Publication Abstract

Proceedings - Fifth International Conference & Exhibition on Piling and Deep Foundations, 1994, Bruges, Belgium, (DFI)

The observational method in value engineering
A.J. Powderham & P. Rutty

This paper describes the application of the Observational Method to a major cut and cover tunnel, the Limehouse Link, in Londonís Docklands. The method was prominent in a range of design alternatives applied under a Value Engineering clause added to contract during the construction phase. The majority of the cut-and-cover tunnel was designed for top-down construction between reinforced concrete diaphragm walls. Very substantial temporary steel props were specified at mid-height below the roof slab. These props presented a major constraint to ease and speed of construction. Using revised construction sequences and carefully controlled working procedures the Observational Method was used to eliminate these props. This afforded substantial cost and time savings. Following this success it was decided to use the Observational Method to try to remove the lower propping from the sheet pile cofferdam used in the bottom-up construction of the remainder of the tunnel. Again analytical modeling followed by carefully monitored construction procedures were undertaken but in this instance observations indicated that the proposal would not be so effective and the benefits accordingly limited. This case history demonstrates the step-by-step application of the procedures necessary to develop an effective use of the Observational Method to the construction of major cut and cover tunneling works. Also shown are some of the benefits in improved understanding of soil-structure interaction revealed by the focused need for monitoring real situations.

 article #834; publication #36 (IC-1994)