This paper presents a simplified deformation analysis for a clay foundation under an embankment using the soil parameters for the constitutive model estimated from plasticity index and the elasto-plastic model proposed by Sekiguchi and Ohta. Based on this method, and using the finite element method, the deformation characteristics of a well documented case history for the Kurashiki trial embankment on a soft ground was investigated. A comparison with the measurements indicates reasonable agreement between the measured and computed values of the deformation characteristics for the multi-soil layers. The predicted lateral deformation, however, overestimates the field measurements. Based on these results, the present method can be concluded applicable to other fields and it may be stated with reasonable accuracy that other case histories with similar characteristics and parameters will probably behave in a similar manner.

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Reconnaissance studies carried out following the October 12, 1992 Dahshour earthquake, near Cairo, Egypt indicated significant sand-boil activities and liquefaction at several locations on both sides of the Nile River near the earthquake epicenter. The study reported in this paper gives a brief account of liquefaction activities during the Dahshour earthquake and reviews the geological and geotechnical characteristics of the Nile Valley and River Delta and the associated seismicity of this region in order to identify areas and formations that may be prone to liquefaction. Data from some 50 sites within the study area were analyzed for a preliminary assessment of liquefaction potential under seismic conditions similar to those associated with Dahshour earthquake. The analysis was made using two different methods, namely, Seed's method, and the Chinese Code method. Contrary to results reported for strong earthquakes, the agreement between the two methods at prescribed moderate ground shaking was found to be relatively poor, as Seed's method appears to underestimate the liquefaction potential whereas the Chinese Code method tends to be more conservative. The results, however, generally indicate that, under seismic conditions similar to the Dahshour earthquake, liquefaction potential should be considered at sites having saturated sand layers with SPT-N values less than 15 blows/300 mm within the top 15 m. The results also emphasize the need for more accurate seismic zoning in Egypt as well as the incorporation of a considerably larger amount of field data to produce reliable liquefaction risk zoning information.

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There is a definite need to detect subsoil liquefaction immediately after an earthquake so that an emergency program can be started as quickly as possible. The method proposed here attempts to interpret the seismic data obtained at the ground surface and to assess the thickness of a liquefied layer. The investigation was initiated by conducting shaking table tests on liquefaction of model subsoil. The test results suggested that the soil is in a state of resonance at the onset of subsoil liquefaction. Hence, the shaking of subsoil at this special moment can be studied by assuming a harmonic motion in the subsoil profile. In addition, the spectrum intensity, that is approximately equal to the maximum velocity, was demonstrated to occur at the time of maximum acceleration. It was also found that the maximum acceleration occurs at resonance and onset of liquefaction. The maximum values of acceleration and velocity of harmonic motion recorded at the surface can therefore be combined to indicate the maximum displacement at the ground surface. A combination of this surface displacement together with the theory of resonant motion makes it possible to assess immediately after an earthquake the thickness of a liquefied layer. An emergency program against liquefaction-related damage can therefore be initiated quickly. This idea was investigated based on model tests as well as seismic case histories, and was found to be reasonable.

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Laboratory shear tests were conducted on moderately dense assemblies of large and small glass beads in both solid and hollow cylindrical triaxial devices using either stress-controlled or strain-controlled lateral boundaries. The specimens were sheared in triaxial compression and extension, maintaining the mean stress constant, and volume strains were monitored. The results indicated that the mold used in preparing the specimen created a strong but localized ordering of particles at the boundary and that this type of initial fabric had an important effect on the volumetric behavior of the hollow cylinder specimens. There were also indications that the strain-controlled and the stress-controlled boundaries produced significantly different volume strains at the initial stage of shearing and that increasing the degree of strain-control decreased the amount of initial contraction. In order to compliment these observations, additional triaxial compression and extension tests were carried out with a series of solid cylindrical specimens of different diameters using the small glass bead assembly. The mean stress was again fixed and care was taken to eliminate friction at the top and bottom boundaries. In triaxial extension, the smaller diameter specimens exhibited densification greater than that of the larger diameter specimens. In triaxial compression, the volume change was approximately the same for all diameter specimens. These results support the presence of an initial local anisotropy associated with the mold and indicate that specimens should be at least 150 particle diameters in thickness in order that this anisotropy be negligible.

