ITC Multi-Value Transmission Projects – 345/161 kV

Project

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.

 

VE Opportunity

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.

Foundation Optimization

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.

Construction

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.

Highlights

  • Value engineered 555 drilled shafts, reducing concrete volumes by approximately 15%
  • VE designs factored in site-specific conditions and MJD’s means & methods
  • Cost and schedule savings contributed to alternate bids being awarded

 

ComEd Fisk High-Voltage Line – 345 kV

Project

The project involved ten drilled shaft foundations to support tubular steel poles for new 345 kV lines just outside downtown Chicago.  Planned structures ranged in height from 90 to over 240 feet, and foundations would be subject to baseline reactions as high as 72,000 kip-ft overturning moment and 415 kip shear.  Geotechnical conditions consisted of uncontrolled fill and soft- to medium-stiff clays underlain by highly weathered to moderately weathered limestone.  Site-specific borings indicated variable bedrock depths ranging from 50 to 85 ft.

Value Engineering Opportunity

Proposed bid-level designs specified drilled shaft diameters between 7 and 17 ft with depths down to 82 ft.  This included three 17-ft diameter shafts to be installed in rock, two with 17-ft rock sockets and one with a 31-ft rock socket.  Looking at these designs, MJ Drilling (MJD) concluded that construction would entail approximately 540 cu yd of rock excavation and would require a 24-hour work schedule to meet deadlines.  MJD suspected bid-level designs were conservative and engaged Quanta Subsurface (QS).  After a brief review, QS agreed several of the foundation sizes could be reduced.

Foundation Optimization

QS began by establishing its own geotechnical design parameters through review of existing geotechnical data and local geologic maps. Using this data, minimum foundation diameters were iteratively selected with consideration to anchor-bolt layouts until an optimized solution was developed.  Foundation designs were also tailored to MJD’s equipment and tooling when potential cost or schedule savings were present.  Overall, the proposed Value Engineering (VE) alternate reduced expected rock-socket lengths by 46%, rock excavation by 60% and concrete volumes by 16%.

Construction

Involving the owner early on in the VE conversation was key to its successful implementation.  Bid level designs had been permitted for construction in advance, and there was concern that the time required to permit new designs would prevent the project from meeting a strict completion deadline.  Upon review, ComEd determined the efficiencies the VE option provided would more than make up for any re-permitting time.

In addition to the reduced excavation and material requirements, the fast-tracked VE designs reduced labor hours by approximately 21%, allowing the project team to eliminate any night work.  The project was completed ahead of schedule and with zero safety incidents, serving as an excellent example of the cost, schedule and safety benefits that can be derived from a collaborative foundation design and construction process.

Highlights

  •  Value engineered 10 drilled shafts, reducing expected rock excavation by 60%
  • Project completed ahead of schedule with zero safety incidents
  • Demonstrates the cost, schedule and safety benefits that can be derived from a collaborative foundation design and construction process.

WFMAC Substations – West Fort McMurray 500 kV Substations

Project

The West Fort McMurray (WFMAC) 500 kV Transmission Line Project includes over 310 miles of high voltage transmission line, expansion of the existing Livock substation, and construction of the new Thickwood Hills substation, all located in Northcentral Alberta. The project is expected to be in-service by mid-2019.

Substation Foundation VE

Bid level foundation designs completed by outside parties included over 1,600 driven piles between the two substations, totaling approximately 1,800 tons of steel. The majority were grouped together to support concrete containment structures. Preliminary slab designs included a deep perimeter beam supported on piles anchored with welded studs at the pile head for concrete anchorage, and an 8-inch-thick concrete slab on a metal deck infill.

Valard requested QS complete value engineering to determine if efficiencies were possible. QS collaborated with the project team to refine designs, creating both cost and schedule savings. This was completed utilizing a self-performed geotechnical study of the substations along with a desktop study done as part of QS’s transmission line work on the project. Soil profiles were developed and applied to structures within the substations.

The containment structure support system was redesigned as a monolithic concrete slab with typical 12-inch thickness and isolated areas of thickened drop-slab construction. Pile sizes and layouts were optimized based on pile axial resistance, and slab reinforcing was tailored to accommodate the layout.

Construction

The slab uniformity enabled construction in a single phase, and the revised pile layout allowed for fewer piles and a reduced total tonnage. Ultimately, just under 1,000 piles totaling 1,575 tons were installed, equating to an approximate 40% reduction in piles and 20% reduction in steel.

