Recently at the Underground Construction Association’s Cutting Edge 2021 Conference, Dan Adams participated in a panel-led workshop, along with other engineers and geologists from the underground construction industry, on a forthcoming update to the Geotechnical Baseline Reports [GBRs] for Underground Construction. Known as “the Gold Book,” this American Society of Civil Engineers (ASCE) publication was last updated in 2007.* The currently proposed update reflects recent changes in the industry. New tunneling equipment and techniques have been developed, and the sizes, lengths, and depths of tunnels are being pushed to the extreme. In addition, alternative contract delivery methods are gaining traction for use on tunnel projects, and the GBR concept has become even more widely used internationally and on conventional nontunnel projects.
Having been involved in several workshops and panel sessions on GBRs, as well as a reviewer and contributor on a number of GBRs since the 2007 edition was released, attendees generally agreed that managing geotechnical risk though GBRs and baselines has been largely successful. Challenges were acknowledged and potential remedies to these were deliberated. However, there were also a number of resonating themes that emerged from the 2021 workshop that may be expanded in an update to the Gold Book. Below are just a few examples:
Experienced Authorship: GBRs are more than just geotechnical data interpretation and are increasingly extending beyond the realm of data analyses, data distributions, and establishing baseline values. The interpretations and conclusions presented in the GBR should be borne from experience and a thorough understanding of construction equipment and processes.
Accurate Representation of the Ground: GBRs are often written with the intent of being the primary document upon which engineers state their geotechnical interpretation and should be authored with this concept in mind. Conclusions and recommendations contained in the GBR can and have been the subject of contractual disputes, but also legal disputes with potential implications for the project owner and engineer. The intent, as outlined in the Gold Book, is not necessarily to “get it right,” but rather to level the playing field among bidders so that each is basing its bids on the same set of assumptions (and are less likely to make an overly optimistic interpretation of the data).
GBRs are not a Guarantee: Project participants, including owners, engineers, and contractors, should approach the development of the GBR with this in mind—that the GBR is not intended to warrant or guarantee that the ground conditions will be encountered exactly as described. Ultimately, the GBR serves as the basis upon which the merit of differing site conditions claims can be evaluated. As many of us in this industry know, the ground contains inherent variabilities that are often difficult to characterize, and it is often cost prohibitive to investigate and determine with certainty what will be in the ground.
GBRs are an important tool in the underground engineer’s toolbox, and their use and success require careful deliberation of the data, as well as a thorough understanding of the ramifications these data will have on the project. Even more importantly, drafting of the GBR requires a constant and open dialogue with the project owner to ensure that not only is the owner educated about the uncertainties in the ground, but that these conditions are understood and managed appropriately within the construction contract. Ultimately, the GBR is a risk allocation document.
*Essex, R., ed. 2007. Geotechnical Baseline Reports for Underground Construction: Suggested Guidelines. Prepared by the Technical Committee for the Underground Technology Research Council of ASCE. Reston, Virginia: ASCE.