The Study Of Dynamic Response And Interaction Mechanism Of Rock Shed Subject To Rockfall Impacting

In recent years,the rockfall hazards has been showing a highly increasing tendency with the frequently earthquakes.The effective measures against rockfall hazards have become crucial to the development of the social and economy in China.Rock fall protection shed is one of the most effective structures to reduce the risk caused by falling rocks,protected roads and railways,mainly if the danger is locally concentrated.However,the researches foundation about rockfall and rock-sheds are relatively weak in China,presently.It is high time to pay enough attention to study rockfall hazards regular and develop the protection measures.In this thesis,dynamic numerical simulation platform was constructed to research the mechanism process of rockfall impacting rock-sheds.Furthermore,one new energy dissipation cushion was proposed.The achievements in this thesis were listed as follow:(1)An elastic-plastic based theoretical method about dynamical responses of rockfall impacting on reinforced concrete(RC)slabs was proposed.A theoretical method of dynamical response of reinforced concrete(RC)slabs was proposed based on the static indentation test and the Olsson's impact governing equations.Compared with traditional method which was based on Hertz contact law that ignoring plastic deformation,the elastic-plastic method presented in this paper was more reasonable and accurate.(2)The energy consumption mechanism of the sand cushion was revealed.In the top of the rock-shed,a certain thickness of sand cushion can play a significant energy dissipation function.The effect of different thickness and d ensity of sand cushion is greatly diverse.Hence,how to determine the thicknes s and density of sand cushion becomes one of the key issues in the shed prot ection design.The test,based on the actual shed tunnel structures as prototype s,used the dynamic finite element numerical simulation to analyze the dynamic response of sand cushions with multi thickness and density under different im pact energy and the mechanism of energy absorption.The results shown that u nder high impact energy,the changes of sand cushion thickness and density were extremely differences on the rock fall impact force,whereas there were simi lar results of energy absorptions with different thickness and density sand cushi ons under enormous impact energy.By field survey and calculation,the optima l effective cushion thickness and density could be obtained to balance both eco nomic rationality and structural reliability.The proposed methods could provide theoretical basis for the rock-shed protection designs.(3)The new rock-shed cushion system combined with geogrid reinforced soil and EPS material was invented.In order to efficiently reduce the impact of rockfall,a novel shed tunnel p rotection combined by geogrid reinforced soil and expanded polystyrene(EPS)geofoam was proposed.Transient dynamic procedures of rockfall impact were c omputationally analyzed by finite element methods to investigate the effects of protection from various factors such as geogrid strength and number of geogrid layers,height of EPS and soil cushions.It was demonstrated that effects of p rotection from geogrid reinforced soil-EPS cushion were extremely efficient,especially for the increases of strength and number of layers of geogrid as wel l as the height of EPS layers.