1 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 * Greatfully acknowledging the Norwegian Road Authorities for financial support for the rockfall tests on the buried flexible culvert

2 Overview Introduction Rockfall and mitigation measures Proposed rock fall protection system Instrumentation of buried corrugated culvert Conclusion Overview Introduction Rockfall & mitigation measures Instrumentation Conclusion End

3 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 Overview Introduction Rockfall & mitigation measures Instrumentation Conclusion End

4 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 Overview Introduction Rockfall & mitigation measures Instrumentation Conclusion End

5 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 Vegetation Structure of the contact surface Overview Introduction Rockfall & mitigation measures Instrumentation Conclusion End

6 Rockfall simulation The falling process can be simulated by in rock fall programs These are based on Monte Carlo simulations Parameter studies can be performed using these programs Simulations can be performed for the possible range of rock volume These stochastically random simulations give a statistical distributed outcome of kinetic energies A rockfall protection system could then be designed using the maximum outcome [m] Detachment zone Trajectories Slope Profile Protection structure

7 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 Overview Introduction Rockfall & mitigation measures Instrumentation Conclusion End

8 Rockfall and mitigation measures (From Yoshida 1998) Overview Introduction Rockfall & mitigation measures Instrumentation Conclusion End

9 5 < H < 20 m 200 < M < 2650 kg Flexible culvert+ strain gauges+ accelerometers Gravel layer H = 1.5 m laser Accelerometer High speed camera Lillehammer Narvik Test site and outline Field test site was Rombakken pukkverk located outside Narvik Outline of field-test procedure Overview Introduction Rockfall & mitigation measures Instrumentation Conclusion End

10 Instrumentation Accelerometers Strain gages deformation measurements High speed camera Overview Introduction Rockfall & mitigation measures Instrumentation Conclusion End Tri-axial Accelerometer V-link® Datalogger Mounted in steel casing USB base station Laptop for program display and data aquisition Strain gage Infrared laser device

11 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 Overview Introduction Rockfall & mitigation measures Instrumentation Conclusion End

12 Selected results (2) Measured transmitted accelerations in culvert Centre profile 3 locations, ACC2 located at the crown Measured bending strains Centre profile 7 locations, SG4 located at the crown Overview Introduction Rockfall & mitigation measures Instrumentation Conclusion End

13 Overview Introduction Rockfall & mitigation measures Instrumentation Conclusion End 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

14 Thank you for your attention Overview Introduction Rockfall & mitigation measures Instrumentation Conclusion End