Masaharu Fukue

The micro-structures of clay given by resistivity measurements

In this study, a structural model consisting of serial and parallel parts with three phase-components, solid, liquid and gas, is developed to give information on soil structures. The structure model is characterized by the ratio of the serial and parallel parts, which have different electrical conductivities at given directions. The ratio is expressed by a structural factor, F. The value of Γ defined by σw/(1−F) is used and examined to characterize the clay structure, where σw is the apparent resistivity of pore water. Experimental results showed that the value of Γ is different for undisturbed and remolded clays for a similar void ratio. For unsaturated clays, it is found that the F value depends on the water content and pore distribution. From theoretical and experimental consideration, it is possible to use resistivity to describe the micro-structure of clay with the model developed in this study.

Use of a resistivity cone for detecting contaminated soil layers

Abstract A cone-penetration technique was developed to detect contaminated soil layers with electrolytes and NAPLs. In this study, laboratory and field experiments were performed to apply the technique. In the laboratory, the change in resistivity was quantitatively examined by adding salt or oil to soil samples. The results showed that the resistivity measurement was varied with an order of ppm for the electrolyte concentration in soil. It was found that the resistivity of sand increased with increasing oil concentration. The effect of oil content was stronger for lower water content of sand. The results obtained from field experiments showed that the resistivity cone can be used for detecting the contaminated layer in soils whose background values are known. Particularly, the instrument can be used effectively for examining the effects of remediation, by measuring the resistivity of the ground before and after remediation, unless the soil fabric changes significantly during remediation procedures.

Filtration of contaminated suspended solids for the treatment of surface water.

As few technologies exist worldwide for the treatment of contaminated surface water, a new approach is currently under development consisting of an in situ water treatment system based on a floating filtration process for adsorbed contaminants such as heavy metals. Laboratory filtration tests were performed for the removal of contaminated suspended solids (SS) from surface water. SS, chemical oxygen demand (COD), and organic carbon (OC) were monitored. Of the four filters (two non-woven geotextiles, a woven geotextile and a sand filter) evaluated, filter 1 (a non-woven geotextile) was the most effective for removal % of the total suspended solids. The results demonstrated excellent efficiency by filter No. 1, for reducing turbidity by 93-98%, as well as SS by up to 98.9% and COD by 65-71% for three sites with initial turbidities of 70, 20, and 120 NTU, respectively. The level of heavy metal removal was 98.9% due the heavy metal content of the suspended solids (60 mg kg(-1) of Cu, 90 mg kg (-1) of Ni, 130 mg kg(-1) of Zn, 200 mg kg(-1) of Cr, and 80 mg kg(-1) of Pb). The development of this technology could potentially protect the public and aquatic plants and animals from dangerous contaminants such as heavy metals adsorbed onto the suspended solids.

Sediments Contamination and Sustainable Remediation

Contents: Introduction to Sediment Contamination and Management. Introduction to Sediments. Characterization of Contaminated Sediments. Remediation Assessment, Sampling and Monitoring. Natural Attenuation/Natural Recovery of Contaminated Sediments. In Situ Remediation and Management of Contaminated Sediments. Remediation of Dredged Contaminated Sediments. Assessment of the Treatment of Sediments. Current State and Future Directions. Index Appendix: Standards and Guidelines.

Consolidation of Sand-Clay Mixtures

Consolidation properties of bentonite-sand mixtures, as reclamation materials, were investigated in the one-dimensional consolidation test. From the relationships between the void ratio of nonclay fraction and consolidation pressure was found the existence of a threshold void ratio at which the frictional resistance becomes dominant during consolidation. The threshold value is slightly greater than the maximum void ratio of sand used for the mixtures. A new standard, which utilizes values of clay content, dry density, and threshold void ratio, is proposed to clarify the boundary between sandy and clayey soils. The salt infiltration into the mixtures causes a rapid settlement but greatly reduces the swelling in unloading stage. As long as the void ratio of nonclay fraction is less than the threshold value, however, the influence of salt disappears.

