For clayey ground including partial sand layers, it is difficult to precisely predict consolidation settlement. The reason is the difficulties in grasping the distribution of partial sand layers and in calculating the settlement by FEM analysis considering the three-dimensional distribution of sand layers. In a clayey ground including partial sand layers, the deposit was improved by installing prefabricated vertical drains and applying vacuum pressure. The distribution of partial sand layers was investigated in detail using the penetration resistance records obtained during installing work of prefabricated vertical drains. The drains were installed by square arrangement of 1.8-m spacing into the ground. The identified three-dimensional distribution of partial sand layers was reflected to three-dimensional FEM analysis, and the influence of sand layers on the settlement was clarified. As a result, it was confirmed that the influence of partial sand layers on consolidation settlement is significant and the settlement can be predicted by the method proposed in this paper.

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Consolidation characteristics of clay, which are compressibility, permeability and consolidation velocity etc., are conventionally represented by relationships between the “arithmetic scaled” volume ratio f or void ratio e and the logarithmic scaled effective stress p, coefficient of permeability k and coefficient of consolidation c_v etc. However, some previous works have suggested that a relation of volume ratio f and effective stress p in double logarithmic scale (logf-logp) is able to express compressibility of clay more reasonably than the one in single logarithmic scale (f-logp). At the exordium of this paper, the rationale of representation of consolidation characteristics of clay including k and c_v by “logarithmic f” than “arithmetic f” was derived from a revisional study on them. Next, experimental results of a series of centrifuge consolidation test for the very soft clay (dredged clay) were examined. Then their results were numerically simulated for two cases of using “logarithmic f” or “arithmetic f”. As a consequence, consolidation curves experimentally obtained were correctly represented by the numerical simulation with “logarithmic f”. Moreover, it was found that more stable and faster calculation is enabled by applying “logarithmic f” instead of “arithmetic f” to the expansion of the consolidation equation.

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Mechanical behaviors of rock masses often become anisotropic due to discontinuities. Mechanical properties of anisotropic rock masses are previously investigated by triaxial tests using boring cores sampled to from different orientations, but which is costly and time consuming. In this study, a new triaxial testing method to characterize deformation properties of anisotropic rock masses is proposed. This method can identify the directions of anisotropy by the directions of principal strains during isotropic consolidation and also can determine 5 elastic parameters of a transversely isotropic rock by the relationships between stresses and strains during both isotropic consolidation and axial compression.

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Soil liquefaction under initial shear stress induced by nearby slopes, embankments and superstructures causes large shear failure in the ground, leading to sliding, tilting and uneven settlement of the structures. In this study, a hollow torsional shear apparatus is used to investigate the effect of initial shear stress acting on horizontal plane on liquefaction behavior of medium to loose sand of relative density D_r≒30, 50% and fines content F_c=0-30%. A series of test results have revealed that the liquefaction failure is categorized into five types; cyclic failure (CF) for α=0, cyclic biased failure (CBF) for small α, biased gradual failure (BGF) and biased sudden limited failure (BSLF) and biased sudden failure (BSF) for larger α. Among the 5 failure types, it is important to pay special attention to BSF type, which may develop abrupt strain increase due to initial shear stress by cyclic loading. In comparing with undrained monotonic loading tests, the mechanism of the abrupt BSF has been clarified. The angle of a yielding surface φ_y’ corresponding to the BSF has been studied under the effect of initial stresses for test specimens with different contractive behavior caused by parametrically changing fines content and relative density. It has been demonstrated that the BSF type failure is controlled by the angle φ_y’ reflecting contractive behavior of sand, irrespective of the magnitude of initial stress.

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The stability of soil-structure systems is usually evaluated using a two-dimensional analysis. However, using a three-dimensional analysis may be one of the best methods to minimize unnecessary seismic safety margins which are potentially included in a two-dimensional analysis. This three-dimensional analysis however requires a substantial amount of man and machine power, which makes this method inefficient. Therefore a pseudo three-dimensional method is proposed for evaluation of the stability of the ground.
The model of this pseudo three-dimensional method consists of multiple two-dimensional cross sections. By utilizing the results of static and dynamic responses from these multiple models, it is possible to create stress conditions along three-dimensional failure surfaces that are similar to those results from a three-dimensional response analysis.
This method was applied to a hypothetical example with weak layer zones and a site with fault zones that actually exists. The first example consisted of three individual cross sections and the second example consisted of more than 10 cross sections. The factors of safety are compared to those from a three-dimensional analysis. The results compared were consistent each other. Therefore it is concluded that the proposed method produced reasonable and accurate results for the design purpose.

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The authors have conducted studies for development of evaluation procedure of the earthquake-induced residual displacement of the retaining wall and for development of an aseismic countermeasure for the retaining wall by the embedment of sheetpile. It was attempted in this study to examine the applicability of the proposed displacement evaluation method of the retaining wall by conducting the relevant simulation using the case histories of the damaged retaining walls during the 1995 Hyogoken-Nanbu earthquake. Calculated residual displacement of the retaining wall reasonably agreed with the observed displacement. In addition to the above, it was also attempted in this study to extend the proposed displacement evaluation method by considering the effect of the sheetpile, which was observed in the shaking table model tests. Simulations using the extended procedure indicated that embedment of the sheet pile could reduce the extent of the earthquake induced damage of the retaining wall during the 1995 Hyogoken-Nanbu earthquake.

