Managing Geotechnical Risks in Design–Build Projects (2018) / Chapter Skim
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Pages 132-151
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A -1 Appendix A: State of the Practice Introduction This section reports on the evaluation of current applications of geotechnical risk management practices using DB project delivery and the way these practices are applied on a variety of project types. For that purpose, several research instruments are utilized: extensive literature review, legal review of case law in the subject, content analysis of 59 issued letting documents from DOTs across the US, two nation-wide surveys to furnish real-time perceptional data regarding current practices managing geotechnical risks, and 11 case study interviews to collect detailed practices from completed DB projects with significant geotechnical risks.
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A -2 Therefore, "successfully managing the geotechnical risk in a DB project is imperative to achieving the requisite level of quality in the finished product." (Gransberg and Loulakis 2011)
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A -3 The major conclusions along with the primary literature source from NCHRP Synthesis 429 are as follows: "DOTs typically select DB to accelerate project delivery (FHWA 2006)
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A -4 is contrary to the state law. The typical DSC clause provides broad relief to a contractor for site conditions that differ materially from what is expected according to the contract documents.
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A -5 the site for highway project extends the length of the highway and may cover many different geotechnical conditions. The question in establishing the geotechnical baseline for DSC clause then becomes one of the scope and extent of geotechnical information furnished by the owner.
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A -6 Figure A 1 - Changes vs ratio of borehole length to tunnel length (Hoek and Palmeiri 1998)
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A -7 evident that spending more upfront helps to reduce the final cost of the project. The research effort concluded that the 1% level was often not sufficient to prevent large cost overruns in British highway projects.
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A -8 Figure A 3 provides a flowchart for the process of developing a geotechnical investigation plan as envisaged in this research.
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A -9 process can establish the expected cost of unmitigated geotechnical risks and these costs can be compared to the benefits of reducing these risks given certain expenditure on testing and investigation, it would then be possible to establish the optimal level of geotechnical investigation. Observational Method The observational method in applied soil mechanics was first introduced by Peck (1969)
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A -10 method follows the traditional steps in risk management, i.e., identification, measurement, and mitigation of risks. So while DB approach creates a challenge for the owner in terms of level of geotechnical investigations needed, it also provides some flexibility in terms of dealing with geotechnical risks and mitigating them.
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A -11 from more adverse values defined by the baseline are allocated to the owner. Without the GBR or some other source for the design baseline it would be difficult if not impossible to assign risk responsibility to contract parties.
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A -12 Figure A 4 - Use of Geotechnical Baseline in DB projects The bidder will use the GBR-B and augment it by their approach and design to come up with a new version of the GBR for Construction (GBR-C)
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A -13 DB contract documents and forms the basis for risk allocation during the design-construction phase. From the above discussion, it becomes evident that baselining the geotechnical conditions is a prerequisite for a fair and balanced risk allocation, especially in case a DSC clause is used in the DB contract.
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A -14 Figure A 5 - Sources of error or uncertainty in soil property estimates (Baecher 1987)
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A -15 uncertainties affecting the project cost and duration. The current practice in designing routine earth structures encountered in highway work, does not involve probabilistic approaches.
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A -16 uncertainties were described. This information sets the stage for posing the main question for this research.
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A -17 The proposed modeling approach follows the conventional risk assessment approach used in various state DOTs and transit agencies. The process has been described in several sources (Allen and Touran 2005; Molenaar 2010; D'Ignazio 2011)
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A -18 Structure (RBS) to categorize risks and to cross-reference risk factors to individuals responsible.
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A -19 Figure A 9 - Generic DB Timeline In terms of categories of geotechnical risks, Van Staveren (2006)
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A -20 Risks can be identified based on the areas listed above. There will be many ways the project team can categorize geotechnical risks.
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