Providing solutions for difficult projects is one of the hallmarks of trenchless technology and the advancement of the trenchless industry. And sometimes that means looking beyond the familiar and trying something new. When tasked with figuring out a way to reroute a PVC water line under a major intersection, water utility WaterOne, Lenexa, Kansas, was forced to look outside its current equipment toolbox to find the answer.
Two of the biggest limiting factors of the project were space and the high traffic volume of the intersection. Conventional directional drilling was an early consideration, but ultimately was not an option because of the limited space available for the drill rig. The surface launched drills were too big for the setback and would have required removing part of the road. This was a several-day project, and with a large drill unit, WaterOne crews would not have been able to remove it each day. The traditional open cut approach was never really a viable option.
To find a workable method, WaterOne officials consulted with trenchless equipment manufacturer TT Technologies, Aurora, Ill., the supplier of its pipe bursting equipment. TT Technologies Trenchless Specialist Joe Abell explained, “While WaterOne is proficient in traditional open cut, surface launched horizontal directional drilling and pipe bursting, none of those options would work for this project. Installing the 12-inch PVC lines, as designed within the given restraints, did not allow for any major disruption to traffic flow and required the road to be open fully each night. To facilitate a successful project, we suggested using a Grundopit pit-launched directional drill.”
A Utility Moving Forward
WaterOne is an independent public water utility serving Johnson County, KS, and surrounding areas. It was established in 1957, when area residents, dissatisfied with the service from their water provider, came together and bought out the Kansas City Suburban Water Company. The group reincorporated as public water provider Water District No. 1 of Johnson County. At that time the utility was supplying up to 5 million gallons per day to area customers.
Today, with nearly 425,000 customers and the capacity to supply up to 200 million gallons of water per day, WaterOne serves customers in 17 cities throughout Johnson County. The utility also serves unincorporated parts of the county and its service connections extend into parts of Wyandotte County and Miami County. They have 380 employees, 6 in-house construction crews and on average they install and rehabilitate about 50 miles of pipe each year. WaterOne is able to grow to meet the demand by following a comprehensive master plan. The organization makes continual investments in infrastructure at the right time.
With approximately 2,800 miles of mains in the system, comprised largely of aging cast iron pipe, WaterOne’s engineering department has segmented the entire system in order to evaluate it and designate priority for main replacement. The water utility has developed a comprehensive in-house trenchless pipe bursting program and is tackling main replacement head on. Abell said, “WaterOne began transitioning to a trenchless program about 14 years ago in 2006 in an effort to look for efficiencies and same money on restoration costs. Restoration costs alone can end up being over 25% of the cost of the entire project. That’s why they started looking at trenchless technologies. Unfortunately, as we mentioned, the pipe bursting method would not be able to meet the requirements of this project because the path of the old main was different than the path of the new proposed line.
Project Restraints & Pulling Possibilities
The main relocation took place in Overland Park, KS at the intersection of 95th and Switzer. The city of Overland Park was in the process of overlaying a highly traveled busy street with almost 30,000 cars a day through this intersection. The old 12-inch cast iron water main crossing under 95th Street needed to be replaced as part of the project. However, because of the considerable traffic count, the city would not allow any lane closures on the North/South corridor during the project, severely limiting project space. Under the suggestion from Abell and TT Technologies, compact directional drilling with a pit launched HDD unit was selected. In order to install the 12-inch main, the north to south bore path needed to circumvent a phone duct, a 4-inch power conduit (3-phase) and a storm sewer line.
Pit launched, mini-directional drills can be utilized for installing water services, electrical conduit, gas services and small main lines. The units are compact and function well in tight working conditions. The unit utilized by WaterOne measures 54 inches long, 43 inches wide and 57 inches tall; provides 13,489 lbf of thrust and pulling force; and 553 ft. lbs. of torque with typical bore lengths up to 150 feet. Hydraulically operated telescopic bracing supports anchor the unit allowing for proper alignment and maximum thrust and pull back capabilities.
Abell said, “One of the nice things about the pit-launched unit is it’s easy to use and portable. The complete unit can be transported in a pick-up truck and operated with a small crew compliment. It also features a patented drill stem plug in that makes loading and unloading the drills simple. The Grundopit is an ideal entry level system for water or gas utilities, cable industries or as a supplement to larger units.”
Putting Pit-Launched HDD to the Test
The pit launched compact directional drill was chosen due to the tight working conditions that prohibited the use of other trenchless applications. A 4- x 12-foot pulling pit was established in the street at the southern limits of the intersection, just outside the curb line. The launch pit was located just within the curb radius, on the edge of the road, heading north. A 4- x 6-foot section of asphalt was removed from the roadway and the rest of the pit stretched back 24-feet through the greenway, ramped at a 30% grade.
Abell said, “Over the course of four days, the drilling and reamer portion of the project was completed. The WaterOne in-house crews proceeded in a diligent and methodical manner; as it was their first use of the compact directional drill. They took special care to make sure to avoid damaging the intersection. A 1 ¾-inch pilot bore was completed on the first day in approximately 2.5 hours.”
Once the pilot bore was established, a reaming pass was completed with a 10-inch reamer on day two. On day three, a 14-inch reaming pass was completed in approximately six hours. Crews were able to prepare an effective bore path for the new pipe by clearing the heavy clay spoil through the reaming process.
On day four, crews prepared for the final 18-inch reaming pass and pullback of the new Certa-Lok® PVC pipe. Approximately 20 feet of the run was reamed with the 18-inch reamer, which was then pushed back, while crews vacuumed out the spoil and cuttings.
A 60-foot string of new PVC pipe was assembled and readied for pullback. Soil conditions in the area consist of heavy clay which was very conducive for drilling. As a result, the drilling required only 500 gallons of bentonite water mixture.
The first section of 60 feet was pulled in without incident. The remaining 40 feet was pulled back in two 20-foot sections. Once in place, the new pipe was tied into the system past another phone duct on the south side with a new tee and triple valve configuration. On the north side, an existing valve was replaced and the new pipe was tied in there. From start to finish, the project took one week to complete.
Abell said, “It was a challenging project and took a good amount of coordination and skill to pull off. Sometimes taking that leap outside of the equipment comfort zone can pay off, and it did for WaterOne.”