A general plasticity based constitutive model is developed for simulating hardening, stress path dependence, volume change and coupling of volume and shear responses of a cohesionless soil, called "munich" sand. The model parameters are evaluated from a comprehensive series of laboratory multiaxial tests on cubical specimens of the material. The proposed model is verified by comparing predictions with observed test results and with predictions of the test behavior by using the finite element method.

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This paper describes a procedure for determining the insitu coefficient of consolidation by observing the dissipation of excess pore pressures generated during piezometer probe penetration. The procedure consists of a curve matching between the computer-generated plots and the field piezometer probe dissipation plot. The computer plots are developed by means of a two-dimensional uncoupled axisymmetric consolidation dissipation of an assumed initial excess pore water pressure distribution. The initial excess pore pressure distribution, calculated using cavity expansion theory, is related to the field penetration generated pore pressures. Computations are made in an incremental manner which permits pore pressure dissipation to occur during tip penetration. The new procedure was applied in studies of three different sites and the resulting coefficients of consolidation showed reasonable agreement with laboratory-determined values.

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The effects of sample preparation methods on the cyclic undrained stress-strain behavior of sands were investigated by means of triaxial and torsional shear tests using two kinds of clean sands and one kind of sand including fines, with a wide variation in the sample density. Four different sample preparation methods were adopted ; air-pluviation, wet-tamping, wet-vibration, and water-vibration. The differences in the effects of sample preparation method were found to be significant in both testing methods. However, specific ways in which the sample preparation methods affected the results were not consistent between the triaxial and torsional shear tests. This indicates that the process of estimating cyclic undrained simple shear strengths from triaxial strengths is not as simple as has previously been considered.It was found that in torsional shear tests the shapes of strength curves in the planes of the cyclic stress ratio and the logarithm of the number of cycles N_c are similar for different sample preparation methods, in the sense that the different curves collapse into a single curve when these curves are moved appropriately along the log N_c-axis. It was also found that for the same sample density the effects of the sample preparation method on the cyclic undrained stress-strain behavior decrease with the increase in strain. A new density index is proposed, from which the cyclic undrained behavior can be estimated for different sample preparation methods and for different kinds of sands until the shear strain becomes around 3% in double amplitude.

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A model which can simulate the deformation behavior of an anisotropic sand under the stress condition including arbitrary rotation of principal stress is proposed. The present model is based on the idea that the deformation behavior of soil is controlled by the sliding deformation on infinite potential sliding planes. Formulation of the two-dimensional stress-strain relationships on sliding planes by employing the quadric hyperbolic relation between shear strain and stress obliquity with the aid of Masing's rule, and application of the extended concept of "Compounded Mobilized Plane" by Matsuoka (1974) make it possible to predict the three-dimensional anisotropic stress-strain relationships. The verification with respect to the deformation behavior of anisotropic dense sand measured in the hollow cylinder apparatus indicates the sufficient capability of this model.

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The wave induced cyclic shear stresses in oceanfloor sands may cause a progressive build up of pore water pressure, leading to instability of the bed. This may constitute an important consideration in the analysis and design of various offshore engineering facilities. This paper presents a simplified procedure for the analysis of wave-induced pore pressure in the oceanfloor sands. A simple model for the generation of pore water pressure is used and the effect of its simultaneous dissipation, is also included in the analysis. Numerical solution is also presented in a set of curves which can be conveniently used to evaluate the wave-induced liquefaction potential of an offshore site with deep cohesionless sediments.

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A traditional method of studying the yielding of soil is to examine the stress-strain response obtained from laboratory shear tests. In this paper, the alternative method is presented and it is to examine the acoustic energy released from soil specimen during shear. A series of drained triaxial tests was performed on sand specimens which had been isotropically pre-stressed, and the on-set of plastic deformation was detected by the measurement of acoustic emission (AE).The test results show that there is a small elastic deformation without AE even for the sandy soil and the end of elastic responses is clearly indicated by the emission of acoustic energy. The results also suggest that the behaviour of the soil is elastic as long as the shear stress does not exceed the yield locus in three-dimensional stress space which is determined by the AE measurement.

