Estimating for leaching-mechanisms of heavy metals are important in order to understand the pollution state of peripheral environments of rock muck disposal sites.

This study examined the mechanisms of arsenic leaching from rock muck disposal sites at acid, alkaline and neutral conditions. The leaching-potential of heavy metals are from rock materials influenced by many parameters; e.g. the existing form of these elements in rock materials, the leaching mechanisms from rock materials, the advection/diffusion in aquifer and adsorption onto ground materials.

We examined the arsenic leaching mechanisms by two type experiments considering water-rock interaction; one is the static batch-leaching test and the other is the leaching te st under water flowing condition in soil tank test.

The results of the static leaching test show that water- rock interaction progresses under high Eh conditions is in constant solid-liquid proportion. It is suggested that the water flow condition leaching test can simulate the arsenite（H₃AsO₃⁰） leaching mechanisms in reduction condition in aquifers.

Laboratory measurements were conducted to evaluate physical and mechanical properties of sandstone and calcareous concretions which were collected from the wave-cut bench in Iwami-tatamigaura, a natural monument in Shimane, with permission of Agency of Cultural Affairs, Government of Japan. Physical properties such as density, porosity and p-wave velocity of sandstone（concretions）were 2.16～2.21Mg/m³（2.50～2.58Mg/m³）, 10.6～14.9%（2.40～4.82%）and 2.30～2.99 km/s（3.69～4.63 km/s）, respectively. Mechanical properties such as uniaxial compressive strength and tensile strength by Brazilian test of sandstone（concretions）were 18.1～26.7MPa（56.9～128MPa）and 1.52 ～6.04MPa（4.03～10.9MPa）, respectively. Weathering susceptibility index, which is defined as the ratio of porosity to tensile strength, was calculated to be 2.1～7.6×10^－2MPa^－1 for sandstone and 2.4～6.7×10^－3MPa^－1 for concretions. Observations of thin sections revealed that carbonate occurs as a matrix in the concretions whereas less carbonate in sandstones with smaller strength. Therefore, the concretions have lower porosity, lower susceptibility of weathering and larger strength than those of the sandstone because of bonding effect by the carbonate.

Geological field survey and hearing at landslide time, analysis of radar rainfall of three Landslides sites, which occurred by North Kyushu heavy rainfall of July 2017 in volcanic rock area. The results of the investigation are as follows：（1） large-scale landslide site formed a structure that facilitated the storage of the groundwater by the fault perpendicular to the slope,（2） medium-scale landslide site was a gentle dip slope structure,（3） shallow landslide site was cap lock structure it seems that the supply of groundwater caused by rainwater was delayed.

As a result of reflecting such geological structure, it became clear that landslide occurred in the order of large-scale landslide, medium-scale landslide, and shallow landslide.

Drainage density has been defined as total stream length per unit area of a river basin. Numerous researchers have measured values of drainage density from topographic maps and have analyzed variables controlling drainage density and found that drainage density is related to climate, vegetation, bedrock geology, time. Usually, it is noticed that increasing drainage density always responsible to the slope failure. In this context, this paper describes some of aspects of drainage density and its relation to the slope failure and debris flows in southwest Japan. In this study, debris flows and landslides selected from Hiroshima disasters in 2014 and disasters of typhoon No.15, 21, 23 in 2004. The relationship between drainage density （D_d） and frequency of slope failure （F_d）, can be expressed in the form of an equation F_d ＝ 2.50×D_d ＋ 0.28. Drainage density will be a good susceptibility index for slope failure and landslides, and would be good index for estimating evacuation time by rainfall in small catchment-base where past disaster data are not available. Therefore, study of drainage density is practical approach for disaster management.

The formation of landslide mass results from dividing into parts by fracture. The authors thinks that the forecast of the collapse mechanism and the place becomes possible from fracture distribution, topography, and geological characteristics. In the case of landslide mass distributed in the old valley, unconformity plane is likely to be sliding surface. In the case of the scale of landslide mass is large, and deep underground become unstable, land slide mass is converted to deep-seated landslide. The detection of sliding surface is difficult only in the core form observation. In sliding surface detection, the distinction method by the core gamma-ray measurement is valid.