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Logistics Is Key During Pre-Design For Linear Pipeline
Borings on government property required some combination of bonding, insurance certificates, excavation permits and/or traffic control. Borings on private property required close communication with the owner, scheduling to avoid crop damage in agricultural fields, or scheduling to follow successful completion of the property owner’s alignment right-of-way negotiation with the project owner.
Successes & lessons learned
Crews developed a rhythm in their field activities that led to an efficient execution of widespread borings. Crews worked 10 days on, four days off, which reduced time spent driving to and from the sites and facilitated a higher, average production rate per shift. Periodically, a driver would carry samples from drill rigs back to the Geotechnology office so sample assessment and lab assignments could begin rather than waiting for the end of the 10-day shift.
One item that would have lowered the overall cost of the subsurface explorations is a longer execution schedule. Four field crews were often hop-scotching along the alignment to boring locations that were cleared for access. A longer schedule or the capacity to get more right-of-way clearances sooner would have simplified field execution and lowered the associated cost. Inability to secure access to all overland borings in a county, for example, led to drilling those that were available, issuing a report and, upon the owner access and review of those reports returning to the area and completing borings, and issuing a subsequent, complete report that included all gathered data.
Design work on this project is essentially complete. Findings in the geotechnical borings did affect pipeline design. In one rather long HDD crossing where six, rather than the typical four borings were drilled, voids, some filled with pressurized gas, were encountered in the upper 50 feet of the bedrock profile. The inability to accurately locate 100 percent of potential voids along the HDD alignment led to a decision to not use HDD in this area and go to a more costly pipe-buried-in-trench alternative.
However, due to economic conditions at this time, pipeline construction is delayed.