Field data indicate that the P-wave velocity in sand or gravel is sometimes much lower than that of water, even if the soil is below the water table. It is well understood that a slight decrease in saturation normally evaluated by the -value has a significant effect on undrained shear behavior like liquefaction of saturated soil. In the first part of this research, theoretical formulations of the -value, P-wave velocity and Poisson's ratio are made by taking into account the decrease in bulk modulus of water due to a mixture of air bubbles. Then, computations are carried out using formulas based on the soil properties of a typical sand or gravelly soils and Masa soil from the Kobe area to make charts correlating the variables. These charts indicate that a small decrement in the -value in the interval of =1.0 to 0. will considerably decrease the P-wave velocity. Thus, the P-wave velocity which is easily measured in the field can serve as a convenient index to quantitatively evaluate the insitu soil -value.

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Based on the methods previously presented by the authors (Yasuhara et al., 1992, 1994, 1996) for predicting the degradation in strength and stiffness of soft clays in the course of cyclic loading, a methodology has been developed to estimate the cyclic loading-induced settlements. The method also includes not only immediate settlements but also post-cyclic long-term settlements due to dissipation of cyclically induced excess pore pressures in soft soils. The simplified formulae included in the proposed methodology are given as functions of the amplitude of cyclic-induced excess pore pressure normalized by the confining pressure, u/p'_c, plasticity index I_p and factor of safety against bearing capacity failure, F_s. The calculations of cyclic-induced settlements were conducted for soft soil deposits with different index and geotechnical properties. The results calculated using the proposed methodology are presented in the form of a design chart to give the settlement versus normalized excess pore pressure ratio relations including the effects of the plasticity index and safety factor for bearing capacity. An example of the calculated results using the proposed procedure for the earthquake-induced settlements of embankments founded on soft clay, is presented to demonstrate the practicality of the method for design at fields.

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Shaking table tests were performed to clarify the settlement in liquefied loose sand of a new foundation incorporating top-shaped concrete blocks. In the tests, blocks of half scale were installed as they are in practice, by using a crusher-run, a lattice of iron rods and iron bars. Shaking table tests were also conducted on foundations with two differently shaped concrete blocks to investigate the effectiveness of the three foundations in reducing settlement. One was a T-shaped concrete block, or a disk-shaped concrete plate with a leg. The other was a conical concrete block without a leg. The results of shaking table tests showed that the foundation with the top-shaped concrete blocks was most effective in reducing the settlement among the three types of foundation. FEM elastic analyses were performed to compute the stress distributions in the models and in-situ ground when the top-shaped concrete blocks were applied and to confirm whether liquefaction resistance of the sand layer below the foundation is large. Moreover, the factor of safety against liquefaction, F_L was evaluated in in-situ model ground, in order to compare with sensitivities against liquefaction in the ground without countermeasures and with top-shaped concrete blocks. For the liquefaction analyses, shear stress in the ground during an earthquake was estimated by dynamic analyses using the SHAKE computer program.

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The original Drnevich Resonant Column apparatus has been designed for testing cylindrical soil specimen with maximum longitudinal and torsional stiffnesses corresponding to approximate resonant frequencies 285 Hz and 318 Hz respectively. This apparatus has been modified successfully and its stiffness has been increased to over threefold in the longitudinal vibratory mode and at least twofold in the torsional vibratory mode. Monterey No. O sand samples prepared at approximate relative densities 43% and 60% were tested with the original and the modified apparatus in the range of effective confining pressures from 49 kPa to 588 kPa. Measurement of dynamic moduli values measured with the original apparatus were up to 23% higher, and damping values up to five times higher than those measured by the modified apparatus.

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In the 1993 Kushiro-oki Earthquake of Richter magnitude ., simultaneous recording of earthquake motions was successfully made at the ground surface and at a depth of 77 meters in a dense saturated sand deposit. The peak horizontal acceleration was 0.47 g on the ground surface and 0.21 g at a depth of 77 meters. The acceleration record at the ground surface showed a distinctive ground response, which consisted of a cyclic motion having a period of about 1.5 seconds overlain by a spike at each peak of the motion. In order to study the mechanism of this peculiar ground response, effective stress analysis was conducted on the dense saturated sand deposit. The model used for this study was a strain space multiple mechanism model, which takes into account the effect of principal stress axis rotation. The recorded earthquake motion at a depth of 77 meters was used as the input earthquake motion for the analysis. Sampling after in-situ freezing was done in order to evaluate the properties of the sand. The results of the analysis indicated that the observed ground response was due to the effect of dilatancy of sand, which plays a significant role in the response of the dense saturated sand deposits during strong earthquake motions.

