In the western regions of china where debris flows occur frequently

the traffic routes always need to go through the debris flow channel

so the piers built in the channels of the debris flow are easily suffered the impact of the big block rock in debris flow.Therefore

the designer generally set up the debris flow protection frustum in front of the piers to protect them.The key parameter of the design of the protection pier is the impact pressure of the big block rock in debris flow.At present

all the methods of calculating the impact pressure are relatively rough and their results are inconsistent with the actual situation.In this paper

on the basis of the Thornton′s elastic-plastic contact model and considering the deformation properties of the protection frusta and basing on the conversation of energy

the impact pressure calculating formula of the big block rock in debris flow is derived.The results have shown that by considering the structure′s elastic-plastic properties

the actual impact pressure caused by big block rock reduces greatly and far less than the nominal elasticity impact pressure.This result agrees better than others with the actual situation more.