Our aim in this study was to achieve an independent reinforced soil structure with pile foundation that can be applied to such structures as earth retaining walls and countermeasures against the collapse of embankments or rockfall impact built on narrow construction sites, such as on slopes. In order to confirm the effectiveness of the application of pile foundation to reinforced soil structures by geogrid for improvement of the lateral resistance of the structure and to investigate the interaction between pile and reinforced soil structure, a dynamic centrifuge model test (25 G) was carried out. Two geogrid reinforced soil, one with piles and one without, were used in a countermeasure to reduce the deformation of a road embankment built on a slope in the event of an earthquake, and the effectiveness of the pile foundation to the reinforced soil structure was considered with regard to it affected the road surface. The details and the results of the dynamic centrifuge model test, as well as the interaction between pile and reinforced soil structure are described, and the effectiveness of the application of pile foundation to reinforced soil structure is discussed in this paper.

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Based on observations from constant strain rate experiments and from creep and stress relaxation experiments initiated at different stress levels it is found that sand exhibits patterns of time effects different from those observed in clays. It appears that time effects in sand may be associated with crushing of particles, and a mechanistic picture of time effects in granular materials is constructed in which time effects depend on interparticle friction, grain crushing and grain rearrangement. This mechanistic picture is based on measured behavior in drained triaxial compression tests on three different sands in which strain rate effects are observed as small to negligible. While creep and relaxation are caused by the same underlying phenomenon, it appears that results of creep tests cannot be obtained from results of relaxations tests, and vice versa. The phenomenon of static fatigue of individual particles seems to be at the root of time effects in sand. A review of previous studies of static fatigue is presented. Triaxial tests on a beach sand incorporating creep and stress relaxation are followed by grain size analysis to prove that grain crushing relate to the observed time effects. Additional triaxial tests are presented in which the effect of water is demonstrated in support of the static fatigue mechanism. Load-controlled tests on individual sand particles in the form of spherical glass beads (quartz) were performed by maintaining constant loads lower than the short term crushing loads. As do rock and concrete specimens in triaxial compression, the glass beads show effects of time to crushing.

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The load capacity of driven piles has been reported to sometimes increase or decrease with time after pile installation. An increase in pile capacity with time is known as setup, whereas a decrease in capacity is referred to as relaxation. In this paper, we review the current understanding of pile setup and discuss how to account for it in design. A total of forty-three dynamic tests were conducted over a period of five months on four H piles and four closed-ended pipe piles driven into layered soil. Test results show that the amount and rate of pile setup are quite different from those observed in other studies. Empirical formulas for predicting setup proposed by several researchers were compared with observations. Of the empirical formulas considered, the Svinkin (1996) lower-bound method predicted the rate of setup on these piles driven in layered soil relatively well. Additionally, some theoretical methods for prediction of evolution of static pile bearing capacity with time were tested against the dynamic pile test results. The bearing capacity from these theoretical methods was found to correspond to approximately 2 times the capacity measured at the end of initial driving by a dynamic test.

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In this study the field feasibility of an innovative thermal technique to improve the performance of prefabricated vertical drains (PVD) used in conjunction with the preloading ground improvement method is investigated. For this purpose, two identical 6.0 m high full-scale test embankments for preloading were constructed over the soft Bangkok clay where a conventional PVD system was installed underneath one embankment and a novel prefabricated vertical thermo-drain (PVTD) system was utilized for the other. The PVTD unit consists of a U-tube made of cross-linked polyethylene plastic (PEX) that is attached to a conventional PVD unit. Preheated water at about 90°C is circulated through the attached U-tube to raise the soil temperature underneath the PVTD embankment. The behavior of the two test embankments were compared in terms of excess pore water pressure and consolidation results. The comparison shows the advantage of a PVTD system over a conventional PVD system. The rate of consolidation increases significantly in the PVTD system due to the temperature effect on the hydraulic conductivity. Moreover, the embankment with the PVTD system generates more settlement due to the thermally induced irreversible contraction of saturated normally consolidated soft Bangkok clay.

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The stability and support effects of large-scale underground caverns located in jointed rock masses are principally ruled by the mechanical behavior of discontinuities. The major deformations of the host rock masses containing underground caverns originate from the normal and shear movements among the walls of discontinuities. Therefore, in the numerical simulations of the deformation behavior of underground structures, how to accurately model the discontinuities becomes a key problem. In this study, a 2-D distinct element code, UDEC, was used to analyze the deformation behavior of an underground cavern of a pumped storage power plant, based on in-situ geological data. The validity of numerical simulation was evaluated by comparing the numerical results with the site measurement data at two cross-sections of the cavern. Some local deformation behavior of the cavern affected by the characteristics of discontinuity distributions was discussed. The influences of cross-sectional shape of the cavern and the orientation of initial ground stress on the performance of cavern were evaluated. The simulation results revealed that the orientation, position and density of discontinuities as well as the cross-sectional shape of a carven influence its deformation behavior and stability significantly.