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The behavior of the soft clay grounds subjected to repeated loading is different from that subjected to sustained loading. The difference in settlement between these two loading patterns should be due to secondary compression over a long period of time. Consequently, soft clay grounds subjected to repeated loading tend to be more compressible than those subjected to sustained loading. Therefore, it is necessary for engineers to predict post-construction settlements under repeated loading. In this respect, the preloading is considered to be promising as a countermeasure to reduce the settlement of clay under repeated loading as well as under sustained loading. The effect of preloading on post-construction consolidation settlement of soft clay subjected to repeated loading after removal of a part of preload is investigated in the present paper. It has become clear that the settlement of a clay sample after preconsolidation is mainly affected by the amount of preload, the degree of consolidation due to the preload, the amount of permanent load and the amount of repeated load after removal of preload. The calculated settlement versus time relations using a method to estimate the amount of consolidation settlement of soft clay grounds subjected to repeated loading after removal of preloading were compared with the observed degree of consolidation as parameters of the intensities of preload and repeated load.

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In this paper, centrifuge shaking table tests were conducted in order to understand the performance of seawalls during a seismic event. The model tests showed that the displacement of the caisson was much affected by the seaward shear deformation of the sand seabed beneath it during shaking. It was also confirmed that an armored embankment played an important role in the displacement of the caisson during shaking. Based on these test results, a two-dimensional DEM-FEM coupled analysis method was newly developed to numerically predict the deformation of seawalls covered with armored embankments during earthquakes. The movements of the armor units were calculated by DE analysis and deformations of the caisson, rubble mound, sand seabed and backfill were calculated by FE analysis considering the non-linearity of the soil materials based on the effective stress. Dynamic interaction was taken into account by delivering the nodal displacements of the finite elements or the nodal forces converted from the contact forces through the imaginary distinct elements defined at the boundaries between the DE and FE domain. The applicability of this method to the prediction of the deformation of seawalls was verified through numerical simulations of the centrifuge model test.

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Seismic records obtained from a seismometer array located in downtown Tokyo Japan for about ten years were inversely analyzed to estimate the dynamic soil parameters. Due to the illposed nature of the problem, the simple and often used "least square method" does not properly estimate the parameters. The Extended Bayesian Method combined with the Akaike Bayesian Information Criterion was introduced to overcome this difficulty. The results obtained were compared with dynamic triaxial test results obtained at the time of the seismometer installation. The shear moduli agree quite well with the estimated results, however the damping ratios estimated are slightly higher than the ones obtained in the laboratory.

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An earthquake of magnitude .6 occurred in the south-east coast of El Salvador on January 13, 2001, causing widespread damage to buildings and several kinds of civil engineering structures due to ground shaking and earthquake-induced ground failures, including several large-scale landslides. This paper discusses the results of the damage investigation conducted in the area after the earthquake, with emphasis on the general features of the earthquake and its effects on the ground damage, specifically the landsliding which occurred in natural slopes and the liquefaction of soil deposits. The occurrence of liquefaction in the alluvial plain exhibited several characteristics in common with those observed in other areas of similar condition. On the other hand, the main cause of slope failures in volcanic deposits was not clearly identified, and several possible sources of slope instability were pointed out.

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This text is concerned with the basic principles underlying current practice in the earthquake response analysis of soft alluvial deposits. Its special interest is focused on the stratification of alluvium that has been modeled in analyses by layers in which soil properties are uniform. Since the age and the effective stress are continuous in the vertical direction, it is possible that the soil-dynamic properties such as shear modulus and damping ratio are not uniform but varying continuously in the vertical direction. From this viewpoint, the conventional idea of uniform layers was examined in detail by conducting detailed investigations in-situ, as well as laboratory tests on continuously collected undisturbed soil samples. The test results show that soil properties continuously vary in the vertical direction within an alluvium. This holds true even when the soil type changes from clayey to sandy. In contrast, a discontinuity of properties was detected at an unconformity of Pleistocene layers where the age and sedimentation process are discontinuous. With this knowledge, an attempt was made to propose a recommendable modelling of soil stratification for practical earthquake response analysis on alluvium.

