Study On An Impact-resilient Steel Buffer Layer For The Rockfall Protection Rock-shed

Rockfall is a kind of common slope geological disaster,which has the characteristics of mix-reasoning,randomness and susceptibility.The rockfall protection measures mainly include active protection and passive protection.Rock-shed is a kind of typical passive rockfall protection structure,which consists of main structure and buffer layer(or buffer structure).Rock-sheds are widely used in rockfall protection projects of mountain-side roads and tunnel entrances in recent years because they are directly built on the top of protection objects and can effectively isolate debris.However,there are many problems in the rock-shed projects such as rockfalls accumulation,components damage,rock-sheds being impact-damaged by rockfalls,etc.The main reasons are the poor buffering performance and resilience of buffer layers,the unclear responsibilities of the components and the lack of effective structural buffer deformation control methods.To solve the problems of rock-sheds,this paper takes the buffer layer of rock-shed as a research object,and an impact-resilient steel buffer layer for the rockfall protection rock-shed were proposed.Combined with impact test and numerical simulation,the system composition,test method,calculation theory and buffering performance of the new buffer layer were studied.The main research contents and results are as follows:(1)The performance requirements of the buffer layers were analyzed from three aspects: buffering performance,resilience and applicability.Based on this,an impact-resilient steel buffer layer for the rockfall protection rock-shed were designed.Consisting of intercepting parts,buffering parts and supporting parts,and all parts are connected by sliding boundary.(2)The substructure test model of the impact-resilient steel buffer layer for the rockfall protection rock-shed was designed.The test equipment and test scheme were determined.Then two impact tests with kinetic energy of 25 kJ and 50 kJ were carried out respectively,and the test results and impact process of impact tests were described and analyzed.(3)The mechanical behaviors and simulation methods of the ring nets,spring rods and wire ropes in the buffer layer were analyzed.The sliding contact relationship between the ring nets,the shackles and the support ropes were determined.The dynamic model of the impact-resilient steel buffer layer for the rockfall protection rock-shed was integrated and established,and then the numerical simulation of the substructure model was carried out by LS-DYNA software.(4)The buffering and energy dissipating characteristics of the buffer layer substructure model were analyzed.The substructure can successfully intercept blocks with impact kinetic energy of 25 kJ and 50 kJ.The buffering process is characterized by three stages,i.e.relaxation deformation,tension deformation and deformation resilience.During two impact processes,the components all show good buffering and resilience performance.The elastic deformation of the ring nets occupies a large proportion in its total deformation,and its residual deformation mainly originates from the loose gap of the cable-net system.The spring rods can significantly reduce the peak of internal force of the support members.The energy storage of the substructure mainly depends on the springs,while the energy dissipation is mainly due to the structural damping.(5)The impact-resilient steel buffer layer can significantly reduce the impact force of rockfalls.When the impact kinetic energy is 25 kJ and 50 kJ respectively,the impact force of blocks can be reduced about 30% by substructure compared with the steel tube supported model.Compared with the sand cushion layer,the substructure can reduce the impact force of blocks by about 73.7% and 71.5%,respectively.Compared with the EPS cushion layer,the substructure can reduce the impact force of blocks by about 67.0% and 64.3%,respectively.the maximum impact force and the maximum impact displacement of the substructure can be approximately calculated by the formulas established by the parameter analysis of spring stiffness and impact kinetic energy.