Subgrade soils contribute to surface rutting and fatigue cracking, the two major distress modes in flexible pavements. Rutting and cracking are accumulated damages done to the pavement structures over load repetitions and are irrecoverable in nature. Current transfer functions used in the mechanistic-based design methods relate these plastic phenomena solely to elastic responses. In this paper, the philosophy of the connection between subgrade and pavement distress modes is reviewed. A finite element method program, ARKPAVE, was used to conduct the structural analyses of flexible pavements. Structural responses suggest that resilient modulus, the only design input of subgrades could not adequately reflect such a contribution which indicates that subgrade soils have not been addressed effectively in current design methods. Based on the prediction model for permanent deformation of subgrade soils which is derived from the results of repeated load testing, an improved design criterion for subgrade soils is proposed. An example of incorporating the permanent deformation of subgrade soils into flexible pavement design, especially for low-volume rural roads, is demonstrated. The stress ratio at the top of subgrade soils, γ_σ defined as the ratio of deviator stress to static strength, is recommended to replace the vertical compressive resilient strain as the design criteria for pavement rutting in future mechanistic-based design guides for flexible pavement structures.

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The mineralogy and chemistry of two marine alluvial deposits with different parent materials, Ariake clay with pyroclastic origin and Bangkok clay with non-pyroclastic origin, were compared and their correlation with geotechnical index properties was discussed. The predominant clay mineral in both clay deposits was smectite, but the smectite in Bangkok clay was found to be of the high-swelling type while that in Ariake clay is of the low-swelling type from the sediment volume determination. The range of the liquid limit and activity was mostly 100 to 140% and 1.25 to 1.90 for Bangkok clay, and 60 to 140% and 0.75 to 1.25 for Ariake clay. A positive correlation existed between the activity and the smectite content for each of Bangkok and Ariake clays, where the greater increasing ratio of the activity for Bangkok clay was attributed to the high-swelling nature of the smectite. The liquid limit of an Na-saturated sample for Bangkok clay increased with increasing NaCl concentration and when substituting Ca for Na in a similar manner to Ariake clay, but the extent of the liquid limit change by such treatments was much smaller for Bangkok clay than for Ariake clay.

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During a self-boring pressuremeter test (SBPMT) a cylindrical cavity is expanded from a finite radius. To determine undrained shear strength, C_u, of a saturated clay, SBPMT data is analyzed using the cylindrical cavity expansion theory, and curve fitting methods. At present, there is no completely consistent and reliable method to estimate the value of modulus of elasticity. In this paper, an alternative method has been presented to first estimate C_u and limit pressure, P_L, using a logarithmic model and then determine initial tangent modulus, E_i, secant modulus at failure, E_sf, and secant modulus at half the value of (σ₁-σ₃)_f, E₅₀, using a hyperbolic-model. Values of C_u determined from this method compare well with those determined from other methods. The predicted values of E_i and E₅₀ compare well with those determined from the triaxial tests. The values of E₅₀ also compare well with the values of modulus determined from unload-reload cycle of SBPMT.

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By employing an undrained cyclic loading ring-shear apparatus, a series of tests to reproduce the dynamic behavior of the Nikawa landslide induced by the January 17, 1995 Hyogoken-Nambu earthquake, is conducted. The test sample is Osaka-group coarse sandy soil taken from the landslide. The initial stress condition acting on a soil element in the sliding surface is applied to the sample. Based on the seismic records monitored at the JR Takarazuka Station, the input seismic wave is synthesized to reproduce the seismic stress acting on the sliding surface. The test results show that the soil failed due to the dynamic loading of the earthquake. The most important results are the excess pore water pressure generation and the acceleration of shear displacement continuing after the main shock. Combined with the grain crushing at the shear zone and the volume reduction in the drained constant-speed ring-shear test, the mechanism of this landslide is interpreted as, shear displacement causing grain crushing in the shear zone and volume reduction, and then resulting in a localized liquefaction phenomenon, "sliding-surface liquefaction". This geotechnical simulation test provides a reasonable interpretation of this highly mobile landslide.

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An analytical model for the pull-out resistance of a rigid soil nail reinforcement in dilative soils is described in this paper. This model can be used to describe the pull-out response of a soil nail or any longitudinal strip reinforcement in dilative soils. An expression of the normal pressure on the shaft of the reinforcement as a function of soil dilation is derived. Based on the assumption that soil is an elastic medium and the soil nail is a rigid rod, an equation to calculate the pull-out resistance of the soil nail is obtained. The equation shows that apparent friction coefficient decreases with the increase of the overburden pressure or applied normal confining pressure around the soil nail. The analytical predictions and experimental results for two published test cases are compared. The first case involves pull-out tests on circular steel bars, and the second case is pull-out tests on rectangular steel strip reinforcements in dense sand. The agreement among the analytical predictions and experimental pull-out resistance results for increasing overburden pressure are good, showing that the apparent coefficient of friction decreases with increasing confining pressure. Thus the analytical model provides a theoretical basis to reasonably predict the pull-out resistance of a soil nail reinforcement in dilative soils.