During construction, QS was responsible for onsite quality assurance of the contractor’s quality control program. Additionally, QS developed and submitted a compliance report that documented the installation logs and any testing and inspection requirements.

Highlights

  • Two new 500 kV substations
  • Value engineering for substation foundation designs resulted in an approximate 40% reduction in piles and 20% reduction in steel

Fox Lake to Lakefield – Transmission Line

Project

The project involved replacement of an existing 161 kV line with a double-circuit 345/161 kV line, and existing 69 kV line with a double circuit 345/69 kV line. It also included a new single-circuit 345 kV line. Wood H-Frame structures were replaced with steel monopoles.

Challenges

MJE Drilling provided drilled shaft installation at 163 structures and performed Thermal Integrity Profiling (TIP) to confirm structural integrity of the foundations. TIP analysis revealed potential fluctuation in select shafts, requiring MJE Drilling to conduct further testing and confirm the integrity of the shafts had not been affected.

QS Scope & Solution

Quanta Subsurface (QS) analyzed the reports to confirm foundation integrity. When potential anomalies were detected, the shafts were further analyzed for specific conditions that may have existed based on the TIP report. Analysis was completed at the point of maximum moment and at the point of the first anomaly to identify any structural concerns.

Drilled shafts are generally installed with uniform reinforcing and cross-sections from top to bottom, as opposed to tapered cross-sections. As such, they inherently have a tremendous amount of reserve capacity at locations above and below the point of maximum stress. This reserve capacity was confirmed in all QS analyses, leading to the determination that all shafts were structurally sound.

Alternatives to TIP report evaluation, including coring the shaft to identify areas of weakness, can be costly and time-consuming, and require additional evaluation. Estimated repair costs could exceed $35,000 per shaft, and full replacement costs could be as high as $250,000 per shaft. QS’s expertise and experience in drilled shaft design and evaluation resulted in all shafts being validated, and no remediation measures required.

Highlights

  • Analyzed Thermal Integrity Profiling reports on 163 drilled shafts to confirm foundation integrity
  • Alternative means of confirmation could exceed $35,000 per shaft and be as high as $250,000 per shaft
  • All shafts were determined to be structurally sound, requiring no remediation

Sunrise Powerlink – Transmission Line

Project

The Sunrise Powerlink included construction of a new 117-mile high-voltage transmission line in Southern California. Challenges associated with shallow bedrock, mountainous rugged terrain, and environmental regulations all contributed to the decision to use micropiles at 235 of the 438 lattice tower locations.

QS Scope

QS was responsible for micropile and steel pile cap design, as well as overall engineering management for foundation work. Micropile design was based on limited geotechnical data and diverse alignment geology, ranging from stiff clays and medium dense sands to granitic bedrock. The structures were grouped into seven load families, and GROUP software was used to design a matrix of foundation solutions based on the range of geotechnical units expected to be encountered. Ultimate Tests were completed to develop average ultimate grout-to-ground bond stresses in distinct geologic units, which were incorporated into foundation matrixes. This allowed the construction team to optimize pile quantity, cased section length, and bond zone length at each site.

Innovation & Quality Control

The majority of the micropile foundations used an innovative steel pile cap, which was designed to provide schedule and budget advantages over concrete pile caps. Cap design was closely coordinated with micropile design to meet design limitations and maintain tolerances required for construction. Both steel cap and micropile designs were analyzed using a 3D finite element program to virtually test the concepts prior to final design and review.

QS provided field engineering support and construction monitoring services throughout foundation construction. Engineering geologists were onsite during drilling activities to identify and monitor geologic conditions specific to the foundation design. This approach allowed for an efficient and cost-effective set of tower foundations to be installed.

Highlights

Lower Churchill – Transmission Line

Project

The Lower Churchill Project is intended to develop the hydroelectric potential of the Churchill River. Phase I, referred to as Muskrat Falls, includes more than 800 miles of high voltage transmission line through the remote, rugged terrain of Newfoundland and Labrador, Canada.

 

Geological Challenges

Original foundation designs included grillage and driven piles. Variable bedrock depths and boggy ground conditions created foundation installation challenges at several structure locations. Soft surficial soils included organic peat bogs, and loose, saturated glacially derived sands and silts, which generally lack bearing support for tower foundations. Grillage foundations were unfeasible in these locations as they rely on a dense soil stratum below the footing bottom. Driven and auger piles were also problematic at numerous sites, as underlying bedrock materials consisted of strong to very strong granite, gneiss, limestone/dolomite, sandstone, and shales, prohibiting pile advancement.

