Laney Find New Tech Solution For Challenging Crossing

Longest U.S. Direct Pipe Project To Date
By Jeff Griffin, Senior Editor | March 2014, Vol. 69 No. 3

Snider said DP technology eliminates the requirement for deep entry and exit pits. It allows pipe to be installed from a surface entry point (with entry casing or a shallow entry pit) to a surface exit point or shallow exit pit. The product pipe is pushed using an above-ground thruster along with a slurry microtunneling machine. Horizontal steering also is possible, if required. The process significantly reduces risks of bore-hole collapse. Pipe is installed by steering an articulated Direct Pipe machine vertically down to desired depth and then up to desired exit elevation.

Because of a low risk of hydraulic fracturing, the DP method can be designed at lower depth of soil cover.

The project is the first time Williams has used the DP procedure for an installation, said Angela Williamson, P.E., Williams’ senior engineer.

“The complicated geology, topography and environmental sensitivities were major concerns for this project,” Williamson continued. “DP is a technology that has had little exposure in the United States. Williams was willing to use the technology because it was well suited to this particular project. Not only was the pipe successfully installed but a record was set for the longest DP installation completed in the U.S.”

DP tech

The Herrenknecht Direct Pipe system consists of a pipe thruster and steerable tunnel boring machine (TBM). A gyroscopic compass is used as the guidance system in addition to a traditional water level to aid in navigating the TBM.

“The pipe thruster clamp is used to thrust the pipe inside the tunnel being mined by the TBM,” Snider continued. “The thruster also provides the face pressure required by the cutter head. The narrow annulus is filled with viscous slurry for lubrication only and is not under significant pressure. A launch seal at the start of the tunnel prevents annulus fluid from coming out of the tunnel.”

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Because of the low annular pressures typically measured during installation, the potential risk of hydraulic fracture of the formation and creating an inadvertent return is greatly reduced, said Snider.

On-site preparations were a major part of the project.