Just after a landslide or landslip occurs, we can often observe in situ that ground water gushs out like a vein-stream from the main scarp or among deposits of the landslide or landslip area. By examining the relation between this phenomenon and the results of various investigations for ground water, such as tracer method, water-level, flowing layer detector, pumping test, water quality, and others, it is inferred that the ground water having a large influence on the landsilde movement or occurrence exists as the state of vein-streams in and around the landslide area.
In many cases the landslide seems to occur or move when the abnormal condition arised in vein-streams by some causes, such as heavy rain, thawing water, earthquakes, embankment, and others.
Accordingly in order to investigate the occurrence and movement mechanism of landslide or landslip phenomena, it is neccessary for us to estimate the existing places of vein-streams in and around landslide and landslip area as accurate as possible. Then the author proposed one new survey method “The underground temperature survey in one meter depth” for the vein-streams in and around them. It was shown, by both a theoretical study and experiments in situ, that this new method was useful one for surveying the ground water like a vein-stream.
By using both the new method to estimate the scales of vein-streams and some methods to obtain the displacement values of landslide soil-mass, it was found that the vein-stream had a large influence upon the landslide movement: As the scale of the vein-stream becomes larger, the displacement values of the soil mass increases; and the scale becoming smaller, the value decreases.

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