1 Introduction

The numerical and physical modeling is the important method of understanding landslide processes. However, when modeling formation and motion of extra-large rockslides and rock avalanches, we face several problems. First, giant size of these features and extreme velocities of their motion intercept their physical modeling with adherence to scaling conditions performed to prove or disprove certain assumptions on mechanism(s) of such rockslides formation and motion. On the other hand lacking of clear and univocal understanding of the nature of such rockslides abnormal mobility complicates selection of motion equation, used for the numerical modeling.

In such situation the " conceptual modeling" when we just qualitatively reproduce any phenomenon or their combination really observed in nature or assumed, based on field observations on the morphology and internal structure of real rockslide deposits, in the lab, seems to be a promising way. It can be exemplified by the successive attempt to model intensive crushing of the rockslide / rock avalanche bodies' internal parts along with retention of the initial mutual position of various lithologies involved in slope failure (Dubovskoi et al. 2008). Such modeling has been performed recently to test some hypotheses proposed to explain formation mechanisms of several large rock avalanches in the Central Asia region.

2 Modeling of the " concealed rock burst"

One of tested hypothesis is that of the " concealed rock burst" that could occur if the slope base composed of the high strength rocks experiences the limit state, i.e. the load exceeds rocks strength. It can lead to formation of the " Prandtl prism" and its instantaneous crush accompanied by effects typical of rock bursts that would supply additional momentum to the collapsing rock mass. It, in turn, increases initial velocity of crushed debris motion and could support its abnormal mobility observed for the numerous case studies. It can be modeled by the uniaxial compression of rock samples in press mould with one side open where forming particles could move after crushing (Fig. 1).

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