Deep Sea Mining With an Archimedes Screw Driven Vehicle

Archimedes screw propulsion is a proven technology for land based vehicles. Especially in rough, impassable terrain they have shown reliable operation, superior traction capabilities and they can be used as a buoyancy body. Typical working territories for Archimedes driven are dredge deposit sites and swamps. The use of Archimedes screws will also prove their value in the deep sea mining application, but it will pose special demands and requirements on the propulsion system design such as: the propulsion system must be able to operate completely submerged and remotely operated. It must also include operational aspects like moving, manoeuvring, traction, friction and to cope with the aggressive environment. It can be said that the propulsion system is an important driver for the design of the SMT. It is an important factor in the SMT total weight and it influences the handling during launch and recovery, the excavation process controllability and the mining planning. This article presents the mathematical model of the Archimedes screw propulsion as developed by IHC Merwede. The model combines the soil mechanics theory and principles and screw geometry as input parameters. The outputs of the model are bearing capacity of the seabed, buoyancy forces, friction forces, maximum realizable traction and power requirement. In order to validate the model, an experimental test setup was built in the soil laboratory at IHC Merwede in Kinderdijk, the Netherlands. Different soil types were used and various experiments were performed to measure the bearing capacity and sinkage, friction forces, traction and forces directed sideways. Valuable lessons have been learned regarding slippage, motion behaviour, adhesion, and bulldozer effects at the front side of the screws.