The shrinkage of allophane soil was studied in relation to structure. The structure was described in terms of two fabric units called S-unit and L-unit which were observed at different magnification levels with a scanning electron microscope. An S-unit is 1-2 μm in diameter and an L-unit is 100-200 μm in diameter. The characteristics of shrinkage and structure which were found to correspond to each other are as follows : (1) the commencement of residual shrinkage at pF 4.1 and the large amount of this shrinkage corresponds to the skeleton which is framed by a series of S-units and wherein allophane is continuously distributed. (2) the increase in normal shrinkage range after remolding corresponds to the breakdown of the structure with L-units and the subsequent release of the void water in the structure by remolding. (3) the reappearance of pF 4.1 as the value at which residual shrinkage commences after remolding corresponds to the fact that S-units remain after remolding. As for the effect of the shrinkage on the structure, it was concluded that the S-units became compacted and then combined, causing the L-units to become rigid. The structure information presented here was applied also to the description of such behavior as the decrease of liquid limit with decreasing water content and the sensitivity of allophane soil.

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Decomposed granite soil is widely distributed in the western part of Japan. This soil is often used as the material for embankment construction. These natural and man-made slopes, however, fail easily due to rainfall. Direct shear tests were conducted on undisturbed and compacted soils by impact and static compaction under unsoaked and soaked conditions. Strength anisotropy was investigated by direct shear tests in which failure planes are normal (H specimen) or parallel (V specimen) to the direction of depth and of compaction. The result shows that compacted soil has less shear strength than undisturbed soil. The shear strength of compacted soil by impact compaction is greater than compacted soil by static compaction. Concerning the strength anisotropy for both undisturbed and compacted soils, the anisotropy of the V specimen is greater than that of the H specimen, irrespective of unsoaked or soaked condition, method of compaction, water content or density. The decrease in shear strength of compacted soil due to soaking is more significant than that of undisturbed soil. This behavior is attributable to the apparent cohesion, not to the angle of shearing resistance. The authors propose a schematic diagram of soil structure in order to explain this behavior.

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A new type of pile, the expander body pile, is described in the paper. This new pile can be used for underpinning of structures which have been damaged, for example, by excessive settlements. The pile consists in principle of a folded steel sheet, the expander body, which is wrapped around the lower part of a steel pipe pile. The expander body can be inflated after the pile has been driven into the ground through the injection of cement grout. The bearing capacity of the pile is then increased partly throught the increased area of the base of the pile and partly through the compaction of the soil around the pile.The ultimate bearing capacity of the new pile can be estimated from either the maximum grout pressure required for the inflation of the expander body or from the results of different penetration tests such as cone penetration tests (CPT), standard penetration tests (SPT) and weight soundings (WST). The calculation methods which are based on the pressuremeter test have been used since the stress conditions at pressuremeter tests correspond closely to those at the inflation of the expander bodies. When results from penetration tests are used it has been assumed that the bearing capacity corresponds to the penetration resistance as determined by cone penetration tests (CPT) of the level of the expander bodies. Comparisons with test data indicate that the proposed design methods will give reasonable results. However, the measured bearing capacity for sand has been somewhat lower than predicted.

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This paper presents the theoretical and experimental studies on the pore pressure developed in saturated sand subjected to cyclic shear stress under partially drained conditions. We analyzed pore pressure buildup obtained under partially drained conditions using the three-dimensional consolidation equation. Though the rate of pore pressure buildup under undrained conditions has previously been used in this type of analysis (Seed et al., 1976 and Sasaki et al., 1982), the rate used in the present analysis was obtained from a series of cyclic triaxial tests carried out under partially drained conditions. Specifically, the pore pressure was decreased to a predetermined level of pore pressure which develops in the saturated sand specimen during each single shear stress cycle. The results of this analysis are useful in estimating the level of pore pressure which can develop, during an earthquake, in saturated sand deposits that have been treated using the gravel drain method. To examine the validity of the analysis, we performed liquefaction tests on saturated sand under partially drained conditions using the shaking table.The following conclusions were reached : The rate of pore pressure buildup under partially drained conditions u_q' is significantly different from the rate of pore pressure buildup under undrained conditions, and it is related to the coefficient of pore pressure decrease denoted by Δu/u^^-, where Δu represents the amount of decrease of pore pressure and u^^- represents the pore pressure before the decrease occurs. Moreover, the calculated results of the pore pressure developed in saturated sand under partially drained conditions are in good agreement with the results obtained experimentally in the shaking table tests.

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A liquefaction test method has been developed to evaluate liquefaction resistances under partially drained conditions. Both the influence of drainage conditions and the effect of cyclic frequencies on liquefaction are evaluated by conducting several series of liquefaction tests under different conditions of drainage including the undrained condition. It has been found that the strength increase due to partial drainage can be well represented by the relative density and the coefficient of drainage effect defined by α^^-=k/(fL), in which k is the permeability ; f is the frequency of cyclic loading ; and L is the length of drainage path. An evaluation method of liquefaction potentials in partially drained conditions has been proposed with an application to a case study.