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Sample quality was studied at two different sites in Japan where thick marine holocene clay is deposited. Six different types of samplers used in this study were : the Japanese standard thin wall samplers with and without piston, the Laval sampler, the Shelby tube, NGI 54 mm and ELE 100 mm piston (ELE100) samplers. Sample quality was evaluated by the unconfined compression test, which is a standard test for evaluating undrained shear strength in Japan. It was found from this comparative study that the sample quality obtained by the Japanese piston sampler is the same as that obtained by the Laval sampler. The Shelby tube and the ELE 100 sampler, however, both provided poor quality samples. It is important in practice to establish a method for evaluating shear strength of soft soils without being affected by sample quality. Three types of laboratory tests were performed to evaluate the influence of sample disturbance on undrained shear strength : laboratory vane test and recompression techniques using triaxial and direct shear testing equipment. It was observed that these methods are quite useful to evaluate shear strength even for poor quality samples.

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A theoretical as well as a numerical study has been carried out with special emphasis on developing a basic understanding of how crack geometry influences hydraulic phenomena such as permeability and hydrodynamic dispersion in cracked bodies. The permeability tensor K_ij is formulated in terms of length, aperture and orientation of cracks plus one more non-dimensional scalar λ depending on connectivity among cracks. By extending the Robinson's formula, a general expression for λ is given as a function of density and anisotropy of existing cracks. Dispersion tensor D_ij con-sists of two different sources. The first comes from the fact that each tracer is forced to move along cracks the directions of which deviate from the mean path. The second comes from non-uniform distribution of hydraulic head throughout a cracked body. The second source has increasing importance not only when crack density is low, but also when crack arrangement is highly anisotropic. The distribution of head becomes extremely non-uniform, especially when overall hydraulic head gradient is parallel to the preferred orientation of cracks. The permeability tensor K_ij is isotropic so long as the related crack tensor N_ij is isotropic. Dispersion tensor D_ij is anisotropic unless the fourth-rank crack tensor N_ijkl is isotropic. Accordingly, any crack body characterized by an isotropic permeability tensor is not necessarily isotropic in dispersion.

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An alternative procedure to evaluate the void ratio of triaxial test samples is introduced. This method is recommended particularly when very loose samples are tested and an important volume change occurring during the saturation process is expected. In addition, using Toyoura sand a comprehensive set of triaxial tests carried out under both undrained and drained conditions of monotonic loading is presented. For the undrained contractive responses, the results showed two stages associated with the steady state. After the peak strength, the deviator stress drops to a minimum value which can be seen as a quasi steady state, thereafter, the strength increases to an ultimate value corresponding to the actual steady state. Undrained dilative responses clearly indicated the existence of an ultimate state developed at large deformations which represents the steady state of deformation. The results indicate that the quasi steady state is slightly affected by the initial mean stress, whereas, the steady state is unaffected by the initial mean stress. Furthermore, the locus of the ultimate states achieved through drained conditions of loading was shown to be coincident with the steady state line evaluated by means of undrained tests. Finally, according to the relative position of the steady state line with respect to the isotropic consolidation curves for the loosest and densest states of a given soil, the index, Relative Contractiveness, R_c, is proposed. It is postulated that R_c is related to the inherent liquefaction vulnerability of a soil.

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A laboratory test method for the determination of the coefficient of earth pressure at rest, K_o, in sandy soils is presented. In this method, initially, a series of undrained cyclic triaxial tests were made on high-quality undisturbed sand samples recovered by the in-situ freezing sampling method (FS sample), in order to obtain the relationship between the shear modulus at very small strain, G_o, and the effective confining stress, σ'_c. Next, the G_o was also calculated based on elastic wave theory by using the shear wave velocity measured at a depth from which the undisturbed samples were recovered. By equalizing the G_o values obtained from these two independent methods, the coefficient of earth pressure at rest, K_o, in the sandy soils, can be determined using the proposed simple method. The K_o-value of a diluvial sand obtained using this method is 0.84. Based on the test results on the sand samples obtained by the rotary type triple tube sampling method (TS sample), recovered from the same soil layer and the same depth, however, the K_o value obtained with this method was 1.44, which is considerably larger than that obtained from the FS sample. The larger K_o value of the TS sample compared with that of the FS sample is because the initial shear modulus of the TS sample is much lower than that of the FS sample for the same level of confining stress due to sample disturbance.