Re-Suspension Technique for Improving Organic Rich Sediment-Water Quality in a Shallow Sea Area

The re-suspension method consists of (1) dispersion of the sediment by air-water jets, (2) pumping of the suspension (small particles and organic matter), (3) settlement in a tank, (4) filtration and (5) disposal of solids (followed by incineration in this case). The pilot test was performed to clean up an area of 3000 m2. The dispersed depth of the bottom was approximately 50 cm. The time spent for the work was two weeks. The amount of re-suspended solid removed from the bottom was about 8 tonnes in dry mass. Since the solids contain high concentrations of chemical oxygen demand (COD), total phosphorous (T-P), total nitrogen (T-N) and sulfides, the remaining sediment was considerably improved. Quantitative analyses showed that the full-scale implementation would enable the removal of about 10% of the re-suspended solids, and reduce COD by 95%, T-P by 50%, T-N by 100% and sulfide by 75% for re-deposited sediments in comparison to the original sediments.

Consolidation Yield Stress of Osaka-Bay Pleistocene Clay with Reference to Calcium Carbonate Contents

Sea bottom has been used as landfill sites to dispose various types of waste and dredged materials. Therefore, the geotechnical properties of seabed are of great importance for the design and practice of reclamation projects. Marine clay layers are known to be geologically normally consolidated. Those clays, however, show pseudo-overconsolidation behavior with a consolidation yield stress pc larger than the in situ overburden pressure p0. As consolidation behavior of those clays under a load around pc is not normal but very complex, the prediction of possible settlement under loading is presently quite difficult. In this study, the Osaka-Bay Pleistocene clays were sampled and subjected to physical and mechanical tests. Based on previous studies, it is assumed in this paper that the disagreement between p0 and pc results from the cementation of marine soils, and that their cementation is mainly due to calcium carbonate. If the assumption made is valid, pc value of a clay sample of which calcium carbonates had been chemically dissolved must be equal to p0 value. In order to verify this assumption, experimental studies has been done. Carbonic-acid water of enough volume to dissolve the calcium carbonates in a clay sample was percolated without breaking fabric structure of the clay skeleton, and pc value of the sample was determined by the constant strain rate of consolidation test. The results showed a definite decrease of the pc value. Consequently, the pseudooverconsolidation ratio of the specimens decreased with the removal of calcium carbonates.

Change in microstructure of soils due to natural mineralization

Abstract If a very long-term stability of soil materials is concerned, it is necessary to consider natural mineralization processes resulting from physical, chemical and biological actions. Precipitation, dissolution and reprecipitation of minerals due to these actions will change the microstructure of soils in terms of void distribution, strength, permeability, etc. Precipitated minerals at the contacts between soil particles may play an important role as cement agent, while the formation of nodules will make soils unhomogeneous. On the other hand, dissolution of minerals produces very large pores. It may cause high permeability of the soils. Therefore, this paper describes natural mineralization under various conditions and discusses the possibility of mineralization in some crucial site, such as a deep excavated-buried ground.

Effects of carbonate on cementation of marine soils

This study shows that calcium carbonate plays an important role as a cementing agent of various marine sediments. The measured vane shear strength of marine soil samples is shown to vary with depth and is strongly correlated with the calcium carbonate content. The results show that an increase in calcium carbonate of 1% causes an increase in shear strength of about 10 kPa. Moreover, under accumulating self‐weight, consolidation is found to be enhanced by calcium carbonate. It was also found that both the cementation and condensation due to calcium carbonate are the major factors accounting for the strength development of marine sediments, beside consolidation. These effects are often greater than those due to grain size effects.

Measurements of Wave-induced Pore Pressure and Coefficients of Permeability of Submarine Sediments during Reversing Flow

Wave-induced pore pressure was measured at a location on the Pacific coast of central Japan with two types of probe. Analysis revealed that the damping of wave-induced pore pressure with respect to the wave pressure at the seafloor was greater than that predicted by published theories, even at shallow depths proximate to the mudline.