Horizontal directional drilling technology
Horizontal Directional Drilling
is a controllable trenchless method of laying underground pipelines, based on using special drilling machines and rigs such as drilling machines – UGNB-3M
- produced by a domestic producer, the NPK Gidrofob RSM
. The international name is HDD or Horizontal Directional Drilling. The length of pipeline laying can vary between some meters to some kilometers, and hole diameter can be more than 1200mm. The HDD method uses polyethylene, steel pipes and pipes made of other materials. It’s important to note that the harmful effect influencing on the environment is minimal.
Horizontal directional drilling technology
Before work starts, soil properties and its constitution are studied closely, existing underground communications are removed; all necessary work authorizations are received and selective soil probing is made. All the results have a primary meaning for choosing the path and tactics of bore hole laying. Special attention should be devoted to an optimal location of drilling equipment on a building site and ensuring safety working conditions for workers and other people. The HDD method is comprised of a four stage process:
1. Pilot hole drilling
2. Pilot hole enlargement
1. Pilot hole drilling
Drilling a pilot hole is one of the important stages of the work, influencing considerably on the result. It is done with the help of a rock-cutting tool – a front-beveled drilling head with an installed transmitter. The drilling head is fastened to the flexible drive bar by means of a hollow pipe; it allows to control the process of drilling the pilot hole and get round detected beforehand underground obstacles in any directions within a usual bend in the extended operating string. The drilling head has two water ports to feed special drilling fluid that is pumped in a bore hole making suspension with crushed rock. Drilling fluid reduces friction of the drilling head and a drill string, stabilizes the bore hole, cools the rock-cutting tool, washes away the rock and removes the cuttings. The control over the location of the drilling head is exercised by the means of a special receiving gear – locator that receives and handles signals from a transmitter built in the drilling head case. Visual information about position, angle and azimuth of the drilling head is showed on the locator display. The information is also shown on the machine operator’s remote display. The data are extremely important for controlling of compliance the path of laying pipeline with the project documentation and they minimize the risk of bending sharply the operating string.
In case of the deviation of the drilling head from the project path a machine operator stops drill string rotation and corrects the direction of the drilling head. Then the drill strings are pushed without rotation in order to correct the drilling path. The drilling of the pilot hole is completed when the drilling head is at a given exit point according to the project.
The drill string is a pipe sized of about 60-80mm in diameter and 1-3m long. At the ends of the drill string are conic outside and inside threaded couplings at different ends of the string. The drill strings are connected to each other one by one as the drilling head moves. Connected in such a way drill strings look like a flexible rope that is used for cleaning sewerage pipes.
An operator can see a turning angle of the drilling head and its direction on the hand locator display, and if it’s necessary to change the drilling direction he gives a drilling machine operator the order: ‘Stop’, and then ‘Rotate by X degrees’ (but it can be done only in one direction conforming to involvement direction of a drill string threads) in order to place the drilling head in the right direction and commands: ‘Move the tool on X per cent forward’. After that the drilling head moves forward on X per cent conforming to an operator’s command, then the drilling machine operator starts to pump water or bentonite with the tool rotation. In this way the drilling is carried out on the given path. Water or bentonite is pumped under regulated pressure through a drilling machine spindle, then through the drill string reaching the drilling head.
Control of the bore moving
The drilling head is at the final point
3. Pipeline pulling
The bore hole is enlarged when the pilot hole drilling is completed. A back reamer or a reamer is attached to a drill string instead of the drilling head. The reamer is pulled from the exit end of the tunnel, back to the machine, enlarging the pilot hole to the necessary diameter. To ensure free pulling of pipeline through the enlarged bore hole, its diameter should be by 35-50% more than pipeline diameter. If big diameter is required, the process of enlargement is repeated some times using several reamers of bigger diameters.
Bore hole enlargement
4. Final stage
There is a pipeline string prepared for pulling on the opposite from the drilling machine site of the bore hole. A swivel is attached to the reamer at the end of the string; it prevents the pipeline from rotating. Then the pipeline is attached to the swivel by the means of a special gripping device. In this way the drilling machine pulls the pipeline string into the bore hole in a project path.
Enlargement with pulling of a pipeline
Engineering and technical personnel turns over operating set of documents to a client, where the actual pipeline position in different planes is stated. It’s obligatory to describe the linkage between the pipeline and landmarks.
Example of an operating scheme
Horizontal directional Drilling Machines
Horizontal Directional Drilling Machines represent complex construction machinery. A typical machine consists of a cradle, a body, bogie (track-type or wheel), a generating unit (diesel engine), a hydraulic aggregate, a drill string feeder, a drill carriage, and a control panel (an operator’s work place).
Horizontal Directional Drilling Machines are produced in the USA, Germany and China. And since 2006 the NPK Gidrofob RSM has begun to produce HDD machines in Russia.
Machines are classified by their maximum tractive force measured in tones. Other important characteristics are maximum enlargement diameter and maximum drilling length.
To date the NPK Gidrofob RSM produces HDD machines of two types:
- a ditch type machine – UGNB-3M4 is a compact, mobile, not expensive machine;
- a track-type machine – UGNB-4 , is analogous to foreign machines but it’s cheaper and adopted to Russian conditions.
HDD location system
The control over the process of Horizontal Directional Drilling is an extremely important aspect. As the drilling head is invisible during the drilling, the uncontrollable drilling can have unexpected consequences. Therefore during Horizontal Directional Drilling the location systems are used to control the process of drilling. The location system represents a probe attached to the drilling head and a special synchronizing device that is held by a location system operator. The probe registers all information about the angle and the direction of drilling, the rotational speed and drilling head temperature. The information is transmitted to a location system operator during the drilling and helps to avoid aftergrowths.
DigiTrak Mark III
The main advantages:
1. Production and technical aspect
• Capability of trenchless construction, repairing and cleaning underground pipelines:
- under rivers, gullies, forest areas; in specific soils (rock, quicksand);
- in guarded areas of high voltage overhead lines, main gas, oil pipelines;
- under conditions of urban housing system if a line is planned to build under motorways, street railways, roads, public gardens and parks;
• Shortening of terms and volumes of organizational and technical agreements before start to work; it’s possible as there’s no need to stop all kinds of transport and/or block motorways and railways;
• Significant shortening of the time for work performance due to using high technological drilling complexes;
• Significant shortening of heavy machinery and workers number using for laying pipelines;
• Shortening of accident risks, and as a result they guaranty to keep a pipeline in operating state for long;
• There’s no need to have external power supply during the drilling due to complete machine autonomy;
• There’s no need to reduce water level under conditions of high ground water.
2. Financial and economic aspect
• Shortening of construction budget due to cuts of the time for work performance and costs on using extra workers and heavy machinery.
• Minimizing costs on power supply for drilling complexes due to their economy.
• There is no need to restore damaged roads and railways, green plantations and urban infrastructure.
• Shortening of maintenance costs on control and restoring pipelines during their maintenance.
3. Socio-economic aspect
• Saving landscape and ecological balance of sites where the works are carried out, exclusion of an anthropogenic impact on the flora and fauna, erosion of banks and bottom deposits of basins.
• Minimizing negative impact on people’s living conditions in the area where the works are carried out.