A strict upper bound solution to limit loads on strip footings over two-layer clay foundation soil is presented. Two mechanisms of failure are considered: one with a continually deforming field, and a rigid-block mechanism. The multiblock mechanism was found to be very flexible in terms of being able to assume different shapes of the deformation pattern. Consequently, this mechanism yielded the least upper bound to the bearing pressure. The method used was adapted to calculations of bearing capacity of strip footings subjected to loads with horizontal components. If the depth of the second layer of clay is sufficiently large, the shear strength of this layer will not affect the bearing capacity. This depth is referred to here as the critical depth, and it depends on the footing width and the combination of the undrained shear strength in the two layers. If the undrained shear strength of the bottom layer is small compared to the top layer, the critical height may be as much as twice the footing width.

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An analysis of seismic passive/active thrust on a retaining wall is proposed, in which Kotter's equation is used to obtain, the distribution of soil reaction on the failure plane. The geometrical conditions in the analysis are similar to those of Mononobe-Okabe's analysis. The distinguishing feature of the proposed analysis lies in its ability to compute the point of application of the passive/active thrust, for which moment equilibrium condition is effectively utilized. The point of application of the passive/active thrust depends upon a combination of several parameters such as angles of wall friction, soil internal friction, backfill slope, wall back and seismic coefficients of vertical and horizontal acceleration. The computed values of point of passive and active pressure coefficients compare closely with available results and the point of application of the active thrust also compares closely with available experimental results.

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This paper shows the effects of the stiffness of an underlying soft clay layer on the strong motion response. Seismic behavior of Kobe's artificial islands during the 1995 Hyogo-ken Nambu earthquake is studied by centrifuge shaking table test. During the earthquake, it is known that the liquefaction damage on artificial islands was different at each site. The authors consider that this is due to the stiffness of the clay layer underlying the reclaimed ground because of the degree of consolidation. The model grounds used for the centrifuge test were made with clay and fill material sampled from Kobe Port Island, and the clay material was consolidated at two different degrees of consolidation, which correspond to those of the Port Island array observation site and the south-western part of Rokko Island. First, from the viewpoint of the reproducibility of in-situ behavior, we compared the seismic response and the ground settlement obtained from centrifuge test with those of the observation data of Port Island. Next, we compared the seismic response of the test results of the different degree of consolidation. It is found that the difference of stiffness due to the degree of consolidation of the underlying clay layer significantly affects the seismic behavior of reclaimed ground. The large damage is not always come to being on the ground with soft clay layer.

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Recent studies have revealed that damage to gas pipelines buried underground is mainly caused by liquefaction of the surrounding soil mass. Therefore, if the occurrence of liquefaction in underground soil where gas pipelines are buried can be detected immediately after an earthquake, a more efficient and quick measure can be implemented to prevent the expansion of damage. With this in mind, a "liquefaction sensor" which is based on the measurement of water level within a hollow pipe inserted underground is developed, instead of the conventional pore water pressure meter which is less durable. Several experiments, ranging from laboratory boiling tests and shaking table experiments to field flow and vibration tests, were carried out to examine the adaptability of the sensor. From these tests, it was observed that the water level inside the pipe increases as the excess pore water pressure in the adjacent ground is increased, and the two variables have a nearly proportional relation to each other. Therefore, the occurrence of liquefaction can be detected by measuring the water level within the pipe of the liquefaction sensor.

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Six centrifuge tests were conducted to study the possible failure mechanisms for open excavations in soft clay with DMM self-supported walls, and the pre-failure soil and wall behavior, as well as the effect of some parameters on the wall external stability. In the tests, in-flight excavation was conducted until failure. The DMM wall was modeled by a wall made from aluminum and acrylic plates, which were instrumented with pressure cells to measure the active and passive earth pressures, and the base contact pressure of the wall during excavation. Upper bound analysis was conducted to verify the efficiency of the currently used design method, and to identify the main parameters which affect the external wall stability. It was found that the failure of the excavations with DMM self-supported walls floating in the clay, took place suddenly without marked pre-failure soil and wall movements. The main parameters which affect the wall stability are the wall dimensions, the soil strength profile, the adhesion between the wall surfaces and the surrounding clay, the strength anisotropy, and the surcharge on the clay surface. The soil strength profile and the adhesion between the wall surfaces and the clay were found to be the most important parameters.

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During the past ten years, the Statnamic load test has drawn attention from the piling community as one of the most economical methods for pile load testing. However, almost all of the research and development have been based on data from field tests. A consistent interpretation is difficult to achieve with such data due to the uncertainty and the complexity of the ground. To overcome this deficiency, the first objective of this research is to develop a system whereby Statnamic load tests can be performed under one constant condition. A small-scale Statnamic loading device for model tests has been developed whereby pre-compressed air is applied instead of gas from an explosion. In this study, two types of piles, friction piles and end bearing piles, are modeled and are loaded with two levels of forces, namely, small loads and large loads. The former loads are for determining the initial stiffness of piles and the latter for determining the ultimate capacity. The second objective of this study is to develop a 3D-FEM program that can analyze various types of loading. For a dynamic analysis, the solution is determined by the direct integration in time domain. The experimental results show the possibility of producing a loading curve similar to that in the original Statnamic load test. The analysis also shows that the force distributions in piles under Statnamic loading are similar to those under static loading.

