A technique called the cement-mixing and mechanical dehydration method (CMD) as one of recycling techniques for soft clay slurry is developed. In order to evaluate the effectiveness of the CMD for increasing the strength of soft clay, a series of unconfined compression tests and several durability tests were performed together with the literature review of unconfined compressive strength in cement-treated soils. Moreover, a series of constant strain rate consolidation tests were also performed to evaluate the effects of cement content and dehydration speed on the permeability of cement-treated clay. The following conclusions are obtained: 1) Literature review and theoretical considerations on the shear strength of cement-treated soils show that an additional treatment for the purpose of increasing the density of cement-treated specimen is effective for increasing the shear strength of cement-treated soil. 2) The mechanical dehydration of soft clay with high pressure is accelerated by cement mixing, where the coefficient of consolidation of cement-treated clay increases as the cement content increases. 3) The high-strength specimen having the unconfined compressive strength of more than 20 MPa can be created from soft clay treated by the CMD with the cement content of over 20% and the dehydration pressure of 20 MPa.

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An experimental study aimed at comparing of creep and fatigue behaviour of grouted sand is presented. Unconfined creep tests and cyclic tests were performed to highlight the creep and the fatigue behaviour of Fontainebleau sand grouted with three types of grout: a silicate grout, a micro-fine cement-based grout and a mineral-based grout. Creep and fatigue results were compared in terms of strain rate, creep slope or fatigue slope, and creep limit strength or fatigue limit strength. Some analogies were observed between the creep and the fatigue behaviours. These behaviours can be compared from a qualitative point of view, since creep and fatigue curves have the same shape (both showing primary and tertiary behaviour), and from a quantitative point of view, under certain loading conditions.

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The soil/water-coupled analysis for unsaturated soil mechanics with the finite element method is used to express the behavior of compacted earth structures exposed to rainfall. The constitutive model, which is proposed by Karube et al. (1996, 1997) and modified by Karube and Kawai (2001), is formulated for initial and boundary problems and coded as DACSAR-U (Iizuka et al., 2000). A deep fill, which consists of compacted, unsaturated soil, was analyzed with DACSAR-U. Different patterns of rainfall were applied to deep fills in finite element simulations. As a result, non-uniform settlement of deep fill can be calculated and the magnitude of settlement of deep fills is dependent on the amount of collapse, namely, the compression due to the decrease in suction. Moreover, delayed settlement due to rainfall and an accumulation of an irreversible settlement due to cyclic rainfall was observed.

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It is generally thought that vegetation has a stabilization effect on a slope; however, very limited quantitative field data are available for verifying this perception. In order to improve our understanding on the vegetation effect on rainfall infiltration and hence on slope stability, a well-instrumented field study was carried out on an unsaturated expansive soil slope in China. The field program consisted of two neighboring monitoring areas (both 16 m wide by about 30 m long): namely a bare area and a naturally grassed area (real slope). Artificial rainfall events were produced in succession in the two areas with a specially-designed sprinkler system. In this paper, the relevant monitored results from the two areas are directly compared and discussed. Prior to the artificial rainfall, the measured higher initial soil suction in the grassed area than that in the bare areas was attributed to the evapo-transpiration effect of the grass. During the rainfall, the presence of the grass greatly increased the infiltrability of the upper soil layer and delayed the onset of surface runoff. The observed delayed responses (i.e., about 3 days) of surface runoff, soil suction and water content to the rainfall in the grassed area was about twice the duration of the delayed response in the bare area (i.e., about 1.5 days). The influence of the simulated rainfall on the changes of soil suction and water content in the grassed area was found to be more significant and about 1.5 m deeper than that in the bare area. The greater depth of influence observed in the grassed area may be attributable to the greater depth of open cracks due to the evapo-transpiration effect of grass.

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The bearing capacity for composite breakwater's mound is considered as a problem of foundation stability. Expected displacement due to mound failure under eccentric inclined load by repeating wave forces is estimated. The displacement is calculated by the use of angular motion equation along virtual failure arc, similarly to Newmark's method in earthquake engineering. A computation program, which takes into account various conditions for individual breakwater, was developed. It has been found that the relationship between the expected displacement and the design safety factor of bearing capacity varies with the ratio of breadth to height for the caisson box. If an allowable expected deformation in service life is introduced in breakwater design, it is prospective to reduce caisson breadth especially in the cases of larger breadth height ratios. The program was used in back analysis of case of breakwater failure that occurred in Tomakomai west port. The settlements of caissons, ranging from 7 cm to 45 cm, were observed after a series of typhoons. By using the high wave record, and accounting for the effect of wave force increase due to incompletely armored wave-breaking blocks, the calculated settlements and horizontal displacements were in agreement with the range of deformations observed in spite of considerable scatter.

