The time-dependent behavior and restraint effects of piles installed in landslide of three different states of ground are discussed in this paper by applying the theory of rheology.
The differential equation for the deformation of pile in elastic ground is derived as
EI⋅∂⁴y/∂x⁴+E_s⋅y=p…(1)
and those for the time-dependent behavior of piles in visco-elastic ground and visco-plastic ground are
EI∂⁴y/∂x⁴+η⋅∂y/∂t+E_s⋅y=p…(2)
EI∂⁴y/∂x⁴+η_V⋅η_B/E_s∂²y/∂t²+η_B⋅∂y/∂t=p…(3)
where, E=modules of elasticity of pile, I=moment of inertia of pile, E_s=modulus of elasticity of soil, η_V, η_B=viscosity of soil.
The solution of equation (2) shows that the deformation of pile in visco-elastic ground continue to increase with decreasing rate and it may cease after some period of time to approach the elastic equilibrium, which is given by the solution of equation (1). However, the solution of equation (3) shows that the deformation of pile installed in visco-plasto-elastic ground continue to increase along the curve of exponential form at the initial stage of the deformation and after some period of time the increment of deformation is accelerated to failure.
The restraint effects of pile in landslide of various states of ground will be estimated as follows: The piles in visco-elastic ground show the effects when the deformation of pile reach the elastic equilibrium, but piling in visco-plasto-elastic ground may be ineffective according to the time-dependent deformation of pile.

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The landslide of Yachi, which occurred on the southeastern part of Akita prefecture, is a typical of rockslide.
The cause of this landslide is essentially due to the geological background, especially to the lithology and geological structure of the Tertiary strata mostly covering this area. The strata are composed of lithologically different two kinds of rock species, namely the so-called “hard shale” and its intercalations of tuff. Based on physical and mechanical tests in laboratory, the landslide surface is inferred to have been formed at the altered tuff bed being visce-ductile in nature.
In addition to this condition, the geological structure, which basically consists of the Narusegawa fault and a synclinorium of the Tertiary strata, might play an important role to develope the landslide of Yachi into the large scale rock-slide.

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We had the chance to survey the landslides in Jawa Island from July 25th '79 to September 5th. And we could find some interesting facts and data. Here I introduce two data shortly.

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Akagawa landslide is in Quaternary formations in the state forest area of Aomori forest. The investigation had been carried out 1972 to 1977. Movement of the landslide is discussed by applying a dendrochronological method, especially by paying attention to such abnomal free forms as tilted trunks, snagged trees and so on.
The following became clear after the investigation. Block slides moved briskly especially in 1927, 1959 and 1965, and geo-dynamic process of the landslide has been made dear for about 90 years.

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The Yokkamachi landslide, which occurred on April 18, 1976, is suitable to precise field surveyings and to interpretations of the development of the landslide for its small in scale.
The base rocks of this landslide formed itself into concave land surface by faults or a large landslide (falltype). After that, the redacted and the oxidated layers covered on the concave land surface in upward sequence. Since a peat layer (10cm) lies between the redacted and oxidated layers, the both chemical coloured layers look upon as an order of the sedimentation, It became cleare that the peat swamp formed in maximum Würm of glacial age (17, 960±540 Y. B. P.) through the pollen analysis and the ¹⁴C dating of the peat samples.
After that, the peat swamp was dryed and clastic matter from upper slope filled gradually on it. And this talus like sediments mass (oxidated layer) occurred landslide and repeated same process more than two times.
The most important factor of this landslide was the water which penetrated into the oxidated layer as superabundance ground water.

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Underground temperature survey at one meter depth was conducted at the Marumi landslide area in Hyohgo Prefecture with the purpose of investigating the flowing channels of the water. Parts of low temperature probably caused by the flow of ground-water were determined after the effect of various factors have been taken off from the obtained data. As the result of the investigation, it was found that there were three zones of the low temperature mainly in the investigated area. We examined the means of those zones with aid of the distribution of vertical temperature in bore-holes drilled in this area and the water temperature in flowing layer. As the result of the examination, it was assumed that those three zones were the place that the usual ground temperature at one meter depth was lowered by the effect of the flowing ground-water.

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