Laboratory tests on friction between normally consolidated Kawasaki clay and mild steel were carried out by using two types of direct shear test apparatuses, namely, simple shear type and shear box type. The excess pore water pressure at the interface was measured. Frictional behaviour obtained was as follows : (1) There existed a critical steel roughness of approximately 10 μm R_max (L=0.2 mm). When the steel surface was smoother than the critical roughness, interface sliding occurred, followed by the reduction in frictional resistance. When the steel roughness exceeded the critical value, however, shear failure occurred within clay specimen, so that the maximum resistance of friction agreed with shear strength of clay. (2) The angle of interface friction in terms of effective stress did not depend on drainage condition and consolidation pressure of clay. (3) The loading speed was influential in the maximum resistance of friction, while less influential for smoother steel surface, and of little influence on the residual resistance of friction at the applied displacement of 10 mm. (4) For the tests of shear box type, shear strength of clay did not agree with the upper limit of the maximum resistance of friction, which was obtained when shear failure occurred within clay specimen. This was due to the difference of shear deformation of clay specimen in the shear box.

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In the conventional method of setting a saturated clay specimen for triaxial testing, water saturated porous stones, wet filter paper and drainage lines filled with water are used (the wet method). Since this method introduces free water to the surfaces of the specimen under zero total stress, under suction pressure, the specimen takes in water and swells. It is shown that this swelling and its effects on the subsequent specimen behaviour can be reduced by setting specimens of clay with dry porous stones and dry filter paper and applying an effective pressure before allowing the surfaces of the specimen to come into contact with free water (the dry setting method). It is further shown that the consequent difficulty associated with achieving a high degree of saturation in the dry setting method can be overcome by a combination of vacuuming, flushing with de-aired water, and back-pressurizing giving degrees of saturation comparable to those obtained by the properly executed conventional wet setting method. The responses of reconstituted specimens of kaolin and an in-situ clay mounted by the dry method are also compared with those mounted by the conventional wet setting method over the whole stress range from saturation to failure in triaxial compression. It was observed that at low stress levels the wet method gives softer specimen response which can result in inaccurate determination of the pre-consolidation stress. The results further suggest that unless the effect of setting method is severe, consolidation to higher stress levels may be enough to erase the effect of setting procedure.

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A series of physical property aud chemical composition tests were conducted on ten fall loam soils, two secondary sedimented loam soils and two alluvial clays, all of which were obtained throughout Aomori Prefecture. Mechanical strength tests were also done for undisturbed and compacted samples of the soils. The main findings were as follows : (1) Silt fractions are what mostly control the in-situ moisture contents which are closely related to the amorphous contents of the fall loam soils; (2) The fall loam soils were categorized into the amorphous rich and the amorphous somewhat high fall loams by an in-situ moisture content of 70%. The amorphous rich loams showed unusual characteristics; (3) The strength of the undisturbed samples increases with an increasing in-situ moisture content for amorphous rich fall loam soils, but decreases for amorphous somewhat high fall loam soils; (4) The strength loss due to remoulding and the strength itself of the compacted samples were uniquely expressed by the liquidity index; (5) The ratio of CBR(compacted sample)/CBR(undisturbed sample) for amorphous rich fall loams becomes higher when the liquidity index increases. Finally, a practical classification chart consisting of the in-situ moisture content and the liquidity index, with two special lines, (W_n=70% and I_L=0.8), was proposed.

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In order to find the proper composition of lubrication layer to be used for element tests of granular materials in the laboratory, a series of direct shear tests between a granular material specimen and a lubrication layer was performed. The granular materials used ranged from a fine sand to a gravel with D₅₀=0.16 mm∼1.85 mm. The lubrication layer consisted of a layer of silicone grease and a latex rubber disk, and its variations. Based on the test results, the following points are shown : (1) For Toyoura Sand (D₅₀=0.16 mm), when a properly designed lubrication layer is used, the apparent frictional angle φ_μ can be as small as around 0.14∼0.16 degrees when a normal stress is 2.0∼6.0 kgf/cm² (196∼588 kN/m²). These values are independent of void ratio. (2) For Hime Gravel (D₅₀=1.85 mm) and Silver Leighton Buzzard Sand (D₅₀=0.62 mm), a proper amount of powder should be added to the original grease in order to improve the quality of lubrication by preventing the squeezing out of grease from the places of stress concentration in the proximity of particles indenting the lubrication layer. At the same time, the amount of powder should not be too much in order not to increase the shear resistance of a mixture of grease and powder. Fly ash is suggested as a proper type of powder. By this method, even for Hime gravel, a low value of φ_μ of around 0.8 degrees at normal stresses of 1.5∼7.0 kgf/cm² (150∼700 kN/m²) can be obtained.

