Development and testing of smart rock bolt for rock stress monitoring

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Insinööritieteiden korkeakoulu | Master's thesis
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Master's Programme in Geoengineering (GEO)
71 + 24
Rock stress often causes unwanted deformations of deep underground spaces and increases the risk of failures. The excavation procedures create changes in surrounding rock mass which can be analysed by in situ measurements. This thesis presents a new method to monitor the rock mass behaviour using smart rock bolt instrumented with strain sensors tracking and evaluating the stress level within the bolt. The development and assembling of the first smart rock bolt prototype are described in detail. The thesis also describes in-situ testing of this new monitoring prototype in a real underground environment. Two identical smart rock bolt prototypes were tested in the test tunnel of an underground research laboratory. The testing setup used two methods to test these prototypes; pull-out force and heat flux applied to the rock mass via rope heaters inserted into symmetrically located boreholes around the smart rock bolt. The temperature progress during the heating test was numerically modelled in advance. The correct functionality of heating test was verified in-situ using a borehole deformation monitoring tool developed for this purpose. The heat causes volume expansion of the rock material which simulates changes in the rock stress. This stress change creates measurable strain that can be back-calculated and presented as values of rock stress. The strain results from monitoring were analysed, cleaned from noise values and imported to REMOS code using rock stress estimation algorithm and modified for use of smart rock bolt. The algorithm requires strain responses on unit loading based on the impact of rock stress. To calculate strain responses, numerical modelling in 2D was used considering three independent cases of rock stress. The final results demonstrate changes in horizontal, vertical and shear rock stress induced by the testing method according to strain change measured by the smart rock bolt prototype.
Rinne, Mikael
Thesis advisor
Janiszewski, Mateusz
rock stress, strain, instrumented rock bolt, in-situ, monitoring, heat flux
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