- The minimum specification for directional drilling shall be as follows:
- A pilot hole shall be drilled between two local pit locations. The drilling system shall incorporate a steerable head, remotely controlled to direct the hole along the correct alignment and grade.
- A back reamer shall be fitted to the drill string in order to enlarge the pilot hole sufficiently to accommodate the pipe.
- The pilot hole shall be supported by a Bentonite slurry which also lubricates the outside of the pipe when it is drawn back through the hole.
- Before the pipe is drawn back through the hole, the leading end shall be sealed to prevent the entry of dirt and slurry.
- The pipe shall be attached to the back reamer and pulled through the enlarged hole.
- On completion of the pipe installation, if the annulus between the excavated hole and the pipe is not filled with slurry within the specified tolerance, it shall be filled with grout.
- The drilling machine shall be carefully aligned to provide a true line and grade. Should the pilot hole or installed pipeline vary more than the specified tolerance from the required line and grade, the Contractor shall open excavate part or all the affected section to rectify the line to the correct line and grade or re-pilot a new line as instructed by the Engineer.
- The pipe pulling equipment shall incorporate a breakaway device fitted to the leading end of the pipe to prevent the maximum pulling load being exceeded.
- The Contractor shall provide evidence from an IANZ approved laboratory that the device is calibrated correctly.
- Where the breakaway device breaks during pipe pulling, the pulling operation shall stop immediately and the Contractor shall determine the reason for the failure and shall take the necessary precautions to prevent a recurrence of the failure.
- Any damaged pipes shall be replaced.
- The maximum pulling load shall not exceed the load given in CS-13.3 -Table 1: Maximum Pulling Load for Trenchless Technology, nor shall it exceed the load that will stress the pipe to 50% of the material yield stress, whichever is the lower.
- The following additional limits shall apply:
Minimum radius = 35m
Maximum length of drill = 200m
Maximum pull rate = 0.5m–1.0m per minute
Table 1: Maximum Pulling Load for Trenchless Technology
||Maximum Pulling Load (kN)
|63mm OD PE80 SDR11
|125mm OD PE80 SDR11
|180mm OD PE80 SDR11
|250mm OD PE80 SDR11
|315mm OD PE80 SDR11
Definitions in this section