Rockfall hazard zoning is not simple to achieve in practice. It involves the different factors: rock block shape and size, characteristics of the topography, and the occurrence of rockfall which depends mainly on some climatic and biological changes that cause a change in the forces acting a rock block. Rockfall hazard maps are often replaced with figures which show the frequency and the corresponding intensity of a predefined rock magnitude. Some attempts are introducing the results of the threedimensional numerical modeling to get the objective zoning based on the mechanical parameters (e.g. kinetic energy). In such attempts, it is important to recognize that the mechanical parameters may be affected by modeling of the physical factors mentioned above. The most important role of the three-dimensional simulation is to display the lateral dispersion of trajectories. In this paper, the influence of controlling factors on the dispersion has been evaluated by conducting 3D simulation. Parametric simulations have been performed at different spatial resolutions using sets of synthetic biplanar slopes characterized by mean inclination and local asperities. The results of the lateral dispersion of trajectories are explained with the width of computed trajectories and the fixed distance along the slope surface from the block launch position.
1. INTRODUCTION
1.1. Rockfall simulations
Rockfall are significant hazards along natural and engineered slope in mountainous region. In spite of usually very limited volumes, rockfall is characterized by high velocity and dispersion. Often this is a cause of the fatal damages to lives and structures. Stability of rock block mainly depends upon physical properties such as block geometry, joint roughness and joint infilling, and slope inclination. When destabilizing factors, e.g. piezometric pressure, temperature variations and external forces acting on a rock block (e.g. earthquake), exceed the stability of the rock block, the rock block will start falling. However, the occurrence of the factors may not be predictable. Rockfall hazard has been usually defined as the probability of occurrence of rockfall of pre-defined magnitude within a given area. This definition can be incorporated in risk based approaches, where risk is a function of frequency and consequences of rockfall occurrences [1]. Rockfall hazard zoning for safety and land using in mountain area requires all distribution of trajectories, the maximum reach and all associated parameters, such as translational and rotational velocity, flight height along a fall path and the probability for a certain location to be reached by a block [2]. Many numerical methods have been developed to compute the sets of all possible trajectories [3, 4]. The reliability of rockfall models depends on their ability to account for the slope geometry, the mechanical modeling for the threedimensional dynamics of block and the energy disipation at impact. The task to model these characteristics is very difficult because of the uncertainty and spatial distribution of these factors [5]. Furthermore, the energy loss at impact is a complex function of block and ground characteristics (block shape and surface material) and is often defined as an empirical function and values.