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A modelling method for highly nonlinear shear stress-strain relations in plane strain compression of a fine sand, Toyoura Sand, which has been used extensively in a large number of model tests by many researchers, is attempted taking into account the effects of many major factors; (1) void ratio, (2) confining pressure σ₃, (3) the initial and maximum shear modulus G_max as observed at strains less than about 0.001%, (4) anisotropic strength and deformation characteristics, (5) strain softening associated with strain localization into a shear band, and (6) the stress ratio during consolidation. The model is based on a modified hyperbolic equation. By the model proposed, a relation from very small strain (0.0001%) to the residual conditions through smooth transition from pre-peak to post-peak relations can be generated for a given condition. A generated stress-strain relation has a tangent modulus which is continuous at the peak strength state between the pre-peak and post-peak parts.

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Based on the recommendations of Berezantzev et al., a new semi-empirical equation for settlement ratio of pile foundations in sand has been derived. The settlement ratios obtained using this equation have been compared with the actual measured values. The comparison indicates that the new equation predicts higher than actual settlement values and is therefore conservative. The new equation is therefore modified in the light of empirical evidence and presented in a generalised form which can be used for square, rectangular, and irregular pile groups. The procedures recommended for the use of the equation in preliminary designs are explained.

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To predict the braking performances of a towed rigid wheel on a soft ground, a new analytical method based on the soil-compaction has been presented. The contact pressure distribution around the peripherical contact part of the rigid wheel, especially the resultant stress between the normal stress and the shear resistance should be calculated by use of the dynamic pressure sinkage curve, considering the rolling locus of the wheel in the direction of the external resultant force between the effective braking force and the axial load. From the plate loading and unloading test, and the plate traction and slip sinkage test, the fundamental terrain-wheel system constants should be determined precisely. And then, the effective braking force could be calculated as the summation of the braking force i.e. the integration of shear resistance developed on the peripherical interface and the locomotion resistance calculated from the total amount of sinkage. As the results, the analytical relations between the braking force, the effective braking force and the slip ratio, the compaction resistance and the slip ratio, the amount of sinkage and the slip ratio, the amount of eccentricity of resultant force and the slip ratio, and the entry angle, the exit angle and the slip ratio could be verified experimentally.

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In areas of Japan with a thick soft clay layer, the Deep Mixing (DM) method, which is one of the soil stabilization methods, is occasionally used for braced excavations. However, some excavations have been interrupted because of unusual behavior. This report analyzes data obtained from field observations during the construction for expanding the Tokyo International Airport. The main reason for stopping the excavation was not an increase in either the strut forces or the bending moments of the retaining wall, but the large heave of the vertical supports. Instead of using the circular failure method, which is extensively used to examine base failure in Japan, a new stability number, N_t, is proposed for braced excavations stabilized by the DM method.

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To meet the increasing demand for air transportation, Ministry of Transport has carried out an offshore development project at the Tokyo International Airport (Haneda Airport). Since the airport is constructed on extremely soft ground reclaimed by dredged sludge, it is predicted that the consolidation settlement will continue after opening the new airport. Extensive observation of the differential Settlement has been carried out during construction of the project. The results of the statistical analyses of settlement show that the damage to the airport pavements due to differential settlement for 10 years will not be serious. It is possible, however, that partial repair work to improve the grade of pavement surfaces may be required.

