Sedro-Woolley, a quaint logging town in Washington, recently increased its trenchless pipe installation program because the program proved to be a success in earlier projects. Trenchless pipe installation minimizes disruptions and costs and is an effective way to install pipes.
Trenchless Construction Services, a construction company specializing in trenchless pipe installation and replacement, was the general contractor for the $3.5 million dollar sanitary sewer improvement project in Sedro-Woolley. The company installed 14 street utility holes and 3,400 lineal feet of 15-inch diameter and 24-inch diameter gravity sewer pipes at a .16 percent grade.
Pipes were placed under and adjacent to State Highway Route 20 and State Highway Route 9. “Our methods were used because of a lack of detour options to maintain traffic flow,” said John Gustafson, owner and manager of Trenchless Construction Services. “Soil conditions, as well as the accuracy of pilot tube micro-tunneling, also made it the preferred method for the 15-inch pipes and 24-inch pipes portions of the project.”
Guided auger boring uses measuring instrument
Pilot tube micro-tunneling, also called guided auger boring, was introduced in the 1990s for installing small diameter sewer pipes and water lines. Guided auger boring systems are similar to micro-tunneling systems with the addition of a guidance system that consists of a camera-mounted theodolite, which measures horizontal and vertical angles, to ensure a high accuracy of the line and grade.
“We chose the Bohrtec guided auger machine because we knew it would give us the needed accuracy,” said Gustafson.
Prior to construction, Trenchless Construction held a meeting with engineers, sub-contractors and company employees to discuss the project. ICON, the New Jersey-based slide rail system manufacturer, Bohrtec pilot tube distributor, and Mission Clay, the No Dig clay pipe manufacturer, made presentations on their products.
“Our goal was to make sure all parties had a clear view of the project scope as well as the products we were going to use,” says Gustafson.
Excavating and shoring open pits
This project required six jacking pits in which Trenchless Construction would place the pilot tube boring machine to jack the sewer pipe between street utility holes. These jacking pits were dug using a hydraulic excavator weighing 54,000 pounds.
Trenchless Construction used ICON’s slide rail system to shore the six jacking pits, which were 11 feet wide by 20 feet long by 14 feet deep. This slide rail system is designed and built to withstand the jacking forces of the Bohrtec BM 400LS pilot tube machine.
“ICON’s slide rail system is very easy to install and saved us a tremendous amount of time,” says Gustafson. It also features temporary sheeting to allow the contractor to extract small sheeting panels rather than large shoring panels to create an opening to install pipes.
The Bohrtec BM 400LS, with a jacking force of 150 tons and 75 tons of pull back force, can perform guided drillings in one, two or three phase procedures: pilot drilling, reamer drilling with steel protective piping; alternative reamer drilling while pushing pipes at the same time, and drilling with welded steel pipes.
A three-phase installation process
Trenchless Construction first performed the three-phase guided drilling installation with the 24- inch diameter clay pipe. This procedure consists of installing the pilot tube to secure an accurate line and grade. When the pilot tube reaches the receiving shaft, a 16-inch casing with an auger inside is connected to the last section of pilot tube in the jacking pit.
The 16-inch casing with auger is jacked into place as the soil is extracted following the pilot tubes. Once the casings and augers reach the receiving pit, a reamer is attached to the 16-inch casing that enlarges the bore hole required for the 24 inch clay pipe. The clay pipe is then jacked to the receiving pit.
Next, Trenchless Construction installed the 15-inch diameter pipe using the two-phase procedure for this installation. “We were able to jack the clay pipe after the initial pilot tube drilling with the casings because of the smaller pipe diameter,” said Gustafson.
Special tools required
Trenchless Construction purchased the 15-inch pipe auger and casings for the project and rented the larger auger and casings for the 24 inch pipe from ICON. “ICON was instrumental in securing the tooling and special equipment required for the specific pipe sizes on the project,” continued Gustafson. “ICON’s employees were always available for consultation and visited the project during construction to assure us that we were using the recommended procedures.”
This first-of-a-kind project in Washington was completed within the allotted time and avoided equipment malfunction delays. “ICON is a very customer focused, professional and knowledgeable company,” said Gustafson.
Since 1999, Trenchless Construction Services has grown to 20 employees and offers horizontal directional drilling, micro-tunneling, pipe ramming and trenchless pipe replacement processes, such as pipe reaming, pipe bursting and slip lining. The company is licensed in Washington, Oregon, Idaho, Montana and Alaska.