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This study explores the production of a new type of pile. This new spiral pile is made of a twisted steel plate, creating a continuous spiral shape. Before starting the large-scale production of these piles, it is necessary to experimentally investigate their bearing properties, which are related to admissible displacement and installation method. It is also necessary to develop an analytical model to determine their bearing capacity. The purpose of this study is to investigate the bearing properties of the spiral pile and the behavior of the surrounding ground. Considering this, the first objective is to examine the effect of the shape of the pile. The installation method and penetration resistances are thoroughly discussed on the basis of the results of static loading tests using model piles. The static penetration tests were conducted under various shaft rotary conditions. It was confirmed that the shaft rotary condition has a significant impact on the penetration resistance and vertical bearing capacity of the spiral pile. The second objective is to show the behavior of the ground during penetration using X-ray computerized tomography (CT). An industrial X-ray CT scanner was used to observe changes in the density of the sand surrounding the spiral piles during penetration. The disturbance area of the ground surrounding the spiral pile was observed using CT images; the images revealed that the disturbance area surrounding the spiral pile was significantly affected by shaft rotary conditions.

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It is well known that the existence of meniscus water affects the shear strength for unsaturated soils. Although natural soils exist as wettable (hydrophilic) soils generally, it is possible that the natural soils become non-wettable (hydrophobic) features due to organic pollutants, natural hazards such as forest fire, and environmental pollution accidents such as oil spill. The non-wettability in soils affects physio-mechanical behaviors, the contact angle and the capillary pressure. The accumulated geotechnical knowledge so far tends to be somewhat limited to wettable soils in the field of unsaturated soil mechanics. Among several research subjects for hydrophobic and hydrophilic sands, this paper presents the empirical verification on which the existence of meniscus water affects the shear behavior for unsaturated soils using artificially synthesized hydrophobic sands. In addition, the obtained shear strengths are discussed by means of the application of the suction stress.

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When an anisotropic stress is applied to a soil, anisotropy of mechanical properties develops. Using a hollow cylinder torsional shear apparatus under different drainage conditions, this study examined effects of fabric anisotropy induced by anisotropic consolidation on mechanical properties of saturated and unsaturated cohesive soils. Although strength anisotropy did not appear under drained condition, that developed under undrained condition in both saturated and unsaturated cohesive soils. However the strength change induced by the strength anisotropy of unsaturated cohesive soil was less than that of saturated cohesive soil. The experimentally obtained results elucidated that this kind of fabric anisotropy generated strength anisotropy caused a change of pore water pressure during shearing in the saturated and unsaturated cohesive soils. Using suction at the failure, it is presented that the shear strength follows the failure criterion proposed by Fredlund et al. even in the specimen with strength anisotropy.

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Countless detached houses were damaged by liquefaction in the Tohoku Earthquake. Judging the necessity to investigate the residents’ consciousness towards building and land, a questionnaire survey targeting detached houses was conducted. We compared the results with past results collected from the Hyogo Southern Earthquake. Furthermore, by investigating the liquefaction damage of detached houses and organizing the amount of subsidence and slope angles of differential settlement, we were able to study characteristics of the ground and building forms that have effect on differential settlement.

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In the reinforcement method by using the cement-mixed muddy soil for the fill type dam embankment, it is necessary to determine the zoning pattern to produce no an extremely large difference in strength between the reinforced zone by cement-mixed muddy soil and the existing embankment.
In this paper, the direct shear tests duplicated the failure mode of the embankment reinforced with the cement-mixed muddy soil was performed to investigate the allowable strength difference between the reinforced zone and the existing embankment. From the experimental results, we suggested that the embankment reinforcing with the cement-mixed muddy soil is regarded as a composite soil if the reinforced zone strength τ_CC is approximately 3.0 times lower than or equal to the existing embankment strength τ_S.

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This paper discussed the coefficient of permeability for prediction of water level and the deformation modulus for prediction of deformation of the model embankment. The seepage and deformation analysis is carried out on the embankment collapse test due to rainfall. As a simulation result, the value of coefficient of permeability of embankment model is larger than a coefficient of permeability by laboratory test. Deformation of embankment of model test can be simulated roughly by considering the nonlinear of deformation modulus.

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In this study, the authors estimated the influence of abnormal signals, obtained by the explorations of underground radars in the road surface lower cavity, by FWD test on the soundness of the pavement in the urban areas. We confirmed that the abnormal signals were classified into cavities, loosening and buried objects, and that the FWD deflection directly above each of the abnormal signals became larger than those of the sound points. However, it was not possible to discover the direct correlations of the FWD deflection with the breadth and the depth of the cavities and the loosening points. Accordingly, we used the “isotropic circular analysis” and confirmed the usefulness of the method of evaluating the risks of sinking and caving in of the points emitting abnormal signals.

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