The Kimachi sandstone, occurred on the southern coast of Shinji Lake, Shimane, Japan, is a stone material composed of medium-grained tuffaceouS sandstone of the Miocene Omori Formation. It has been quarried for processing into various household utensils and stone lanterns since the Burial Mound Period. The sandstone is homogeneous, isotropic, soft, and not brittle in its mechanical properties, and therefore easy to carve with traditional chisels and other tools. However, the sandstone's rapid weathering and deterioration is a serious shortcoming as a stone material.
A distinguishing feature of the weathering of this sandstone is a rapid change of rock color from bluish gray to brownish, reflecting oxidative changes in the iron components of the sandstone. Therefore, the change of color of the rock surface over time can serve as an indicator of the weathering rate of the sandstone.
Rock color values a* and b* (CIE L*b* color measurement system.) of the surface of two samples of the sandstone were repeatedly measured with a colorimeter (Minolta CR-800). The Samples were kept unde natural room temperature and humidity conditions in a laboratory during more than two years, and their color changes with time were analyzed.
The repeated measurements of the color values showed that both a* and b*values initially increased rapidly with time, but their rates of increase slowed with time. Here, the positive b* value, which expresses the yellow color component, was used as the major index of the change of rock color from bluish gray to brownish. The change in the b* value with time t (day) was graphically determined and could be described by the equation b* =2.35logt+4.40.
The empirical relation between uniaxial compressive strength q_u (MPa) of cyliIldrical specimens of the salldstone and the b* values measured on their surfaces was also determined. From this relation and using the equation mentioned above, the decreasing value of q_u (MPa) over time t could be expressed as q_u=40-4.0logt. According to this equation, it takes about 102 years from the time that Kimachi sandstone is exposed to attain the level of weathering resulting in a 50% reduction in its strength.
The changes in color values a* and b* were not independent during the weathering process; the two values were related to each other linearly. The slopeΔb*/Δa* of the line graphically determined from the linear relation was around 3.5, which corresponds to the gradient of color values during the formation of goethite, which is brownish, as a result of oxidation of iron at normal temperature. Therefore, the brownish color of the sandstone may be attributable to the formation of iron compounds by oxidation of iron dissolved from the numerous andesite fragments and chlorite that compose the sandstone.
The rock color changes with time not only at the rock surface, which is in direct contact with the atmosphere, but also within the rock. To obtain information on the rate at which oxidation proceeds inward from the outer surface, color values were compared between the outer surface of a rock specimen and the faee of a cut plane of the same specimen, which was cut 59 days after the first color measurement. Consequently, slight change of color values was recognized an the cut plane. This means that the oxidation attains at the depth of 2 cm from the surface during 59 days.

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Quaternary laminated and stratified mud formations distributed along the Anegawa River running on the western foot of Mt. Ibukiyama, eastern Shiga Prefecture, are interpreted as dammed-lake deposits on the basis of their lithology, distribution, and the presence of landslide debris accumulated below the western and southern slopes of Mt. Ibukiyama.
The mud formations are subdivided into the younger and older lake deposits. The former, in part, consists of thinly laminated sediments including clastic fragments, diatom frustules, siderite framboids, and organic materials. The laminaewere formed annually by the cyclic repetition of blooming of diatom in early spring, siderite formation in summer as anoxic lake condition, and later clay mineral accumulation, plus periodical inputs of coarse clastic materials and organic matters from the catchment area. The ¹⁴C ages of plant remains embedded in the younger and older lake sediments are scattered around 5, 000 cal BP and about 30, 000-40, 000BP, respectively. The age data together with the duration of the varved sediments accumulation, fall age of tephra, and descriptions in ancient documents indicate that the large-scale landslides on the western slope of Mt. Ibukiyama forming a dammed lake along the Anegawa River and accumulating thick sediments in the lake have occurred at least two times.

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Lightweight embankment technology is increasingly being accepted for use in construction projects to solve soft ground problems. The most important advantages offered by this technology are reduced foundation soil improvement costs and reduced construction period due to the reduced loading on the ground. Previous work has shown the maximum temperature inside field test bodies ranged from 80-100°C, and the unconfined compressive strength of core samples of foamed mixture lightweight soils did not reach the design strength. At this time, we have focused on the effects of ternperature increase of fill induced by cement hydration on the unconfined compressive strength of foamed mixture lightweight soils at a construction site. This paper describes the influences of high temperature under curing on unconfined compressive strength and structure of foamed mixture lightweight soil at constant volume. We found that unconfined compressive strength decreases significantly from 20 to 90°C. The unconfined compressive strength cured for 28 days at high curing temperature (80 to 90°C) is about 50-60% that of specimens cured at 20°C. The influences of high temperature under curing on the structure of foamed mixture lightweight soil at constant volume are also investigated.

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This paper presents the distribution, characteristics, and activity of faults which constitute the Lake Ohara fault system, by the combination of new fault-outcrop investigations, trench excavation survey, and borehole drillings, with previous studies for the fault system. The fault system is composed of 7 active faults; the Lake Ohara, Western Mt. Kido, North-western Yamaguchi Basin-Marginal, R. Yoshiki, Shimogo, Eastern Ube, and R. Niho faults. In the first part of this report, based on a review of previous studies, geomorphologic and geologic data about the fault system and constituent active faults are compiled. Second, results of the investigation performed in this study are described in detail. It is pointed out that no movement has occurred on the Lake Ohara fault in the past 3, 200 years. In contrast, the Western Mt. Kido fault might move approximately 3, 500 years ago, simultaneously with the Shimogo fault. It is supposed that these two active faults move at a recurrence interval of-21, 000 to>24, 000 years. Although each constituent fault has a different average slip-rate of a vertical component, it ranges from 0.01 to 0.08m/10³ years.

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In Miyazaki Prefecture, slope failure disaster and flood disaster occurred due to the heavy rain accompanying the passage of typhoon 0514 early in September 2005, causing great damage. In the area of Mt. Wanitsuka (1, 118m), which is about 20km southwest of Miyazaki City, the total rainfall from September 3rd to the 6th reached 1, 013mm, resulting in large-scale slope failure particularly in the northern slope; debris flows occurred in the upstream area of the Kiyotake River, and a lot of earth and sand deposited in the lower stream of the river. There were two types of slope failure, collapse and landslides. In the upstream area of the Hiroto River in Kitago Town, large-scale slope failure occurred, which led to the formation of a natural dam.

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