GRUNDODRILL 18 ACS – the perfect solution for a demanding bore task

However, the pipe route path partially ran along a tight footpath, parallel to the river Saalach. Along part of the route, the installation work had to be interrupted at an extremely tight passage adjacent to steep rock walls bordering the footpath.

The government safety organisation blocked the use of open cut installation at this section, which covered an approximate length of 250 m, due to the danger of falling rocks. It recommended the application of an HDD installation method for this section. Due to the rocky nature of the ground, hard dolomite rock of UCS 220 N/mm2, it was decided to utilise a Tracto-Technik GRUNDODRILL 18ACS HDD machine. The machine is designed use in alternating and difficult geological conditions and was therefore deemed ideal for this bore. The width of this GRUNDODRILL rig, being only 2.3 m, proved to be a great advantage with the tight footpath being between 2.5 and 3 m only. Due to these tight conditions the support truck had to be set up behind the drilling rig, causing some disturbance to the individual working steps, which could not be co-ordinated as efficiently as wouldhave been liked. Other than this there were no other difficulties on the bore, as the path was closed to public use being Wintertime, due to the risk of falling rocks. For the drilling crew, this meant that safe working needed special attention, as the ground in the vicinity thawed during the day, causing minor stone falls.

An advantage of the GRUNDODRILL 18ACS rig compared to other drilling rigs was the relatively low drilling fluid consumption. In addition, the water required to complete the bore was pumped out of the adjacent River Saalach. This meant the drilling fluid was always ready for use, without the usual time consuming interruptions for preparation, re-filling, transportation etc. Also, the used fluid quantity, which had to be pumped out and disposed of, was lower than usual. The bore path, which had to remain within the footpath width, ran through fill soils which included rock. Several bends in the footpath had to be negotiated. Therefore, before starting to bore, Bore Planner Software from Tracto-Technik was used to precisely calculate the optimum bending radius for each curve.

After carrying out the pilot bore, which was underatken using a 1.8 m long Rockbreaker bit of 6.75 in (170 mm) diameter, the most difficult part of the project had been completed. The boring operation demanded a lot of patience and intuition from the bore crew, Uwe Zimmermann and Hubertus Goeddecke. After each drill rod length a critical evaluation of the bore progress as well as simultaneously extrapolating the course of the next rod length was necessary, taking the data indicated on the touch-screen-display into consideration.

After upsizing the pilot bore to the required diameter using a 10 in (250 mm) diameter hole opener, the bore hole was prepared for the pipe installation using a so-called Cleaning-Run. This was completed to ensure that the new sewage pressure pipe could be pulled in over just one day using a 230 mm diameter Barrel Backreamer.

After the successful completion of this operation, which was demanding in many ways and taking into consideration the poor weather conditions on site, the project team responsible for the works were very satisfied.

The application of HDD in this sensitive area had to be carried out carefully, due to landscape protection regulations, however, the 2 to 7 m deep, 236 m long bore in rock and in difficult to access terrain, was completed perfectly.

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