THE CONSTITUTIVE RELATION OF DEBRIS FLOW 1
摘要
In order to investigate the stress constitutive relation of debris flow, the experiments of two phase mixtures consisting of neutrally buoyant grains and interstitial liquid medium are performed on a large annular cone plate type shear cell, in which the shear rate is uniformly distributed. Four types of grain (polyethylene, plystyrene and paraffin wax spherical grains, crushed walnut shells) and various liquid (the mixture of water, alcohol or solution of sugar or MgCl 2) are used in the tests. The results showed that the grain stresses occur during shearing not only by collision but also by contact and friction. If the concentration is high, the yield strength of mixture is obvious. According to the result of tensor analyses, a quadratic polynomial of shear rate is adopted as the stress constitutive equation. All coefficients of each term are analyzed by regression using the test data. The ratio of shear stress to normal pressure for each term are different. The ratio of the quadratic terms is smaller than that of constant and linear terms. They are respectively near the values obtained in the inertial and macro viscous regions by Bagnold. In the initial region of flow curves, there is a small special section, which is called “initial section”. It behaved different from other part in the high shear rate region. The initial section is more obvious and the yield strength is stronger as the grain concentration is high and the surface feature of grains is irregular.