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An inverse analysis technique which is firmly based on non-linear regression method has been adopted to estimate Young's modulus of layered ground using the pile settlement model proposed by Poulos and Davis (1980). This is purely an elastic model, therefore no slip between soil and pile could be taken into account. In this method, not only mean value but also uncertainty involved in it can be quantified. Furthermore, a prediction procedure based on the First Order Second Moment (FOSM) method is also proposed. Two sets of bored pile loading test data consisting of pile top settlement and load distribution along pile shafts at various loading stages from the Bangkok area are analysed. It is found that more reliable estimation of parameters is possible if they (i.e. Young's modulus of each layer) are estimated based on several pile loading test results which have been conducted in a variety of geological settings and pile configurations. However, the prediction may not directly reflect accuracy of the estimated results, i.e. good prediction can be obtained if the geological conditions and the pile configurations are not very much different from the ones used in the estimation. On the other hand, erroneous prediction could result if these conditions are very much different. All these outcomes are explained based on data structure of pile loading tests which exhibit the multicollinearity.

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Laboratory tests on friction between cohesive soils and mild steel were carried out using a direct simple shear type of test apparatus. The cohesive soils were normally consolidated Kawasaki clay and four kinds of normally consolidated sand-clay mixtures. All tests were carried out under consolidated drained shear condition. Frictional behaviour observed was as follows : (1) There was little difference in the maximum coefficient of friction between the tests with different mixture ratios of sand. After sliding had occurred between steel and a soil with a high clay fraction, however, the residual coefficient of friction at the applied displacement of 15 mm was much smaller than the maximum coefficient of friction. (2) The critical value of steel roughness is the boundary value whether interface sliding occurs or not. It was larger for a soil with a higher sand fraction. (3) For the friction of sand-clay mixtures with steel roughness of 20 and 30 μm R_max over a gauge length of 0.2 mm, interface sliding and shear deformation of the soil specimen proceeded simultaneously. (4) Frictional behaviour was classified into three failure modes, namely full sliding at the interface, shear failure within the soil, and the mixed behaviour where interface sliding and shear deformation of the soil specimen proceed simultaneously.

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The size effect of the height of granular (sand) test specimens in a triaxial compression test is explained by the bifurcation theory. With reference to the analogy between the imperfection-sensitive bifurcation behavior of shell structures and the experimentally-observed size effect of sand specimens, we present a hypothesis that the influence of initial imperfections for sand specimens decreases inversely proportional to their height. We derive several pertinent power laws for imperfection sensitivity that offer information on bifurcation, and have assessed their validity based on experimental data. Further we propose a method for obtaining the idealistic stress ratio versus strain curve for an infinitely-high specimen by asymptotically extrapolating the experimental curves. This method has successfully simulated and categorized the bifurcation-behavioral characteristics of dense and of loose sand. A caution is exercised that the true material properties would be much stronger than those observed in experiments due to the size effect. It has been demonstrated that the softening of the experimental stress versus strain curves arises from the bifurcation, instead of the softening of the material properties.

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The concept of effective strain is proposed as a reciprocal concept of the effective stress. The effective strain is defined as strain minus volumetric strain due to dilatancy. Though the overall volume of granular material remains the same during shearing involving no volumetric strain increment, the volume of void can change due to the rearrangement of the particles. On this reflection, it is postulated that the relative displacements of the centers of the particles which are in contact in granular materials are, in the average, consistent with the effective strain. This leads to the concept of the effective strain energy which is defined with respect to the effective strain. Though a plasticity model with micromechanical background (Iai, 1993b) is not exactly expressed in the associated form, its flow rule becomes associated if it is defined in the effective strain space. Drucker's stability postulates defined with respect to the effective strain energy are also seen to be satisfied by the present model. Thus, introduction of the concept of the effective strain may be one of the efficient approaches to solve the controversy over the non-associated flow rule and Drucker's postulates in the constitutive modeling of granular materials.

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Most of the minimum requirements of discharge capacity of prefabricated vertical drains are based on tests carried out on straight drains. However, after being installed in the ground the drains are subjected to deformation due to ground settlement. In order to obtain a more realistic value of discharge capacity, a mcthod of testing the performance of a prefabricated drain has been proposed. In this method the effect of drain deformation is incorporated so as to simulate closely the field conditions. Typical results of tests on several prefabricated vertical drains are presented and discussed to illustrate the importance of the test.

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