PROCUREMENT AND MODELLING OF THE OBSERVATIONAL METHOD FOR MANAGING GEOTECHNICAL UNCERTAINTY

摘要

It is widely recognised that a significant proportion of cost overruns on construction projects result from unexpected ground conditions. A common approach in geotechnical engineering is to predefine design before construction commences. Such predefined design generally leads to poor value, either solely due to the wasted resources of over design or with the delay and additional extra cost of dealing with unforeseen ground conditions. Under appropriate contractual conditions an alternative approach to manage the uncertainty associated with ground conditions may be used, based on a flexible design that is able to be adapted to suit the actual conditions found during construction through monitoring and feedback. Case studies of applications of this approach, known as the observational method, are presented to demonstrate the significant benefits that have been derived from managing geotechnical uncertainty in this way. The observational method requires integration of construction processes and teams and is therefore dependent on an appropriate style of management, more akin to modern approaches such as partnering, than traditional fragmented processes. An example where failure in the management of the process led to a tunnel collapsing during construction is used to illustrate the importance of clear responsibilities in a project team that chooses to implement this type of design. A danger with collaborative approaches to project delivery is that responsibilities are not clearly defined. To overcome this a process modelling approach is described for ensuring robustness in the observational method process and a further practical example is given of an application of this approach.