Model Tests On Continuous Line Bucket Mining System

ABSTRACT Authors have been studying the continuous line bucket (CLB) mining system, which is one of the mining methods to mine manganese nodules from deep sea floors, mainly through the model tests in an indoor test tank. According to the results of the indoor tests, very small-scale field tests of the CLB mining system were carried out in depths of 50 to 8O m to pick up problems due to natural phenomena such as currents, winds, and waves and to understand an actual CLB mining system affected by these phenomena. It is significant to circulate the loop line, which hangs many buckets, between the sea floor and the ship smoothly at the operation of the CLB mining system. The traction machine using umbrella-type wheels was adopted for these field tests. As a result, satisfactorily smooth circulation of the loop line, which hung 75 buckets (about 1,500 cc in volume each), was obtained. It becomes clear that smooth circulation of loop line results in stable operation without the rope being tangled even when the ship alters her course. However, it may be entangled when the circulation is not smooth. In order to avoid tangling the rope, some experiments on the method not to reduce the span between the descending and ascending lines were examined in these field tests. A continuous monitoring for behavioral patterns of buckets and rope line on the sea floor also was tried by using a pinger. INTRODUCTION Authors have been studying model tests of the continuous line bucket (CLB) mining system in order to have a deeper understanding of this system as one of the mining methods used for recovering manganese nodules found distributed over the deep sea floors. The model tests mostly were conducted in an indoor test tank. In such tests, however, there are limits to detection of the problem area resulting from alteration of natural phenomena such as currents, winds, and waves. For further development of the CLB mining system, it should be considered important that we find solutions for problems that surfaced on the basis of the experimental results obtained from field tests. In this context, we conducted small-scale field tests on the applicability of the CLB mining system in Sagami Bay in water depths of 50 to 8O m. In such field tests, the bucket behavior on the sea floor cannot be observed as in laboratory tests. It will have to be an indirect observation through the use of some measuring instruments. When a field test was conducted in 1975 at a site with 430 m of water depth, a Bucket Behavior Recorder, which was developed for this particular field test, was used to measure the dredging path of the bucket and the shape of the dredging line took on the sea floor. The data obtained by this Bucket Behavior Recorder were almost identical to those already obtained through laboratory tests.