Tough Challenges with Pilot Tube Microtunneling Project in Queens, N.Y.

Bancker Construction of Islandia, N.Y., successfully completed the installation of two 6-in., HDPE sewer pipes under the PepsiCo bottling plant foundation using pilot tube microtunneling technology while incorporating a new Pull Back Expander from ICON Tunnel Systems specifically designed to attach to the pilot rods and pull the HDPE pipe back into the pilot hole.

Over the past five decades, Bancker has completed numerous sewer line installs; however, this project was not your typical sewer line install. The PepsiCo bottling plant had a failing 40 year-old cast iron sewer line located under the plant floor in need of replacement. Project engineers determined that HDPE pipe would be selected for replacing this sewer line because the size and strength of this pipe met the specifications for their project.

These two new sewer lines would also need to run under the plant floor and various rooms such as a storage room, refrigeration room and the lab, which happens to be one of the most sensitive areas in the plant.  In addition, the plant would need to stay operational at all times during construction.

“There were many factors to take into consideration while planning for this project, more than your typical sewer install,” says Charlie Madsen, vice president of Bancker Construction.  “We knew the new sewer lines would need to be installed in a timely manner without disrupting plant operations. In addition, because of the sensitive nature of the bottling process, air quality was another issue we had to take into consideration.”

Bancker determined that open-cut construction to install the new sewer line was not an option as it would cause too many disruptions, as well as create too much dust and debris inside the plant. Directional drilling was also ruled out due to its lack of accuracy, large site layout and vibration from tooling could possibly disrupt the lab and bottling equipment. Bancker then turned to ICON Tunnel Systems and its pilot tube microtunneling technology as the sewer pipe installation method.

“Pilot tube guided auger boring has proven over the years to be one of the most accurate methods for installing gravity sewer pipes on line and grade,” states David Crandall, vice president of ICON Tunnel Systems. “Typically, pilot tube guided auger boring machines jack clay or steel pipe once the initial drive is made. Since this project called for HDPE pipe, we recommended our new Pull Back Expander attachment. This attachment allows us to successfully make the initial bore on line and grade, then pull HDPE pipe back through the bore instead of jack. HDPE pipe is typically pulled through the bore as jacking it with a machine on long drives will damage or even destroy the pipe.”  

“Other aspects of the project that made pilot tube microtunneling and the Pull Back Expander ideal were the soil conditions and pipe size,” says Dan Paster, national guided auger boring consultant for ICON Tunnel Systems. “The soil was soft sand with trace amounts of gravel and small cobbles, which allowed for further displacement of the soil by the Pull Back Expander after the initial pilot tube install. What this meant was no spoils had to be removed or dealt with during the installation process.

The microtunnel drives would not be an easy task for Bancker and ICON. They would first excavate the jacking pits outside of the building, next to the foundation wall. The jacking pits were 20 ft long x 10 ft wide x 8 ft deep and shored with Bancker’s ICON steel trench box. ICON Tunnel Systems supplied a Bohrtec BM600LS guided auger boring machine, which was then placed in the jacking pit with the theodolite guidance system.  

The First Drive

For the first drive, Bancker hand excavated the 4-ft x 4-ft tie-in pit, which was 107LF inside the plant from the jacking pit. “The tie-in point was located in the actual bottling section of the plant,” says Madsen. “There was very little room in this particular section of the plant so storing equipment, HDPE pipe and creating a true receiving pit was not an option.”

To solve the tie-in point issue, Bancker was allowed to excavate a receiving pit in the refrigeration room, which was located between the jacking pit and tie-in point.

Bancker and ICON made the initial drive on line and grade from the jacking pit, through the receiving pit and into the tie-in point. Once the pilot tube reached the tie-in point, they reversed the pilot tube back to the receiving pit. The next step of the drive called for the removal of the pilot tube head and attaching the Pull Back Expander to the front of the pilot rod. “The Pull Back Expander is threaded at the attachment end like a pilot tube head,” says Paster. “Removal of the pilot head and attaching the Pull Back Expander only takes a few minutes.”

They then proceeded with jacking a short portion of the HDPE pipe between the receiving pit and tie-in point. “Because the length from the receiving pit to the tie-in point was under 20 ft, we were able to successfully
jack the HDPE pipe into place,” says Madsen.

The team then attached another HDPE pipe to the head of the Pull Back Expander and successfully pulled the HDPE pipe to the jacking pit. Bancker then fused both pipes together in the receiving pit.

The second drive also used the Pull Back Expander but was located at a different section of the building and had much shorter distance of 76 lf.

With both drives there were a number of existing utilities in the way such as a main water line, roof drainage lines, electrical lines and old brick and cement foundation piles.  

“The accuracy of the pilot tube system was crucial as it kept the bores on line and grade though out the project,” says Madsen. “It also allowed us to stay exactly 3 ft under the concrete foundation, which eliminated vibrations and heaves in the concrete while boring. In addition, both the pilot tube and Pull Back Expander attachment displaced very little soil during the project. This allowed for us to speed up the installation process and finish ahead of schedule as we did not have to deal with removing spoils.”

Since 1982, ICON has steadily grown in technology and expertise to become a full-service trench shoring and pilot tube guided boring company and industry-leader in underground construction projects. ICON has the in-house resources to handle projects of any size in any location across North America and provides a comprehensive line of services that include consulting, design, engineering, manufacturing and distribution, leasing and equipment rentals.

Matt Roskie is an account executive with Advantage Marketing Communications.