Observational Method in Geotechnical works

Question

Describe the rationales of Observational Method in geotechnical works?

Answer 1

Idea of Observational Method was first debated by Peck in the Rankine Lecture in 1969. The Observational Method is usually adopted in the geotechnical works in construction phase, though it is also possible in the design stage.
In essence, in conforming design by engineers during the stage of planning, the design is based on the approach of over-conservative or most unfavourable conditions due to the lack of precise and actual site information.

During successive construction, with particular site information and condition available, the Observational Method is implemented in which the actual design is revised on the basis of conditions with instrumentation monitoring. If the results of monitoring shows that the performance of reviewed design approaches the limit of acceptable risk level, then it shall get reverted to the planned modification which is based on the unfavourable conditions and therefore, the risk level dropped back to original design. Else, the reviewed design shall remain and this results in reduction of the cost without comprising any safety of works.