Mechanics of the breakout phenomenon

Theoretical and numerical analysis of the process of extrication of objects from the water-saturated subsoil, such as the seabed, is presented. The forces needed to lift up such objects from the sea bottom are larger than the submerged weight of those bodies, because of some processes which take place in the subsoil. The theoretical model of these processes is derived from the assumption that the seabed is a porous and deformable two-phase medium, the pores of which are filled with compressible fluid. Then, the model is applied to the analysis of one-dimensional and axi-symmetrical problems. It is shown that during the extrication the, subsoil is unloaded, and consequently the pore water pressure decreases, which results in generation of suction forces at the contact area between the body and subsoil. These suction forces should be overcome in order to lift up the body, and this process has been designated as the breakout phenomenon. The model proposed enables calculation of forces necessary to extricate objects from the seabed, as well as the time necessary to raise such objects under a constant breakout force. In this latter case, the process of pore water changes due to filtration phenomena was taken into account. Experimental results are also presented and discussed. (C) 2003 Elsevier Science Ltd. All rights reserved.