QS Scope & Solution

The contractor engaged Quanta Subsurface (QS) to provide design-build foundation alternatives for sites predicted to experience installation challenges. QS designed micropile and drilled pipe pile options, as well as one-of designs for locations where subsurface conditions required a combination of foundation types. These included driven pile with rock anchors and driven pile with micropiles.

Micropile designs were developed for both self-supporting towers and guyed structures. They incorporated consideration of bog to depths of up to 25 feet, as well as variable bedrock quality. The approach provided a flexible solution that could be adapted onsite should conditions deviate from those noted in the pre-construction characterization borings, or where pre-construction borings could not be attained.

A drilled pipe pile is a single foundation element, combining properties of both drilled shafts and micropiles. Designs were developed for support of guyed structures where bedrock was anticipated to exist at relatively shallow depths, but where grillage support was deemed unfeasible.

Foundation designs were tailored to the installing contractor’s specific equipment, tooling and capabilities, allowing for cost and schedule efficiencies. In total, micropiles were installed at 161 structure locations and drilled pipe piles were installed at 131.

Highlights

  • Variable bedrock depths
  • Variable & deep boggy ground conditions
  • Micropiles & drilled pipe piles designed as alternatives to grillage and driven pile

Moxie Freedom – Substation

Project

MJE Drilling (MJ) was contracted to install drilled shafts at the Moxie Freedom Substation in Northeast Pennsylvania. The foundations would support six H-Frame structures and one 180-foot monopole, all with potentially significant embedment into bedrock. Original designs included drilled shafts with diameters ranging from 9 to 12 feet, and rock embedments ranging from 11 to 28 feet. Designs for the largest structure consisted of a 12-foot diameter, 34-foot deep shaft with a minimum shaft embedment into rock of 28 feet.

 

Challenges

Available geotechnical data indicated significant variability in depth to bedrock. MJ engaged QS to review geotechnical data and structure loading, and determine if an alternate design could be utilized should shallow rock be encountered at any of the shaft locations.

Qs Scope & Solution

Rock socketed drilled shafts pose unique challenges for designers and contractors alike, and this topic has become a national focus of the Deep Foundation Institute’s Drilled Shaft Committee. Traditional design approaches for drilled shafts that encounter a shallow rock contact surface include deeper and/or larger diameter shafts. On this project, QS developed alternative designs which incorporated detailed geotechnical assessments and constructability reviews derived from continuous interaction with MJ. The final value engineered designs, and those ultimately approved by the facility owner, resulted in an approximate 40% reduction in shaft/concrete volume and a 60% reduction in total rock socket depth. The drilled shaft supporting the 180-foot monopole specifically, was redesigned as an 11-foot diameter, 25-foot long shaft with a minimum shaft embedment into rock of 7 feet.

Highlights

  • Geotech data indicated significant variability in depth to bedrock
  • Alternative designs incorporated detailed geotech assessments and constructability reviews
  • Final designs reduced shaft size by approximately 40% and rock socket depth by 60%

Koolau-Wailupe 46 kV – Transmission Line

Project

Hawaiian Electric commissioned the replacement of several structures along the Koolau-Wailupe # 1 & #2 46 kV Circuits line on the island of Oahu. The project featured difficult access, with steep, rugged terrain and unpredictable weather patterns, and included the additional challenge of working under existing overhead lines.

QS Scope

Quanta Subsurface (QS) was selected to provide a design-build foundation solution at nine 46 kV self-supporting steel pole structures. Collaborating closely with contractor Crux Subsurface (Crux) to incorporate the company’s specific means and methods allowed for optimized designs. Steel cap micropile foundations were selected to accommodate helicopter-supported operations and short construction windows due to inclement weather. Crux’s specialty helicopter-portable equipment and the compact materials required for micropile construction were ideal for project conditions. Additionally, the steel pile caps could be fabricated offsite and flown onto installed piles quickly and efficiently.

Design Successes

During construction, the owner determined micropiles would be an efficient solution at four additional structure locations. These four foundations were added to Crux’s scope and an expedited design package was requested. QS successfully performed and submitted the requested designs in less than five days.