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The Split Hopkinson Pressure Bar method (S. H. P. ) provides a ready means for direct analysis of material dynamic response. Soil Specimens generally present poor mechanical properties, thus the classical experimental device has to be adapted. An original experimental arrangement "Three-Dimensional Split Hopkinson Pressure Bar" (3-SHPB) is proposed. It allows measurement of the complete three-dimensional dynamic response of soils. Experiments are oedometric type tests (rigid confining cylinder) involving dynamic radial stress measurement. Pseudo Poisson's ratio is then determined and the influence of strain rate is shown. In addition, other types of confining systems are used : soft and semi-rigid confinement and low impedance tests are performed. Results on different loading paths are compared with others on sands and clays. Analysis at grain-size level gives further elements on the comminution process.

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The paper focuses on the development and modelling of residual cyclic pore water pressure, u, in clay during undrained cyclic strain-controlled loading. Data obtained from a series of NGI type cyclic simple shear tests were employed. In addition to the amplitude of cyclic shear strain, γ_c, the number of cycles, N, and the overconsolidation ratio, OCR, a new component is incorporated in the conventional characterization of u. This new component is the volumetric threshold shear strain, γ_tv, of clayey soils, below which for all practical purposes u does not develop. The lack of understanding of complex clay microstructure and the associated interaction between clay particles during cyclic shearing makes the modelling of u in a manner other than curve fitting rather difficult. This is especially true in regard to the development of negative u in overconsolidated clays. A model based on the systematic curve fitting of the pore pressure data expressed in terms of γ_c, γ_tv, N and OCR is presented. The possibilities of the incorporation of such a model into existing numerical tools for simulation of the seismic and ocean wave loading response of natural soil deposits are briefly discussed as well.

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To study the mechanism of permanent ground displacement due to liquefaction, shaking table tests on 24 soil models were conducted. In these models, the slope of the ground surface, the thickness of a liquefied layer, the density of the liquefied layer and some other factors were changed. Permanent ground displacements did not occur at the boundary between the liquefied layer and the lower non-liquefied layer, but occurred in the liquefied layer with a constant shear strain. Relationships between the displacement and the thickness of the liquefied layer or the slope of the ground surface were also obtained. Then, vane shear tests and cyclic torsional shear tests were carried out to measure the rate of reduction of shear strength or shear modulus. By the cyclic torsional shear tests, it was clarified that the shear modulus decreases to a very small value due to liquefaction. Based on these test results, a simplified procedure for the analysis of permanent ground displacement was proposed. To confirm the accuracy of this procedure, it was applied to the models used for the shaking table tests and to typical soil cross sections of soil at Niigata City. Finally, some measures to prevent permanent ground displacement were discussed based on the shaking table tests and analyses.

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The framework of a methodology proposed by the authors to evaluate the permanent deformation of embankments due to earthquake motions is briefly presented first. In the proposed method, both static and dynamic stress analyses are performed by the finite element technique to determine the stress conditions of the finite elements in an embankment both before and during an earthquake. Based on the characteristic features of the dynamic stresses during earthquakes, static and dynamic stresses are applied to laboratory specimens to simulate the in-situ stresses as precisely as possible. The moduli of the soils used in the original static analysis are modified through softening parameters in accordance with the residual strain potentials of each element. Using the modified moduli, the residual deformation of the embankment is evaluated. The methodology is applied to two embankments in Japan which suffered severe damage during past earthquakes. The first case study gives a calculated permanent displacement as large as 1.81m, indicating considerable instability of the embankment which actually failed completely. In the second case study, the calculated settlement is 27cm, compared to the observed settlement of 21cm. Therefore, the results of the analyses show reasonably good agreement with the observed deformations of the embankments due to the earthquakes.

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A methodology to assess the permanent deformation of earth fills such as dams and embankments subjected to a shaking of an earthquake is presented. The method consists of a hybrid use of the static and dynamic response analyses and the laboratory soil tests by means of the triaxial torsion shear test apparatus. The static as well as dynamic analysis are made first using the finite element method to obtain the initially applied static stresses and also the time histories of shear stress during an earthquake. The tests are performed by applying the time histories of three components of dynamic stress plus the static state of stress thus obtained to the representative samples placed in the test apparatus. The residual strain potential obtained from the tests is incorporated into the static analysis to evaluate the final configuration of the earth fills deformed by the earthquake shaking. This methodology was applied to assess the seismic behavior of an earth dam in Japan.

