Abstract: The literature reveals little about the prediction of the closing process of clamshell dredging buckets when cutting sand or clay under water. The results of research carried out, mostly relates to the use of clamshells in dry bulk materials. While good prediction of the forces (in dry materials) involved are possible by measuring the closing curve, the very prediction of the closing curve of clamshells in general, seems to be problematic. Because the dredging business is concerned with water saturated sand or clay has to be dredged, the research into the closing process of clamshell grabs had to start from scratch (except for the kinematics of clamshells). In 1989 the research carried out by Great Lakes Dredge & Dock Company resulted in a numerical method of calculating

the closing process of clamshell grabs in water saturated sand and clay, which simulates the closing of a clamshell so that production and forces can be predicted. The calculation method is based on the non-linear equations of motion of the buckets and the sand cutting theory Miedema. A clay cutting theory is implemented in the numerical model but will not be taken into consideration in this paper. In 1991, Great Lakes and the Delft University of Technology carried out laboratory research in which a scale model clamshell was used. This research, carried out in dry and in water saturated sand, resulted in a verification and validation of the calculation method with respect to the closing curve, the angular velocity and the pulling force in the closing wire. This paper contains results of the lecture notes of Vlasblom [22], a literature survey, the equations of motion of a clamshell grab, background to the sand cutting theory, results of the computer program CLAMSHELL, and it

will give some of the results of the research carried out with respect to verification and validation of the computer program, whilst a short preview into future research is given.