Normal Impact Test of a Spherical Rockfall

Rockfall hazard is becoming increasingly fierce due to the higher intensity of human activities in recent years, but research on the impact process has almost come to a standstill, and there is no available method to solve the impact characteristic parameters of the falling rock. The free-fall drop of a spherical rockfall on three different granular layers was examined, and the acceleration value of the falling rock with time was assessed with a three degree of freedom linear accelerometer. Then, the velocity of the rockfall and penetration depth were successively obtained by computing the integral and double integral of the acceleration over time. The time-history curves of the acceleration and velocity of the rockfall and the curve of the acceleration with the penetration depth show that the time-history curve of the rockfall velocity can be characterized by a logistic function. The acceleration time-history curve has the characteristics of a unimodal pulse, and the acceleration curve with the penetration depth is similar in shape to an inverted “U”. The cushioning effect of the sand is the best and that of the gravel layer is the worst in these three different granular layers.