An approximate method of analysis has been developed to estimate the settlement and load distribution of large piled raft foundations. In the method the raft is modelled as a thin plate, and the piles and the soil are treated as interactive springs. Both the resistances of the piles as well as the raft base are incorporated into the model. Pile-soil-pile interaction, pile-soil-raft interaction and raft-soil-raft interaction are taken into account based on Mindlin's solutions. The proposed method makes it possible to solve problems of large non-uniformly arranged piled rafts in a time-saving way using a PC. The method can also be used for the deformation analysis of pile groups by setting the soil resistance at the raft base equal to zero. The validity of the proposed method is verified through comparisons with existing solutions. Two case studies on settlement analyses of a free-standing pile group and a large piled raft are presented. In the analyses, applicability of the equivalent pier concept is also examined and discussed. The computed settlements compare favourably with the field measurements.

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A simple but automated pneumatic loading system that can control the stress and strain rates for one-dimensional (1D) compression of clay was developed. The rate-dependency of stress-strain behaviour due to the viscous property of clay was investigated by 1D compression tests on standard-size specimens by various loading methods: 1) Standard Consolidation Tests (SCTs), stepwise increasing the axial stress two times every one day; 2) ordinary Constant-Rate-of-Strain (CRS) tests at different strain rates; 3) special CRS tests including unloading and reloading cycles with different stress amplitudes at strain rates of which the absolute value was either kept constant throughout respective tests or changed at the start of reloading; and 4) special CRS tests including a number of sustained loading (SL) during otherwise primary loading or unloading or reloading at constant strain rate. Sufficiently low strain rates were employed to ensure essentially fully drained condition. The followings were found. Despite that the newly developed pneumatic loading system is rather simple, 1D compression tests following such various loading histories as above can be performed on four types of clay rather accurately. The stress-strain behaviour of clay is significantly rate-dependent, exhibiting significant creep strains at SL stages. The creep strain rate is significantly different whether SL starts during otherwise primary loading or unloading or reloading, controlled by the magnitude and sign of the initial strain rate at the start of SL. The whole observed trends of rate-dependent stress-strain behaviour can be qualitatively explained by the non-linear three-component elasto-viscoplastic model extended to cyclic loading conditions.

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A stress path method for computing the settlement of normally consolidated clays is presented. The proposed method introduces the characterization of the stress-strain behavior that eliminates unnecessary experimental cost due to uncertainty in the design stress path. For arbitrary control of the effective stress during consolidation, a technique of back-pressure equalization, which enforces the immediate drained condition on the soil specimen without change of the effective stress state, was used. To account for nonlinear anisotropic response in computing the consolidation strains, the iteration procedure was designed. For the proposed method, the stress path experiments on the normally consolidated kaolin were conducted. An example illustrating the feasibility of proposed method in precisely calculating the settlement is shown for a circular footing on the clay stratum.

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A compression (P-) wave velocity measurement system was improved to evaluate vertical small strain Young's modulus of sand and gravel specimens. The wave was generated using a multi-layered piezoelectric actuator attached to the top cap of a triaxial cell specimen and received with two piezoelectrical accelerometers at two different positions on the specimen's side. This system includes use of a peak to peak travel time based on excitation records that were triggered by single pulse or sinusoidal wave and stacked for 128 times. The vertical Young's moduli (E_d) obtained by using this dynamic measurement were then compared with the statically measured vertical Young's moduli (E_s) that were evaluated by conducting small unloading/reloading cycles on the same specimen. Two series of tests using medium and large size specimens, respectively, were conducted on three kinds of material namely Toyoura sand (D₅₀=0.23 mm), sieved Chiba gravel (D₅₀=3 mm) and original Chiba gravel (D₅₀=6 mm). No significant effect of specimen size was observed on E_s and E_d of Toyoura sand. E_d was found larger than E_s in all three types of materials while the difference between the two was not the same. Combined effects of the dry density and the wavelength in the dynamic measurement were then discussed.

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Failures of earth dam embankments and river dikes, which are constructed of sandy soils with low dry densities, have been observed to occur during rising of water levels. In this paper, a large-scale physical model test was conducted in order to investigate the behavior of a small dam embankment as water levels rose. The test results were simulated by use of a consolidation analysis method coupled with an elastoplastic model for unsaturated soils. All parameters used in the simulation were obtained from element tests; oedometer, triaxial compression, soil water retention, and permeability tests. First, in order to verify the parameters identified, direct shear tests were simulated using the consolidation analysis method; results of the simulation and the tests were consistent. From the embankment model test it was found that the crest of the embankment moved upstream at the first stage of impounding and then moved back. After a seepage surface appeared on the downstream slope, tension cracks occurred on the downstream slope, and sliding occurred through the crack and the downstream toe. The results of the simulation were consistent with those of the model test. This consolidation analysis method could be used to simulate the complex deformations induced by saturation collapse and shear strains and even failure behavior. Old embankments constructed with loose densities might have histories in which cracks occurred on the downstream slopes when the reservoir water level rose, and their stabilities might have decreased.