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Sampling induces structural modifications in clay which depend on the stress and strain paths followed during sampling history. A complete description of disturbance is very difficult, because it originates in situ during drilling and is completed in the laboratory with reloading at the pre-existing stress conditions. In this paper, only the effects of undrained relief of confining effective stresses are investigated for reconstituted natural clays of varying plasticity. During undrained stress relief, negative pore pressure (suction) occurs ; this residual stress was selected as a reference parameter for disturbance appraisal and compared with initial conditions before unloading. For the same type of soil, consolidation was carried out in various stress conditions (isotropic and anisotropic), and both normally consolidated and overconsolidated specimens were made. After undrained unloading, residual stress was evaluated by means of a controlled swelling technique using a modified oedometer and a triaxial device. This method was validated by comparisons with suction plate measurements performed on reconstituted kaolin clay specimens. Experiments showed various causes of loss of suction in samples, related to plasticity index, stress history, stress conditions and released stress level. For normally consolidated non-structured clays, undrained stress relief gives rise to some important disturbance processes, more evident for anisotropically consolidated samples. Residual stress may be considered meaningful for stress relief disturbance appraisal.

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The effects of stabilizing piles on the stability of a slope are predicted by the three-dimensional elasto-plastic shear strength reduction finite element method. The soil-pile interaction is simulated with zero-thickness elasto-plastic interface elements. The numerical results are compared with those obtained by Bishop's simplified method, where the reaction force of the piles is determined by Ito-Matsui's equation. The effects of the pile spacing, pile head conditions, bending stiffness, and pile positions on the safety factor are analyzed. The shear strength reduction finite element method shows that the pile head conditions and bending stiffness can considerably influence the stability of the slope, but this cannot be indicated by the limit equilibrium method. The positions of the pile row have significant influence on the stability of the slope. The shear strength reduction finite element method indicates that the pile row needs to be installed in the middle of the slope for maximum safety. By contrast, Bishop's simplified method shows that the piles should be installed slightly closer to the top of the slope.

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Even in normally consolidated or lightly overconsolidated clay foundations failures can occur some days/weeks after the load application is completed. Such an event can sometimes be attributed to creep-like failure. In this paper, the time dependent failure of a homogeneous normally consolidated soft clay foundation has been investigated using soil-water coupled elasto-plastic finite deformation analysis. The inviscid subloading surface Cam-clay model, which can express smooth transition from overconsolidated states to normally consolidated states during reloading, was used for the soil. With drained boundaries a clay foundation can experience failure, instead of consolidation, with the elapse of time after the end of load application. The foundation stays apparently stable for some time until it experiences a sudden failure. The occurrence of such a delayed failure in an elasto-plastic soil foundation is triggered off by the predominant pore water migration over the drainage from the soil mass due to softening that results in the increase of excess pore water pressure under this constant load. With time, the region in the foundation under higher excess pore pressure expands outward progressively from the centerline until failure. The pore pressure increase under constant load is similar to observed cases that registered increase in piezometric heads. When the magnitude of load at the end of construction is comparatively low, i. e. comparatively below the stationary load, only the consolidation process proceeds.

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Damage to sewer pipes in Kushiro City caused by the January 15, 1993 Kushiro-Oki and the October 4, 1994 Hokkaido-Toho-Oki earthquakes is reported and analyzed. Based on the results of a damage survey for restoration work of the pipes and on those of a boring survey conducted near both the damaged and undamaged sites, analyses are performed on the condition of the backfill and the original soil layers surrounding the pipes. In the wetland and flood-plain region, liquefaction of the backfill soil was considered to be the major cause of the damage, while existence of a peat layer with low permeability and/or a sandy layer that is liquefiable in the original soil was considered to affect the extent of the damage. In the terrace region, instability of the original slope was also considered to have caused the damage.

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Some experimental problems encountered when determining Steady-State (SS) or Phase Transformation (PT) envelopes and their projections in the state diagram are studied ; 1) accurate assessment of the void ratio (e) at the end of the consolidation process ; 2) the effects due to the membrane compliance ; 3) effectiveness of lubrication ends and 4) influence of specimen slenderness on the lateral strain uniformity. The specimen's dimensions after its formation were continuously monitored by measuring axial and radial strains locally. Both conventional undrained triaxial tests and constant volume tests with continuous correction for the membrane penetration effects were performed at constant cell pressure using loose saturated Toyoura sand. The adopted lubrication system worked effectively up to an axial strain of 4% for specimens with a height to diameter ratio of H/D=2, while for H/D=1 lateral strains were uniform until the end of the tests (ε_a=25%). The SS and PT envelope and their projection in the state diagram (SS or PT line) were established based on results from 29 tests. The condition which triggers the softening behaviour, i. e. the so called Critical Stress Ratio (CSR) envelope was also determined. The test results showed the importance of careful control of the test factors mentioned above determining the undrained behaviour of saturated very loose sand under truly constant conditions.

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The correct solution to bearing capacity factor N_γ due to soil self-weight is not available by the classical theory of plasticity, so numerical approximation based on limit equilibrium method or limit analysis is required. Limit analysis using upper-bound theorem can give an upper-bound solution for the bearing capacity problem. If the critical failure mechanism is found, such an upper-bound solution is a good approximation for the correct one. By employing the equivalence of limit analysis and limit equilibrium method a straightforward procedure is proposed in this paper to determine the critical failure mechanism in solving the least upper-bound solution of bearing capacity N_γ. This procedure proves to be efficient in accommodating various loading or geometrical conditions. The least upper-bound values of N_γ in a variety of cases are presented and comparisons with other accepted methods are made in the paper.

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