Testing of soft clays using bevameter for deep-sea mining machine

Abstract

India has been developing technology for deep-sea mining in the Central Indian Ocean Basin from 6000m water depth. The Central Indian Ocean Basin (CIOB) is abundant in nodules which are rich sources of minerals like manganese, copper, cobalt, and nickel. The intended mining machine has to collect the nodules from the seabed, crush them, and pump it to an interim station before transfer to the mother ship at the sea surface. The mining machine has to be supported on very soft seabed of shear strength less than 5kPa. The maneuverability of mining machine becomes very critical while operating in such soft soils. One of the major challenges involved in deep-sea mining is the mobility of the mining machine on the soft seabed with predictable and controlled sinkage. Prediction of traction force for a tracked vehicle on very soft clays has been difficult. The existing studies in this area are mainly for soft clay of shear strength about 5kPa. Conventional terramechanics approach for the prediction of traction forces for tracked vehicle is based on Bekker’s Theory. Bekker’s Theory uses bevameter shear tests to understand the shear behavior of soil. The shear tests help to establish the shear stress–shear displacement relationship of soil which helps to predict the traction forces. The present study aims to identify the shear parameters for very soft clays of less than 3kPa shear strength, which can in turn be used to predict the traction developed in vehicles. Experimental studies were performed using a bevameter setup to determine the shear parameters of very soft clays. The influence of the variables like ring size, height of blades, number of blades, and normal stress on the shear behavior of the soil was examined experimentally.