The presence of saprolites and transition rock in subsurface materials created additional design challenges. Saprolites are complex materials that behave as a soil in engineering terms, but may still exhibit some rock properties. Precise identification of saprolite zones is integral to micropile design and the successful performance of the foundation. Onsite monitoring allowed QS to accurately identify areas of concern, and all thirteen foundations were installed successfully and economically.

Highlights

  • Thirteen replacement self-supporting steel poles, situated in three different locations and supporting two circuits
  • Foundation locations feature rugged terrain and steep slopes
  • Majority of construction completed under in-service overhead lines

Devers to Palo Verde 2 – High Voltage Transmission

Project

The project consisted primarily of two new 500 kV transmission lines built within existing corridors – one 111-mile line and one 42-mile line. Crux Subsurface was selected to provide micropile foundation design-build services for 43 lattice towers and 13 permanent helipad structure locations due to challenging subsurface conditions and limited access.

QS Scope

QS was responsible for all aspects of micropile foundation design and field support. Geotechnical design parameters were established for anticipated subsurface conditions, and a decision matrix for foundation installation was developed. Standard penetration tests were performed during installation to confirm subsurface conditions, and combined with the matrix to optimize pile quantity and length at each foundation location

Advanced analysis techniques, including the strut and tie method, were used to design concrete pile caps with less reinforcing than conventional methods. Additional design services included recommendations for an ultimate load testing program, geotechnical design review, and design support during construction. QS also supported the prime contractor in determining slope/excavation stability per Cal/OSHA standards, designing remediation and reinforcement where required.

Highlights

Geotechnical variability created foundation design challenges. Conditions ranged from loose sand to highly weathered bedrock, with slopes varying from flat to 45 degrees. Using unique methodologies to determine soil resistance at sloped locations, QS was able to optimize tower elevations at micropile foundation sites. This optimization effectively decreased required excavation and concrete volume required for the pile caps, positively contributing toward project cost and schedule.

  • Micropile design for 43 lattice towers and 13 permanent helipad structures
  • Provided recommendations for ultimate load testing program, geotechnical design review, and design support during construction
  • Optimized tower elevations to decrease required excavation and pile cap size

WFMAC Transmission – West Fort McMurray 500 kV Line

Project

The West Fort McMurray (WFMAC) 500 kV Transmission Line Project includes over 310 miles of high voltage transmission line, expansion of the existing Livock substation, and construction of the new Thickwood Hills substation, all located in Northcentral Alberta.  The project is expected to be in-service by mid-2019.

Geotechnical Profiling and Foundation Design

QS conducted a desktop study of two proposed alignments.  This included collection and review of available project and public information along the alignments; geo-referencing of over 50 geologic maps; and reports on the surface and subsurface geology, hydrogeology, and geomorphology.  18 expected soil profiles were developed, and primary and secondary foundation types were selected for approximately 2,600 structures between the two alignments.  Bid level designs for multiple soil profiles and foundation types were subsequently developed for pricing.

Following route selection, a limited geotechnical investigation was completed.  Results from this and the indicative pricing were used to refine soil profiles to 17.  IFC foundation design packages were developed through 30%, 60% and 90% stages with Owner and contractor reviews.  Final designs included drilled shafts, driven piles, helical piles & anchors, and grouted anchors.

Geotechnical Investigation

QS managed a comprehensive geotechnical investigation program, completing borings at each of the 1,392 structure locations.  Between two and five geotechnical drills operated simultaneously to remain ahead of construction, averaging around two borings per day per rig.  Specific challenges included drilling in extreme cold, in environmentally sensitive areas, and during ice breakup.  The resulting data was used to select the optimal foundation type for each structure.

Construction

Helical pile anchors were the primary foundation type, supporting 1,182 guyed structures.  QS was responsible for onsite geotechnical confirmation, quality assurance and compliance reporting.  13 work fronts operated simultaneously at times, with up to 7 driven pile, 6 helical pile, 1 drilled shaft, 1 pre-drill, and 1 anchor testing crew running concurrently.

The revised 17 soil profiles proved highly accurate, with approximately just 2% of structure locations encountering unexpected geotechnical materials.  QS developed an additional 4 general soil profiles to mitigate this, as well as a handful of site-specific foundation designs.

Highlights

  • Over 310 miles of new, 500 kV high voltage transmission line
  • Preliminary geotechnical profiling to develop bid level designs
  • Geotechnical borings at 1,392 structure locations to optimize foundation selection