An equation for estimating in-situ undrained shear strength (q_u(I)) of natural deposits is derived as q_u(I)/2c_u(I)=1.0-0.285 ln p_m/S₀ through the unconfined compression test (UCT) and K₀ consolidated-undrained triaxial compression test (CK₀UC). The q_u(I) of natural clay deposits can be estimated from the q_u value multiplied by the reciprocal number of q_u(I)/2c_u(I) of the equation using the suction (S₀) and q_u obtained from UCT for a specimen, where c_u(I) is in-situ shear strength measured from CK₀UC and p_m is two times the effective overburden pressure divided by three. The q_u(I)/2c_u(I) values were unrelated to I_p, q_u and p_m/S₀ and the mean value of these ratios was 0.98 in the range of I_p=26~110 and q_u=12~178 kPa. The mean values of the ratios for q_u, q*_u(I) and q_u(I) to 2c_u(I) were 0.629, 0.998 and 0.977 and the standard deviation of those ratios were 0.14, 0.10 and 0.16, respectively. Therefore, it can be seen that the improved method is appropriate as well as Shogaki's basic method (q*_u(I)). The mean values of q_u(I)/2c_u(I) were 0.94, 0.99 and 0.91 for Iwai organic and soft clay plus Kahokugata clay, respectively. The coefficient of variations of the q_u and q_u(I) values were (13~14)% and unrelated to soils, q_u or q_u(I) values. Therefore, the applicability of the improved method newly developed in this study can be confirmed for Kahokugata and Iwai clays as well as Iwai organic soils. The proposed method is a simple and easy one for practical engineering usage.

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This paper describes a spatial interpolation procedure for settlements to increase the reliability of subsidence mapping. For this study, a spatial interpolation method based on the ordinary Kriging method was investigated for applicability to a land subsidence area in the northern Kanto plain. First, the spatial variability of settlements using a semivariogram was investigated in detail. For a short distance, the semivariogram of settlements increases. However, after the maximum value at about 35 km, the semivariogram decreases because settlement observation locations are typically arranged around an area in the center of a severe land subsidence zone. Therefore, the semivariogram is only useful up to that maximum value for investigating spatial variability of settlements in a land subsidence area. A spatial interpolation procedure based on Kriging method is proposed. Applicability of that procedure is investigated through comparison of estimations with observations. Drawing both estimations and standard deviations of those estimations represents a reliable land subsidence map. Moreover, to improve the map's accuracy, new allocation for monitoring settlements is undertaken by installation in areas where the estimation standard deviation is greatest. The effect can be investigated using simulated results in the distribution change of the estimated standard deviation.

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Gravity retaining walls are widely used in Japan because of their simplicity of structure and ease of construction. In design procedure, the seismic coefficient method is widely employed, in which the earth pressure and inertia force are calculated by converting the seismic force into a static load. Earth pressure is usually calculated by the Mononobe-Okabe formula, which applies Coulomb's earth pressure computed from the equilibrium of forces in the static state. However, the Hyogoken-Nambu Earthquake of 1995 prompted the need to reexamine seismic design methods for various civil engineering structures. Gravity retaining wall is one of such structures whose seismic design has to be reexamined and rationalized. At this moment there is no clear empirical basis for converting the seismic force into a static load. The design method has to take into account the behavior of gravity retaining walls during earthquakes. At the Public Works Research Institute, model tests were conducted on gravity retaining walls using a centrifuge. The acceleration and displacement of a retaining wall and its backfill as well as the earth pressure acting on the wall were measured simultaneously together with the deformation behavior of the wall and its backfill, using a high-precision high-speed camera. The data show that the hypothetical conditions of the Mononobe-Okabe formula do not appropriately express the real behavior of backfill and gravity retaining walls during earthquakes.

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A fault consists of a zone of heavily fragmented granular rock (gouge), which is confined between two rough walls made of fractured rock. The granular gouge is the result of previous fracturing of the wall rock by the combined effect of compressive and shear stresses. Through time, the granular fault gouge will experience various episodes of further fragmentation (crushing) as a result of the mobilization by shear of the fault walls. The evolution of crushing in a simulated gouge material was studied using laboratory ring shear tests and DEM ring shear simulations. The laboratory ring shear tests were developed using sugar as a weak granular material. It was found that the residual friction coefficient of this material maintained a constant value regardless of the severe degradation of the particles. This degradation was induced by increasing the angular deformation or increasing the applied vertical stress. Moreover, it was found that the grain size distribution of the original uniform material evolved toward a fractal distribution of sizes. The results from the DEM simulations confirmed those from the laboratory tests and provided also a visualization of the evolution of crushing. Event though originally DEM does not consider particle breakage, this was allowed by replacing particles fulfilling a predefined tensile failure criterion with an equivalent group of smaller particles.

