Study on Deformation Behavior of Sediments and Applicability of Sealants in Seabed Mining

Abstract

The importance of rare earth resources is increasing and a lot of investigations are conducting all over the world. As a result, it was discovered that abundant deep-sea mud contained rare-earth elements on the deep-sea floor. The suction mining method can be one of the effective seabed mining methods to recover these seafloor sediments. However, it is required to evaluate the deformation behavior of the sediments in seabed mining in terms of environmental evaluation. For this reason, this study investigates the deformation behavior of sediments with different water contents by a laboratory suction test. In the test, the sediments filled in a box whose size is 155 mm× 50 mm×180 mm are vacuumed with a suction pump. The suction pressure of the pump is adjusted to 4.0 kPa, the diameter of the suction pump is 10 mm, and the duration of suction is 8 seconds. The results show that suction volume increases with an increase of water content/liquid limit ratio. In addition, the deformation behavior can be categorized as three shapes based on water content/liquid limit ratio; sharp, cone-shaped, and gentle circular arc when the ratio of water content/liquid limit is under 1.3, from 1.3 to 1.6, and over 1.6, respectively. Furthermore, the application of sealants on the sediment surface is effective to reduce the environmental disturbance although its density has to be the same level as the density of sediments to inhibit sinking the sealants.