H.D.D. is the abbreviation of Horizontal Directional Drilling, is one of the trenchless methodology. Generally, when encountering obstacles while trenching or crossing river, railroad highway etc., HDD is an option for installing pipelines. Only two working pits at entry and exit side are required during construction period, without continuous excavation along the road can reduce impact to residents and environment effectively.

Horizontal directional drilling can be separated into 4 steps: Pilot hole->Reaming->Swabbing->Pull back

Pilot hole: Drill in from entry point, continue drilling and follow the designed route until it reach to punch-out point.
Reaming: Enlarge the bore hole by a proportion to a specific size.
Swabbing: Use reamer to swab through the bore hole to ensure that it’s clean and free and is ready for pull back operation.
Pull back: Pull in the scheduled pipeline from exit point to entry point.