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Earthquake induced flow slides of saturated or partially saturated sloping ground have taken place in man-made earth structures during past earthquakes. Two series of dynamic centrifuge model tests (1:50 scale) were conducted to simulate the behavior of embankment fills and infinite slopes resting on a stiff sloping base. Conditions that yield earthquake-induced flow slide were investigated. The test parameters included soil density, slope angle, level of phreatic water and shaking intensity. The test results showed that downward deformation increased with decreasing soil density, increasing phreatic water elevation and shaking intensity, and that there existed a threshold soil density below which flow slides occurred. Undrained monotonic loading torsional simple shear tests were also conducted. Conditions inducing very large deformation or flow slide that were obtained by the undrained shear tests were consistent with those observed in the model tests.

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Several cyclic torsional drained simple shear tests were performed on Toyoura sand in order to investigate the stress-dilatancy relationship under a large number of regular and irregular loading cycles. In particular, effects of different factors such as initial anisotropic stress state, initial confining pressure, density and shear history on this relationship were studied. It was found that the stress-dilatancy relationship changes suddenly after each loading reversal with a contractive behavior. When loading reversal occurs at a higher value of stress ratio, more contractive behavior is observed after the reversal. Although the stress-dilatancy diagrams of different cycles start from a different extent of contraction in irregular loading, they converge to a common one as stress loading continues. Test results showed that initial confining pressure and initial anisotropic stress state do not have any important effects on the stress-dilatancy relationship. It was found that density and shear history affect the stress-dilatancy relation. Change of stress-dilatancy relationship due to increase of density or shear history leads to less contractive behavior. Results of this research provide complete and accurate information on the stress-dilatancy relationship under a large number of regular or irregular cyclic loading and effects of different factors on this relationship. This information can be used in the modeling of cyclic stress-dilatancy relations and volumetric strain. The investigated volume change and stress-dilatancy relationship in this study together with seepage analysis can predict the excess pore water pressure for liquefaction analysis.

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The effects of the size and solubility of an air bubble on the B-value and P-wave velocity of a partly saturated sand are discussed. The relations between B-value and P-wave velocity are determined for large triaxial specimens with D_r=64% and 84%. Theoretical formulas have been derived for determining the P-wave velocity of a partly saturated sand containing air bubbles. It is shown that: (1) the solubility of air bubbles in the pore-water significantly affects the relations between B-value and P-wave velocity; (2) the practical coefficient of solubility of air bubble pressured in the pore-water is about 0.002; (3) the B-value and P-wave velocity increase with a decrease in the air bubble size. This tendency is significant, when the diameter of the air bubble is less than about 0.005mm.

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This paper describes a new calculation method for seismic displacement of retaining walls. A macroscopic failure surface and a plastic displacement potential in the general load space are considered in the method to evaluate the subgrade reaction force from foundation ground. The method is capable of calculating not only horizontal, vertical or rotational displacement alone, but also their combined effect. The method is validated through comparison with centrifuge test results of a gravity retaining wall with dense backfill sand subjected to strong base shaking. The calculated displacement components, that is vertical, horizontal and rotational displacement at the end of shaking, compared well with those measured. It also appeared that previously proposed conventional displacement calculation methods based on Newmark's sliding block analogy might underestimate the displacement. The assumption of the constant frictional coefficient may be responsible for this. The proposed method is limited to retaining walls resting on soils where dramatic degradation of soil strength due to the generation of excess pore pressure does not occur.

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This paper presents an analysis of the yielding and plastic hardening of uniformly-graded samples of a silica sand subjected to one-dimensional normal compression. Single grains of silica sand have been compressed diametrically between flat platens to measure indirectly tensile strength. Approximately 30 grains were tested for each of the following nominal particle sizes: 0.5mm, 1mm and 2mm diameter. It was found that the data could be described by the Weibull statistics of brittle ceramics, and the Weibull modulus could be taken to be about 3. 1. Uniform aggregates of the same sand were then compacted to maximum density and subjected to one-dimensional compression. The initial particle size distributions were 0.3-0.6mm, 0.6-1.18mm and 1.18-2mm, and aggregates were subjected to stresses of up to 100MPa. All particles were initially of similar shape, and hence the initial voids ratios of the aggregates at maximum density were approximately equal. The yield stress was defined to be the point of maximum curvature on a plot of voids ratio against the logarithm of effective stress, and found to increase with decreasing particle size, and to be approximately proportional to the tensile strength of the constituent grains. However, the plastic compressibility index was found to be approximately constant and independent of the initial grading, and a fractal distribution of particle sizes appeared to evolve under increasing stress. There is evidence to suggest that the aggregates evolve towards a fractal dimension of 2.5 under high stresses.

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The paper presents a study of the effects of initial fabric and shearing direction on cyclic deformation characteristics such as stress-strain response, shear modulus and damping ratio from drained static cyclic tests on medium dense Toyoura sand using hollow cylinder apparatus. The apparatus allows independent control of stress components, σ_z, σ_θ, σ_r and τ_zθ, and accurate measurement of strain components, ε_z, ε_θ, ε_r and γ_zθ, over a wide range of strains from 10^-3% to 10%. Three methods of sample preparation, air pluviation, water pluviation and dry rodding, were employed to produce different initial fabrics. Samples were sheared cyclically in p'-constant plane along the direction of major principal stress 0°(90°), 22.5°(-67.5°) and 45°(-45°) relative to the direction of deposition. Anisotropic behaviour was observed in stress-strain response and the secant shear moduli defined separately for each direction of major principal stress. However, the equivalent shear modulus was found to be little affected by the direction of the major principal stress. In addition, the effect of initial fabrics was not significant. The same was found for the hysteretic damping ratio.

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