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Experimental investigations indicate that an anisotropically consolidated clay changes its undrained shear strength depending on the experimental procedures and/or direction of shear. It is needed to formulate the anisotropy of undrained shear strength of clays for use in reliable analyses of shear failures of foundations, embankments, retaining walls etc. In this paper, the anisotropy of undrained shear strength is formulated assuming the anisotropy induced by the initial anisotropic stress state. Theoretical considerations on the undrained behaviour of normally and overconsolidated clays are made on the basis of a constitutive equation. Two equations describing the undrained state and the failure state are derived and, applying these equations to axi-symmetric stress state, derived are some equations which give the theoretical values of the undrained shear strength to be obtained from the triaxial tests on normally and/or overconsolidated clays. The validity of the equations are examined by the comparison of the calculated strengths and the experimental strengths reported in the past.

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A probabilistic slope stability model was developed that includes soil shear strength and pore pressure as random variables. A local estimation technique called the nearest-neighbor method was utilized for simulation of the spatial variability of saturated soil permeability values. The spatial variation in the soil permeability causes a variation in the position of the phreatic surfaces during steady-state seepage flow and, hence, pore pressures. A number of permeability sets were generated and the resulting series of phreatic surfaces were calculated. A series of slope stability computations was made combining the spatial variability of pore pressures and soil strength yielding a probability density function of the factor of safety. The probability of failure was computed from the mean and standard deviation of the factor of safety. The resulting probabilistic model was applied to a hypothetical embankment. In addition, a sensitivity study was performed on the influence of the variability of soil permeability. The results indicated that the variability of soil strength and soil permeability has a large influence on the outcome of the probabilistic analysis and that there is a large discrepancy in the magnitude of the probability of failure if the pore pressure uncertainty is excluded from the probabilistic slope stability analysis.

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An earlier model by the authors for the seismic liquefaction of sands is revised and extended. The model, based on liquefaction case history data and the hypothesis that increase in pore water pressure is proportional to the density of seismic energy dissipation, relates pore pressure increase during an earthquake to the earthquake magnitude, epicentral distance, initial effective overburden stress and standard penetration value of the site soil. The principal assumptions of the original model are examined and a revised model proposed. This includes an allowance for constant-Q material attenuation between the earthquake source and site and a non linear relation, based on laboratory testing, between pore pressure increase and density of dissipated seismic energy in the site soil. The effect of model uncertainty on probabilistic estimates of liquefaction hazard are examined, and a factor correcting for uncertainty is obtained in closed form.

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By using vertical and horizontal samples of undisturbed fibrous peat containing the amount of organic matters of 20%-80%, the volume change behavior during compression-swelling-recompression was investigated under an isotropic stress condition, and the change of pore diameter distribution due to compression was measured with a porosimeter apparatus. Moreover, in order to investigate the volume change behavior during drained shear on the isotropically normally consolidated specimens, the two series of triaxial compression tests, in which axial stress was increased while lateral stress or effective mean stress was maintained constant, were performed.Test results indicate that the large majority of openings of undisturbed samples of peat by has the pore diameters in the ranges of 100 μm-0.1 μm, and by compressing, the number of openings with the pore diameter of 0.1 μm-0.1 μm increases. The volume change of void space due to isotropic effective stress increment can be quantitatively estimated with the two inclinations C^^-_c and C^^-_s of compression-swelling line plotted on ln e vs. ln p' plane. Also, it was found that the amount of dilatancy of normally consolidated peat showed the linear relation against shear stress ratio and the rate of that to total volume change of peat element was roughly 0.3 over a wide range of shear stress ratio. Furthermore, it was verified that the total volume change could be represented by the sum of change due to the increment of effective mean stress and that due to the increment of deviatoric stress.

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This study concerns the effects of continuous rotation of principal stress axes on excess pore water pressure development during cyclic loading. Continuous rotation of principal stress axes has been known to exert some influence on the development of excess pore water pressure and failure of sand during cyclic loading. In an effort to investigate this aspect of the problem, several series of cyclic undrained tests were carried out in a static manner on saturated sampes of sand using a triaxial torsion shear apparatus. In this test apparatus, a hollow cylindrical soil specimen is subjected to a simultaneous application of both triaxial and torsional modes of shear stresses, which brings about the continuous rotation of principal stress axes.The test results indicated that, while the angle of internal friction remains unaffected, the continuous rotation of principal stress axes substantially reduces the resistance of sand to liquefaction by generating a greater amount of excess pore water pressure than in the case without the rotation.Some special tests were also performed to examine the effects of previous liquefaction on the undrained behavior of sand during the subsequent cyclic loading. The results show that the sand having previously experienced large deformations due to liquefaction exhibit a highly anisotropic stress-strain characteristics, whereby reducing the resistance of the sand drastically when sheared in certain directions.

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Model test results for the ultimate pullout capacity of shallow rectangular vertical anchor plates embedded in saturated clay have been presented. The width-to-height ratio of the anchor plates used in the tests has been varied from one to five. The ultimate pullout load of an anchor can be expressed in the form of a nondimensional breakout factor. Based on the experimental results, an empirical equation for determination of the ultimate pullout load has been presented.

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