»HDD – an excellent solution for complex pipelines as well as household utilities and smaller crossings.«
This technology has been a success in the Slovenian market introduced a few years ago by our company in the area of horizontal drilling and trenchless rehabilitation of pipelines (sewers, water…). We have continued to improve the technology, and we are striving for technological perfection, as shown by our enviable results. 
Implementation of horizontal bores using HDD directional drilling
Lengths
Implementation of bores up to 1.5 km in length.
Materials
The technology allows implementation is category II to VII soils.
Pipes from f 32 mm to f 1200 mm may be drawn.
Specifications
The technology is based on basic direction or guidance of drill heads, which means that we can implement the planned bore in accordance with a previously prepared project. The lengths of individual bores are linked to the geological composition of the terrain and individual geographic characteristics. Objectively, the maximum length of an individual bore is 500 m, depending on the diameter of the bore and the geological-geographical conditions. Classic implementation of boring takes place in category I-IV soils; work is also possible in category V and higher soils, as is drilling in rocks with the use of special drilling tools.
After completion of the bore, PE/HD or protective metal pipes of diameter 500 mm or more are generally drawn. The technology allows multiple pipes to be drawn simultaneously. It is essential that each bore can be implemented with horizontal and vertical curves, radius > 40 m, which enables undisturbed implementation of subsurface drilling of all types of waterway, municipal, road and other infrastructure.
Implementation of works
The work procedure for this technology comprises a series of technological steps:
Preparation of the bore project involves production of a geodesic snapshot of the terrain. Based on the data obtained – longitudinal profile of the route – we prepare a bore project with the investor’s required parameters and full details. The project is then submitted for examination and confirmation. After confirmation, bores are implemented with maximum deviation from planned clearances of 5%.
The boring and pipe-drawing procedure is divided into three phases:
Phase 1 – production of pilot bores
Phase 2 – widening or redrilling of the bore to the desired diameter
Phase 3 – drawing pipes
The drill head of the pilot bore is guided using the previously prepared project, enabling real-time monitoring of the accuracy of the route and the depth of drilling. Drilling is carried out with real-time injection of a mix of bentonite and water, which serves to protect the drawn pipe against possible damage.
After implementation of the pilot bore, a reamer is installed on the bore rod to expand the bore to the planned diameter, which must be at least 30% greater than the diameter of the drawn pipes. Return boring or reaming of the bore also involves the addition of bentonite mix, which serves to stabilise the bore and protect the pipes against damage. This creates a bentonite lining ca 5-10 cm thick around the drawn pipes. As previously emphasised, one or more pipes can be drawn simultaneously, depending on the diameter of the bore. During drilling, precise recording of the bore is carried out for the purposes of producing a geodesic snapshot and the documentation for executed works. Bored material is not disturbed during drilling, and so the depth of drilling is not important. For drawing we use continuous pipes (discs 50 and 100 m long) or aligned welded pipes on rods.
In the case of drilling using the HDD method, we mostly advise the use of coated PE/HD pipes which we supply to the Slovenian market together with our German partner, Egeplast. These are standard PE/HD pipes coated with a protective layer of mineral-reinforced polypropylene (PP), the advantage of which is considerable resistance to mechanical, UV and chemical damage. Such pipes do not require additional protective pipes, and are suitable for direct drawing in bores.
During drilling, excess bentonite mix is discharged at the entrance and exit of the bore. Using special pumps, this is pumped out and – using a mobile recycling appliance – it is prepared for reuse. This ensures the environmental acceptability of the project, since excess bentonite wash does not need to be removed for permanent disposal.
Advantages
The drilling procedure using HDD technology is economic and quick, does not impact the environment during and after implementation, and does not have environmental consequences. After completion of drilling, it is possible to restore the original state without major interventions. Horizontal directional drilling can be carried out wherever work with classic excavation is not possible, cost-effective or otherwise feasible. The main advantages of horizontal drilling are that bores can where necessary be carried out at greater depths, under built and other structures, and under various natural barriers (e.g. underneath rivers, where waterproofing is ensured; no impact on traffic for bores under roadways so that traffic can flow without interruption throughout construction; or beneath environmentally sensitive areas where any intervention would leave unacceptable damage).
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