At the Kamenose Landslide Region, nine wells and tunnels were excavated from 1979 to 1979, in accord with the outcrop observation of the wells, landslide surface, geological stracture and characteristic of sliding zone were clarified. Therfore we can make suggestion of geological background for the process of the landslide development in detail.
On the whole, the process of the landslide development is controlled by following conditions.
1. Geology of this area consists of Ryoke granitic rocks and the Miocene Nijo Croup and the Plio-Pleistcene Osaka Group. Landslide took place in the Nijo Croup distribute enclosed by granite The Nijo Group that is consists mainly of andestic lava flow, pyroclatic rocks some intercalated tuffaceous sand stone and conglomerate, are divided into two formations disconformably. The lower formation is called Harakawa formation with Myojin lava, the upper formation called Jyogashiro formation with Dolokolo lava.
In the Shimizudani block, the western part of the Kamenose Landslide area, the slip surface is along disconformity between Harakawa formation and Jyogashiro formation.
In the Toge block, the eastern part of the Kamenose Landslide area, the slip surface is formed in the tuffceous sand and conglomerate called the Kamenose conglomerates which are intercalated with lava. By observing the sample from the slip surface original minerals of tuffceous rocks were altered and disturbed.
Therefore tuffceous rocks alter easily to clayey soil with bearing of ground water. The Upper lava has many open cracks and a good permeability. Then the groundwater is gathered at the bottom of, lava and tuffceous part between the lavas seemed to be formed easily to shear zone
2. The dip of Nijo Group is south-west. By the effect of gravity the upper lava slips along the tuffceous rocks. The tilted block that the north-west side of Yamatogawa fault dips south west, controlled by Neotectonic movement and it seems to continue now.
3. Divergence of landslide mass controlled by the faults and reliefe of the basement rock. The direction of slide and the activity is more or less different from each other.

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In general, it is difficult to explain the occurrence of a landslide with stability analysis based on routine tests on an overconsolidated clay like the Shimajiri mudstone, and a problem always arises in selecting the kind of strength parameters to be used.
This report deals with the relationship between the occurrence of landslide at Maaji Housing Area and the characteristics of residual and peak strength, slaking, geology and so on, and also considers the determination of average shear strength parameters required to compute the stabilization of unstable slopes and design of cuttings both in the Shimajiri mudstone.
Results obtained are as follows:
1. The landslide mentioned above is a compound slide where the slip surface passes through the foundation rock and the fill.
2. Geologically, the foundation rock consists of a mudstone in the Shimajiri group which belongs to the Neocene period, and the rock is widely distributed in the central and southern part of Okinawa-jima. The Shimajiri group has the tectonic discontinuities such as minor fault, bedding plane, joint and hair crack exist, and their main strikes are almost in accord with a direction of landslide movement. Such geological conditions mentioned above are closely related to the occurrence of this landslide.
3. Due to the physicochemical and strength characteristics of the mudstone, the cutting plane and natural slope are weathered and softened as time goes, and many fissures are developed and become weak planes in the mudstone.
4. The parameters of residual strengths obtained by ring shear test are: c_dr=0 and φ_dr=10.7° in the mudstone sampled close to the slip surface, c_dr=0 and φ_dr=15.1° in the mudstone from scarp, and c_dr=0.075kg/cm² and φ_dr=19.2° in the slurried mudstone.
5. The parameters of peak strengths obtained by triaxial compression test are: cf′=2.779kg/cm² and φf′=43.2° in the mudstone sampled close to the slip surface.
6. The brittleness index of the mudstone I_B is about 90% for a normal effective stress of 2.0kg/cm² and it is larger than that of the Blue London Clay.
7. The parameters of average shear strength acting along the slip surface at the failure, c′ and φ′, can be determined by introducing the residual factor R and the failure criteria of Mohr-Coulomb to the c′-φ′ relationship obtained by back analysis. The parameters in case of the present landslide are: c′=2.17t/m² and φ′=13.9°.
8. R is larger, being above 0.90. This fact indicates that the average shear strength in the landslide is close to the residual shear strength as in other landslides occurred in the Shimajiri mudstone.

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[in Japanese]

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