FTTH project OSP notes: Trenchless Methods

Horizontal Directional Drilling (HDD)

Short notes for HDD machines operations

The working principle of the HDD

The working principle of the HDD

1. In very simple terms, HDD is a drilling process where a drill head is steered underground. This method is adopted by all companies but habitually, subcontracted to specialists.
2. HDD is the preferred method to cross roads, highways, railway lines, rivers and all other services that may prove to be too dangerous or costly to cross using conventional methods like trenching and/or ploughing.
3. The depth of any hole drilled for the installation of a new service, must be at least 800mm below surface of the road, or as per client spec.
4. In what follows, a brief overview on the 3 installation stages:

  • I. Pilot drilling
  • II Reaming the initial pilot hole
  • III Pulling back the duct in the reamed hole

5. The course of the drill is monitored and can be controlled as rods progress following an upward sloping path, before emerging at an intended point.

Horizontal Directional Drilling (HDD)

Horizontal Directional Drilling (HDD)

6. The drill head is then removed and replaced with a back reamer, ± 20% larger than the duct or cable to be pulled into the hole.
  The duct is attached to a swivel connection on the back reamer. The drill-rods and reamer are rotated and pulled through the hole, enlarging it and pulling-in the duct at the same time.
  The whole operation is carried out with pressurized drilling mud, which both carries away the spoil and supports the hole.
7. Rigs capable of drilling up to 300 meters in one drill are available and various sizes of ducts can be installed with this equipment.
8. The covering must not be less than three times the final diameter of the drilling hole and at a minimum of 1.5m.
9. At river crossings the distance between the bottom of the water and the drilling hole should be 10-times the diameter of the pipe and not less than 3m.
10. Soil removal during the drilling process is the responsibility of the contractor.
11. If the accuracy of the drilling is not specified in the wayleave, the area in which the drilling may wander should not exceed a 40mm diameter around the predetermined axis.
12. As always, the location and depth of underground services must be pre-determined before drilling can commence – as sudden deviations are not possible to bypass obstacles.

Hammerhead Mole

Hammerhead Mole

Hammerhead Mole

1. Hammerhead Moles provide a cost effective alternative to HDD (sometimes referred to as mini-HDD). They are apparently easy to use, simultaneously boring and installing a duct.
2. To begin with, both an entrance and exit trench or hole must be dug at the allocated positions.
3. The Hammerhead Mole is then inserted into the abovementioned hole in the direction of boring and the boring process commences. A duct-pulling attachment allows for the duct to be installed at the same time the bore is made.

Road Reinstatement

Road Reinstatement

Road Reinstatement

1. The permanent reinstatement of the surfacing typically consists of 100 mm hot-mix asphalt. The lower 70 mm must be compacted and rolled asphaltic black base (26.5 mm nominal stone size, continuously graded) and the top 30 mm (4.75 mm nominal stone size, continuously graded). Coldmix may be used only for temporary reinstatement.
2. The reinstated surfacing must be at least 100 mm wider than the trench on both sides to accommodate any edge breaks.
3. On completion of the work concerned the authorized person must fill in a completion notice and return it to the road authority within twenty-four (24) hours.
4. The road authority will then arrange a site meeting to do an inspection and to issue a certificate of completion if all requirements have been met.
5. A twelve (12) month guarantee period for permanent reinstatement by the wayleave holder, or the fourteen (14) day maintenance period for temporary reinstatement by the authorized person, commences on the day after the issue of the certificate of completion.
6. Rubbish, and other objectionable material of any kind, must be legally disposed of, absolving the client from any liability connected therewith.

Latest Blog

About Us

Why FTTH can save telecom cost

FTTH: saving money

【Our Goal】

Benefits our customers via Fiber Network (FTTH).

【FOT Telecom】

Your reliable fiber network equipment and service provider: Read More

Contact us

Email: sales@fiberoptictel.com fiberoptictelecom@gmail.com SKYPE: fanny-lee2007 SKYPE: fiberoptictelecom Tel: +86-20-22098370
Add.: Jitang Industrial Zone, No.8 Nanyun Five road, Huangpu, Guangzhou. 510663
ContactUs.com