A general computational procedure is developed in this paper for calculating the long term response, and more specifically the evolution with time of the accumulated residual settlement of a traffic platform under the action of repeated vehicle loading. It is based on a structural analysis approach, which incorporates as an essential feature, the use of a cyclic constitutive law for the constituent materials, formulated on the basis of cyclic triaxial tests. A numerical tool has been set up with the help of a finite element code, in order to simulate experimental tests performed on reduced scale models of a railway track platform. A first comparison is being made between the numerical simulations and the experimental results, as regards the long term evolution of the residual settlement.

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This paper proposes a procedure to investigate the effect of construction control on the safety of driven piles, and provides a theoretical basis to verify and support existing empirical factors of safety (FS) and resistance factors used to account for the effect of construction control. The procedure is formalized in the Bayesian framework. In particular, how the FS and resistance factor can be determined in a rational manner based on on-site dynamic pile tests is explored. Five design methods for driven piles are investigated to illustrate the proposed procedure and parametric studies are performed to evaluate the effect of number of tests or analyses on the updated FS. The results indicate that the required FS can be reduced and resistance factor can be increased considerably through careful construction control, which depends on design methods, on-site test methods, and the level of control implemented. The required FSs and resistance factors after construction control obtained from this study are consistent with the existing empirical values. After sufficient control tests, the required FSs and resistance factors for different design methods are not sensitive to the accuracy of the individual design methods.

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There are well-established procedures for assessing the combined horizontal and vertical load capacity of isolated, shallow-depth pad foundations. However, when the pads act together in an interconnected group, as they do, for example, under an offshore platform, some of them may be unloading whilst the loads increase on others. How the pads in such groups respond to a monotonically increasing horizontal load up to failure; how their diameter and spacing might best be assessed for specific design loads; how their safety, with respect to load, might be improved by shallow-depth burial and how things change if the horizontal load is not distributed equally between the pads, are less well understood questions. The paper presents a simple, new methodology for investigating these problems together with numerical examples of its application.

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During strong ground motion, pile foundations are subjected to two special effects. First, behavior of the soil surrounding the piles is nonlinear. Second, large inertial forces are generated in the soil around the pile heads, causing separation between the soil and pile. In this paper, a new approach is presented to overcome material nonlinearity of the soil as well as geometrical nonlinearity arising due to separation. The analysis is performed in two steps. To account for material nonlinearity, equivalent linearization is used in conjunction with a hyperbolic model of the soil. The hyperbolic model defines the nonlinear stress-strain relationship of the soil. To deal with separation, a Winkler soil model is used. The dynamic stiffness reproduced by the soil model is changed according to the degree of separation. Depending on the level of excitation, different cases of separation arise which are investigated with skeleton curves. It has been found that due to separation, dynamic response of the soil-pile system increases whereas the dynamic stiffness decreases significantly.

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The conventional elastoplastic model premising that the interior of yield surface is a purely elastic domain is incapable of describing the plastic deformation by the rate of stress inside the yield surface. Thus, it is inapplicable to the description of cyclic loading behavior. Besides, the traditional elastoplastic model is independent of the stress rate component tangential to the yield surface. Therefore, it predicts an unrealistically high stiffness modulus for nonproportional loading process deviating significantly from proportional one. The extended tangential-subloading surface model proposed by Hashiguchi and Tsutsumi (2001) would be capable of describing the cyclic loading behavior and the inelastic strain rate induced by the stress rate component tangential to the subloading surface. In this article, the extended tangential-subloading surface model is applied to the prediction of deformation behavior of sands subjected to various loading ranging from proportional to cyclic nonproportional loading. The validity is verified by comparing with the various test data. Then, it is revealed that the incorporation of the strain rate due to the stress rate component tangential to the subloading surface is of importance for the description of nonproportional loading behavior.

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Proper warning and evacuation are essential for mitigating sediment-related disasters during heavy rainfall. For this purpose, a scientific and rational rainfall index should be established in accordance with regional geological and topographical characteristics. A new rainfall index, named R′, is proposed through a revision of the Rainfall Index R_f. The effect of preceding rainfall prior to a disaster-inducing rainfall is taken into account in this newly-proposed Rainfall Index R′ by utilizing the concept of “effective rainfall”. Rainfall records which were made during a serious disaster on June 29, 1999 and on September 15, 1999 in Hiroshima district were analyzed. Some other cases were also examined and taken to verify the effectiveness of this newly-proposed rainfall index. As a result of the study, it was found that R′ is superior to R_f for judging the occurrence probability of a sediment-related disaster from on-going rainfall records. It has also been shown from several cases in the past that R′ can identify not only area and time, but also mode and size of a disaster due to slope failures on Masado (decomposed granite soil) slopes which are widely spread around Hiroshima area.

