Soil-rock mixture, as a widely spread kind of natural geological material, is common in disasters of shallow strata, such as landslide and debris flow, and thus has been drawing more and more attention from engineering and geological fields in recent years. The differences between soil and rock block in particle size and strength brings a great variability of micro- and macroscopic mechanical properties, such as internal friction angle. The mechanical parameters of soil-rock mixture exhibit a distinct spatial variability. Besides, the content of rock in soil-rock mixture can make a considerable difference in the mechanical properties. Size effect also has a certain impact in the mechanical properties of soil-rock mixture. Therefore, a reasonable determination of mechanical parameters of soil-rock mixture becomes a big problem in an accurate calculation of geological engineering. To study the impact brought by the aforementioned factors, in this paper, representative element volume (REV) is introduced to describe the minimum size of soil-rock mixture block, of which the mechanical parameters vary little as the block size grows larger, so that the parameters of this certain size can be used for geo-engineering. The random field theory is associated with the finite difference method (RFDM) in order to analyze precisely REV of internal friction angle on soil-rock mixture. Based on Monte-Carlo Simulation method, numerous numerical models of soil-rock mixtures are established. Numerical models vary in model size, content of rock and loading speed. Triaxial compression tests in different pressure conditions are simulated. Triaxial principal stress curves of soil-mixture are studied. Calculated results show a clear relationship between the REVs of friction angle and the above-mentioned factors, respectively, which can be used for further stability analysis and safety assessment of geological engineering, especially slope engineering.

1. Introduction

Due to the complicated geological condition, natural geological disasters are extensively distributed, such as landslide and debris flow. Soil -rock slope is a kind of slope which is prone to landslide. According to statistics (Sun Guomei, et al., 2005), over 80% of landslides happens in soil-rock slope in Qinling-Bashan Mountain, Shaanxi Province, China. In June 2002, 3 large rapid landslides involving rock and soil happens in northern British Columbia, Canada. (Geersema, M et al., 2005). Therefore, the study on the mechanical properties of soil-rock mixture is gradually highly concerned.

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