HDD design is key when choosing the right rig and tools for each work. Therefore it is crucial to perform topographical surveys as well as geological investigations of the surrounding area in order to get a clear idea on the soil to drill.
Besides, it is normally mandatory to identify the potential utilities installed underground (telephone, water, gas, electricity) by using GPR.
When facing complex projects such as river crossing it is also very helpful to perform an study based on electrical tomography that will determine extension and depth of the geological formations coupled with a bathymetry survey to collect data about the sea/river bed.
Once all these details have been collected it is time to perform a both technical and economic study to know to what extent the project is feasible.
Before beginning any project it is necessary to prepare the jobsite, paying special attention to entry and exit pits, where the pipe will be welded and then pulled into the tunnel.
It consists of drilling a borehole following the layout designed previously, thus connecting entry and exit pit and by means of a special directional bit and flexible rods whose orientation can be changed if required.
Bit orientation is real-time controlled by means of steering systems.
Directional bit is pushed into the ground from the entry pit. As it is connected to the train of rods through which drilling mud is injected, drilling operation keeps going on. To maximise eroding power it is necessary to increase the mud injection capacity. This complements the bits eroding capacity but also removes detritus out of the tunnel up to the entry pit.
In hard soils it is mandatory to drill using mud-motors, which powers the drilling bit when facing high-difficulty soils.
The navigation helps to ensure precisely, and every moment of the day, the location of the top of perforation, his inclination, and other information like temperature and so on.
Normally performed in opposite direction by pulling the reamer into the borehole and once the pilot one has been drilled. Reamer is assembled to the train of rods at the exit pit. This process can entail more than one step, depending on the final diameter pursued.
Once the final diameter has been reached and before installing the pipeline it is usual to clean the tunnel and verify whether there are no sub-diameter points i.e. no obstacles for pipe installation.
Mud is made of bentonite, water and detritus mixed. It is pumped from the exit pit towards a recycling unit that separates fluid from detritus. This fluid can be used more times afterwards whereas dry detritus are thrown away.
Butt welding is a technique used for connecting PE80/PE100 pipes and accessories whose diameters are 63mm or higher. It consists of smoothing ends down, melting them (210±10 ºC) by a heat source and pushing them against each other (DVS-2207- standardised force values).
Once the pipelines are connected inner burrs are also smoothed out before welding more pipes.
HDPE 100 has very beneficial characteristics such as:
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