Investigation of buried flexible culvert subjected to rockfall
Investigation of buried flexible culvert subjected to rockfall loading - A brief summary of instrumentation and data aquisition from full-scale tests of rock fall impact on a buried flexible culvert Roger Ebeltoft Departement of geotechnical engineering Norwegian University of Science and Technology 1 * Greatfully acknowledging the Norwegian Road Authorities for financial support for the rockfall tests on the buried flexible culvert
Overview Introduction Rockfall & mitigation measures Overview • Introduction • Rockfall and mitigation measures • Proposed rock fall protection system • Instrumentation of buried corrugated culvert • Conclusion 2 Instrumentation Conclusion End
Overview Introduction Rockfall & mitigation measures Instrumentation Introduction • Rockfall is classified as a natural hazard. It is important to protect infrastructure exposed to rockfall • Increase of traffic density in rockfall prone areas makes protection structures necessary • Rockfall events are rare, site specific and object related • Difficult to describe loads for those hazards in codified format (No codes exist in Norway) • Appropriate solution for rockfall protection must be decided in each case 3 Conclusion End
Overview Introduction Rockfall & mitigation measures Instrumentation Introduction • Protection system consisting of corrugated steel culvert covered with a cushion layer for tunnel portals is proposed • A full-scale test have been performed to investigate the application of buried flexible structures subjected to rock fall loading • Diagrams and graphs presented in the instrumentation section are preliminary results of this full-scale study 4 Conclusion End
Overview Introduction Rockfall & mitigation measures Fundamentals of rockfall • Rocks usually consist of joints. Normally these joints are intact, however due to insufficient strength, water pressure in joints and in cold regions freezing/thawing can cause detachement of rock mass • Detachment of rock block(s). Falling process determines the kinetic energy of the block • The main parameters describing the falling process are • Profile of the slope • Coefficient of restitution • Geology • Morphology 5 • Vegetation • Structure of the contact surface Instrumentation Conclusion End
Overview Introduction Rockfall & mitigation measures Instrumentation Rockfall simulation • The falling process can be simulated by in rock fall programs Conclusion End [m] Detachment zone Trajectories • These are based on Monte Carlo simulations • Parameter studies can be performed using these programs Slope Profile Protection structure [m] • Simulations can be performed for the possible range of rock volume • These stochastically random simulations give a statistical distributed outcome of kinetic energies 6 • A rockfall protection system could then be designed using the maximum outcome
Overview Introduction Rockfall & mitigation measures Rockfall and mitigation measures • Typical mitigation measures • Active measures • Scaling • Netting • Shotcrete sealing • Other types of cover for exposed rock surfaces • Passive measures • Berms • Ditches • Barriers • Fences • Galleries 7 Instrumentation Conclusion End
Overview Introduction Rockfall & mitigation measures Instrumentation Rockfall and mitigation measures 8 (From Yoshida 1998) Conclusion End
Overview Introduction Rockfall & mitigation measures Instrumentation Test site and outline • Field test site was Narvik Rombakken pukkverk located outside Narvik Lillehammer Accelerometer • Outline of field-test procedure 200 < M < 2650 kg 5 < H < 20 m High speed camera Gravel layer H = 1. 5 m 9 Flexible culvert+ strain gauges+ accelerometers laser Conclusion End
Overview Introduction Rockfall & mitigation measures Instrumentation V-link® Datalogger Mounted in steel casing • Accelerometers • Strain gages • deformation measurements Laptop for program display • High speed camera and data aquisition Infrared laser device Strain gage 10 Tri-axial Accelerometer Conclusion End USB base station
Overview Introduction Rockfall & mitigation measures Selected results (1) • Measured penetration depths from tests • Deceleration history results • Accelerations measured • Filtered to remove high frequency noise • Typical history for low-energy impacts • Velocity and penetration found by integration 11 Instrumentation Conclusion End
Overview Introduction Rockfall & mitigation measures Selected results (2) • Measured transmitted accelerations in culvert • Centre profile • 3 locations, ACC 2 located at the crown • Measured bending strains • Centre profile • 7 locations, SG 4 located at the crown 12 Instrumentation Conclusion End
Overview Introduction Rockfall & mitigation measures Instrumentation Conclusions • Vertical rockfall tests have been conducted on corrugated culvert with a cushion layer • Large amount of data have been collected (only few presented herein) • Evaluation of these data are currently in the process • Comparison with semi-empirical methods • Comparison with 3 -D finite element method 13 Conclusion End
Overview Introduction Rockfall & mitigation measures Instrumentation Thank you for your attention 14 Conclusion End
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