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Progressive change of microfabrics of deep-sea sediments during early diagenesis was analyzed using two drill cores collected from the Sites U1305 and U1306 of the Integrated Ocean Drilling Program Expedition 303 in the Labrador Sea in the northwest Atlantic Ocean. Microfabrics were analyzed by scanning electron microscope and deduced from anisotropy of magnetic susceptibility. Different microfabrics in three layers were distinguished in both cores: Surface layer with general void ratio >2.5, subjacent layer with void ratio 2.5-1.5, and deep layer with void ratio <1.5. Microfabrics of the sediments change downward (toward deeper part), as well as magnetic susceptibility anisotropy. Microfabrics in the surface layer are non-directional and characterized by the presence of many macropores larger than 10 μm in diameter. Clay platelets in this layer are linked to each other with edge-to-edge or high-angle edge-to-face (EF) contact. In the underlying layer, contact relations of clay platelets change to low angle EF type. Coarse siliciclastic fractions of this layer show horizontal preferred orientation, most probably due to overloading of the surface layer. Sizes of macropores decrease to several μm in diameter. In the lowest layer, clay platelets take horizontal preferred orientation according to further burial consolidation. Thus, the microfabrics of the sediments are developed from non-directional to preferred horizontal orientation with burial consolidation by following processes; 1) rotation of coarse grains in the layer with the void ratio >2.5 and 2) change of clay microfabrics in the layer with the void ratio <2.5.

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This study examines the effects of compaction on peak strength and small strain stiffness of large prismatic specimens of gravel by conducting monotonic and large cyclic loading triaxial compression tests. The specimens were prepared using an automatic compaction system while measuring quantitatively the compaction energy. For the evaluation of small strain stiffness, a static technique using small cyclic vertical loading with local strain measurement and a dynamic technique using P-wave measurement were employed. It was revealed that the peak strength of compacted gravel increased in a non-linear manner with the increase in the compaction energy. On the other hand, the difference between statically and dynamically measured small strain Young's moduli was reduced as a result of increase in the compaction energy. The peak strengths of three almost equally dense specimens were found similar to each other irrespective of the difference in the loading histories with/without large cyclic loading. However, the values of the axial strain at the peak stress state were different among the three specimens, affected by the different loading histories.

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An experimental study on the mechanical response of anisotropic seabed to wave force and oscillation of man-made structures such as wave dissipating blocks and breakwaters was performed on a model soil box with two-dimensional plane strain condition. Using model ground comprised of Toyoura sand reconstituted by air-pluviation method, a series of cyclic loading tests on model structures under several foundation conditions was conducted at a loading pattern which is capable of simulating the various stress states induced by both oscillation of structure and wave force. Test results showed that the strength and deformation characteristics of model sand deposits are basically identical to those estimated from the conventional cyclic undrained triaxial test and are different depending strongly on the changes in the depositional condition of the ground. Based on the results of model testing, the applicability of countermeasures constructed by both side wall and sheet pile was investigated to prevent ground failure. Considering the model testing results, it was also found that the installation of side walls beneath structures and sheet piles into the ground are advantageous as countermeasures against progressive failure on sand ground subjected to wave loading.

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Based on a series of shaking table model tests, it was found that the effects of 1) subsoil and backfill deformation, 2) failure plane formation in backfill, and 3) pullout resistance mobilized by the reinforcements on the seismic behaviors of the geosynthetic reinforced soil retaining walls (GRS walls) were significant. These effects cannot be taken into account in the conventional pseudo-static based limit equilibrium analyses or Newmark's rigid sliding block analogy, which are usually adopted as the seismic design procedure. Therefore, this study attempts to develop a simplified procedure to evaluate earthquake-induced residual displacement of GRS walls by reflecting the knowledge on the seismic behaviors of GRS walls obtained from the shaking table model tests.
In the proposed method, 1) the deformation characteristics of subsoil and backfill are modeled based on the model test results and 2) the effect of failure plane formation is considered by using residual soil strength after the failure plane formation while the peak soil strength is used before the failure plane formation, and 3) the effect of the pullout resistance mobilized by the reinforcement is also introduced by evaluating the pullout resistance based on the results from the pullout tests of the reinforcements. By using the proposed method, simulations were performed on the shaking table model test results conducted under a wide variety of testing conditions and good agreements between the calculated and measured displacements were observed.

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In this paper, based on the model proposed by Zhang et al., 2007, a miner modification for the evolution equation of overconsolidation is carried out at first and then a unique description of the overall mechanical behaviors of Toyoura Standard Sand (TSS), a typical clean sand, was conducted, in which the eight parameters for describing TSS is kept constant no matter what kind of loadings or drainage conditions may be. In the theoretical simulation, based on conventional drained triaxial compression tests and undrained triaxial cyclic loading tests. the material parameters of TSS are determined. By using the uniquely determined material parameters, other tests under different loadings and drainage conditions are simulated by the constitutive model. The capability of the model to describe uniquely the overall behaviors of the sand under different drainage conditions and different loadings with one set of fixed parameters is verified.

