Study on the unsteady excavation of submarine soft rock mass

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The mechanism of excavation experienced in some excavators, for example grab bucket, clamshell bucket etc, is mainly occupied by unstable excavation, in which the excavating depth is varied with the progress of excavation. Therefore the experiments on the unstable excavation were carried out for soft rock mass and the basic properties were clarified with some theoretical or experimental methods. At first the relationship between the forces applied to cutting edge and the displacements were analysed based on experimental results and several factors affecting the relations were investigated. Then the excavated rock volume was evaluated based on the results of the previous consideration. FEM analysis by use of elasto-plastic constitutive equations were also carried out in order to compare with the experimental results and to check the failure pattern of rock ground in the vicinity of the cutting edge. Finally these research results are applied to a real excavator to check the appropriateness of this study. Parameters mainly used in this study are rake angle, excavating distance, vertical penetration force and shear strength of soft rock. The para-meters except the shear strength can be obtained from the size of the excavator. The main targets of this study were therefore (1) to give formula on excavating resistance and the locus of cutting edge on the basis of the input information about the shear strength, (2) to check the appropriateness of the formula by applying them to a real excavator.