The MVP transmission lines are a joint effort between ITC Midwest LLC (ITC) and MidAmerican Energy Co., involving approximately 400 total miles of 345 kV transmission line through Minnesota and Iowa. Three of these segments include the 23-mile Huntley to Ledyard line, the 55-mile Colby to Ledyard line, and the 20-mile Kossuth to Ledyard line.
MJ Drilling (MJD) planned to bid on foundation work for all three segments, which included 555 drilled shafts supporting a combination of steel monopole and H-Frame structures. The segments had similar geotechnical data and base designs, and MJD suspected the large shaft diameters and significant embedment into rock left room for potential savings. MJD engaged Quanta Subsurface (QS) to perform additional analyses, and confirmed that design refinements could offer cost and schedule savings.
QS worked with MJD to value engineer the shafts and present an alternate bid to the Owner. Acting as foundation Engineer of Record, QS worked to reduce conservatism while ensuring requirements for foundation structural capacity and performance were met. Designs were also tailored to MJD’s specific tooling and capabilities to create construction efficiencies.
Challenges included working with limited geotechnical data, and having to focus design efforts on specific areas of the alignment to accommodate accelerated scheduling requirements. Understanding MJD’s critical path schedule allowed for a staggered submittal approach and early design review, ultimately limiting risk to the project schedule. Working in conjunction with MJD and the Owner also allowed for accelerated delivery of structure loading and connection information.
The VE alternatives reduced neat line concrete volumes by approximately 15%, 14% and 16.5% over each base bid, and ultimately resulted in MJD being awarded all three foundation contracts.
Subsurface conditions encountered during construction required design modification at several structures. Those of most significance included artesian water and bedrock at different depths than expected. These types of anomalies can result in major schedule delays and subsequent cost increases. However, due to consistent collaboration between the Owner, Contractor and Engineer, required foundation modifications were optimized and efficiently installed with minimal impacts.