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Title: The influence of close proximity blasting on the performance of resin bonded bolts.
Author: Mothersille, Devon Kenningtham Vernon.
ISNI:       0000 0001 3427 8260
Awarding Body: University of Bradford
Current Institution: University of Bradford
Date of Award: 1989
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Full scale field trials, carried out during the construction of the Penmaenbach Tunnel in North Wales, have shown that two-speed resin bonded rock bolts are resilient to close proximity blasting. Fully grouted 6m long rock bolts, installed within 0.7m of the tunnel face, have shown no significant signs of distress or failure. Instantaneous loads of up to 40% of the characteristic strength of the bolt were observed together with average residual load losses of 5% of the working load, which compares favourably with the acceptable tolerance of 10% working load stipulated by current practice. Analysis has also shown that rock bolts with low prestress sustain greater vibrations and proportionately higher dynamic load changes during blasting. However, bolts with relatively high prestress loads sustain greater induced loads. Empirical relations have been established to describe rock bolt behaviour in terms of induced vibration and scaled distance. In particular, a predictive equation relating dynamic load changes in the experimental rock bolts to scaled distance, is presented. Calculations based on approximate bolting costs have indicated that cost savings of up to 38% of the total bolting cost could have been effected if the results of this work had been implemented at the design stage. Physical modelling work has confirmed that the distribution of loads in the fixed anchor of a resin bonded bolt are non-linear when both static and impulsive loads are applied to the bolt head. Corroboration of the field results has also been established with respect to the significant influence of initial prestress load on dynamic load change. Complementary finite element modelling work has successfully predicted fixed anchor load distributions under static and dynamic loading conditions. Attempts to establish a detailed relation between distance from blast, magnitude of charge and change in residual load, for low to medium capacity rock anchorages on the West Portal of the tunnel, were thwarted by the poor performance of instrumentation with respect to temperature sensitivity. However, a simplistic approach to analysis has enabled the establishment of a tentative predictive relationship.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Rock bolt behaviour