Research On Laws Of Incipient Sand Movements On Bed With Low Moisture Content And On Declining Bed

Many researches have been done in the forming mechanism of incipient sand movements in the past decades and no agreement has been reached on their causes. Current studies mostly focus on some factors leading to sand movements such as the density and size of the sands. This thesis will explore two other influencing factors—the moisture content of sand bed and the gradient of sand hill, aiming to contribute to the prevention of sand movement and the wind-sand flow theory.Adopting Bagnold's threshold wind velocity model, this thesis has got a functional relation between threshold friction velocity and moisture content, and induced an equation with the empirical coefficient C. This equation indicates that threshold friction velocity increases with the rise of moisture content. The increase is obvious when the moisture content is less than 0.5%, and not obvious when the moisture content is more than 0.5%. In addition, threshold friction velocity does not always increase with the rise of the sand diameter and there is an extremum of the sand diameter. The velocity decreases with the increase of the sand diameter when the diameter is less than the extremum and increases with the increase of the sand diameter when it is more than the extremum.This thesis studies the conditions of incipient non-uniform sand movement on slopes with exposure degree, equivalent grain size and flow resistance, taking the mutual hiding-exposing action between sands into consideration. An equation has been induced about the incipient non-uniform sand movement on slopes, which is then turned into one on plat lands. Threshold wind velocities in the previous studies have been applied to test the coefficient of the equation. The correlational coefficient between threshold wind velocity and the empirical data is 0.823, indicating that it is reasonable to reflect the effect of non-uniformity on incipient sand movement with exposure degree, equivalent grain size and flow resistance taken into account.