The next step in the evolution of risk management and Geotechnical BaselinernReports (GBR’s) is to better capture and mitigate residual and unidentified risks.rnGeotechnical Baseline Reports (GBR’s) have generally been effective at communicatingrnground conditions for use in bid preparation and evaluation of differing site conditionrn(DSC) claims, but often do not address geological uncertainties remaining from the subsurfacerninvestigation program and associated residual risks. Uncertainties and residualrnrisks might be covered in a risk registry (if one was completed) or a geotechnical interpretivernreport, but these documents are generally not part of the contract documents.rnContractors and construction managers may not recognize these risks and managernthem. The occurrence of some residual and unidentified risks can have strong negativernconsequences for the owner, contractor, and engineer. Contractors, construction managersrnand owners tend to rely upon GBRs as an end-all document that covers all thernreasonably expected ground conditions, which leads to possible misconceptions thatrnresidual uncertainty does not exist or is acceptable, or that no significant differing siternconditions will be encountered. Over reliance on baselines without scrutinizing the projectrnrisk register and without any attention to mitigating residual and unidentified risksrncreates the potential that significant uncertainties may not be adequately addressed.rnResidual risks from non-baselined uncertainties and uncertainties associated with thernbaselines (known unknowns) and unidentified risks (unknown unknowns) may not havernbeen mitigated by any contractual mechanisms. The result may be ground support,rncontrol of water or other failures in spite of an extensive subsurface exploration andrngeotechnical baselining effort. Furthermore, parties to the tunnel contract may not realizernhow little margin exists with some baselines and how “close to the edge” of geotechnicalrnfailure (low safety margin) actually exists with the planned means and methodsrnof construction. Coupled with a highly competitive bidding environment, the results canrnbe very costly at the least and even dangerous to human life and health at the most.rnRealistic residual risks and unidentified risks should be captured and addressed byrnproactive risk management. If the resulting risk profile is high enough to be of concern,rnthese risks can often be mitigated by additional subsurface investigation during design,rnbidding or construction; by selected prescriptive specifications; by payment provisionsrnwithin the contract; or by effective use of the observational method.
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