SPIDER® Rock protection system - Geobrugg AG

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SPIDER ® Rock protection system / Technical documentation / March 2010 Fig. 10: Test to investigate the infl uence of the boundary rope on the supporting behavior and the forces Fig.11: Hemp rope for releasing the block Fig. 12: Measuring the direction and inclination of the force measuring cells using a geologist’s compass and an inclinometer 6 To permit the performance of the tests under the most natural conditions, a more or less cubical test block from the neighboring stone quarry was used, whose roughness corresponded to the rock in the area of the test site. Its weight was 1160 kg. Two lengths of reinforcing bar bent to form loops were cemented in to the top edge of the test block. These enabled the block to be suspended and brought into position using a crane rope (Habegger). The block displacement was measured via a cable pull potentiometer with a maximum measuring length of 1500 mm. Specially developed aluminum force measuring plates were used to measure the forces transferred via the net to the various anchorage points. In this way it was possible to adapt these optimally to the test conditions. With large scale fi eld tests the main problem is to record all relevant infl u- ences but avoid as far as possible unavoidable constraints which are not quan- tifi able using measuring techniques. Therefore on the basis of many years’ test experience, the anchorages, including the geometry of the niche were selected so that these could be defl ected and loaded more or less freely and without constraints. In addition to the electronic recording of the forces, the direction vectors of the force measuring cells were measured before and after the test. This enabled the reaction of the net and the boundary ropes on the anchorages to be determined as realistically as possible. Another test comprised suddenly causing the block to slip. This was achieved using a hemp rope which thanks to the friction through twice encircling the suspension, was able to be released manually. As a basis for the back calculation the anchor points were calibrated with an accuracy of +/- 5 cm. The following fi gure shows the spatial position of the anchorages. A marks the suspension point. Points 13 – 16 represent the positions of the spiral anchors.
FRICTION TESTS Before starting with the actual tests using a rope net, friction tests were carried out as a basis for the subsequent analysis of the forces. The friction angle between the test block and the sliding surface was able to be determined by making a distinction between static and sliding friction. The force necessary to hold the block in place was measured in order to determine the static friction. To measure the sliding friction the block was lowered in a linear fashion by means of a cable crane (Habegger) over a length of approximately 0.20 - 0.25 m and the force was measured dependent upon time and displacement (cf. fi g. 19). The force fl uctuations are due to the lever movement necessary for actuating the Habegger. The dark staircase line describes the displacement of the block over time and the grey line shows the force in the cable over time. The curves up to the start at 17 sec. result from the relieving of load via the chain hoist. The results from the friction tests were as follows: for the static friction, a friction angle of ϕ = 28 – 29° H and for the sliding friction, a friction angle of ϕ = 24 – 25°. G Fig. 13: Central perspective side view showing the spatial position of the anchor Fig. 14: Friction tests Fig. 15: Result of a friction test for measuring the sliding friction. The dark staircase line describes the displacement of the block over time and the grey line shows the force in the cable over time. The curves up to the start at 17 sec. result from the relieving of load via the chain hoist. 7
Page 1 and 2: SPIDER ® Rock protection system Us
Page 3 and 4: Based on material technology innova
Page 5: It was also possible to mount a str
Page 9 and 10: Since a discussion of the test resu
Page 11 and 12: forces from static back calculation
Page 13 and 14: Represented in Table 3 are the forc
Page 15 and 16: KNOWLEDGE GAINED AND CONCLUSIONS FO

SPIDER® Rock protection system - Geobrugg AG

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