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This paper shows development and application potential of newly developed H-joint steel pipe sheet piles (SPSPs) in SPSP structures. The authors have developed a new H-joint SPSPs technology from a simple idea in which two steel pipes are connected by H-steel section welded on them in order to improve the performance and widen application areas of SPSP technology. The H-joint SPSP is expected to remediate problems of traditional joints in SPSPs. Installation accuracy, proposed field segment joint using a fillet welded splice plate and lateral bearing capacity for H-joint SPSPs were examined by field construction tests, full-scale bending tests and centrifuge model tests, respectively. Parametric studies using beam analysis were conducted to show that the cross sectional dimensions of SPSP foundations can be reduced by using H-joint SPSPs and to estimate a joint efficiency (μ) for design of H-joint SPSP foundation structures. The following observations were made from the studies: (1) H-joint SPSP can be installed with high driving accuracy due to rigidly welding 2 steel pipes and H-steel in a factory, (2) The proposed field segment joint for H-joint SPSP using a splice plate is strong and effective in bending, (3) H-joint SPSPs have high rigidity hence large lateral bearing capacity making them suitable in ensuring the stability of SPSP foundation structures, (4) A joint efficiency of H-joint SPSP foundation is larger than that of SPSP foundation with traditional joints, and (5) H-joint SPSP contributes to reducing the number of piles based on the reduction of the size dimension of the SPSP foundation.

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This paper presents a three-dimensional elastoplastic model for predicting the hydraulic and stress-strain-strength behaviour of unsaturated soils. The model is generalized using the transformed stress method to three-dimensional stress states by assuming that the shapes of the failure surface and the yield surface in the deviatoric plane of the average skeleton stress space are given by the SMP criterion. Hydraulic hysteresis in the water-retention behaviour is modeled as an elastoplastic process with the elastic region of the saturation degree decreasing with increasing suction in the S_r-log s plane. The effect of void ratio on the water-retention behaviour is studied using test data obtained from controlled-suction triaxial tests on unsaturated compacted clay. The effect of change in degree of saturation on the stress-strain-strength behaviour and the effect of change in void ratio on the water-retention behaviour are taken into consideration in the model, in addition to the effect of suction on the hydraulic and mechanical behaviour. Model predictions of the stress-strain and water-retention behaviour are compared with those obtained from triaxial tests on unsaturated soil along isotropic compression, triaxial compression and triaxial extension stress paths with or without variation in suction. The comparisons indicate that the model has well predicting capabilities to reproduce the hydraulic and mechanical behaviour of unsaturated soils under three-dimensional stress states.

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The viscous properties of three types of geogrid polymer were evaluated by sustained loading tests lasting for 30 days at a load level about a half of its nominal rupture strength. The sustained loading tests were performed during otherwise monotonic loading (ML) at constant strain or load rate, unlike the conventional creep tests, in which the strain rate immediately before the start of sustained loading, which controls the creep strain rate, is not controlled or even not recorded. The following are presented in this study. The tensile rupture strength measured by ML that was started following a 30 day-long sustained loading was essentially the same as the one at the same strain rate at rupture obtained by continuous ML without any intermission of sustained loading. This fact indicates that creep is not a degrading phenomenon. Then, if free from chemical and mechanical degrading effects, the strength of a geosynthetic reinforcement (for a given strain rate at rupture) can be maintained until late in its service life. A non-linear three-component model is used to simulate the experimental results from the previous and present studies. The model can simulate very well not only the load-strain behaviour during ML with and without step changes in the strain rate and the one after sustained loading, but also the time histories of creep strain during sustained loading for short (one hour) and long (30 days) periods.

