[in Japanese]

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High-swelling montmorillonite shows tremendously large viscosity as compared with low-swelling kaolinite. However, the effect of swelling ratio cannot explain the difference of viscosity quantitatively. Therefore, the effect of interacting force between particles on viscosity was introduced. That is, viscosity was assumed to be determined as a function of particle-number density instead of particle-volume fraction. The new viscosity equation which contains hydrodynamic interaction due to collisions was proposed and the increasing rate of viscosity was calculated for the suspensions of clays which have no surface charges. Compared with our measurements that both kaolinite and montmorillonite took almost the same increasing rate of viscosity at the same particle-number density, it was found that interacting force between particles dominantly determined the viscosity.

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This study aims to elucidate the alteration mechanism of mortar surface reacted with seawater and the relationship between characteristics of secondary products on the surface and salt concentration of seawater. The experiment was carried out in closed system using two kinds of mortars which were made from high-early-strength portland cement (HES) or alumina cement (AL) and silica sand, and two kinds of artificial seawater with half or twice of salt concentrations. Tablet type specimen (3.5-cm diameter, 1.0-cm height) was treated with seawater of 200.0 mL during 20 days. Results of the experiment showed that white products were crystallized on the surface of a tablet in each case. The products were characterized using SEM and XRD. In HES, petal shaped brucite, Mg(OH)_2, was produced by the reaction of portlandite, Ca(OH)_2, with Mg component in seawater. In AL, needle or column shaped aragonite, CaCO_3, was formed. Under high salt concentration of seawater crystalline size of brucite is relatively large in HES, production of aragonite are promoted.

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The Nankai Trough is located at 200km south from Shikoku Island, southwest Japan. It is elongated about 400km from west to east. The Nankai trough is subduction zone between the Philippine see plate and the Eurasian plate. Many earthquakes have been occurring along this trough. Therefore The Nankai Trough is one of the major concentrations of strong seismic activity regions. The mud and sand deposits composed of marine and sub-marine sediments are found on the Oceanic crust as late Cenozoic trench sediments. Numerous geophysical surveys and conventional coring transects have been completed in this region. Several legs of Deep Sea Drilling Program (ODP) had performed the coring near The Nankai Trough. In this time, some drill core samples were collected from the bore hole of ODP Leg.190, Site1174 preserved at the ODP center of Texas University A&M, USA. This bore hole reaches to almost Oceanic crust about 1100m in depth. Therefore the borehole specimens are included of the trench-wedge deposits, Upper and Lower Shikoku Basin facies with decollement. The primary purpose of this study is to synthesize the results of clay mineralogical analysis for the core samples by means of X-ray diffraction, Electron probe microanalysis, Atomic absorption analysis, Differential thermal analysis and Transmission electron analysis. In particularly clay mineralogical characteristics of specimens collected from decollement were compared with the other specimens to discuss about the formation mechanism of decollement. In this study 38 specimens were collected from drilling cores, the drilling cores were divided into three facies, such as trench-wedge fades (〜483.23mbsf), Shikoku Basin facies (483.23〜660.99mbsf) and Lower Shikoku Basin facies (660.99〜1102.45mbsf), respectively. They consist mainly of sub-marine mud with turbidities silt and sand, sub-marine mud with tuff and mud without tuff bed, respectively. The following minerals were measured in this site: chlorite, smectite, illite, kaolinite, quartz and plagioclase. The weight % of clay minerals was analyzed by the peak-intensity weighting method. Although the clay mineral assemblages show some diversity through the depth, smectite and illite are the most abundant clay minerals throughout the sampled section. Most abundant smectite was characteristically recognized in the specimens from decollement. Smectite is abundant in the Shikoku Basin facies and decreasing with depth. On the other hand, abundant of illite is increasing with depth. Depend on the CEC values obtained by Atomic absorption analysis, the exchange cations in the interlayer of smectite are recognized almost Ca ion with K and Mg ions. However smectite in decollement consists characteristically of Ca ion with a small amount of Na ion. K ion tends to be increasing with the depth. It is recognized by transmission electron microscopic observation that the particle sizes of smectite in decollement are larger than in the other facies. Smectite formed in the decollement consists a large amount of interlayer water, comparing with the other facies, according to the result of Differential Thermal Analysis. These smectite as mineral group name was identified to be montmorillonite as mineral species. It is noted from these examination results that large amount of smectite characterized by clay mineralogy is formed in the decollement near the Nankai Trough(Leg.190 Site1174). This mineralogical characteristics of smectite is close similar to that occurred along the slip surfaces of landslide

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