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The paper describes a precise technique to compute the limit state exceedance probability of typical earth slopes and geosynthetic-reinforced soil (GRS) slopes using a low-discrepancy sequence Monte Carlo (LDSMC) method and an importance sampling with low-discrepancy sequence Monte Carlo (ISLDSMC) method. The LDSMC and ISLDSMC methods can efficiently compute the accurate limit state exceedance probabilities of typical earth slopes and GRS slopes with a limited number of simulations. This study presents a practically useful nomogram of seismic deformation and limit state exceedance probability with variable slope heights, backfill soil properties, and geometries. A simple estimation of the limit state exceedance probability of the GRS slopes is given based on the results of the conventional deterministic analysis. The results of these analyses show that the LDSMC and ISLDSMC methods are practically useful, efficient, and accurate for the limit state exceedance probability calculation.

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Three-point bending tests and plane strain compression tests were conducted to investigate tensile and shear failure in cement-treated sand. The bending test results were used to evaluate the tension fracture energy and crack opening displacements. From these results, the tension-softening relation was obtained using the energy balance approach. In the plane strain compression tests, the strain localization zone that occurs during a strain-softening process and the local displacements across the shear band were identified by an image analysis. The shear-softening relation and the energy consumed during the shear failure were estimated based on these local displacements. After the test, the shear bands that appeared on the specimen surface were observed with a microscope. This microscopic observation revealed the appearance of shear fracture zone and provided information on the thickness of the shear band. Moreover, we discussed the difference in the energies consumed by the tensile failure and the shear failure.

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Monotonic and cyclic behavior of the interface between a structure and gravelly soil was investigated using systematical tests. A series of monotonic and cyclic tests of the interface between a steel plate and gravel were conducted using a large-scale test apparatus through varying gravel types, surface roughnesses of steel plates, normal boundary conditions, magnitudes of normal stress and displacement amplitudes. Microscopic movements and crushing process of soil particles were measured coupled with macroscopic stress-displacement relationship response. Based on the results, it is concluded that monotonic and cyclic behavior of the interface between a structure and gravelly soil is significantly different from that of gravelly soil itself. Main behaviors of the interface includes: (1) shear strength is proportional to normal stress; (2) the interface between a steel plate and gravel exhibits insignificant strain softening; (3) normal displacement accumulates and the accumulation rate decreases with increasing shear cycles, but varies in well-regulated manner within a single shear cycle; (4) shear deformation is composed of indispensable slippage component on the contact surface and soil deformation component constrained by the structure nearby while the latter mainly contributes to volumetric change due to dilatancy; (5) mechanical response is dependent on shear direction due to cyclic shear application after an initial shear application; (6) evolution of stress-displacement relationship response are governed by the evolution of physical state including particle crushing and soil compression due to shear application; (7) main factors influencing on behavior include surface roughness of the structure, characteristics of the soil and magnitude of normal stress.

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Mudflow type failure of a gentle fill slope occurred at Dateshita, Tsukidate town during the 2003 Sanriku-Minami earthquake in Japan. The flowed fill material was pyroclastic sediment that was classified as a volcanic sandy soil with pumice. This study conducted laboratory shaking table tests to examine the change of the water retention nature that is attributable to vibration of this volcanic sand under an unsaturated condition. An electrical moisture sensor measured the change of the apparent volumetric water content of the soil mass with various water contents during and after shaking. The apparent volumetric water content was increased by shaking under the condition of a certain extent of water content. The extent of the water content corresponded to an in-situ one. Suction changes of the soil mass as a consequence of shaking were also tested from various initial suction states for both the drying and wetting processes. The suction change caused by shaking disturbance was observed. The suction change direction depends on the initial suction state. It is considered that the observed nature in two tests results, which is attributable to the peculiarity of the volcanic sandy soil with pumice, may be related to mudflow-type slope failure.

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The objective of this paper is to investigate three dimensional (3-D) failure patterns in sand due to a laterally loaded pile using X-ray CT. Here, a new apparatus of model loading test in which X-ray CT is employed for monitoring failure pattern of the ground around a pile was developed and a series of model loading tests were conducted using this apparatus. CT scanning was done for the model ground at several levels of loadings which were applied at the pile head. Not only cross sectional images for the ground but also those in 3-D were reconstructed. A proper image processing analysis was conducted in order to obtain effective CT images. And, the failure patterns of the ground under laterally loaded piles were visualized. It is emphasized that three dimensional failure patterns of the ground due to laterally loaded pile were visualized for the first time using X-ray CT.

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A rational method for evaluating the skin friction of non-displacement piles in sandy soils is presented by reconsidering the model which has already been proposed by the authors. The revision of the model is mainly made by assuming the soil-pile interaction mechanism as a simple direct shear mode in relation to the large strain state of soils. The model is characterized by a coefficient of effective horizontal stress averaged through the whole length of the pile derived as a function of a large strain state friction angle. The characteristics and ability of the model are shown by the parametric studies and the applicability of the model is verified through a database of full scale pile load tests.

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