In this paper, an analysis based on Prandtl's failure mechanism is proposed for the evaluation of bearing capacity factor, N_γ, using the limit equilibrium approach, coupled with Kotter's equation. Except for shape of the failure surface, no other assumptions are needed in the analysis. A methodology based on Kotter's equation and force equilibrium conditions is developed to identify the correct location of pole of the log spiral and hence the unique failure surface. Using moment equilibrium condition, the point of application of passive thrust is determined. The proposed N_γ values are compared with other available theoretical predictions and experimental results. They show a good agreement with some existing theoretical results and also show a better agreement with available experimental results. The analysis shows that pole of the log spiral lies at the footing edge for general shear failure conditions and the point of application of the passive thrust is strongly influenced by angle of soil internal friction.

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A hybrid foundation consisting of a mat foundation and a small number of complementary bearing piles was developed based on a completely new concept and applied to a building construction project in order to evaluate its effectiveness and applicability. The new concept is to maintain a constant pile axial force to avoid pile fracturing even if the building settles due to consolidation of the subsoil. Measured items were the axial forces of the piles, the deformation and settlement of the building, and the relative displacement between the piles and the mat. Then the measurements were compared with a numerical analysis. The measurements show that the reaction control device installed at the head of the pile worked effectively and the comparison between analytical and measured values shows that the behavior of the hybrid foundation can be numerically predicted in the design process.

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A hybrid foundation for buildings consisting of a mat slab and a small number of complementary bearing piles has been developed. In order to secure the subgrade reaction force against the mat foundation, the building itself must subside together with the soil. A reaction control device having a special kind of slide system is necessary in the hybrid foundation in order to deliver a certain magnitude of load from the mat slab to a pile head, because the settlement characteristics of bearing piles are different from those of shallow foundations. The static and dynamic behaviors of the hybrid foundation including reaction control devices are investigated through both experiment and numerical analysis based on a full-scale foundation model without soil. It was confirmed that the reaction control device smoothly absorbed the relative vertical displacements between piles and the mat slab while keeping the pile bearing forces constant, and the hybrid foundation transferred the lateral force of the mat slab to piles effectively.

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Using a simplified model, the load-settlement behaviour of a geosynthetic-reinforced soil is for mulated. The model and formulation are flexible to accommodate inhomogeneity of the medium and multiple reinforcement layers with no or very little extra computational effort. The developed formulation is verified by using the finite element method and is confirmed to be efficient and convenient for computation. Compared with the previous simplified soil model, the present model can be defined uniquely by soil material properties alone and has an adequate mechanism to reproduce the behaviour of a continuous medium including the shear load transfer. A previous simplified model was found to be inadequate for deep soft soil. Also, it was found that at relatively large load levels, multiple reinforcement layers are as effective as a combination of a single reinforcement layer and gravel layer in reducing the settlement.

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The applicability of the SHANSEP method was examined for six different natural clays, namely Louiseville (Quebec, Canada), Bothkennar (Scotland, UK), Yamashita (Yokohama, Japan), Amagasaki (Japan), Rakusai (Kyoto, Japan) and Singapore. All of these clays are somewhat overconsolidated and their OCR range between 1.9 and 5.0. It was confirmed that post-depositional stress change had taken place for the latter three clays, although their OCRs could not be fully explained only by the stress history. Some or all parts of the overconsolidation for the objective clays may have been created by reasons other than the stress change, such as ageing or cementation. The undrained shear strength (s_u) of these clays was examined using the SHANSEP method and compared with that obtained using the recompression method. All the soil samples were recovered using the Japanese standard fix piston or equivalent samplers, and strength evaluation was done using the triaxial and the direct shear apparatuses. It was found that the stress-strain relations as well as stress paths are somewhat different between the SHANSEP and the recompression methods : that is, larger strain and smaller internal friction angle at failure for the SHANSEP method. However, difference in s_u measured by the two methods was surprisingly small, the ratio ranging between 0.9 and 1.1. This research has led us to the conclusion that considering the variation in sample quality in practical soil investigation, the SHANSEP method is a quite useful method in evaluating the design undrained shear strength of a soil, which is free from sample disturbance. It should be noted, however, that the yield consolidation stress, which is an important soil parameter in SHANSEP method, is affected by sample quality.

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Liquefaction and settlement of reclaimed ground with gravelly decomposed granite soil, which had liquefied during the 1995 Hyogo-ken Nambu earthquake, was studied by a centrifuge model test using in situ soil material and the earthquake record. Three ground models used for the centrifuge test were made with different particle size ranges : 1) under 30 mm, 2) under 2 mm, and 3) 2-30 mm water-washed. A reclaimed layer of about 16 m thickness was modeled in 1/40 scale. The following results were obtained from this study : 1) Inferring from maximum acceleration response, independent of the above three grain size distributions, it was considered that shear failure occurred at a depth between K.P. -8 m to -12 m due to strong motion. 2) The liquefaction degree was not uniform in the depth direction. In grounds consisting of particles smaller than 2 mm, destructive liquefaction occurred at a lower depth ; also, volume compression at a corresponding depth was larger than that at the upper portion. 3) In the case of only-gravel content, no cumulative excess pore water pressure was generated because of high permeability. Settlement after vibration was also smaller compared with two other cases. 4) Permeability during the pore pressure dissipation process, which was identified from back analysis, was higher than the value obtained from the laboratory permeability test ; it also gradually approached laboratory test values during dissipation.