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An investigation was conducted into the bearing capacity characteristics of a structured naturally deposited clay soil by means of a soil-water coupled finite deformation analysis based on unconventional elasto-plastic mechanics. The constitutive equation of the soil skeleton was expressed using the Super/subloading Yield Surface Cam-clay model (SYS Cam-clay model), an elasto-plastic constitutive equation model proposed by the authors to describe the mechanisms (structure, overconsolidation and anisotropy) at work in the skeleton structure. To allow a theoretical consideration of a typical bearing capacity problem, a case was assumed in which vertical displacement was applied through a rigid foundation possessing friction. The main conclusions of the study were:
(1) In a highly structured soil, a peak appears in the load-settlement relation, accompanied by a considerable localization of strain and a clearly visible slip line. In a soil of high initial anisotropy, the area of failure is more confined and the peak load is smaller than in an initially isotropic soil.
(2) In the case of a highly structured soil possessing an initial imperfection, even if this is very slight, a sensitive response occurs, leading to an asymmetrical deformation mode. At the same time, the load-settlement curve “bifurcates” from the path the same soil exhibits when it is deformed symmetrically, so as to display a larger decrease in load.
(3) If loading is relaxed from a rapid rate (≒ completely undrained), at which virtually no migration of pore water can occur in the soil, to a rate that is slower, the peak load will gradually increase with the partial draining effect. If the rate of loading is reduced still further, a point will eventually be reached where no drop in load is observed and it becomes impossible to distinguish clear boundaries for the area of failure. Depending on the rate of loading, it may be possible to see the clear appearance of a compaction band, caused by soil structure decay in the area of strain localization.
These findings aim to show that the inclusion of a concept of soil skeleton structure in an analysis of this sort is not only a very natural step to take, but also an advance of the greatest importance.

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Estimating increase in undrained shear strength s_u of clay is an important purpose of consolidation analysis as well as settlement prediction when multi stage loading for construction of earth structures on soft clay is concerned. The present paper investigates the increase in s_u with regard to rate of consolidation. Since values of s_u are usually evaluated as a function of effective vertical stress σ_v′, rate effect on shear strength increment ratio in normally consolidated state s_un/σ_v′ is first discussed considering the fundamental concept expressed by the equation of s_un/σ_v′=s_uf/σ_y′, in which s_uf is in-situ undrained shear strength and σ_y′ is consolidation yielding stress. The paper also describes two case histories where actual increases in s_u were observed in soft clay deposits. The first site is located offshore Osaka-bay where a large-scale seawall was constructed, and soft clay in the site was improved by sand drains. The second is a reclaimed land in Yanai City where a sand fill and a subsequent test embankment were conducted on a soft clay deposit without improvement by vertical drains. It is found from the study that: (1) rate effect on s_un/σ_v′ cancels rate effect on σ_y′, and the equation mentioned above is valid regardless of the rate of consolidation, and (2) the in-situ values of s_un/σ_v′ observed in the two sites vary from 0.27 to 0.37 as consolidation progresses, and they are well related to rate of consolidation. According to the experience at the two construction sites, values of s_un/σ_v′ with regard to rate of consolidation are proposed for design use at field/construction sites.

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In this paper the K-stiffness Method as originally proposed by Allen et al. (2003) is re-examined using a total of six new case studies-five from Japan and one from the USA. A common feature of the walls in this new data set is that the walls were all constructed with a vertical face and a granular backfill. However, the walls varied widely with respect to facing type. This new data set together with data for vertical walls previously published by Allen and Bathurst (2002a,b) and Allen et al. (2002) is now used to isolate the effect of the facing stiffness factor on reinforcement loads and to adjust the original equation that was developed to calculate its value. The paper also shows that predicted reinforcement loads using the current AASHTO Simplified Method in the USA and the current PWRC method in Japan give the same reinforcement load predictions, and both grossly over-estimate the values deduced from measured strains. The new data set is used to slightly refine the estimate of the facing stiffness factor used in the original K-stiffness Method. The original and modified K-stiffness Method are demonstrated to quantitatively improve the estimate of the magnitude and distribution of reinforcement loads for internal stability design of vertical-faced geosynthetic reinforced soils walls with granular backfills when compared to the current American and Japanese methods.

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A theoretical model for predicting the soil-water characteristic curves of simple granular soils during different wetting and drying processes is proposed. In this model, the irregular pores in a simple granular soil are assumed to be regular symmetrical cone-shaped capillary pores. The wetting and drying processes of the soil are considered to be the filling and draining processes of the symmetrical cone-shaped capillary pores. The degree of saturation of the soil is determined by estimating the amount of water in the cone-shaped capillary pores. The suction in the soil is estimated by applying the so-called capillary law to the cone-shaped capillary pores. The influence of the closed air bubbles in pore water on the soil-water characteristic curves is also simulated in the theoretical model. All model parameters in the model have definite physical base. The model is verified using experimental data.

