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Directional Drilling

Drilling Applications :

- Gas and oil pipelines : A major use for HDD is installing high pressure gas and oil pipelines under obstacles like waterways, airports, and major roads and other large natural features or urban structures. By putting the pipeline deep underground, often in solid rock, it's protected from damage by dredging, anchors or surface trenching. It also protects it from accidental or deliberate damage, helping to manage risk and eliminate threats to the pipeline.

- Water and sewerage : As with gas and oil, HDD can be used to carry water and sewerage pipelines under and around almost anything. Lucas has also used HDD to drill directly into deep underground sewer tunnels. Apart from avoiding the cost and disruption of surface trenching, HDD's ability to maintain a precise gradient and travel deep underground has dramatically reduced the need for pumping stations, simplifying the sewerage system and reducing long-term costs.

- Telecommunications : As well as carrying conduits for fiber optic cables beneath rivers and other obstacles, Lucas has used HDD to carry them to near-inaccessible mountain tops and microwave transmission towers. By placing them deep into bedrock beneath the coastal sands and surf zone, these fiber-optic cables are protected in the most vulnerable part of their route.

- Electricity : High-tension cables can be placed deep underground, protected from damage and avoiding surface obstacles.

- Environmental protection and remediation : HDD has a wide variety of environmental uses: draining landslip-prone hillsides, extracting methane gas from coal seams before mining, restoring sand to beaches, creating underground barriers to reduce movement of contaminants, draining slag heaps and rubbish dumps.

Directional Drilling Machines



Horizontal Directional Drilling View



Directional Drilling Method Statement

Purpose: Install utilities (Pipes & or cables) underground, without disturbing ground surface.

- As per the drawings provided for the location where directional drilling works to be carried out, detailed information of the existing utilities, proposed route drawings and references marks.

- Carry out survey to locate all existing utilities by making trail pits and by using Electronic detectors if necessary to trace underground utilities and then to make soil test to understand the ground condition. A surface level is taken prior to all Drilling works.

- Make a bore plan (profile)clearly mentioning all existing utilities, exact location of entry and exit pits and the different levels in which the directional drilling (Pilot bore) is to be carried out.

- Prepare the drilling location with all necessary safety materials, machines and required length and dia meter of HDPE pipes joined together using butt fusion welding machine.

- The machine (drill unit) is anchored to the ground, location supposed to be the entry pit with anchor stakes for proper fixing the machine.

- The pilot: a sonde contained metal body with angled bit is drilled into the ground in the desired angle as to start the pilot bore as per the bore plan or profile made.

- Fluid mixing system (Bentonite mixer): the Ditch Witch FM 13 mixing system comes with a 1000 gal mixing capacity and can attain a maximum flow rate of 300 gal per minute. Normal flow rate used is 10 gal per minute during pilot bore and 30 gal per minute during back reaming/pipe pulling.

- The fluid: a mixture of Bentonite (pure clay oil) and water mixed in a proper proportion to obtain good slurry is sprayed with pressure through the pilot head (angle bit) at 10gal per minute to lubricate the drill procedure and to cool the electronic tracking device sonde inside the pilot.

- The locater: an electronic signal receiver is used to track the pilot from the ground surface. This helps the head to deviate to desired angle and depth as the pilot is pushed by the drilling unit without rotating and later drilled by pushing and rotating the pilot.

- When the drill head reaches the planned destination it is steered to the ground surface and obtained in the receiving place on exit pit made.

- The reamer: the back reamer is designed and made in different shapes and sizes so as to reach the user requirement according to the soil condition and size of the pipe to be installed as the size differs from diameter 110mm, 200mm, 225mm, 300mm,350mm,380mm, 415mm, 450mm and 480mm so as to be used for installation pipes diameter differing from 100mm,110mm,160mm,180mm,200mm,315mm,400mm and also installing number of pipes together like 3 way,4 way and 6 way of 100 mm and 110 mm, 3-way and 4 ways of 160mm, 180mm pipes and also 3-way of 200mm pipes.

- The back reaming: when the drill head is received in the exit pit it is then de-attached from the drill pipes and a back reamer is attached to it which is then pulled back to the entry side using slurry with a pressure depending on the soil condition (30 gal per minute for normal soil). The back reaming process is made a number of times in different sizes to reach the required size of drill whole for the pipe to freely run through it.

- Pipe installing: a swivel is attached to the back reamer, connected to the pipes to be installed, towing to the machine (entry pit) side. Back reaming and pulling the pipes at the same times will allow the pipes to be installed underground without excavation, during this process the drill fluid will assist the lubrication factor and creating a slurried area around the drill hole for the pipe to be installed without any void.

- The back reaming and pull back will continue until reamer and pipes reach the launch side of the directional drilling, then disconnect swivel and towing head from the pipes will complete the drilling work.

- A surface level is again repeated later six months and one year after the directional drilling job is finished as for the surface settlement limit is not more than 2mm at a period of six months and not more than 5mm at a period of one year. The formula for maximum surface settlement is :

Smax = 0.313 VLD2/i

D      excavated diameter of bore/tunnel
I       distance form bore/tunnel centerline to point of inflexion of settlement trough
Smax  maximum settlement with a settlement trough
VL     volume loss as ratio of notional excavated volume of tunnel

As per O’Reilly and New proposal the relation between i and Zo for normal soil is :
i = 0.28Zo – 0.12

Butt Welding of PE pipes

Butt Welding is the most common method to joint HDPE pipes, stub ends, tees, elbow, bends etc.

The pieces to be welded are not added any welding material but the surfaces to be pointed are heated up by means of a heater plate. The melted surfaces are then pressed together and the molecule chains will thus intrude each other and form a strong joint. There is no chemical connection between the molecule chains; the strength of the joint is based mainly on cohesion between the molecules.

The pressure applied in the weld will vary from stage to stage of the welding operation. For each size of a welding machine the respective hydraulic pressures to be used for different outside diameters and wall thickness.

Provided that the pipe ends are properly trimmed butted and aligned, the ends softened by the heat will fuse and will remain so when the weld cools. A small bead has been formed inside and outside during the operation.

The butt-welding is carried out with machines specially designed for this purpose. The machines have a strong body frame, guide rods for the pipe end trimmer electric heater plate. The compressive thrust is produced hydraulically or by means of lever or spring mechanism. To achieve a good welding result one always has to use a machine for the operation.

Working Procedure

The Butt fusion operation is divided in to the following steps :
- Fixing of pipe to the machine
- Aligning and trimming of pipe ends
- Heating up of surfaces to be welded
- Removal of heater plate
- Welding
- Cooling
- Dismantling of the pipe from the machine Inspection