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In this paper, based on experimental results a new constitutive model, using skeleton stress and degree of saturation as independent state variables, is proposed for unsaturated soil, in which the influence of the degree of saturation can be properly described. In the model, a very simple moisture characteristics curve considering moisture hysteresis of unsaturated soil is also proposed. The moisture characteristics curve can not only be applied to secondary drying process but also primary drying process originated from slurry soil. The constitutive model is able to describe not only the behavior of unsaturated soil but also saturated soil because the skeleton stress can smoothly shift to effective stress if saturation changes from unsaturated condition to saturated condition. Meanwhile the overconsolidation, one of the main features of soils that are discussed in the models for saturated soils, is also considered together with the degree of saturation. Other mechanical features such as structure of soil and stress-induced anisotropy can be easily incorporated into the proposed model within the framework of the present research. It is known from the simulation that the main features of unsaturated soil in isotropic consolidation test and triaxial compression test under drained and exhausted condition with different confining stress and suction can be qualitatively described.

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In this study, microbial precipitation of carbonate was observed using high microbial urease activity, and it was found that the ratio of Mg/Ca affected the types of crystals produced. Without Mg²⁺, calcite was produced using only CaCl₂, while the presence of Mg produced Mg-calcite, magnesite and/or possibly dolomite of round, spherical or fibrous shapes, depending on reaction time, pH and Mg/Ca ratio. The carbonate produced contributed to the development of cementation for sands. The presence of Mg showed a relatively strong cementation of the carbonate.

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It is well known that strain localization and microstructural changes are important issues in the onset of failure problems. In particular, unsaturated soil exhibits more brittle failure due to the collapse of the water meniscus, caused by shearing or the infiltration of water, than saturated soil. The aim of this paper is to observe the strain localization behavior and the microstructural changes in partially saturated soil during the deformation process using microfocus X-ray CT. The microfocus X-ray CT system employed in this study has a very high spatial resolution of 5 μm, which is enough to visualize the sand particles and the other particles individually. In addition, X-ray CT scans can be performed under triaxial conditions. The strain localization of fully saturated, partially saturated, and air-dried sand specimens during triaxial compression tests is observed and discussed. The microstructure of unsaturated soil, consisting of soil particles, pore water, and pore air, is successfully observed in partial CT scans. Through a comparison of the microstructures in the shear bands and in the initial state, the microstructural changes are discussed.

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Stress and strain history play a major role in defining the final grading of a soil, and by studying how the particle size distribution of a soil evolves with stress and strain it may be possible to highlight some important aspects of the sediment past history. In this paper, the characteristics and evolution of the grading of a till from Iceland, so-called Langjökull sediment, are examined. Specimens of the till were tested in compression (triaxial, oedometer tests) to very high pressures, and in shearing (triaxial, ring shear tests) to very high strains. The change in grading corresponding to particle breakage during compression and shearing was monitored using sieve analysis and scanning electron microscopy. The results show that the particle size distribution of the till, which is well graded, does not evolve when the till is subjected to high stresses or strains. Additional tests on specimens made of the larger-sized till particles did however show signs of breakage during testing. This suggests that the current natural grading of the till was achieved by incessant shearing during its past history, and corresponds to an ultimate, “critical” grading. This is confirmed by the mineralogical analysis of the sediment, which highlights a single parent rock and weathering of the particles by mechanical processes only.

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Colloid-facilitated transport enhances migration of strongly sorbing compounds (e.g., radionuclides, phosphorus, heavy metals) in soil and groundwater. Mobilization, transport and deposition of soil colloids are the underlying processes governing colloid-facilitated contaminant transport. Although significant progress has been made in simulating mobilization and transport/deposition of model colloids in different collector systems, it may be inadequate for the prediction of natural colloidal behavior in the subsurface. This study quantifies the leaching of natural volcanic ash soil colloids (NC) as well as the simultaneous transport of applied water dispersible soil colloids (WDC) in aggregated volcanic ash soil columns. Two water-saturated soil columns were irrigated with artificial irrigation water (AIW) at an intensity of 80 mm/hr for 60 hours. Two additional columns were irrigated at the same intensity, but a colloidal suspension of 5 mg/L was applied after 20 hours for a period of 20 hours. Effluent colloid concentrations were measured in each experiment. HYDRUS-1D was used for the simulation and estimation of colloid transport parameters. The results clearly showed different kinetics for applied colloid transport and natural colloid leaching. Transport of applied WDC followed first-order attachment kinetics, while the two-site equilibrium/kinetic model with equal fractions of equilibrium and kinetic sites best described the leaching of NC. Coupling these best model approaches well predicted the simultaneous leaching of natural and applied colloids, hereby providing a useful tool for the design of colloid-based in-situ soil remediation systems.

