PRCI PR-222-9218

L51697e

Louisiana Tech University/TTC

Need: The horizontal directional drilling (HDD) technique is specially suited for pipeline crossings of waterways, beaches, roads, vulnerable natural regions, railroads and airports. The HDD method is a two-stage process consisting of navigating a drill stem underground along a predetermined design route and the pulling back of the product pipe through the prepared hole. One of the major problems faced in HDD projects is subsurface exploration and locating of existing underground obstacles. HDD equipment must avoid these obstacles if at all possible.

Benefit: This study was conducted to: 1. Determine the state-of-the-art for obstacle detection in horizontal directional drilling technology. 2. Examine all possible techniques for obstacle detection. 3. Evaluate the most promising and suitable techniques for further development. 4. Determine further work necessary to reach a 100-foot (30 m) target. 5. Make recommendations for HDD contractors.

Result: There is no single method of subsurface investigation which will find all of the probable obstructions to a drilled river crossing every time. However, some of the current methods may be combined to give a little better picture of what the problems may be on a particular crossing job. The research group feels that at present state of development of the field, that surface GPRs may find some limited use on the shore approaches, sonar (subbottom profiling) will be of some value under the water-covered portion of the proposed route, and a magnetic survey should be conducted to avoid surprises. The objects of these surveys is to obtain better information on the placement of the boreholes in order to obtain the best information for the crossing. Dry land surface seismic, as well as more traditional marine seismic and resistivity studies, may be employed. The research group feels that the information gained per unit cost will not be as high with these methods as with the GPR and subbottom profiling. It should emphasized that the objective of applying these surface methods is not to get major amounts of information on the subsurface at the depths to which the pipeline is to be drilled, but, rather to obtain and enhance the planning on the physical placement of the conventional boreholes to find this information. It is thought that after the borehole sampling has been completed, the information from these three methods may be combined to give a much more accurate picture of the subsurface area in question. The research group feels that on some river crossings, thought to be representative, that before drilling boreholes, GPR, subbottom profiling, and a magnetic survey should be employed to complete the path engineering to see if this information will prove worthwhile in the conventional geotechnical development of the crossing.

Product Details

Published:

01/01/1994

Number of Pages:

128

File Size:

1 file , 6.6 MB