HERTZ THEORY BASED STUDY ON PUNCHING CHARACTERISTICS OF ROCKFALL IMPACTING ON SHED-TUNNEL STRUCTURE

Rockfall is a serious geo-hazard in mountainous area. The shed tunnel is one of the main engineering measures to prevent rockfall. It has the great actual meaning to study the dynamic response characteristics of the shed tunnel under the impact of rockfall. Based on Hertz theory,the impact mechanics model of rockfall is established assuming that the rockfall is a rigid spherical body and the shed is a beam. Then the maximum impact force of rockfall impacting on the shed slab with different thickness cushion are derived at different speeds. Moreover the limit punching shear velocity of rockfall is obtained. The results show that the impact force of rockfall on the shed slab decreases with the increase of cushion thickness,while the cushion with finite thickness can only bear a certain limit of impact energy,The larger the rockfall size and impact velocity is,the greater the stress of the shed plate becomes. When the impact energy exceeds the ultimate bearing strength of cushion material,the cushion would no longer dissipate energy,furthermore,the small impact velocity of rockfall could cause the shed tunnel without cushion damaged,and the reasonable cushion thickness is of great significance to prevent rockfall.