An observation of groundwater behavior has been made around a tunnel during its excavation to investigate the phenomenon of erosion and collapse caused by groundwater in Neogene Pliocenean unconsolidated sandstone.
The observed data showed that the behavior of groundwater is affected by the impervious and continuous layer, and that the vertical flow is dominant in the near field of group-well and the approximation of horizontal uniform flow does not give good results.
Using Theis' unstable well theory and the observed drawdown heads, several sets of hydrogeological constants for the aquifer were obtained by direct search solution. These values corresponded with those obtained by discharge test, and no major change in these values obtained during excavation, in spite of multi-layered geological structure.
The predicted drawdown heads for unsteady state conditions corresponded well with measured data.

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During tunnel-excavation in unconsolidated ground, it is necessary to pay attention to erosion or collapse caused by groundwater flow.
So an observation of groundwater has been made around a tunnel in Neogene Pliocenean sandstone.
By investigating the relation between groundwater behavior and factors concerned with the erosion or collapse of the face of an inclined shaft, it was showed that the occurrence of erosion is mainly influenced by groundwater flow, degree of consolidation and grading composition.
The concentration and its variation with time of radio-isotope in groundwater leads an estimation of the subsurface flow pattern when the erosion or collapse is accompanied with the mixing flow of groundwater clustered by those duration time in each porous geological basins.

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Gravitational mass rock creep structures are commonly found in the Sambagawa crystalline schist region in the Kanto Mountains. The structures are classified into the following four types: overturned fold, chevron folds, fracture zones, and topples. The mass rock creep, except for the toppling, is the main mechanism for the landslide topographies characterized by the moving directions of masses that make acute angles with the dip direction of the bedrocks. These landslide topographies are more abundant in comparison with the other types of landslide topographies which make the obtuse angles with the dip direction.

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