Can GBR baselines be reasonably measured during construction? – Some case studies

ABSTRACT: Although the application of geotechnical baseline report (GBR)-based contracts is now fairly commonplace in most North American jurisdictions on tunneling projects, the jury is still out as to whether or not the setting of GBR baselines has resulted in equitable and satisfactory allocation of geo-risks between Owner and Contractor. One of the shortcomings of GBR contracts is the difficulty in reliably and practically measuring or tracking one or more baselined parameters during the normal course of construction. Since the focus of the contractor is in the safe execution of the work as efficiently as possible, the verification of GBR baselines is seldom a priority until the later stages of a project when the broader cascading impacts on schedule and production - attributable to in-ground issues - may become more apparent. Similarly, consultants may not have any mandate from Owners to take responsibility for the tracking and measurement of GBR baseline parameters during construction. In many cases, such as for in-tunnel work, safe access to the heading by the inspection agency may not be practical without a shut down in the work. In other cases, such as the case of microtunnels, access is impossible and only indirect evidence can be collected, potentially of dubious value. Moreover, many GBRs lack clear statements as to who is responsible for taking such ‘measurements’, how such measurements must be taken and how they need to be statistically interpreted. This paper presents a series of case studies of water and wastewater related projects in Southern Ontario (Canada) involving tunneling and microtunneling where claims were made against the GBR. The GBR baselines that were tested included the frequency and size distribution of cobbles and boulders and overburden undrained shear strength. The means of measuring the relevant GBR baseline parameter(s) under ‘dispute’ are described for each project and the logic applied to the assessment of merit of the claims is reviewed.