The results of laboratory studies on the uplift behaviour of short piles in uniform sands are presented. Smooth and rough mild steel piles (12.7 mm in diameter) in two uniform sands were used in the investigation. Tests were conducted for dry and submerged conditions of soil placed at either of the two densities (loose or dense).The uplift capacity was found to increase with L/D ratio, pile roughness, soil density and particle size. Pile movements of about 5% of pile diameter in loose sands and about 10% of pile diameter in dense sands were found to be necessary to mobilise the uplift capacity. These values are much more than 3 to 6% required for shaft loads during push-in tests. The unit skin frictions during pull-out tests are significantly less than during push-in tests, especially in case of rough piles for which it is as much as 80% less. Submergence resulted in reduction of uplift capacity in all cases, earth pressure coefficients, however, reduced only in case of piles in dense sand and remained almost unaffected for piles in loose sands.

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In land zoning and resources extraction industry, hazard delineation normally constitutes an essential element in the processes of planning and engineering operations. The basic requirements for hazard delineation are increased safety and effective operations, and the most common method of hazard delineation involving multiple criteria is the overlay method.In this paper, fuzzy set operations are proposed as a tool to synthesize hazard indices of grid points or zones from a set of overlay plan maps. The proposed synthesis or aggregation procedure is based on the subjective nature of hazard index assessment and the multiple criteria associated with the overlay maps. These multiple criteria are nomally complex for analysis by conventional mathematical approaches, and are assumed here to be generally non-interactive.The procedure is simple to use, suitable for general multicriteria modelling and can be readily implemented on a computer.

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The performance of low embankments constructed on soft clay foundations both during and folllowing construction has been studied using centrifuge models. Model embankments were constructed during centrifuge operation on foundations prepared with an overconsolidated layer overlaying normally consolidated soil.In one of the model tests the embankment collapsed a short period after the end of construction. Measurement of displacements and excess pore water pressure in the foundation enabled the development of progressive failure to be observed. It was possible to identify zones of high shear strains, indicating the development of a potential slip surface, from equivalent inclinometer plots. Total stress and effective stress analyses of the embankment stability were assessed.Using the technique of staged construction greater embankment heights were safely achieved on an identical foundation. Pore water pressures were observed to rise following the end of construction chiefly as a result of pore pressure spreading. Values of construction pore pressures normalized by the change in vertical effective stress agreed well for each lift. During consolidation maximum horizontal displacements at the embankment toe were proportional centreline settlements.

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This paper develops a numerical procedure to provide an appropriate lower-bound solution for the wide range of problems of stability analysis. To represent the equation of equilibrium, the stress field is discretized in the similar manner as in FEM. To isolate a particular stress distribution, the problem to find the lower-bound solution is formulated as an optimization problem. When optimizing the bearing capacity, for instance, the problem is to find the stress distribution which maximizes the footing pressure within the limitations of satisfying the equations of equilibrium and of no-yield condition. The formulated optimization problem is solved numerically by a nonlinear programming technique. This procedure furnishes a reasonable solution for the problems not only of the bearing capacity analysis but also of the slope stability analysis. The results of several case studies by using the procedure are also reported.

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This paper investigates the collapse of rigid assemblies under applied forces, by using a two-dimensional model of contacting rigid discs. Expansions are made rigorously for both the frictionless and the Coulomb-frictional contacts, respectively. For the frictionless assemblies, some existing mathematical theorem and an associated calculation procedure are introduced, which are precisely applicable to their mechanics. As for the frictional assemblies, by employing new decompositions of a contact force and its relative displacement, conjugate to each other, and by showing the existence of frictionless rigid assemblies of another kind with common static conditions to them, it is concluded that the limits of their static equilibria do not coincide with the collapse initiations.

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Multiple series of cyclic loading tests with continuous rotation of principal stress direction were carried out on samples of Toyoura sand compacted to different relative densities under different initial stress ratio K₀ using a triaxial torsion shear test apparatus. In order to reproduce the wave-induced stress conditions occurring in an anisotropically consolidated soil element in the seabed deposit, the K₀-consolidated laboratory test specimen was subjected alternately to the triaxial mode and to the torsional mode of cyclic alteration thereby producing a continuous rotation of principal stress direction. In addition to this, it was considered necessary to perform the cyclic loading test such that the progressive buildup of lateral strain in the sample is inhibited in order to simulate the actual strain condition in the field. The condition of no lateral strain was imposed on the test specimen by reducing the vertical stress at the end of each cycle of the cyclic stress application.The results of such tests indicated that, for all densities of the samples tested, the effects of the initial stress ratio K₀ on the cyclic strength can be taken into account through its influence on the mean principal stress.