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This paper addresses a proposal on the three-dimensional elasto-viscous consolidation theory and discusses on its applicability. In order to predict the three-dimensional consolidation behavior of clayey ground improved by vertical drain system, one-dimensional consolidation theory based on an elasto-viscous liquid model proposed by Yoshikuni et al. (1994), which can express secondary consolidation without considering any distinction between normally consolidated and overconsolidated regions, is extended to three-dimensional condition. This theory is applied to the consolidation of a hollow cylindrical body that models a clayey ground improved by a vertical drain system. Then, a rigorous solution of elastic consolidation theory, a FEM solution based on elasto-plastic theory and a FDM solution using three-dimensional elasto-viscous theory are compared with the test results obtained using the three-dimensional consolidation test apparatus developed by the authors (Baek and Moriwaki, 2004). Based on the results of analyses, it is evident that the three-dimensional consolidation theory proposed by authors could simulate the consolidation behavior of clayey ground improved by vertical drains, such as the secondary consolidation and the radial displacement during the three-dimensional consolidation process.

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We propose a new hysteretic rule for p-y curves to be used in the dynamic analysis of deep foundations. We first examine the results of past lateral cyclic pile load experiments to clarify the characteristics that are to be modeled in the load transfer hystereses in p-y curves. We then undertake an analytical study of soil element behavior when subject to cyclic passive (compressive) and active (extensile) deformation. We found that the soil resistance intensity to piles varies with different cyclic loading patterns, as the stress-dilatancy behavior in soil varies with cyclic loading patterns. We developed a new hysteretic rule that satisfies the observed dominant characteristics. Although the proposed hysteretic rule has its background in the peak-oriented rule, it is further extended to be a function of the loading pattern. Numerical tests using the proposed model showed that the model is capable of reproducing observed differences in the behavior of piles subjected to fully-reversed cyclic loading and one-sided cyclic loading, even though the typical peak-oriented rules are unable to predict these outcomes.

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Two-dimensional (2D) and three-dimensional (3D) model tests of tunnel excavation with nearby existing foundation are carried out to investigate the influence of the existing foundation due to the interaction between ground and the existing structures. Three types of foundations: flat foundation, group-pile foundation and piled raft are considered. 2D and 3D finite element analyses using subloading t_ij model are also conducted. The deformation mechanism and distribution of earth pressure during tunnel excavation in the ground with nearby foundation are found to be different from those of green field condition. Surface settlement trough due to tunnel excavation in the ground with existing foundation does not follow the usual pattern of a Gaussian distributive curve, which can be observed in the case of green field. Especially, in the case of pile foundation, D_p, the distance between pile tip and tunnel is an important factor for the ground deformation and surface settlement. For a short distance D_p, although the length of pile is long, the ground deformation is concentrated at a place near the front pile and the rotation of foundation becomes larger. The maximum surface settlement in the case of existing foundation is also larger than those in the case of green field. Due to the existing foundation, unsymmetrical distributions of earth pressure occurred at the bottom of the ground due to tunnel excavation, both in model tests and numerical analyses. The earth pressure at the crown of tunnel in the case of existing foundation is almost the same as those in the case of green field. The arching at the shoulder of tunnel in the case of existing foundation, however, is much larger than those in the case of green field due to the dead load exerted on the foundation. The numerical results agree well with the results of the model tests.

