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Rockfall in St. Leonard (VS)

A rockfall test site in the MTA quarry in St. Leonard, Canton Valais in Switzerland, has been used from 2009 to 2012 during the project CTI-Attenuators to examine the processes during rockfall and to study the behavior of a new flexible rockfall protection system.

Steinschlag in St. Leonhard    
KTI-Attenuator Block T3  

The unique load case closer models the occurrence of rock falls

The specially designed test site consisted of a 20 m high acceleration ramp with automated rock release mechanism. It enabled vertical potential energy to be guided to horizontal impact with a test barrier, while additionally rotating the test block. The unique load case generated at this test site closer models the occurrence of rock falls. The apparatus are installed at the top of a 50 m long and 50° rock slope and enable the release of both natural rock boulders and artificial test bodies.

The flexible protection systems under testing are known as rockfall attenuators or hybrid barriers. Their design is a combination of standard drape nets and flexible rockfall barriers. In this case, an impact zone constructed of a high tensile spiral rope net intercepts upslope rockfall. Rock blocks are then guided through a tail drape section and contained to the base of slope. They utilize boulder impacts with the net and its interaction with the slope to attenuate the velocity and trajectory of rockfall.

High speed video cameras are installed along the test slope

High speed video cameras recording up to 250 fps were installed along the test slope, they captured in detail the test boulder path from its release to its final resting point. The video data enables a back analysis of the trajectory and velocity of the rock boulder and a calculation of its kinetic energy. The use of natural rock boulders during testing allows the influence of different rock boulder form to be analysed. An important application of the data generated during the experiments is a calibration of rockfall simulation programs.  

Significant for the study of the Hybrid barrier systems were the initial impact energy and the exit velocity. Through this an energy balance could be calculated and the working attenuation affect of the test barriers be evaluated. In addition to this, load cells sampling at a rate of 2'000 Hz are used to the measure acting cable forces in the test barriers. Goals of the barrier testing were to identify their attenuating capacity and optimize their design, developing criteria for their design and installation.