INNOVATION March-April 2017

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GeoPacific Consultants Ltd. completed excavation and shoring design for a construction project near Vancouver's Rogers Arena. P HOTO : G EO P ACIFIC C ONSULTANTS L TD .

What Is Down There? And Whose Fault Is It? Managing Risk Associated with Geotechnical Results

Gregory Miller, P.Eng., LLB

Construction is an exercise in risk allocation among various parties—typically the owner, the contractor(s) and the consultant. Who takes the risk is usually a matter of negotiation. Risk in construction—especially where underground works are involved—is largely a function of uncertainty. The more is known about what lies underground, the less is the risk that something unforeseen will impact the costs of the work. Uncertainty, and therefore risk, in underground works can be reduced through geotechnical investigation and good design based on the results of that investigation. However, uncertainty prior to construction can never be completely eliminated. Geotechnical Investigation Depending upon the type of project, several means of investigating what might be encountered under the surface of the ground exist. Local knowledge and a review of aerial photography may provide clues. Geophysical investigations may help. Test pits and test borings provide direct evidence of what will be encountered—at the very limited locale of the pits and borings. To be useful, the raw data obtained by

investigation must be interpreted by those with specialized skill and knowledge. Logic suggests that more data should allow for greater confidence in the interpretations. However, data comes at a cost, and it is difficult if not impossible to correlate the cost of more investigations with cost savings that might accrue from better interpretations. In the end, any interpretations of data from geotechnical investigations are merely predictions of what might actually be found. Courts have expressly recognized the limitations on interpretations as: …predictions that are based on some theory of probability. A bore hole tells you what is at the bore hole, all else is extrapolation and interpretation…, 1 and: …no one can ever know with certainty what will be found during subsurface operations…. 2 Owners are not required to conduct geotechnical investigations before undertaking a construction project, 3 nor do firm guidelines exist directing owners to produce the raw data or the data with an interpretation. If owners do produce

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