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The residual effective stress (p'_r) was measured for various clayey soils collected from various parts of the world, including Japan. All samples studied in this paper were retrieved by the same sampling method, i.e., using the Japanese standard sampler. However, measured p'_r/σ'_vo, where σ'_vo is the in situ effective overburden pressure, considerably varied for different sites as well as with depth. This paper examines main factors governing the p'_r value, focusing on location of the sample in the sampling tube; transportation of the soil samples; time duration between retrieval of the sample and extrusion of the sample from the sampling tube; overconsolidation ratio (OCR); clay content and plasticity index (I_p). In addition, the p'_r values are correlated to the volume change generated when the in situ σ'_vo is applied in the oedometer test, which is extensively used for assessment of the sample quality. The largest measured value of p'_r was found at one third of the sample length from the cutting edge of the sampling tube. The effects of the transportation and the time duration from the sampling to the extrusion of the sample are not prominent for the p'_r value. Any clear relations between p'_r and Δe/e_o are not found, where Δe and e_o are the void ratio change caused by applying σ'_vo and the initial void ratio, respectively. Among factors examined in this paper, OCR is the most effective factor: i.e., as OCR increases, p'_r/σ'_vo ratio increases for every studied site. However, when compared at different sites, the p'_r/σ'_vo ratio at the same OCR is considerably different. In spite of some exceptions, there exists a tendency that p'_r/σ'_vo ratio increases with the increase in the clay content as well as I_p.

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In order to evaluate the effects of cementation on the mechanical properties of cement-treated soil, a series of isotropic consolidation and undrained triaxial compression shear tests were performed for cement-treated specimens of Ariake clay, Akita sand, Rokko Masado and Toyoura sand. This paper evaluates factors affecting the shear strength of these cement-treated soils. The following conclusions are obtained: 1) Cement-treated soil has a normally consolidated line in e-ln p' space which depends on the mixing cement content. The consolidation yield stress, p'_y, of cement-treated soil increases with increasing cement content and initial specimen density. 2) Changes in cohesive strength due to cement-treatment can be represented by a tensile effective stress, p'_r. Strength properties can then be normalized by the augmented consolidation stress, (p'_c+p'_r). 3) The shear strength properties of quasi-overconsolidated clay can be represented by the yield stress ratio, R=(p'_y+p'_r)/(p'_c+p'_r). 4) The undrained shear strength of cement-treated soils can be represented as a power law relation of the yield stress ratio, R, and the augmented consolidation stress.

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The cyclic resistance of clean sand improved by silicate-based permeation grouting is examined based on laboratory triaxial tests. Specimens were prepared by the methods of sedimentation and wet tamping. In the former method, dry sand was poured into the silicate-based solution. In the latter method, grouting was conducted by permeating silicate-based solution through wet-tamped nearly-dry specimens as well as through wet-tamped nearly-saturated sand specimens. The overburden stress was applied on some of the grouted saturated sand specimens during a curing period typically of one month. For all of the specimens prepared in different ways as above, the non-destructive measurements were first conducted of velocities of P-wave and S-wave propagation through the samples prepared under varying B-values. The aim of these measurements was to examine whether the small-strain properties of grouted sand specimens with gelled soil fabrics can be evaluated in the general framework of the theory of poro-elasticity. The undrained cyclic triaxial test was then conducted on each of the specimens. The influence of grouting on dry sand and saturated sand, and the effects of sustained application of an overburden stress during the curing period were examined drawing attention to the inner structure of grouted sand and its effects on the cyclic resistance.

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This report uses load-transfer approach for analyzing the load-displacement response of piles socketed in weathered rocks typically found in Mumbai region. The field information used in the load-transfer analysis is obtained from conventional site investigations and does not necessitate elaborate tests. The load transfer behaviour of each stratum is expressed as a non-linear function. Empirical relations are used to express rock mass modulus and limiting values of unit side and base resistance in terms of unconfined compressive strength of intact socket material, which implicitly take into account the site-specific conditions. More than twenty pile load test data were back-analyzed before generalizing the governing parameters applicable to this region. This report demonstrates a wide range of applications of load transfer approach which includes the load-displacement behaviour and separation of elastic and net pile displacements.

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The Coulomb's Failure Criterion for materials is commonly and implicitly applied to the stress components on failure plane. In this paper, it was attempted to apply the Coulomb's Criterion not only to the failure plane but also to general planes which have various directions relative to the principal stress components at failure conditions, and it was shown that the previously proposed well-known criteria for materials could be expressed by an unified simple equation. This fact indicates that the direction of the plane for the Coulomb's Criterion is a material property as well as the friction ratio and cohesion. The revised Coulomb's Criterion was applied to simulate test results, and it was shown that the model could reproduce the test data fittingly.

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