Masaki Kitazume

The tremendous potential of deep-sea mud as a source of rare-earth elements

Potential risks of supply shortages for critical metals including rare-earth elements and yttrium (REY) have spurred great interest in commercial mining of deep-sea mineral resources. Deep-sea mud containing over 5,000 ppm total REY content was discovered in the western North Pacific Ocean near Minamitorishima Island, Japan, in 2013. This REY-rich mud has great potential as a rare-earth metal resource because of the enormous amount available and its advantageous mineralogical features. Here, we estimated the resource amount in REY-rich mud with Geographical Information System software and established a mineral processing procedure to greatly enhance its economic value. The resource amount was estimated to be 1.2 Mt of rare-earth oxide for the most promising area (105 km2 × 0–10 mbsf), which accounts for 62, 47, 32, and 56 years of annual global demand for Y, Eu, Tb, and Dy, respectively. Moreover, using a hydrocyclone separator enabled us to recover selectively biogenic calcium phosphate grains, which have high REY content (up to 22,000 ppm) and constitute the coarser domain in the grain-size distribution. The enormous resource amount and the effectiveness of the mineral processing are strong indicators that this new REY resource could be exploited in the near future.

Strength Variance within Cement Treated Soils Induced by Newly Developed Pneumatic Flow Mixing Method

In the study, field and laboratory tests were conducted to investigate the degree of strength variance within cement treated soils. The cement treated soils were the dredged soils mixed with a small amount of cement. They were produced by Pneumatic Flow Mixing Method, which had been recently developed in Japan. In the paper at first the outline of Pneumatic Flow Mixing Method system is presented. Then several backgrounds causing the strength variance within the cement treated soils are described. It is found that the cement-water ratio of treated soil s was stable, which was monitored and controlled during their production. The effect of mixing adequacy of the soil-cement mixture and that of non-homogeneity of dredged soils on the strength variance is also discussed. Finally the effective measure to reduce the strength variance is described.

Utilization of Pneumatic Flow Tube Mixing Technique (PFTM) for Processing and Stabilization of Contaminated Soft Sediments in the NY/NJ Harbor

ABSTRACT A pilot study was conducted to evaluate the use of the pneumatic flow tube mixing method for stabilization and solidification of soft sediments dredged from the New York/New Jersey Harbor. The study included a comprehensive laboratory investigation aimed at determining the ideal mix for pneumatic flow tube mixing stabilization, and a pilot-scale demonstration of the pneumatic flow tube mixing technique in the field. Material stabilized during the demonstration was analyzed through unconfined compression tests, needle tests, laboratory vane shear tests, and flow tests in the laboratory and the cone penetration test in the field. Curing times for the samples were 3, 7, 14, and 28 days. The three cement content mixes were 4, 8, and 12% by weight (wet weight). Pneumatic flow tube mixing was demonstrated to be an efficient and rapid method for soft sediment stabilization with the resulting material showing uniform quality of mix meeting, New Jersey Department of Environmental Protection’s geotechnical and environmental fill placement criteria.

Centrifuge Model Tests on Influence of Slope Height on Stability of Soft Clay Slope

The deep mixing method was developed in Japan in the 1970s and has been frequently applied to on land and marine constructions. The group column type improved ground is often applied to stability of embankment and soft ground. The current design procedure of the improved ground assumes the external and internal failures. The authors start a research project to investigate the applicability and the design procedure of the group column type deep mixing improvement on the stability of soft clay slope. As a primary research of the project, a series of centrifuge model tests and numerical analyses were carried out to investigate the influence of slope height on stability and deformation of soft clay slope. The study reveals that the height of embankment at failure increases with decrease of height of slope and can be evaluated by the Fellenius slip circle analysis precisely.

A Parametric Study on Evaluation Of Stability of Column Type DM Improved Ground

The deep mixing method, an in-situ soil stabilization technique using cement and/or lime as a binder, is often applied to improve soft ground. The group column type improvement is extensively applied to stabilize foundation of embankment or lightweight structure. An improved ground design method is established in Japan mainly for reinforcing embankment, in which two failure patterns related to external and internal stabilities are assumed. The author conducted a research project on the failure mechanism and stability of the group column type improved ground subjected to embankment loading. The project involves investigating the failure criteria of two stabilities and the failure mode related to the external and internal stability. These studies have revealed that the current design method may overestimate the stability of improved ground because inadequate failure modes are assumed. However, as far as the author knows, there have been few cases recorded of serious failure or large deformation in the group column type improved ground under embankment loading. This is a discrepancy against the overestimation in the current design method. In this paper, a parametric calculation on evaluation of the stability of column type DM improved ground was carried out to investigate the characteristics of the current and the proposed design methods.

Ground Improvement in Tokyo/Haneda International Airport Expansion Project

Tokyo/Haneda International Airport was found in 1931 as a first primary airport in Japan where a runway of 300m was operated. The airport was expanded several times for cope with the rapid increase in air transportation. In order to cope with the recent and future increases in air transportation, the construction of the fourth runway was started in 2006. The runway is constructed on the man-made island close to the existing airfield. As soft soil stratums were stratified at the construction site, several ground improvement techniques were employed for the ground. In this paper, application of the ground improvement techniques at the site is briefly introduced as well as the outline of the construction project.

Twenty nine years of experience with physical modelling of geotechnical problems in port structures

At present, centrifuge model testing has become an important tool for investigation of complex geotechnical natures. In 1980, the Port and Harbour Research Institute (PHRI) constructed the Mark I geotechnical centrifuge, whose effective radius was 3.8 m. Since then, the PHRI carried out many tests on fundamental and practical research projects. Unfortunately, since 1989, undesirable vibrations of the concrete pit floor had frequently occurred during the operation of the Mark I centrifuge. Therefore the maximum operative acceleration had to be limited below 50 g for safety reason, which in fact led to serious limitations to research projects to be studied. Consequently, the PHRI had decided to construct a new centrifuge, namely the Mark II. Based on the statistical studies on the actual operation, the major dimensions and capacities of the new centrifuge was decided to be the same as the Mark I. In 1989, the PHRI had started the construction and completed in 1994. In 2001, the PHRI became an independent ad...