The provision of a safe and economic rock support system is of primary importance for any excavation programme. If the excavation is to be developed by explosives, then the effect of blast forces on the performance of the rock support system must be considered. A review of current literature has highlighted a general lack of information regarding rock anchorage performance under blast loading. With this in mind, a full scale field test programme was undertaken to study the effect of close proximity blasting on resin bonded rock bolts, during the construction of the Pen y Clip Tunnel in North Wales together with a re-analysis of data from a previous study at the nearby Penmaenbach Tunnel. In both cases, accelerometers were used to monitor vibration and hydraulic load cells recorded the changes in rock bolt load during production face blasting. For the Pen y Clip trials, an additional monitoring system was developed which incorporated load cells positioned along the length of specially made experimental rock bolts. Further trials were conducted at an Edinburgh City Centre site to assess the likelihood of damage to temporary, cement grouted rock anchorages whose fixed anchors were positioned as close as 5m from nearby tunnel blasting. These trials involved the measurement of vibrations, both on the anchor head and down specially constructed boreholes, together with lift off load testing. Analysis consisted of the time and frequency domain examination of the signals, recorded on FM magnetic tape, from the three sets of field trials. Resin bonded rock bolts installed in microdiorite and rhyolite were found to be highly resilient to blasting, even those positioned down to lm from full face tunnel blasting. Temporary anchorages in mudstone were more susceptible to blasting but damage could be limited by monitoring of vibrations and careful control of blast parameters. The frequency response of the anchor head was found to be dependent on the characteristics of the anchorage and the nature of the environment in which it was installed. This raises the possibility that the analysis of spectral responses could form the basis of a technique for the non destructive testing of rock anchorages.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:635953 |
| Date | January 1993 |
| Creators | Holland, David Charles |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU603184 |
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