ABSTRACT
As complexity and unpredictability exist in nature, careful observations and interpretations of what can be measured become prerequisites for geotechnical engineers to conduct safe and economical construction works. Observational methods have evolved from basic visual procedures, conducted on site, to sets of sophisticated procedures using modernized measuring instruments and computer-based back analysis techniques. From the wide range of procedures available for modern tunneling engineering in this field, the present paper tries to trace the brief history of a series of back analysis procedures in which the identification of strain distribution is sought as the primary goal in order to achieve a solid and reliable routine of observations and data interpretations. The discussion starts by showing why knowledge of the strain distribution is important; and it is then expanded to cover several back analysis procedures, including application examples, formulated for linear and nonlinear material behaviors. The current states and limitations of the procedures available today suggest that the identification of the stress distribution should be the ultimate goal for the future.
