Kansas City Power & Light (KCP&L; Kansas City, Missouri) and its contractors bored a 385-ft hole underneath a major highway where 88,000 vehicles travel each day. The road remained open during construction, and when the city decided to build a new ramp, KCP&L had to complete the major underground crossing to get the circuits to nearby neighborhoods.
The project represented the largest and most unique boring project in the utility's history, due to the depth of the bore pit, length of the crossing and lessons learned. During the overall project, KCP&L invested $4 million to relocate cable connected to two bridges and two overhead highway crossings, and to make many alterations to the system.
The work was part of the Kansas Department of Transportation's (KDOT) 10-year, $127 million “Orange” project to widen and install new infrastructure at the I-435 highway corridor. The freeway corridors and surrounding interchanges currently operate beyond their intended capacity, resulting in congestion, accidents, poor peak-hour levels of service and difficulty changing lanes, according to KDOT. The construction project aims to handle expected growth in traffic volume by adding a fly-over ramp and interchange, and widening the I-435 highway.
KCP&L, which services more than 500,000 customers in a 4600-sq-mile service territory, manages 1700 miles of transmission lines, 10,000 miles of overhead distribution lines and about 3400 miles of underground distribution lines. Before KDOT began its project to improve the roadways, KCP&L had to make many changes to its existing infrastructure. Linemen rebuilt the overhead line across I-435 on the west side of Corporate Woods, a corporate office park. Line crews also had to rebuild another line and work on numerous side streets. In total, KCP&L worked on approximately 52,000 ft of line.
During the entire time KCP&L worked on the project, the utility had to maintain power to the Kansas City Scout road monitoring system. It also had to keep all 11 circuits hot during construction, because the circuits tied into hospitals, major office parks and residential areas.
KDOT conducted the project over six stages from 2004 through late 2007. The department coordinated these stages, and KCP&L worked its schedule around the deadlines. In terms of time frame and dollar amount, this ongoing project is the largest KDOT road project in history.
To manage the large-scale project, KDOT adhered to a tight schedule, and awarded the general contractor incentives and penalties for its performance. Since KCP&L worked directly with the general contractor, the utility was also responsible for meeting the schedule and getting the work done on time.
Trying to meet the schedule was even more difficult because the utility had to coordinate with many different contract employees and contract crews. While KCP&L's underground crew pulled cable and did all the splicing, the utility subcontracted the boring work to Capital Electric Construction (Kansas City).
Boring Through Rock
The boring portion of the project proved to be a learning experience for the entire construction team. KCP&L spent three months on the boring project under 69 Highway, which had a bluff on both the east and west sides. Contractors had to dig a 40-ft-deep pit on one side of the highway, bore a 42-inch hole to put steel casement with 12 conduits in that opening and take it 385 ft to the other side of the highway.
To get through the rock, the workers bored through solid limestone and shale rock, which delayed the project. Capital Electric brought in a boring rig from Nebraska that had a special bore head designed for this type of construction.
The boring crews also relied on a depth locator. The head of the boring unit had an indicator that located the signal that was given off of it. Because the highway had to remain open, crews had to find a way to determine the depth going across the highway. If the boring machine hit rock, it would have had a natural tendency to come up to the surface. If that happened, it could have made a hump in the highway surface. If workers dug deep enough, however, it wouldn't put pressure on the roadway up above. Workers dug a 40-ft trench, and crews had to make sure that the trench was deep enough on each side of the highway so no conduits were exposed.
To successfully complete the boring project, KCP&L's survey crew coordinated with the KDOT team to locate any existing utilities underground and identify any obstacles. Crews performed the pre-locates about three days prior and at the start of excavation. A survey crew staked and marked the job parameters, so the workers knew exactly where the bore pit and the road construction were going to take place.
Technology also played a central role in the boring project. For the first time on this project, the workers used a certain type of GPS locating device to determine the new roadway parameters and line up the direction of the boring machine. The device allowed the bore head to be aligned correctly and placed at the right depth.
The workers also used lasers to guide the boring head to make sure it lined up correctly when it met its destination. A rotating drill bit has a tendency to veer to the right, so the laser technology made sure that the bore was staying straight.
KCP&L and its contractors not only had to dig a bore pit for the conduit, but the companies also had to devise a way to take the conduit from 40 ft below the ground up to the roadway and back to a major street. To accomplish this task, KCP&L designed a loop around the bridge with flexible pipe, which helped speed up the project. If contractors had to cut rigid pipe and cut angles, it would have taken a significantly longer period of time. When workers pulled cable, it was much smoother, and they could pull through gentle sweeps rather than at hard angles.
KCP&L also had to discover a strategy to prevent the concrete from sliding down 40 ft into the bore pit. The utility solved this problem by creating new dams for the concrete and pouring the concrete mixture on top of the conduit.
When workers installed the conduit, however, the mixture of cement melted the pipes. Three ducts completely closed down due to the heat of the concrete. The project was delayed about three weeks to reroute the conduit.
KCP&L now has a specification for any grout going into any underground steel sleeve. The utility changed the mixture between fly ash and Portland cement, which is what creates the heat. The different ingredients in the grout mixture won't heat up to a level that can melt the pipe.
Since heat can't escape through the steel sleeve, the workers in the field had to find ways to heat and cool the sleeve. To reduce heat buildup, KCP&L installed cooling and ventilation pipes on both ends and welded those together. The utility and its contractors also had to perform another 20-inch bore next to a 48-inch bore to make up for the damaged conduit.
Since that time, KCP&L hasn't had any other problems like this one on any other project, and hopes that through preventive measures, it won't happen again.
KCP&L learned many lessons on this project and has carried this knowledge onto other projects. It was one of the first major bores the utility has done in a long time, and KCP&L also had to build a relationship with governmental entities and many contractors. Throughout the project, KCP&L had to get the work done on time while making sure its reliability was tier one.
Dale Myers is a project manager in charge of distribution projects for Kansas City Power & Light (Kansas City, Missouri). During his 28 years with KCP&L. He has served as the superintendent of resource management, fleet manager and purchasing agent. email@example.com