Direct Drilling - most popular technology of the trenchless pipeline crossing construction
Directional drilling (DD or HDD meaning horizontal directional drilling) for preparing boreholes for pipe-laying is one of the most advanced technologies for trenchless construction of the pipeline crossing and repairing them.
Directional drilling technology is successfully used in the construction of closed crossings of main pipelines through water, roads, mountains and other types of natural and artificial obstacles. The work of directional drilling equipment has a high level of complexity and requires detailed engineering preparation of the construction site. As a trenchless pipelaying method, directional drilling has a number of advantages over other technologies.
The using of directional drilling eliminates the need for expensive underwater operations involving divers and other specialists, as well as shore protection works. The method not only helps to save on additional costs, also it is environmentally friendly for coastal and aquatic resources, protects automobile and railways from the damaging effects of construction processes.
The point of directional drilling technology is the use of specialised drilling equipment, which consist of a drilling rig, reamers and other utilities, located at the point where the pipeline must enters in the ground. According to the project documentation, the pilot drilling along a pre-defined pipeline route must be carried out. Then, special equipment (reamers) gradually enlarge the borehole up to the diameter of the pipeline and the walls are strengthened. Then at last the pipe bundle is put into the prepared borehole. The main circumstance for the successful implementation of crossing by directional drilling is the constant monitoring and, if necessary, adjustment of the pipeline’s route under the ground.
All the process of directional drilling may be divided on to tree main phases:
Stage 1 – is the drilling of a pilot bore with a drill rod with a cutter attached to it. During drilling, the inner cavity of the rod is fed with mud to strengthen the walls of the borehole.
On the 2-nd phase there is the borehole enlarged to the pipe diameter by ‘calibrating’ it with a rotating reamers. The soil that is drilled at this stage is collected in a special pit. It will then be disposed of.
In the final phase, the pipeline is dragged through the drilled hole using machinery and checked for the integrity of its insulation coating.
Despite the fact that the directional drilling method has its limitations in the applied geology, BELTRUBOPROVODSTROY JSC has more than 70 successfully implemented closed crossings built using this method. Including in conditions of perennially frozen soils as well as elevated temperatures of the southern European countries (Serbia, Bulgaria, Italy etc.)
*the photos are for illustrative purposes only