Estimation of sinkage and breakout forces for tracked vehicle for soft soils

Abstract

Deep seabed polymetallic nodule mining machines have to operate in extremely soft ocean floor having soils of shear strength in the order of 1-3 kPa. The extent of sinkage and pullout force or breakout force required to lift the mining machine from the seafloor bottom needs to be evaluated for the successful operation and retrieval of the mining machine. In most of the cases the breakout force exceeds the submerged weight of object. Most of the empirical equations for estimating breakout forces are based on the bearing capacity phenomena. In the present study experimental investigations have been carried for obtaining undrained or immediate breakout forces on flat plates, plates with involute grousers and single track unit of Undercarriage unit. The magnitude of forces so obtained from the experiments has been compared to those calculated from the empirical equations. Studies on the extent of sinkage in soft sediments is critical for quantification of resistances encountered by the mining machine which influences the maneuverability of the mining machine. Experimental investigations have been carried out on flat plates, flat plates with grousers and single track of undercarriage unit as a part of sinkage studies. Sinkage has also been studied by Finite Element Methods using MohrCoulomb material model neglecting angle of internal friction angle as soils were fully cohesive and solving through explicit methods.