Effects of Coarse Particle Size on Critical Bed Slope to the Beginning of Movement in Water-soil Mixes

Western Andes in Peru are characterized by semi-arid climate and an arid coastal strip in its lower land, with a large number of ephemeral currents that only transport flows in the wet season. Many of these streams are composed of alluvial or fluvio-glacial material that, in the presence of precipitations, are dragged forming mudflows or debris flows that are usually called "huaycos". The economic losses caused by the fall of huaycos and floods surpass 70 million dollars by year, making necessary a management plan and mitigation against the occurrence of these phenomena.

The present article analyzes the effect of coarse particles on the conditions to beginning of movement of biphasic flows. For this purpose, it used a rectangular channel of variable slope, 4m long and 0.40x0.40m cross section, built specifically for this purpose. The design of the experiment proposes to define a reference silty-clayey soil matrix, add a certain volume of water and experimentally define its creep slope. In a second stage, for the defined concentration, different volumes of fine sand will be added gradually and in each case the slope will be evaluated again until reaching the creep, so that for each concentration of solids a relation between the average diameter and the pending creep. The reiteration of the experiment will allow to obtain a family of curves to develop a multivariable relationship between the average diameter (D50), the concentration of solids (Cwi) and the yield slope (Sc).

This article is a first attempt to better understand the huayco phenomenon and to try to define the conditions for the initiation of movement for prevention purposes, and its subsequent application in disaster management.