations there is always a certain degree of subjectivity in assessing

the characteristic soil parameters. The range of characteristic shear parameters

assigned to the same set of laboratory experiments by 90 geotechnical engineers has

been used to design a spread foundation. The resulting geometrical dimensions are

remarkably different. It is concluded that geotechnical calculations are rather estimates

than exact predictions. Thus for intricate geotechnical projects a sensitivity

analysis should be performed to find out critical scenarios. Furthermore a continuous

appraisal of the soil properties during the construction process is indispensable.



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