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Data from cyclic loading tests on sand-fine mixtures made of Ahmedabad sand and quarry dust are presented. Tests were performed at constant void ratio, constant relative density and constant sand skeleton void ratio, for a variety of fines contents. Instead of looking at the direct effect of fines content on the cyclic response of the sand-fine mixtures, a novel approach of analysing the cyclic test data is proposed, by normalising these data with respect to state. The important difference with other similar work on plain sand is that the reference line for normalising must take account of the fines content. Simple definitions of equivalent void ratio, which take account of fines content, have been used. The results presented indicate that state plays an important role in defining the cyclic resistance ratio and pore water pressure generation during cyclic loading.

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Ageing effects on the elasto-viscoplastic property of compacted moist cement-mixed granular material (GM) were evaluated by performing a series of non-standard drained triaxial compression (TC) tests. Two types of GM, crushed gravelly soil from a quarry and crushed concrete aggregate (i.e., a recycled material), were used. The specimens were produced by moist-compaction and then cured at constant water content under unstressed conditions for seven days. They were re-cured basically for two days under different stress states during otherwise drained TC loading at a constant strain rate. Yielding characteristics upon the restart of drained monotonic loading (ML) at a constant strain rate toward ultimate failure at the same or increased or decreased confining pressure were evaluated. The stress-strain behaviour before the stress state reaches the current yield locus is very stiff and highly reversible. Unlike elasto-plastic materials exhibiting no ageing effects, the yield locus expands during sustained loading at a fixed effective stress state due to not only yielding associated with creep deformation, controlled basically by the viscous property, but also ageing, controlled basically by time-elapsing. The shape and location of current yield locus depends on the location of the current stress state relative to the current ultimate failure envelope. The observed yield characteristics were analyzed based on a newly introduced interactive double-yield concept while in the framework of the non-linear three-component elasto-viscoplastic model that takes into account ageing effects as well as an interaction between ageing and inviscid yielding (and its potential decay by irreversible straining). The trends of stress-strain-time behaviour observed with the two types of cement-mixed GMs are essentially the same.

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Shallow skirted foundations are an attractive solution for supporting offshore platforms that are subject to uplift due to overturning or buoyancy loading. In practice, gapping may occur along the skirt-soil interface leading to a detrimental effect on uplift capacity. This paper presents results from beam centrifuge tests that investigated the effect of gapping on the transient and sustained uplift capacity of shallow skirted foundations. The results indicate that the transient uplift capacity following the formation of a gap was around 60% of that for intact soil contact along the skirt-soil interface. Under sustained uplift, the time to accumulate a displacement of 1% of the foundation diameter was reduced by an order of magnitude due to the presence of a gap.

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On the basis of the method for received waveform reconstruction that the authors had previously proposed on bender element test, this paper discusses the required characteristics of frequency response of the test system and frequency-swept signal, which are essential for the method, from the view point of reconstruction accuracy. In order to argue influence on characteristics of frequency response, frequency responses of several bender element test systems are experimentally identified by using eleven kinds of frequency-swept signals. Test results show that the frequency response of the system is substantially determined by the kinds of sample and identification of frequency response is affected by characteristics of input frequency-swept signal. Then reconstructed received waveform is calculated and compared to observed waveform. A normalized cross-correlation function is proposed to estimate quantitatively the degree of similarity between two waveforms and applied to the reconstructed and observed waveforms. This comparative analysis reveals that accurate identification of frequency response in a given frequency range leads to accurate waveform reconstruction. Also, test results show an additional advantage of this reconstruction technique in a noisy environment.

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In order to investigate the seismic behavior of conventional type and geosynthetic-reinforced soil retaining walls, 1-g model shaking tests were conducted. Model walls having a height of about 50 cm were placed on a subsoil layer and backfilled with a layer of dense dry Toyoura sand. They were subjected to several steps of horizontal irregular excitations. As a result, generation of negative pore air pressure in the backfill was observed. The maximum amplitude of the negative pore air pressure during each shaking step increased with the base acceleration. Based on analyses of the measured data, it was inferred that such negative pore air pressure was caused by outward wall displacement relative to the backfill and not by dilative behavior of the backfill. It would cause a reduction in the seismic earth pressures exerted from the backfill. This feature suggests an advantage of a rigid full-height facing for reinforced soil walls over the segmental types of facing. A simplified numerical procedure to evaluate earth pressure was applied while considering the effects of the negative pore air pressure, and it could qualitatively simulate the measured behavior in terms of the seismic earth pressure and the angle of failure plane in the backfill.

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It is common knowledge that the engineering properties of clays are greatly influenced by the type of pore fluids. However, the impact of the pore fluids on the geotechnical properties of the samples is even more dependent on the type of mineral and interlayer ions. Completely different behaviours could be observed with identical pore fluids but different clay minerals and vice versa. The liquid limit, plastic limit and undrained shear strength were determined for two types of smectites with different interlayer cations, namely Ca and Na-smectite. The pore fluids were varied by using different dielectric constants (ε) and electrolyte concentrations (n₀). The results show that the two kinds of soils respond in a similar way but with a different magnitude depending on the ion occupation.

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