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This paper describes the stabilizing mechanism of a slurry trench excavation in soft clay under normal consolidation. Diaphragm wall construction, using the slurry trench method, is increasingly being applied to soft clay. To ensure the reliability of this method, it is important to clarify the stabilizing mechanism of slurry trench excavation. With regard to soft clay, Dibiagio et al. (1972), Aas (1976), Tamano et al. (1984), and Kanatani et al. (1984) discussed stress conditions in the trench wall. In this research it was recognized that the mechanism of trench wall stability in soft clay was to be studied. The experimental trench used for our study was 1 m wide, 9.5 m long, and 21 m deep. The clay layer comprises normally consolidated clay with an undrained shear strength of 29-73 kPa. Mechanical behavior measurements during experimental trench excavation are shown. Based on these measurements, the mechanism of trench wall stability is discussed; lateral inward displacement of the trench wall (up to 20 mm) caused the lateral pressure (earth and water pressures combined) acting on the trench wall to decrease below its original level at rest (before the trench excavation) and then to reach a balance with the slurry pressure, thereby maintaining trench wall stability. Consequently, normally consolidated soft clay yields only a slight trench displacement which achieves a balance between slurry and lateral pressures, thus permitting use of the diaphragm wall employing the slurry trench method.

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Dynamically-induced liquefaction of a saturated loose sand stratum is studied in centrifuge model simulations. A laminated container subjected to base excitation is employed to replicate one-dimensional shear beam conditions. Level site and mild infinite slope simulations are conducted at Rensselaer Polytechnic Institute (RPI) and California Institute of Technology (CalTech). The observed acceleration, pore pressure and lateral displacement responses show a high level of consistency, and are used herein to estimate the corresponding dynamic shear stress-strain histories. These histories shed light on the mechanisms of : (1) propagation of liquefaction through the stratum, and (2) soil response during liquefaction, and its effect on ground surface acceleration and lateral deformation.

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The presence of allophane and halloysite minerals impart special properties to volcanic ash soils including the absence of any correlation between the engineering properties and index properties for these soils. The plasticity angle has been suggested as a measure of the allophane content of volcanic ash soils by soil scientists and (plasticity angle) is defined by the angle, relative to the A-line intercept, where the Atterberg limits of the volcanic ash soils occur on the Casagrande plasticity chart. This technical note examines the correlations between plasticity angle and engineering properties of volcanic ash soils. The Atterberg limits and engineering property data for volcanic ash soils were taken from literature. The results of the study suggest that the plasticity angle is a good indicator of the shear strength (represented by φ'_peak and φ'_residual values) and compressibility (represented by C_c/(1+e_o)) properties of allophanic and halloysitic soils from quite different geographical regions. The strong relationships between plasticity angle and engineering properties is attributed to the dependence of the plasticity angle as well as that of the engineering properties on the allophane content of the volcanic ash soils.

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A new, simple method is presented for testing triaxial soil samples along constant strain increment ratio paths. In this method, by adjusting the ratio of the diameter of the top cap at the free end to that of the soil sample before a test, strain path testing with a constant strain increment ratio (the ratio of the radial strain increment Δε_r to the axial strain increment Δε_a) can be achieved using a double-cell triaxial apparatus with a simple automated control system. This is identical to the system used for consolidation and expansion tests under K_o-conditions. Test results show that : (1) strain path testing with a constant strain increment ratio can easily be performed for a triaxial soil sample in any moisture conditions (saturated, partially saturated or dry); (2) the relationship between the deviator stress ratio q/p' and the deviator strain ε_s=2(ε_a-ε r)/3 of sand observed in constant strain increment ratio path testing is hyperbolic in form, and the mobilized maximum deviator stress ratio depends on the magnitude of the strain increment ratio adopted in the testing; and (3) the relationship between the mobilized maximum stress ratio and strain increment ratio obtained from constant strain increment ratio path testing does not agree with that determined by Rowe's stress-dilatancy equation.

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