Three equations to estimate the permeability coefficient of fracture system in rock mass are presented.
These equations are obtained from theoretical consideration of flow behaviors in a fracture with roughwalls and elaborate measuring of some features in actural rock mass such as the as the roughness of fracturewall, distribution of fracture width and the average spacing width.
These equations can also be used to calculate the permeability tensor of rock masses.

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The failure process of rocks by freezing and thawing cycles cannot be fully understood. However, it isvery important to confirm this process for the assessment of durability of material rocks for use as riprap ofrockfill dams. The auther has been conducting laboratory freezing and thawing test on material rocks to confirmthis process. From a series of tests, the following results have been obtained.
1) The number of freezing and thawing cycles to failure (The auther defined this cycles as freezing andthawing life) shows wide fluctuation and this phenomenon is an essential properties of the failure process ofrocks by freezing and thawing cycles.
2) Exponential, log-normal, Weibull, McCall and gamma distributions are all applicable to describe thedistribution characteristics of freezing and thawing lives of rocks.
3) From the distribution characteristics of freezing and thawing lives, and the change of physico-mechanicalproperties, it is concluded that the failure process of rocks by freezing and thawing cycles is serial andcumulative like the fatigue failure process of metal.

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On the 24th June 1978 a landslide occurred at Shiraki, Okuchi-shi, located in the north of Kagoshimaken, Japan; destroying two inhabitants and two houses and causing the damage in a road and a paddy field.The landslide occurred during the improvement-work of road and at the time of heavy rainfall, in the cuttingslope of weathered and fissured overconsolidated clays derived from volcanic rocks. In this paper the originand mechanism of the landslide are described and analysed from the standpoint of geotechnical engineering.In order to investigate strata, geological structure and ground water condition in the landslide area, electricprospecting, electric logging, drilling survey, groundwater tracing and interpretations of aerial photograph andof topographic map were performed. The dependence of the landslide on rainfall also was investigated.Physical and mechanical properties of clays were cleared by means of laboratory soil tests.
The strata consisting of lava, upper tuff and lower tuff with a great may of joints and fissures wereformed by the hydrothermal alteration and the weathering of volcanic rocks. The slip surface observed waslocated in the dipping joints with the seam contained montmorillonite between clayey upper tuff and clayeylower tuff.
The condition of rainfall was 300 mm in the effective accumulated amount of rainfall and 26 mm in theamount of hourly rainfall preceding the time of activation of the landslide, and fully satisfied the rainfalllevel of threshold value of slope-movements in the southern Kyushu.
This landslide is classified as the rockslide of weathered materials derived from volcanic rocks in a ridgyterrain.
Physical properties of upper clay (clayey upper tuff) are typically Gs=2.70, ω=82%, ωL=103%, ωP=69%, clay fraction (<2μm) =35% and bulk density=1.40 (t/m³). Its mechanical properties are c'=0.5 tf/m²and φ=34°C in the peak strength, φ=14°C in the residual strength, overconsolidation ratio=3.0, residual factorR=0 and brittleness index IB=1.00-0.64.
Stability analyses using the conventional slice-method based on the effective stress gave the decrease incalculated factor of safety owing to the cutting of hillside and the saturation of ground.

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