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This study endeavors to predict the settlement that could occur in the future at a site where settlement due to embankment loading is already occurring at present. In the site studied here, large residual settlement of as much as 70 cm has already occurred in the 4 years since it entered into service. It is believed that settlement will also continue in the future because excess pore pressure is still present within the clay layers. Furthermore, according to the method of evaluation proposed previously by the authors, which is based on the sensitivity and compression index ratios, it can be judged that the ground includes clays that are sensitive to disturbance and have a strong possibility of large residual settlement. In this paper, simulation of the settlement observed up to now at the site as well as prediction of the settlement that could occur in the future was carried out by deducing the higher compressibilities possessed by the in-situ clays compared with the undisturbed clay specimens in the laboratory. The soil-water coupled finite deformation analysis was employed using the analysis program GEOASIA, in which the constitutive equation for the soil skeleton is mounted with the SYS Cam-clay model. In addition, the effect of modifying the vertical section of the embankment by overlaying in order to counter the settlement was also investigated by numerical analysis. The results showed that such a countermeasure cannot be expected to lead to faster consolidation and that it may require massive funding over a long period of time to cover the maintenance and management costs involved.

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Cement-treated clay with air foam, which is called Super Geo-Material (SGM), was developed to utilize dredged clay in an effective way. As SGM is mainly used at levels below the ground water table, water permeability and absorption properties of SGM will affect the durability of the material. In this research, the changes in SGM permeability and absorption as functions of the air foam fraction were investigated. First, permeability tests with triaxial apparatus and constant rate of consolidation tests were conducted on samples containing less than 10% of air foam by volume. From the results, air foam was found to be an impermeable medium in SGM. Secondly, a series of permeability tests and absorption tests were conducted for the SGM with different fractions of air foam while observing the specimen with a micro focus X-ray Computed Tomography (CT) scanner. The results showed that the permeability of SGM increased dramatically due to the appearance of interior water channels when the air foam fraction exceeded 30% by volume. The density distribution change and water absorbed zones of the specimens during absorption tests were estimated using the X-ray CT data. From these results, the air in the SGM was found to be progressively substituted with water from the surface to the inside of the specimen and the substituted zone expanded as it made its way to the specimen interior. The expansion velocity of the substituted zone was not affected by the coefficient of permeability but by the fraction of the air in the specimen.

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The degree of saturation of ground is conventionally measured at discrete points using transducers, soil moisture sensors, etc. In this paper, a novel method was developed to directly measure the degree of saturation of continuous region of ground by noting the variation in color of the ground as the amount of moisture in the soil changes. In this research, a series of experiments was conducted for the purpose of developing a method to measure the degree of saturation of ground by digital image processing. From photo images taken at various soil moisture contents, the colors of the images were converted into numerical values which were then related to known degrees of saturation. The results of the experiments showed that a method to measure the degree of saturation of ground by image processing was possible. The relation between degree of saturation and luminance value can be expressed in terms of second degree function. Good results were obtained for two soil samples with different colors and grain size distributions. The margin of error was in the order of ±5%. The method was validated through vertical seepage tests, where good agreements were obtained between the measured degrees of saturation by tensiometers and those estimated from the proposed method. The method illustrates the possibility of measuring the degree of saturation of a larger portion of the ground, which is difficult to perform using conventional procedures. With this method, contour diagrams of degree of saturation can be produced, making it possible to visualize the propagation of the saturated region.

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In order to investigate the deformation characteristics under a wide selection of stress history, ten series of stress probing tests on p′-constant shear stress plane on dense Toyoura sand are conducted by using hollow cylinder apparatus. This paper presents yielding behavior and non-coaxiality of Toyoura sand obtained from the tests. The stress probing tests consist of ten series of shearing tests each of which starts from systematically chosen individual initial stress point. Each initial stress point is subjected to load-unload stress history. The yielding characteristic is interpreted by means of a concept of multiple yield surfaces model which has three yield surfaces representing linearly elastic behavior limit, commencement point of rapid development in plastic strain and elasto-plastic range. As a result, an experimental evidence of the isotropic hardening, i.e., isotropic expansion of yield surface, induced by anisotropic loadings is obtained. This is what was tacitly assumed in the application of plastic flow rules. However, misalignment of directions between principal stress and principal plastic strain increment is observed. Moreover, plastic strain increment direction is found to be influenced by the given stress increment direction. These facts suggest the non-coaxiality between stress and plastic strain increment due to shear stress increment, even during monotonic loading with isotropic hardening. The plastic strain increment direction diverges from the normal direction to a surface which is a circle with its center nearly at the origin on p′-constant plane and which passes through the current stress point.

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This paper describes the field performance of prefabricated vertical drains (PVD) used in combination with reinforced embankments on peaty ground. A large-scale field test of PVD adopted in combination with an embankment reinforced using galvanized steel grid was conducted on peaty ground in Hokkaido, Japan. Although the site was characterized by extremely soft peaty ground, a stable, high embankment 11.8 m in thickness was successfully constructed through the combination method. A consolidation-accelerating improvement from the PVD and a reinforcement effect from the steel grid were clearly observed, and settlement of the PVD-improved peat layer corresponded roughly with Barron's solution with consideration to well resistance. However, it was necessary to make the coefficient of consolidation nine times as large as that seen in the results of oedometer testing. The surcharge embankment allowed a reduction of the coefficient of secondary consolidation for the overconsolidated peat layer (overconsolidation ratio: approx. 1.13) to approximately 60% that of the normal consolidated layer.

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