Views:19 Author:William Wei Publish Time: 2020-04-16 Origin:Site
HDD boring machine is a method of installing underground pipelines, cables and service conduit through trenchless methods. It involves the use of a HDD boring machine, and associated attachments, to accurately drill along the chosen bore path and back ream the required pipe.
HDD boring machines are typically heavy-duty vehicles fitted with track drives, operator controls, and boring machinery. Materials used for pipes include PVC, polyethylene, polypropylene, ductile iron, and steel. The technique has extensive use in urban areas for developing subsurface utilities as it helps in avoiding extensive open cut trenches. The use requires that the operator have complete information about existing utilities so that they can plan the alignment to avoid damaging those utilities. Since uncontrolled drilling can lead to damage, for standardization of the techniques, different trenchless technology promoting organizations have developed guidelines for this technique.
HDD boring is a three stage process:
The first stage consists of drilling a small diameter pilot hole. Drilling fluid is pumped through the drill pipe to the drill head where high pressure jets and the head will grind the soils ahead of the drill bit. The drilling fluid will also carry the cuttings back to the entrance pit at the HDD boring machine.
Location and guidance of the drilling head is an important part of the drilling operation, as the drilling head is under the ground while drilling and, in most cases, not visible from the ground surface. Uncontrolled or unguided drilling can lead to substantial destruction, which can be eliminated by properly locating and guiding the drill head. There are three types of guiding systems for locating and steering the drill head. All three systems have their own merits, and a particular system is chosen depending upon the site requirements.
Walk-over locating system: A sonde or transmitter located behind the drill head registers angle,rotation, direction, and temperature data. An electromagnetic signal encodes this information. Then a handheld receiver on the surface can decode the signal from a sonde or transmitter and the machine operator get the steering directions accordingly.
Wire-line locating system: With a Magnetic Guidance System (MGS), the tool reads inclination and azimuth. This also has a secondary means of location verification that utilizes wire grids laid on the ground surface. This information is transmitted through a wire-line fitted within the drill string. At the HDD boring machine, a navigator performs calculations to confirm the direction and location of the drill head.
Gyro-based locating system: The gyro-based locating system is the most accurate system. It is free of some of the limitations inherent in other systems, such as vulnerability to magnetic disturbance, inability to access areas above a drill path, and a large tolerance of trajectory.
The second step is to pre-ream the pilot hole and enlarge it to a size sufficient to safely install the product lines. A reamer is pulled back and rotated while pumping drilling fluid to cut and remove solids to enlarge the hole. Pre-reaming speeds will vary depending on existing soil conditions and the amount of cuttings that are removed from the hole.
The final step is the pullback of the pipe within the pre-reamed hole. The drill rod and reamer will be attached to a swivel, which is utilized between the product line and the reamer to prevent any torsional stress from the rotating drill string being transferred to the product pipe. As the product pipe is pulled into the drill hole, drilling fluid is pumped downhole to provide lubrication to the product pipe.
HDD boring machine is done with the help of a viscous fluid known as drilling fluid. It is a mixture of water and usually bentonite or polymer continuously pumped to the cutting head or drill bit to facilitate the removal of cuttings, stabilize the bore hole, cool the cutting head, and lubricate the passage of the product pipe. The drilling fluid is sent into a machine called a mud recycling station which removes the drill cuttings and maintains the proper viscosity of the fluid. Drilling fluid holds the cuttings in suspension to prevent them from clogging the bore. A clogged bore creates back pressure on the cutting head, slowing production.