A critical shear stress for mud erosion are investigated experimentally.
　In this study, three types of experiments on mud erosion were conducted. The critical shear stress τc for currents was investigated in the series of Exp.1 and τc by waves in the series of Exp.2 and Exp.3. A depth of mud layer for these experiments is 9 cm, 0.5 cm, and 9 cm, respectively. The depth of mud layer in Exp.2 is so thin that mud layer didn't make a wave action odserved in Exp.3. Effects of the mud movement on erosion was investigated. Main results are as follows.
(1)Mud suraface fails with cracks or small mud displacements when mass erosion occurs. Since mud failure is related to the yield stress which represents ciritcal stress for mud movement or mud shear strength, τc agrees well with τy in the series of Exp.1 and Exp.2.
(2)The critical shear stress is defined as the shear stress on the mud surface when the shear stress in the mud surface exceeds τy.
(3)According to the above definition, τc by waves is smaller because shear stress within the mud exceeds τy due to the wave motion.