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Elastic wave propagation in saturated soil is investigated in order to grasp the frequency dependent wave propagation property of actual soil. First, a closed form solution of Biot's equation is derived under a one-directional wave propagation condition. Then, the frequency dependent properties of waves in various soils such as clay, silt, sand, gravel and soft rock are computed and discussed. The behavior is shown to be classified into three states : low frequency, high frequency and transient. Properties hardly change in the low and high frequency states. The degree of saturation is shown to hardly affect the shear wave property, but it greatly affects the dilatational wave property, especially in a highly saturated condition. Permeability hardly affects the properties at low and high frequency states, but it does change the frequency range of the transient state. Next, the applicability of Biot's formulation is examined and the high frequency state derived from Biot's equation is shown to be valid when permeability is larger than that of silt. Finally, it is shown that various mechanical properties can be evaluated using the frequency dependent characteristics of the wave, some of which are difficult to measure in situ with conventional tools.

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Realization of a 3- TV system using the present day HDTV is proposed. This system is based on the stereoscopic principles transmitting the left and right eye view images of the object on multiplexed video lines. In the receiver, the video lines are demultiplexed, the missing lines are interpolated and the stereo pair of images are reconstructed in two picture tubes. By means of a bicircularily polarized viewing system, these stereo pair of images are made to offer a true 3- vision. This system takes the advantage of high resolution offered by teh HDTV system and at the same time adds only a minimal complexity to the circuitry of the HDTV transmitter and the receiver for converting the HDTV into 3- TV.

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In view of the significant role of the water film effect in flow failure for a liquefied sandy deposit, the mechanism of water film generation is numerically studied based on a 1-dimensional model test. The process of water film growth and decay can be simulated to a certain extent by a simple consolidation analysis, which indicates that only a small difference in permeability in layered sand is enough for a water film to develop. A 1 G shaking table test for a two-dimensional slope model with an arc of silt within a saturated sand is then addressed to discuss the dilatancy effect exerted in sheared sand during flow failure. It is possible that, once the water film is formed, the transmission of shear stress through it is interrupted, leaving the sand below free from the dilatancy ; this eventually allows the water film to stay without being absorbed during flow failure. The result of another shaking table test for a trapezoidal slope with horizontal silt seams indicate that water films beneath the seams enable the soil mass above them to laterally flow along water films very gently inclined even after shaking. If a silt seam breaks due to excessive pressure in the water film, it triggers re-liquefaction in the upper sand and leads to further instability.

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Very few attempts have been made to evaluate the liquefaction resistance from a ductility viewpoint. The authors propose a new method to evaluate the ductility of soils against liquefaction, based on the energy dissipation capacity obtained from stress-strain loops of the constant-strain-controlled cyclic triaxial test. The method makes it possible to evaluate the liquefaction resistance against large earthquakes like the 1995 Hyogoken-Nambu earthquake. The effectiveness of the proposed method is explained using the test results of various soils. To confirm its effectiveness, a comparison was made of the energy dissipation capacity for Masado soil on Kobe Port Island obtained from the cyclic triaxial test, the array observation data and the seismic response analysis. The energy dissipation capacity obtained from the above three procedures shows very consistent results.

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An empirical equation in use for estimating the pseudo-elastic shear modulus, G_f, of subsoil, associated with shear strains less than 0.001% is proposed in this paper. In a series of in-situ seismic cone tests performed nationwide, the profiles of both G_f and the in-situ void ratio, , with depth were successfully characterised at five sites, each comprising a soft clay layer deposited in the Holocene era. The database which comprised the original data from the field and laboratory tests, coupled with similar information on well-documented Holocene clay deposits in Europe, was statistically analyzed in attempts to determine a generalised relationship with which G_f of soft clay may be reasonably estimated only from routinely available borehole data; that is and the current geostatic effective overburden pressure, σ'_v. An empirical relationship, G_f=5, 000 -1.5√(σ'_v) (kPa), was derived from the statistical analysis applied to data from seven different clays worldwide, for which extended over a range between 1 and 5, and the overconsolidation ratio ranged roughly between 1 and 2. The applicability of the proposed relationship was evaluated for two case records, each in which the clay exhibited unusual behavior; i.., the undrained shear strength remained more or less constant with depth due to the existence of artesian pressure at one site, and, at the other, G_f decreased, whereas increased, with depth. It was demonstrated that even in these clay deposits exhibiting exceptional profiles, the proposed relationship was capable of predicting G_f with a reasonable accuracy by determining the profiles of and σ'_v with depth. In addition, the prediction when compared to G_max from carefully performed laboratory cyclic tests, yielded a better estimate of G_f from the in-situ seismic survey. Despite the fact that the empirical relationship was initially designated to estimate G_f of soft clays, it may be equally applicable to sandy deposits. This was verified by comparing it to similar, and well-established, relationships developed for sands. A case record as such is also described for a loose sand deposit at Higashi-Ohgishima in Tokyo Bay which was placed in 1960's by land reclamation.

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