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Matsuoka (1974) proposed a two-dimensional stress-dilatancy equation of granular materials on the mobilized plane through the direct box shear tests on assemblies of aluminum and photoelastic rods, which was expressed as τ/σ_N=λ(-dε_N/dγ)+μ. In this paper, the stress ratio τ/σ_N and the strain increment ratio -dε_N/dγ are approximated to be tan χ^^- and tan θ^^-, respectively, on the basis of the numerically simulated results for a simple shear test by DEM. Here, χ^^- and θ^^- denote the average angle of the interparticle forces to the normal of the mobilized plane and the average interparticle contact angle on the mobilized plane, respectively. It was found that the difference between χ^^- and θ^^-, denoted as δ, varies slightly during shear. The angle δ is related to the average interparticle contact force f₀, the slope κ of the straight line that characterizes the distribution of the average interparticle contact forces against the contact angle, and the average interparticle contact angles θ^^- on the mobilized plane. The intercept μ in the stress-dilatancy equation is interpreted as tan δ. The influences of interparticle surface friction, grain shape and confining pressure on the stress-dilatancy relation are examined. It was found that the angle δ is not very sensitive to the interparticle surface friction angle φ_μ, except in the lower value of φ_μ, and independent of the confining pressure. However, it is affected to some extent by grain shapes. Various results of the newly developed in-situ direct shear tests on various granular soils are presented to support the arguments in this paper.

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In the companion paper of Shibuya et al. (2002), a four-dimensional local boundary surface (4-D LBS) applicable for understanding anisotropic shear behaviour of an isotropically consolidated loose Ham River sand (HRS) has been experimentally established by using four stress parameters : the shear stress, t=(σ^'₁-σ^'₃)/2 ; mean effective principal stress, p'=(σ^'₁+σ^'₂+σ^'₃)/3 ; the direction of major principal stress relative to the vertical (=deposition direction), α ; and, the relative magnitude of intermediate principal stress, b=(σ^'₂-σ^'₃)/(σ^'₁-σ^'₃). In this paper, the results of additional sets of hollow cylinder (HC) tests on the anisotropically consolidated samples are newly presented, and are interpreted after the framework of LBS. Undrained initial anisotropy of the loose HRS when subjected to a consolidation path with the effective stress ratio, K, fixed at 0.5, was manifested in a set of HC tests performed using different, but fixed in each test, α values under the conditions of b=0.3. The shape of a LBS of the anisotropically consolidated sample was demonstrated in a three-dimensional (t, p', α) space in another set of tests, in which the principal stress directions were continuously rotated in various manners. The undrained LBS of the initially loose samples of HRS which have undrained initial anisotropy and limits the effective stress space to be occupied by any undrained paths, was found to be not unique in shape, but pertinent to an anisotropic fabric formed at deposition and modified throughout the consolidation history which followed. The effects of the consolidation path were highlighted by examining the undrained strength at peak conditions.

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Experimental evidence suggests that a mutual relationship between anisotropy and structure of clays exists. It was hypothesized that development and decay of the structure of clays (called structuralizing and destructuralizing) can be regarded as development of anisotropy and decay of anisotropy (isotropization), respectively. Using this hypothesis, an anisotropic rotational hardening rule was incorporated in the Sekiguchi-Ohta elasto-plastic constitutive model. The subloading surface concept was also introduced to model the plastic deformation inside the yield surface more accurately. The proposed model provided some rational as well as physical explanations for the experimental facts. Using the proposed model, it was possible to simulate the apparent softening behavior observed in anisotropically consolidated specimens. For isotropically consolidated specimens, no softening was observed, which is consistent with the experimental data. At the critical state, the undrained shear strength of the anisotropically consolidated specimens was the same as that of the isotropically consolidated specimens. This is due to both specimens having the same soil structure after large shearing. The shape of yield surface obtained from stress probe tests was investigated by simulating the tests with the proposed model. Typical data of the stress probe tests of natural clays shows that the yield surface generally has a smooth elliptical shape. By modeling the rotation of yield surface, the proposed model was capable of simulating this 'apparent' yield surface.

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Mobile soil constituents such as soil colloidal matter and dissolved organic matter may affect the mobility of phosphorus (P) in soils. Phosphorus leaching of two fractions (colloidal and dissolved phosphorus) was studied in soil column experiments, using a surface loam soil from Higashi-hiroshima, Japan, with a high Olsen-P content (93 mg-P/kg). Repacked soil columns with or without artificial macropores were prepared. Artificial irrigation solution (0.085 mM NaCl+0.015 mM CaCl₂ solution) was applied for 6 hrs at an intensity of 10 mm/hr or for 2 hrs at 30 mm/hr. Six irrigations were applied to each column with 42 hr intervals between irrigations. Colloidal phosphorus (CP) leaching showed a minor increase with time. Dissolved phosphorus (DP) leaching was almost constant. DP dominated total phosphorus leaching with a contribution of 81-86%. Higher CP and DP leaching at lower irrigation intensity and from soil without macropores were observed. A high correlation between DP leaching and dissolved organic matter (DOM) leaching was seen (R²=0.82∼0.86). Batch experiments were conducted to investigate P sorption and results showed that phosphorus was sorbed to or formed complexes with dissolved organic matter. This study shows that DOM-facilitated transport is likely to be a dominating process for phosphorus leaching from high-P surface soils.

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