Numerical Simulation Of Passive Protection For Rock Fall

Unstable rockfall, which is one of the geological hazards that occurs frequently on railways of mountain area, often greatly threatens the railway operation. The flexible passive protecting technology is an effective protecting measure against the danger of unstable rockfall. With its strong protecting capability, low cost and good adaptability to the site, it is widely used in the engineering practice. With the scientific research project of automatic monitoring and warning for the typical geological hazards in railway from Chengdu to Lanzhou, the studies on passive protecting technologies for unstable rockfall were carried out, in order to provide the technical supports for the applications of fiber bragg grating in automatic monitoring and warning technology about unstable rockfall. It is of great significance in ensuring the safety of railway operation.Based on comprehensive investigation and analysis, the mechanism of interactions between unstable rockfall and passive protecting net, the dynamic responses and the failure models were emphatically researched from the perspective of structure and mechanics. What’s more, threshold values of real-time and automatic monitoring and warning system of fiber bragg grating for unstable rockfall were briefly discussed. The main contents of this dissertation are as follows:(1) Comprehensively investigated and analyzed the current research status of geological hazards monitoring at home and abroad, especially the unstable rockfall and introduced the applications of passive protection and fiber bragg grating in civil monitoring in detail.(2) The failure models of passive nets were summarized; including rupture of wire rope nets, rock fall collide and cross the top of protective nets, instability of posts, failure of break ring and structures totally overturn,.(3) The software ANSYS/LS-DYNA and the explicit theory were briefly introduced. Then, the process to build the finite element model for flexible passive nets was emphatically illustrated, which consists of specifications and system structures of passive nets, selections of elements and material models, mesh generations, restrictions and load conditions, contact definitions and contact algorithms, calculation control technologies.(4) With the prototype of RX-050passive nets, which are popularly used in the market, the dissertation attempts to build three-dimensional finite element simulative model with the software ANSYS/LS-DYNA. Four levels of kinetic energy and three models of collision were taken into account. Evaluation indexes that consist of components’energy, axial forces of wire rope, deformation of passive nets, velocity and acceleration of rock fall, force and displacement of post were analyzed synthetically. The research suggests:the axial force in side anchor rope and support rope and the displacement of post in X direction are sensitive, which are suitable to be early warning factors.