筆者らは，長年にわたって，高温岩体地熱発電の設計に資するために，数値解析モデルの開発に携わってきた。ところが，我が国においては，高温岩体に関する研究プロジェクトは2004年に中止され，一部の研究が完成しないままに残されている。本報告はその研究において独特のものとして開発された二つの完全3次元数値解析システム，一つは有限差分法に基づくモデル，もう一つは境界要素法に基づくモデル，について述べるものである。筆者らは，高温岩体地熱発電に対する研究調査が将来において再開されたときに，本報告が役立つことを願っている。

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Our research was carried out based on comparison of the internal structure and the physical properties of rock in order to understand the mechanism of frost heave.
We conducted frost heave tests on 5 types of rocks to understand the frost susceptibilityof rock. Ohya tuff, Kimachi sandstone, Noboribetu soft rock and Maruseppu tuff formed frost heave. Sapporo soft rock only did not occur frost heave. From these test results, the former were classified as frost susceptible while the latter was classified as non frost susceptible.
Our research focused on the internal structure and the physical properties of rock. Permeability test and gas adsorption test by Bet method were conducted to understand internal structure of rock. And we compared the physical properties of frost susceptible rock and non frost susceptible rock. Pore size distribution, mineral composition, and strength in dry and wet condition etc. were measured. These measurements clarified certain differences between frost susceptible rock and non frost susceptible rock.
Main results obtained in our research are summarized as follows:
(1) Frost susceptible rock has a large surface area. A larger surface area enables a rock to hold a higher amount of unfrozen water on the surface while freezing, which means a smoother supply of water for ice lens formation and thus leading to a higher frost heave rate.
(2) Non frost susceptible rock has a higher permeability than frost susceptible rock.
(3) Water penetration in frost susceptible rock is more restricted due to the smaller pore radii than in non frost susceptible rock, which has greater pore radii. The permeability of rocks depends on the pore radii.
(4) In the case of rock, which has a larger surface area or higher clay mineral/zeolite content, the tensile strength in wet condition is lower than in dry condition.

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It is well known that the temperature of slurry ice manufactured with the concentration of salt water in the range of 1.0∼2.0wt% can be accurately maintained in the range from -0.5 to -1.5°C. Now, pioneering work on a slurry ice manufacturing apparatus has already been made practicable by researchers in Canada and Germany. In their approach, ice particles made with the concentration of salt in sea water are blended with a solution consisting of a mixture of sea water and fresh water. However, the apparatus is very large. The authors therefore intend to develop a slurry ice manufacturing apparatus that uses only one unit to produce slurry ice from the solution of salt with a concentration below 1.0wt%. As a result, the authors successfully developed the generator in the apparatus on the basis of the method in which the ice layer produced on the heat transfer surface is swept out using scrapers. In addition, in order to establish the design engineering of this generator, experiment has been carried out to study the amount of ice produced from 1.0∼4.0wt% NaCl solution and measure the concentration of salt. The results indicate the following: (i) The speed at which ice is produced is determined by the initial concentration of the salt solution and remains constant when IPF≤20 IPF : ice packing factor). (ii) The speed of ice production can also be controlled by adjusting the temperature of the refrigerant. (iii) The thermal conductance of the ice layer tends to change with the salt concentration of the solution.

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In order to develop porous silicon nitride ceramics with tailor-made pore structure for "Bio-filter", suitable sintering aids were investigated. They must inhibit densification while promoting the α-β transformation to develop the fibrous β-Si₃N₄ crystals that would be essential for high toughness. The conventional technique for developing porous Si₃N₄ using a removable substance such as starch gave much lower porosity than the volume fraction of starch when MgO was used as a sintering aid. It was found that BaCO₃ met the necessary conditions, probably because the decomposition temperature was as high as the liquidus temperature, and the internal CO₂ pressure effectively inhibited the densification while promoting the phase transformation. The addition of 7 mol% as BaO gave about 44% of porosity at a sintering temperature as high as 1850°C. It was observed that the porous body consisted of interlocked fibrous β-Si₃N₄ crystals with sub-micrometer pore sizes.

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In a previous work, a polymer having a low softening temperature was used as a binder of wood-chip and sand pavement system to prevent the crack formation in the pavement. Although the polymer prevented the crack formation, the mechanical properties such as durability and elastisity of the pavement were decreased. This means that there is a trade-off problem between the crack formation and the mechanical properties.
In this work, the effects of softening temperature of the binder on the mechanical properties of the wood pavement have been investigated. It is found that the value of marshall stability decreases and the amount of dispersal of composite materials in the pavement increases with decreasing softening temperature of the binder.

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In recent years, an increasing number of urban soil contamination cases has been found during redevelopment of former factory sites. Hydroclassification technique, separating heavily contaminated fine soil particles from contaminated sites, is one of the economical remediation techniques for contaminated soil by heavy metals, but the separated fine soil particles are generally landfilled because of the difficulty in removing heavy metals strongly adsorbed on them.
In the previous study, the authors have investigated the mechanism and the optimum condition of chlorination-volatilization technique to eliminate heavy metals from inorganic waste and found it was needed to heat up around 1273K.
In this paper, a new remediation technique for lead contaminated fine soil particles is proposed. This technique is composed of chlorination and subsequent warm water extraction. In the chlorination step, water-insoluble lead complex is chlorinated to be water-soluble lead chloride without volatilization, by heating the soils with MgCl₂-CaCl₂-KCl salt mixture at relatively low temperature. By subsequent warm water extraction, lead chloride is leached out. Effects of chlorination conditions, such as time, temperature, composition of the salt and added salt ratio, on lead behavior were investigated. It was proved that lead concentration could be reduced to be below Japanese environmental standard.

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