Direct Pipe Method Proves Comes To U.S.

November 2011, Vol. 66 No. 11

Because of an existing parking lot and nearby veterinary clinic, the team had only a 10‐foot exit pit off an existing 30‐inch line, leaving a very small margin for error in the pipe arriving on target. Pipe segments were supplied in 40‐foot sections and were joined on site. In this scenario, a method such as HDD would not have been an option due to the lack of room on both sides of the bore. HDD requires construction of a pilot bore plus multiple hole opening in preparation for the product pipe installation.

More complications
As an extra complication, REM’s team encountered a solid rock mix of coral and limestone at 293 feet into this bore. Since the machine stopped cutting at that point, REM was faced with the challenge of pulling the machine back and replacing the cutting head with the AVN-800, a mixed soil cutting head that is specifically designed for rock.

The original head used for the two previous bores was the AVN‐600, a soft formation cutting head that is designed to be used to cut sand and shell. Due to local geological risks, REM also preferred this method for its ability to cut through virtually most types of soil while maintaining an accurate alignment with the intended course.

During the two hours it took the team to remove and replace the cutting head, the bore path was left open but it did not collapse. The team proceeded with drilling back through the original 293 feet and an additional 90 feet. The Direct Pipe method also kept REM from having to perform an open cut at two locations, which resulted in a cost savings for the owner. Even through this challenge, the team was able to speed up the drilling process efficiency by utilizing the Herrenknecht Pipe Thruster.

If needed, the pipe thruster applies up to 500 metric tons of additional pushing and pulling power and increases feed rates up to five meters per minute. Overall, REM found they only had to apply a maximum 100 tons of pushing force during the rock installation.

To supplement the use of the Pipe Thruster, REM Directional has recently designed a pre‐fabricated anchoring assembly to expedite the time it takes to set up a Direct Pipe bore site.

After three successful pipe installations using the Direct Pipe method, REM Directional officials say it is a cost effective, simple method of trenchless pipe installation.