The authors recognized in the previous study that major problem of the quality of aggregate containing montmorillonite group was rather in workability loss than in properties of hardened concrete such as reduced strength or resistance to freezing and thawing and increased of drying shrinkage. In this study, the influence of montmorillonite group on the fresh concrete properties, especially setting property was examined. The main results obtained in this study are as follows:
1) Flow value was reduced and setting time was accelerated in mortar containing montmorillonite group compared to those in mortar without montmorillonite group. These phenomena related to montmorillonite group content and cation exchange capacity of aggregate.
2) Aggregate containing montmorillonite group, indicating high water absorption, affected both flow value and setting time. But aggregate without montmorillonite group, having high water absorption, simply affected flow value, did not setting time.
3) Potassium ion and sulfate ion concentration of pore solution obtained by mortar containing montmorillonite group was low compared to that of mortar without montmorillonite group at the early age. The ratio of exchangeable potassium ion at surface layer to that of in core of aggregate containing montmorillonite group was increased through the early age of mortar.
4) Accelerated setting was observed in case of mortar containing montmorillonite group which exchangeable cation was exchanged by sodium or calcium ion, but not observed in case of that exchanged by potassium ion.
5) In the case of mortar containing montmorillonite group, the third exothermic peak was observed be-tween first peak and second peak in hydration process. The third peak was not recognized in the case of mortar without montmorillonite group. The accelerated initial setting was observed during the third peak period. The calorific value of the third peak closely related to the montmorillonite group content of aggregate and reaction ratio of gypsum of cement.
6) From the results described above, accelerated setting by montmorillonite group might be caused by following process. Ion exchange between calcium ion in montmorillonite group of aggregate and potassium ion in mortar pore solution from cement happens. Calcium ion concentration of pore solution is increased.Dissolution of gypsum from cement is controlled by high calcium ion concentration of pore solution. Hydration process of cement mineral, such as C₃A and C₃S is changed. Accelerated hydration is recognized as third exothermic peak. Finally, accelerated setting by aggregate containing montmorillonite group occurs.

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In this paper, the consolidation test was performed for argillaceous rocks sampled from every formation of Kazusa Group (belonging in Pliocene or Pleistocene).
The results obtained by investigation of the consolidation characteristics and consideration of the relation between this characteristics and geological classification are summarized as follows:
(1) The correlation between stratigraphy and consolidation yield stress can be confirmed by considering initial void ratio e₀.
(2) As initial void ratio e₀ is larger, the effect of aging by cementation is more remarkable in same member or formation. And, the e-log p curves approach gradually each other in normal consolidation region in excess of yield point regardless of difference of initial void ratio e₀.
(3) In every formation of Kazusa Group, on extended condition that samples are consolidated to 0.1-0.2 in void ratio or to 2000-3000 kgf/cm² in stress, it is considered that the e-log p curves tend to draw near each other applying extrapolation method.

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The purpose of this paper is to investigate the strength and deformation characteristics of the Neogene siltstone sampled from middle formation of Kazusa group.
The following results are obtained by triaxial compression tests on the variable confining pressure changed for wide range under undrained (UU and CU) and drained (CD) conditions.
(1) The stress-strain curve in overconsolidation range shows clearly strain hardening-softening character regardless of undrained or drained conditions.And the curve shows strain hardening character under drained condition and strain hardening-softening character under undrained one in normal consolidation range.
(2) Though the path of effective stress shows the peculier behaviour of soft rock in overconsolidation range, the path is recognized the same tendency as alluvial clay in normal consolidation range.
(3) It is recognized that most of failure is brittle type in overconsolidation range, and “cast shape” failure or shear failure unless volumetric change depend on undrained or drained conditions in normal consolidation range.
(4) The preconsolidation stress of Kakinokidai formation is assumed from 35kgf/cm² to 40kgf/cm² by the results of triaxial compression test and constant strain rate consolidation test.

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Huge debris flows and slope failures occurred at Ryu-ga-mizu district, Kagoshima City on August 6, 1993. They were directly induced by a long rainfall of over 2, 000 mm, continuing at a rate of 259.5 mm per day. The topographical factor of the slope angles from 30 degree to 40 degree in the wall of Aira caldera also contributed to the disaster. We estimated three mechanisms of the occurrence of those debris flows and slope failures as a result of field survey. These mechanisms are as follows;
1) Rain water penetrated into well-permeable pumice flow deposit layer and permeable welded tuff layer superposed on non-permeable silt layer. Then, because of an increasing ground water flow rate, collapsing occurred at surface of pumice flow deposit layer and welded tuff layer.
2) Collapsing of pumica flow deposit layer occurred on account of an increased gush out of ground water through the boundary between silt layer and pumice flow deposit layer.
3) Rain water penetrated into pumice flow deposit layer. Increasing pore-water pressure in the layer caused the collapsing.

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