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A series of experimental trial for estimating the coefficient of earth pressure at rest, K₀, is presented. The developed apparatus is a modified Oedometer covered with pressurized chamber specially designed for K₀ determination based on the principle of effective stress originally proposed by Ohta et al. (1979). K₀ is estimated from the developed apparatus primarily by means of load cell and auxiliary by means of pore pressure transducer aiming at confirming the test results. K₀ triaxial consolidation is carried out to verify the result of purposed method. K₀ values are obtained using Oedometer tests on two samples one of which is taken horizontally and the other is taken vertically from a block sample and K₀ values from empirical equation are also estimated for comparison. It was found that the proposed method gives a comparable K₀ of kaolin to K₀ triaxial consolidation method but somewhat higher than those from empirical equations and lower than K₀ obtained using Oedometer.

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Previous studies of mechanical properties of solid residue byproducts such as coal bottom ash have been restricted to small and intermediate shear strains of approximately 0.1-20%, due to the limitations of the standard equipment used (e.g. triaxial and direct shear tests) and to confining pressures up to around 1.5 MPa. The objective of the present research was to study the behavior of coal bottom ash sampled in southern Brazil, ranging from very small to very large shear strains, as well as to high isotropic pressures, to determine its complete behavior. Comparisons are made with results from a granular soil with a similar grading and also with those of uniform sand with similar average particle size. High pressure isotropic compression and bender element tests, as well as standard triaxial tests and ring shear tests were carried out on compacted specimens of coal bottom ash, a sandy residual soil with a similar grain size distribution, as well as on a uniform sand. In order to explain the effect of the particle morphology of the coal bottom ash on its mechanical behavior, an investigation was also undertaken based on thin section and scanning electron micrographs, which revealed intra-particle voids in the coal ash. The results indicate that the general behavior of the bottom ash compares favorably with conventional granular materials, providing a promising solution to the disposal problem, and also an economic alternative to the use of conventional soils as construction materials.

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The stiffness at small strains and non-linear stress-strain relation of compacted cement-mixed well-graded gravelly soil as well as the ageing effects were evaluated by drained triaxial compression tests on compacted moist specimens cured for different periods at isotropic and different anisotropic stress states. In all the tests, the initial stress-strain relation at small strains less than about 0.001% was essentially elastic and the initial Young's modulus, E₀, was essentially the same as the E_eq value evaluated by applying unload/reload cycles under otherwise the same conditions. The E_eq values were rather independent of strain rate. The E_eq value from the first unload/reload cycle applied during otherwise continuous ML became noticeably lower than the elastic modulus evaluated at the same stress state, more as approaching the peak stress state. After a number of small unload/reload cycles and long sustained loading, the E_eq value became closer to the elastic modulus due to a decrease in the viscous effects. The ratio of E₀ to the compressive strength (q_max) was similar to that of concrete but noticeably larger than those of uncompacted cement-mixed soil, sedimentary softrock and unbound gravelly soil. Both E₀ and q_max increased with time by ageing, while the E₀/q_max ratio decreased with time. When ML was restarted at a constant strain rate after ageing with a shear stress, the tangent stiffness became very high for a large stress range with a substantial change in the non-linearity of stress-strain relation.

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To evaluate the effects of reinforcement type in terms of stiffness, viscous property, rupture strength, shape and loading history on the stress-strain behaviour during primary, sustained and cyclic loading of reinforced sand, a series of drained plane strain compression tests were performed on Toyoura sand. The sand specimens were reinforced with two types of polymer geogrid as well as two types of metal grid, having largely different stiffness values and surface conditions. Despite that the effects of reinforcement type on the overall stress-strain characteristics of reinforced sand and their rate-dependency are significant during primary loading, the effects are much smaller than the difference in the stiffness of reinforcement. The effects of reinforcement type on the global unloading behaviour and the residual strain by cyclic loading during otherwise global unloading are generally insignificant or negligible. The residual strains by cyclic loading of reinforced sand became substantially small by preloading as well as pre-sustained loading and pre-cyclic loading at higher load levels. With this procedure, polymer geosynthetic reinforcement, which is much more extensible and viscous than metal reinforcement, can be used to reinforce soil structures allowing very limited residual deformation.

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The uniaxial compressive strength of intact rock is widely used as the sole factor to estimate the side resistance of drilled shafts socketed in rock. However, the side resistance should also depend on in situ rock mass characteristics such as rock type, strength, joint frequency, and weathering conditions. In this study, a new approach is proposed to estimate the side resistance of rock socketed drilled shafts. The approach is based on the GSI rock mass classification, and the Hoek and Brown failure criterion. Inclusion of all these factors into the proposed method explains, to some extent, the differences that are obtained when various empirical methods are used. Comparisons between observed side resistances from field case studies and estimated side resistances with the proposed method show a good correlation. The method appears to be robust since the results are relatively insensitive to estimation from the different rock mass classification and properties and are comparable with predictions from previous empirical correlations.

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