Engineering Uncertainty: The Struggle Between Facts and Beliefs in Geotechnics

Dr Burt Look
AGTRE Pty Ltd, Queensland, Australia.

ABSTRACT
This paper has 2 parts; 1) Cognitive Dissonance in geotechnical practice and 2) Risk and uncertainty in practice. To advance geotechnical engineering practice, bridging the gap between empirical judgment and statistical analysis is essential.
Cognitive dissonance—conflicts between beliefs and knowledge—shapes many geotechnical practices. Despite evolving knowledge, outdated methods persist. Engineers often arrive at different conclusions despite identical data, suggesting that changing behaviours – not acquiring information – is the challenge. Heuristics, or mental shortcuts, aid quick decision-making but can lead to errors.
Codes and standards reflect past experiences, but even limit state codes are not a reliability analysis. A characteristic value addresses risk indirectly by choosing a cautious value + a partial factor. Any single point value is unlikely to be realised in the real world. A best estimate, even with upper and lower bounds, rarely captures all uncertainties. Statistics clarify this disconnect.
However, statistical methods must be correctly interpreted as context, assumptions, and data quality matter. Engineers may misuse statistics by assuming homogeneity, and incorrect probability distribution or a best fit trend line applies where variability is high.