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A simple and general elastoplastic constitutive model for clay is proposed that describes the stress-strain behavior of clay under various stress paths in three-dimensional stresses. This model takes into account precisely not only the influence of the intermediate principal stress on the strength and deformation characteristics of clay but also the influence of the stress path on the deformation characteristics of clay. The former influence is considered by using the mechanical quantity t_ij which is a generalized idea of the extended concept of "Spatially Mobilized Plane" (briefly SMP^*), and the latter influence by dividing the plastic strain increment into two components regardless that only a yield function and a strain hardening parameter are employed. Furthermore, the soil parameters of the proposed model are easily determined in the same manner as the well-known Cam-clay model.The validities of the proposed model are checked by analyzing various element tests on clay under triaxial compression, triaxial extension and plane strain conditions and comparing these analytical results with the experimental results.

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A series of cyclic undrained triaxial tests was performed to evaluate the effects of several factors on the cyclic undrained behavior of Toyoura Sand. This study was performed in parallel with a cooperative test program (Toki et al., 1986) where at five laboratories similar tests were performed following the same specified tes tprocedure. It was found by the present study that the cyclic undrained triaxial strength of air-pluviated loose and dense Toyoura Sand is rather insensitive to the change in (1) the loading frequency between 0.05 Hz and 1.0 Hz, (2) the height to diameter ratio H/D between 1.5 and 2.7 for non-lubricated ends, (3) the sustained compression period between 6 minutes and 16 hours and (4) the degree of end restraint for H/D=2.0 and 2.4, whereas the strength is affected by the change in (1) the method of pluviating sand through air when specimens are loose, (2) the speciman diameter and (3) the deviation from the isotropic stress condition during compressing the specimen. It is also suggested to evaluate the effects of various kinds of system compliance is such a unified form as shown in the paper. It is concluded that unaccountable and subjective scattering in the cyclic undrained triaxial strength data can be reduced to a small value without large difficulties by controlling the factors which influence the data, whereas the effects of system compliance on the measured strength should be taken into account appropriately even for fine sands as Toyoura Sand.

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A cooperative test program of cyclic undrained triaxial tests was performed by five laboratories for both loose (D_r=50%) and dense (D_r=80%) air-pluviated specimens of Toyoura Sand, which is a clean fine uniform sand having sub-angular to angular shaped particles. This test material has been widely used in Japan for the study of sand liquefaction. The tests were performed following the specified test procedures described in this paper. It was found that the cyclic undrained strength value for a specimen diameter of 5 cm is slightly larger than that for a specimen diameter of 7∼10 cm. The major part of the scattering of the data was found due to different specimen diameters. For a similar specimen diameter, a very good degree of agreement for cyclic undrained strength value was obtained.

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A numerical procedure to determine the location of the critical noncircular slip surface giving the minimum factor of safety is presented taking into account the effect of strength anisotropy of the soil in slopes. Comparisons are made with the critical noncircular slip surface in the soil slope with isotropic strength. Several case studies prove the strength anisotropy does not greatly influence on the location of the critical slip surface, but considerably affects the value of safety factor.

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A new test facility for inducing liquefaction in a large mass of saturated sand by cyclic shear is described. The sand specimen is 4 m wide, 6 m long, and about 5 m deep, and the cyclic shear stresses are applied by rotating a pair of walls hinged at the bottom, thereby forcing the sand specimen to deform. Based on elastic stress analysis, the ratio between the cyclic shear stress and the vertical effective stress is nearly constant within the middle part of the specimen, simulating the probable condition in level ground during earthquakes. When liquefaction is induced, the behavior of the sand is similar to that which has been observed in the field during actual earthquakes, and the time histories of excess pore water pressure and shear deformation are also similar to those which have been observed in shaking table tests on saturated sand. Thus, the test facility can induce liquefaction in a large mass of sand at a fraction of the cost of shaking table tests. The large size and sturdy construction of the facility enables one to follow normal construction procedures in preparing realistic test specimens for evaluating the effectiveness of various methods to mitigate liquefaction hazard.

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This note presents an upper bound calculation on bearing capacity factors for a circular footing on clay, of which strength increases linearly with depth. The results are compared with the values obtained by the slip line method as well as the equivalent values for square and strip footings. The values of the bearing capacity factor N_c obtained by the present analysis are found to be very close to those calculated by the slip line method, and also close to those for a square footing. It is confirmed that the shape factor of N_c decreases significantly with the increase of non-homogeneity of soils.

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