Large scale shaking table tests were performed on the gravel drain system as a countermeasure to liquefaction of the sand deposits. The size of the shaking table is 12 m×12 m and the size of models is 12 m in length, 3 m in depth and 2 m in width. The model sandy grounds with gravel drains and the half buried type road model were horizontally excited to investigate the effects of the gravel drains to prevent liquefaction of the sandy ground.Furthermore the cyclic laboratory soil tests and the finite element analyses were performed on the generation and dissipation of the pore water pressure during cyclic loadings. The following conclusions were obtained. i) The increase of the pore water pressure during the excitation becomes smaller near the gravel drain. The effective area of the gravel drain in this series of tests was less than 50 cm from the gravel drains. ii) The dissipation of the pore water pressure after the end of excitation can be accelerated by the gravel drain. iii) The large uplift acted on the half buried type road model by the pore water pressure generated during the excitation in the case that no countermeasure to liquefaction was installed in the model ground near the half buried type road model. On the other hand the uplift was remarkably reduced by installing gravel drains below the half buried type road model. The vertical gravel drains installed at both sides under the half buried type road model effectively functioned to stabilize the half buried type road model by preventing the water and sand flow from the outside area of the gravel drains. iv) The gravel drain system can be a good countermeasure to liquefaction of the sandy ground around the half buried or buried type structures, if it is appropriately designed. It is advantageous to use the gravel drains in such a way because the gravel drains with a filter zone can be easily installed around the half-buried and buried type structures since the ground is usually excavated before constructing such structures. v) The generation of the pore water pressure was calculated by using the two dimensional finite element computer program "SADAP" considering the dissipation of the pore water pressure. The calculation offered the relatively reasonable results on the pore water pressure buildup during the cyclic loading.

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Two series of drained and undrained cyclic tests were performed statically on cubic specimens of loose saturated sand, using a true triaxial test apparatus. Changes in three principal stresses were programmed so that they could twice produce two load cycles, each having different directions on the octahedral plane in three principal stress space. The first load cycle was always executed in the direction corresponding to the conventional triaxial compression. The second load cycle was executed in the direction different plane, from that of the first loading. The third and fourth load cycles were carried out in the same directions as the first and the second load cycles, respectively, but with an increased amplitude. Analysis of the drained test results showed that both volumetric and octahedral shear strains produced in the second loading tend to increase as the direction of the second loading deviates from that of the first load cycle. Similar results were also obtained for the pore water pressure and octahedral shear strain behavior in the undrained tests. It was then concluded that the effect of previous load history tends to taper off as the direction of the current loading swerves from that of the previous loading, and when the current loading takes a direction exactly opposite to that of the previous loading, its memory almost completely disappears and the sand behaves as if it were in a virgin state.

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Five embankments were rapidly constructed on an alluvial marine clay under a very low factor of safety. One embankment failed and two others must have been on the verge of failure. A stability analysis with the total stress method for each embankment was reported by Hanzawa et al. (1980) and showed quite good agreement with the field behaviour of embankments when the undrained strength of the clay was evaluated from the modified Bjerrum's method in considerations of the effects of anisotropy and strain rate.In this paper, a stability analysis with the effective stress method as well as comparison of measured and predicted excess pore water pressure is presented. Excess pore water pressure was predicted using pore pressure coefficient, A-value in consideration of the effect of strain rate on pore pressure behaviour and the predicted values showed good agreement with the measured values in spite of the fact that piezometers were installed in considerably different types of clay. Strength parameters, c' and φ' of the clay are discussed in detail in the light of fundamental properties of normally consolidated aged clay and a procedure for determining c' and φ' for short term stability analysis is proposed. Factors of safety obtained by the effective stress method were 20% to 30% higher than the reasonable values evaluated from the field behaviour of each embankment and strongly suggested the necessity to take consideration of the effects of anisotropy and strain rate in determining c' and φ' for practical stability problems.

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In the present paper the authors attempted to evaluate quantitatively the screening effect of reinforcement piles in sand backfills by centrifuge model tests. A thin steel plate and a perspex plate with a hinge at the bottom were used as model walls. The reinforcement consisted of thin steel bars tied at the top and bottom. The ratio of the diameter of the pile to the spacing of piles was varied. The model tests were carried out under 30 g of centrifugal acceleration with the measurement of total force on the wall and the observation of failure mechanism in the backfill.From the tests with no reinforcement in the backfill, it was found that the failure mechanism and the total force on the wall compared well with the prediction by the Rankine theory on the basis of the angle of shearing resistance deduced from the plane strain shear tests. The screening effect observed for the present tests was considerably smaller than that reported by other workers, and it was larger for the smaller diameter of the piles. The difference of flexural regidity of one order did not give rise to any significant difference in the screening effect.

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About 130 steel piles of 15 m length with L-shaped cross-section were driven into natural soil deposits at 10 stations for corrosion tests under a wide variety of soil conditions. Prior to driving, thicknesses of the test piles were measured and physical, chemical and electrochemical characteristics of the soil deposits were investigated. The piles were withdrawn approximately 2, 5, and 10 years after driving and the corrosion rates were evaluated.The test results obtained in this 10 years research indicate that(1) the withdrawn piles were generally in excellent condition, corrosion effects were minimal and independent of soil condition, (2) the average corrosion rate was approximately 0.01 mm/year per both faces of a pile over the period of 10 years, (3) the corrosion of the inner face of a pipe pile seems to be the same as the outer face, (4) it is difficult to find any particular soil parameter which influenced the corrosion rate most decisively, and(5) any effect on corrosion of steel composition (mild steel, copper-bearing steel or weathering steel), cathodic protection or protection by painting was not evident. Influences of welding, cold-working, and underground electric leakage current were insignificant.

