Discussed herein are formulae for designing landslide-restraint piles with the horizontal subgrade reactions in consideration. With the intensity of the subgrade reaction p assumed to be lineally proportional to the horizontal displacement of pile axis y, that is,
p=k_h⋅δ⋅y
where δ is the pile diameter and k_h is the coefficient of horizontal subgrade reaction, there are still three different approaches: the first one assumes the force of landsliding H as acting only along the slip surface and the pile length as being infinite both upwards and downwards from the slip surface; the second one assumes, with the loading condition as the same, the pile length as being infinite downwards only; and the third one assumes H as distributing all along the pile above the slip surface while the root part of the pile being infinite.
Observations in large-scale shearing tests in situ and excavations of yielded piles in situ present us three markedly different curves of pile deflection as illustrated in Fig. 5. Any of piling formulae are to explain the differences between these three.
Fig. 1 shows a case in which the pile was so constructed as to yield only to the shearing force but actually ran to rupture by bending moment. Landsliderestraint piles are recommended to be due tested against the rupture by bending moment.
§1 presents the general solution to the elastically supported elastic pile under distributed load; §2.1 the solution particular for the case with additional lateral force H₀ and bending moment M₀ at the head; §2.2 that for the free-head pile and §2.3 that for the pile only under H₀ and M₀. §2.4 deals with pile of finite lengths both above and below the slip surface. As is seen in Fig. 6 or in Fig. 11 the point of y2=0 is likely to deepen far below the slip surface with the value βh decreased: the finite-length-pile formula presented in §2.4 will be warranted. Fig. 10 is the chart for easy calculation of M_max and based on exps. (11), (6), (7) and (8), the parameter being n, the fourth root of the ratio of k_h values. Fig. 11 gives values for calculating resultant subgrade reaction and necessary length of pile below the slip surface. The meanings of symbols are:
EI: rigidity of pile, δ: diameter of pile
k_h: coefficient of horizontal subgrade reaction
y: displacement of pile axis,
E_s=k_h·δ·y and β=4√E_s/4EI: for the landsliding mass,
E_s, and β for the part below the slip surface
n=β/η, h: depth to the slip surface
K=η/E_s H: resultant force of landsliding
η: load conversion factor
=2H/h² for hydrostatically distributed load
i: deflection angle, M: bending moment, S: shear
ε, ν and ν: dimensionless factors of deflection, bending moment and shear, respectively.
ρ and λ₀: dimensionless factors of rusultant subgrade reaction and root length of pile, respectively.
Note: Suffix 0, 1 and 2 or head bar denote pile head, sliding mass and the root part of the pile, respectively. Numbers with asterisk refer to those in the literature.

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When we treat the soft ground phenomena such as landslide and land-subsidence, it is always an important subject how the pore-water which is one of the constituent elements of the clay responds to external stresses.
In order to make clear the phenomena experimentally and more minutely, not depending on the existing hypothesis, the author examined it rheologically based on laboratory measurements with small pore-water pressure sensors which was inserted into the clay directly.
As the result, it became clear that the pore-water pressure itself consists of the recoverable elastic component and the nonrecoverable plastic component, and the response of the internal pressure to external stress changes with the variations of water content.

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In order to estimate the location of veins of ground-water, underground temperature survey at one meter depth was conducted at the Miyagami land slide area in Hyogo Prefecture. On the basis of he result of the survey, four water-collecting wells were constructed in and around the vein (shown Fig. 4). The Effectiveness of these works was examined by the results of the observation of ground-water level of nineteen bore holes in the land slide area from 1973 to 1977.
The following important results could be drawn from the investigations.
1. A large quantity of water which can be collected by drainage works exist in the vein of ground-water estimated by the survey.
2. A small water was observed in the well constructed outside the vein, but a large quantity of gushing water was observed when some draining bore holes were made toward the vein from the well. On the other hand, the works of the well through the vein was troubled with gushing water and extrusion of soil during construction.
3. The water-level of some bore holes digged in the vein falled remarkably in comparison with other bore holes.

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