Pendulum drilling Pendulum drilling for monitoring the Emosson dam

Transcription

1 2015 Pendulum drilling Pendulum drilling for monitoring the Emosson dam Diamantbohr Gruppe Bolimattstrasse 7, 5033 Buchs Verfasser: B.Steiner/Ph.Wingeier Photograph: Satellite image of Lac d`emosson Source: Internet

2 Abstract The Diamantbohr Group was instructed by ARGE Emosson to undertake two pendulum drilling projects for the dam monitoring system. The bore holes were required to have a depth of 28 metres and to be drilled with a diameter of 160 millimetres. The specified tolerance was a maximum deviation of 2 cm in the X and Y axes. At a bore depth of 28 metres, this is equivalent to a deviation of less than one millimetre per metre of the bore hole. Subsequently, a chrome steel pipe was cast into the bore hole. This would later be used to hold the measuring device. Diamantbohr Group Pendulum drilling at Lac d Emosson Page 1

3 Contents 1 Site information Location Main tasks Cutting out the drilling bays Pendulum drilling Pipe installation Measurements/Checks Measurements Conclusions Precision drilling (pendulum drilling) Measuring the drilling trajectory Locating and inserting the chrome steel pipe Diamantbohr Group Pendulum drilling at Lac d Emosson Page 2

4 1 Site information 1.1 Location This lake is surrounded by the Alpine peaks of Le Cheval Blanc, Pic de Tenneverge, Mt. Ruan and Tour Sallière, and is dammed by means of an arch dam at an elevation of 1930 metres above sea level. In order that half the dam did not lie in France and half in Switzerland, the national border was relocated to the west of the dam in exchange for a piece of land on the other side of the valley. Fig. 1: Vieux Emosson dam Fig. 2: Impression of Lac d Emosson Lac d Emosson Reservoir in Switzerland Lac d Emosson is a reservoir in the western region of the Canton of Valais in Switzerland. It lies within the municipalities of Salvan and Finhaut. Surface area: 3.27 km² Elevation above sea level: 1,930m Catchment area: km² Diamantbohr Group Pendulum drilling at Lac d Emosson Page 3

5 2 Main tasks 2.1 Cutting out the drilling bays In order to make it possible for the two pendulum drillings to be carried out at the intended location, a bay needed to be prepared for each within the existing tunnel. Hydraulic drilling and cutting units were used to drill and carve the bays into the solid concrete wall. The wall of the tunnel was widened using the peeling system, i.e. the equipment described above was used to cut the wall back piece by piece, eventually leaving a bay measuring approx. 2.50x2.50x1.50 metres in which to install the drilling system. Fig. 3: 1) Existing tunnel 2) Section of drilling bay 3) Planned 28 metre bore hole Diamantbohr Group Pendulum drilling at Lac d Emosson Page 4

6 2.2 Pendulum drilling A special drilling rig was constructed by our in house workshop so that a bore hole with a tolerance of one millimetre could be provided within the narrow bay. The rig was constructed in such a way that it could be set up as simply as possible. This equipment could not incorporate any deviation if it was going to meet the requirements with regard to precision. Fig. 4 and 5: Installation of hydraulic drilling system (rig) Diamantbohr Group Pendulum drilling at Lac d Emosson Page 5

7 Once the drilling equipment had been installed, work on drilling the bore itself began at the position determined by the surveyor. In all, one bore hole with a 160 millimetre diameter and a drilling depth of 28 metres had to be prepared in each of two drilling locations, positioned about 50 metres apart. Fig. 6: Installing the drilling pipe The continuous drilling system was used to push the drilling task onward metre by metre, until the required level of 28 metres had been achieved. The accuracy of the drilling operation also needed to be checked repeatedly throughout the drilling operation. The removal of the drill cores turned out to be particularly labour intensive, and was also technically difficult to achieve beyond a certain depth. Diamantbohr Group Pendulum drilling at Lac d Emosson Page 6

8 Diamantbohr checked and logged the position of the X/Y drilling axis after each metre. This allowed corrections to be made to the drilling direction during the initial phase. A reverse pendulum was used as a counter control. The bore holes were measured using a tried and tested traditional method. Two buckets were connected to each other and filled with water. In each bucket was a floating ring holding a metal rod with the measuring pendulum. The measuring pendulum had exactly the same dimensions as the internal diameter of the thrust shaft, as well as the appropriate weight. Fig. 7: Simple construction of a reverse pendulum Diamantbohr Group Pendulum drilling at Lac d Emosson Page 7

9 Once the pendulum had engaged at the required depth, any deviations could be measured at the entrance to the drilling pipe. After the 28 metre drilling depth had been reached, the surveyor then repeated the electronic measuring process. It became apparent that the traditional system using the reverse pendulum delivered the same result as a modern measuring device. Fig. 8: Measuring the drilling axis by the string on the reverse pendulum Once the measurements had been taken, the drilling pipe could be withdrawn from the bore hole. Diamantbohr Group Pendulum drilling at Lac d Emosson Page 8

10 2.3 Pipe installation Screw connection chrome steel pipes were manufactured for the pipe installation work that also formed part of this contract. Fig. 9: Schematic illustration of the chrome steel pipe lining This was sealed as it was screwed together and sunk into the bore hole with a locating ram also designed by the company. Diamantbohr Group Pendulum drilling at Lac d Emosson Page 9

11 Fig. 10: Aid to locate (freely hanging) the chrome steel pipe before insertion. After the pipe had been installed, its position was once again re measured to a one millimetre tolerance. Where any deviations from the requirement were detected, the special headstock was used to re orient the pipe. Diamantbohr Group Pendulum drilling at Lac d Emosson Page 10

12 Grout was then poured into the hollow space between the bore hole and the chrome steel pipe. Injection hoses with a discharge outlet were inserted at an interval of three metres in order to guarantee that the grouting extended to the bottom. Once the grouting material had hardened, the surveyor carried out a final measurement. The completed work was then handed over to the Customer. Diamantbohr Group Pendulum drilling at Lac d Emosson Page 11

13 3 Measurements/Checks 3.1 Measurements The final measurements undertaken by the surveyor were handed over to the Customer with a log of the work. The deviations were lower than the tolerance, indicating that an accurate pendulum bore hole could be handed over to the Client. Fig. 11 and 12: Electronic measurement log to a depth of 28 metres Diamantbohr Group Pendulum drilling at Lac d Emosson Page 12

14 4 Conclusions The Diamantbohr Group developed and applied three innovative and extremely accurate solutions for the execution of this contract, located at an elevation of almost 2,000 metres above sea level. These provide the best possible advertisement for the business itself, and for the drilling and cutting sector as a whole. 4.1 Precision drilling (pendulum drilling) Highly qualified employees and motivated senior executives worked to realise two 28 metre deep core drillings with a diameter of 160mm, with a deviation of just 15mm. This is an absolutely first class achievement with regard to both drilling technology and precision. 4.2 Measuring the drilling trajectory Diamantbohr controlled and logged its own drilling operation using the cost effective reverse pendulum system. The staff therefore knew the position of the drilling axis at all times, and could check whether any directional corrections were required. 4.3 Locating and inserting the chrome steel pipe A locating structure designed and built in house was used to insert and install the freely hanging chrome steel pipe precisely vertically into the bore hole. Diamantbohr Group Pendulum drilling at Lac d Emosson Page 13