ABSTRACT
The fundamental and far-reaching contributions of K. Terzaghi and R. B. Peck to the development of applied soil mechanics are legendary and profound. Right from the start, the observational method (OM) played a key role. The observational method is most effective where the critical observations can be reliably obtained through simple measurements. The deflection of a retaining wall is a common example of a critical observation. The key to success in applying the OM is in identifying the critical observations and having the means to obtain and act upon them in a safe and timely manner. A key example of the limitation caused by the inability to reliably obtain critical observations arose during the design development for Terminal 5 at London’s Heathrow Airport. The critical observations may be derived from settlement data, but there would be unknown factors influencing the building response.
