Bucking Failure Mechanism Of Support Structure In Flexible Rockfall Barriers And Optimization Design Countermeasures

The flexible rockfall barrier system is a kind of structure which realizes the interception and energy dissipation of the hazard-affected body through its own nonlinear large deformation and large slip between components.Because of its remarkable interception effect,it is widely used in the prevention and control of geological hazards occurring on shallow slope such as collapse and rockfall.However,in practical application,the system is often destroyed or failed due to unreasonable structural design and improper component configuration.The catastrophic failure of the flexible rockfall barrier system is a complex nonlinear dynamic coupling process,but considering the coupled calculation theory of flexible protective structures and loads,the research of structural failure behavior is relatively scarce.Accordingly,in this paper,field investigations were carried out on actual cases of the failure of the flexible protective structure.Coupled models of flexible protective structures-rockfall were established,and the inversion analysis was used to study the fragmentation of rockfalls during movement.and the catastrophic destruction behavior of flexible protective net structures.Then,the correlation between support ropes on controlling of slip and deformation and the steel post buckling failure was proved.Finally,the full-scale test was carried out to verified the corresponding design strategies which were put forward on the grounds of the failure mechanism.The main research contents of this paper are described as follows:(1)The research status of rockfall disaster movement and structural failure modes of the flexible rockfall barrier system was analyzed and summarized(Chapter 1).This paper summarizes the research status by three parts: the mechanical behavior of the whole flexible rockfall barrier system and its components,the primary failure modes of structures,and the fragmentation of rockfall during movement.The shortcomings of the existing research were pointed out,and the research contents and technical route of this paper were expounded.(2)Two disaster interception cases of the flexible rockfall barrier system were investigated in the field(Chapter 2).Combining with the investigation means such as observation method and test method,respectively,the site investigation was carried out respectively for two flexible protective structure engineering projects of Jiguanshan Highway in Jiguanshan town of Chongzhou city and K1564 of Jingkun Expressway in Jiange County of Guangyuan City.The two worksite disaster features and the structural features of the flexible rockfall barriers were studied,and then the interception performance and the main failure modes of the barriers were analyzed.(3)Inversion analysis of the rockfall impact evolution and the disaster effect of the flexible protective structure in the investigation site was carried out(Chapter 3).The discrete element model of rockfall and the coupled models of flexible protective structures-rockfall loads were established.Then,the two-dimensional and three-dimensional movements of rockfall disaster were simulated,and the motion characteristics of rockfall considering impact fracture were studied.In this paper,the coupling impact dynamic behaviors of two flexible protective structures are compared,and the failure reason and failure mechanism of the flexible rockfall barrier system at worksite 1 are analyzed emphatically.The results show that due to the improper structural design and the lack of sliding deformation capacity of the support ropes,the buffer mechanism of the system cannot be formed,which leads to the buckling failure of the steel post.(4)Furthermore,26 groups of different numerical models were built for parameter analysis and sensitivity analysis,and the correlation between parameters controlling slip and deformation of the support rope and axial internal force of the steel post was studied(Chapter4).The research results show that the different steel posts are influenced differently by parameters controlling slip and deformation of the support rope.For the side post,the slipping deformation of the support rope is negatively correlated with the post-rope stucking coefficient and the working tension of the energy dissipating device.And for the middle post,the slipping deformation of the support rope shows a positive correlation with the slip length,but is negatively correlated with the post-rope stucking coefficient and the working tension of the energy dissipating device.When the slip performance of the support rope is worse,the axial force mutation of the steel post is more obvious,and the steel post is more prone to buckling.The sliding performance control parameters have different influences on the axial force peak value of steel post,and the parameter with higher sensitivity factor is the main influence parameter,which should be considered and adjusted in the optimization design of system structure.(5)Countermeasures for optimal design of protective net were proposed,and numerical simulation and full-scale impact test were carried out for analysis and verification(Chapter 5).Two improvement schemes were proposed for the structural failure of the flexible rockfall barrier system at worksite 1,and the dynamic behaviors of the system before and after improvement are compared and analyzed.Based on the optimized design strategies,a 750 k J full-scale impact test was carried out to verify the improved system.The results show that the improved flexible rockfall barrier systems have no damage,meet the standard of class A product defined in the specification,and have good impact resistance and energy dissipation performance.