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Several series of stress-controlled repeated triaxial compression tests are carried out on a remolded soft clay. Cyclic strength and deformation behavior are analyzed in terms of both effective and total stresses and discussions are made particularly on the influence of stress-induced anisotropy.From the effective stress point of view, the followings are emphasized as main conclusions.1) The cyclic undrained strength is almost independent of the frequency and the duration of repeated loading2) The cyclic strength tends to decrease due to remolding effect a little degree.3) The dynamic pore-water pressure normalized by the confining pressure can be expressed by a unique hyperbolic function in relation to the shear strain.On the other hand, a consideration in terms of the total stress on cyclic strength and deformation is characterized by : 1) Within the range of the low confining pressure, the cyclic strength surpasses the static one by 5 through 20%.2) The cyclic strength and the deformatoin modulus are not so strongly influenced by loading frequency.On anisotropically and isotropically consolidated clays, the difference in dilatancy and deformation is caused by the pre-shear effect. This fact is recognized from the viewpoint of the effective stress and the total one.On the contrary, the cyclic strength depends on the strain amplitude. However, as long as the cyclic strength is defined at the 15% strain amplitude, no difference between strengths of anisotropically and isotropically consolidated clays can be expressed in terms of both effective and total stresses.

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A seepage failure problem of a piece-wise homogeneous sand column subjected to a vertically upward seepage flow is treated theoretically from the standpoint of design of a loaded filter (or an effective overburden pressure of a loaded filter) which is placed on the top of the sand column. Specifically, a five-layered sand column which is a typical example of the general multi-layer case is considered. The critical state chart for seepage failure of the five-layered sand column is obtained by using an analytical method developed by the authors. This chart indicates almost all the information about seepage failure of the sand column : the mode of failure of the sand column, the stability of the sand column in its critical state, the state within the sand column, the effects of a loaded filter, the safety factor for seepage failure of the sand column, and so on. Thus it is concluded that, in a seepage failure problem of a piece-wise homogeneous sand column (or, in design of a loaded filter which is placed on the top of the sand column), to obtain the critical state chart of the sand column is most important.

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In order to study pore water pressure response and liquefaction characteristics of sand which has previously experienced liquefaction, two series of cyclic triaxial shear tests were run on loose saturated sand specimens in a static manner. In the first test series, sepcimens were subjected, at the end of the cyclic loading, to a large axial strain oriented to the triaxial compression under very low effective confining pressures in order to produce a state of liquefaction. After reconsolidation, the specimens were again subjected to the same sequence of cyclic stresses as before. The test results showed that the pore water pressure response and, hence, resistance to liquefaction of the presheared specimen was essentially the same in the second cyclic loading as the response of pore water pressures exhibited by the virgin specimen during the first cyclic loading. It was speculated that a newly formed cross anisotropic structure of the specimen during the application of the large preshear towards the triaxial compression had the same vertical axis of symmetry as that of the virgin specimen which was formed under gravity by the method of pulviation in water. In the second series of tests, a large axial strain oriented towards the triaxial extension was applied, at the end of the first cyclic loading, to a specimen under very small effective confining pressures, leading eventually to a state of liquefaction. After reconsolidation, the specimen was again subjected to the same sequence of cyclic stresses as before. It was found that the pore water pressure response in the second cyclic loading of the presheared specimen was different from the pore water pressure response exhibited by the virgin specimen during the first cyclic loading. This difference was ascribed to the fact that a newly formed cross anisotropic structure of the specimen formed during the application of the large preshear towards the triaxial extension had a horizontal axis of symmetry, as opposed to the vertical axis of symmetry preexistant in the virgin specimen formed by the method of pluviation in water. As a result of these observations, it was argued that a subsequent liquefaction of a sand which has previously been liquefied depends not only on the magnitude of preshear but more significantly on the direction of the preshear which is executed under very small confining pressures at the end of the previous cyclic loading.

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A rational method is presented for estimating the effect of multidirectional shaking on the basis of two parameters which can readily be determined from unidirectional cyclic shear tests on saturated sand under undrained conditions. The method is based on the assumptions that the generation of excess pore water pressure due to cyclic shear in one direction is independent of that in the transverse direction, and that the relationship between the shear stress amplitude and the number of cycles to liquefaction is linear in a log-log plot. The effect of multidirectional shaking estimated by the proposed method is in good agreement with that observed in the laboratory by other investigators. It is indicated that reduction of liquefaction resistance due to transverse shear becomes more pronounced when the excess pore water pressure starts building up earlier or the shear stress amplitude vs. number of cycles curve becomes steeper.

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As one method to reduce negative skin friction on a pile it can be considered that the pile is tapered. This principle is based on the fact that, when the surrounding soil settles down relatively faster than the pile, it separates off from the pile surface. In order to verify this fact, model tests of negative skin friction were done, using four piles having the following kinds of taper; 10 to 1000, 5 to 1000, 1 to 1000, and 0 to 1000, i. e. straight. For those tests a small steel bin was used where a base plate supported by piston cylinders was lowered as slowly as possible so that the sand filled there could settle down, developing negative skin friction on the pile surface.As a result, it could be concluded that the negative skin friction could be reduced by roughly 90% for 10 to 1000, 80% for 5 to 1000, and 50% for 1 to 1000 in comparison with a straight pile.

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