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This paper presents a method of analyzing, with the aid of an electronic computer, the flexural behavior of a batter pile due to ground settlement. In the method used here, a pile was devided into four sections according to ground conditions and Winkler subgrade was assumed for subsiding clay ground. To investigate applicability of the method, both laboratory and field tests were performed. In the laboratory tests, eight steel plate piles, each 1.78 m long, were used as four coupled piles with inclination angles of 5°, 10°, 15°, and 20°. In the field tests, four steel pipe piles, each 38.7 m long, were installed as two couples through an embankment 2.5 m thick with an inclination angle of 15°. For one of the couples, the two piles were asphalt coated. Strains in the pile shaft increasing with time were measured with the ground settlement in both tests. In addition to the author's method, the elastic finite element analysis and Sato's method were also examined. Consequently, the following points were clarified : (1) The maximum bending moment is proportional to the pile inclination and to the ground surface settlement ; (2) Although asphalt coating is useful for negative skin friction even with a batter pile, it seems disadvantageous from the point of view of bending ; and (3) While all three analytical methods provide good approximations of the test results, the best agreement was obtained by the author's method.

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In design of pile structures used for port and harbor, and offshore structures which are to experience large deformation, analyses taking non-linearity of soil-piles system are needed.A common practice in analysing such pile-structures is first to evaluate deformation characteristics of the soil-piles system in terms of pile-top stiffness and then to perform a stress calculation of superstructures by the displacement method. However, it requires a considerable amount of calculation to find out the pile top stiffness satisfying the compatibility condition because the system is highly non-linear and superposition is not to apply.In this paper a method of non-linear analyses for lateral resistance of piles is proposed, featuring less computation volumes than those of the existing methods. Loading test data are examined to validate the method. A derivation method of the pile-top stiffness is also presented.

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A case record of design, construction and field observation of a quaywall on coral debris mixed soil is described. Matrix of the foundation soil is the calcareous intermediate soil, in which porous finger corals form a loose skeleton. Preliminary design of the quaywall by the total stress analysis with φ_u=0 condition, in accordance with the current design manual, indicated a necessity of extensive soil improvement. Considering a possibility of higher value of the in situ permeability due to the porous finger coral skeleton, the effective stress analysis was employed by tracing the change in distribution of the excess pore water pressure with time throughout the series of construction stages. Change in the design method has led a substantial reduction of construction cost.Results of field observation suggested that this particular design was a little too conservative. The governing factor to this overdesign seemed a possibility of far larger in situ permeability than that used in the design. An engineering question of how to cope with this kind of geotechnically difficult soil is discussed.

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Laboratory model test results for the ultimate uplift capacity of group piles embedded in clay have been presented. The length-to-diameter ratios of the group piles tested under this program have been kept at 12 and 15. The group uplift efficiency varies with the embedment ratio, number of piles in the group, and the center-to-center spacing of the piles. For the present tests, a group efficiency of about 100% is reached at a center-to-center spacing of 6 to 7 pile diameters.

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The new failure criterion of J₁·J₂/J₃=const. which has been proposed on the basis of the "spatially mobilized plane (SMP)" is introduced as a failure criterion for granular materials (J₁, J₂ and J₃ : the first, second and third effective stress invariants). This failure criterion is called the Matsuoka-Nakai ("SMP") criterion. The Tresca and Mises criteria are usually adopted as failure criteria for metals, and the Mohr-Coulomb and Matsuoka-Nakai criteria for granular materials such as soils. The Matsuoka-Nakai criterion has a concept of averaging the Mohr-Coulomb criterion, in such a way that the Mises criterion has a concept of averaging the Tresca criterion. Such interesting relationship among the Tresca, Mises, Mohr-Coulomb and Matsuoka-Nakai criteria is discussed by reviewing their physical meaning, their forms of equations and their shapes in three-dimensional stress space.

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This paper develops a numerical procedure to back-analyse the horizontal and vertical permeabilities for saturated zone, from the measured time-history of ground water level. By using a combination of saturated and unsaturated seepage analysis by finite element method and of mathematical programming technique, the procedure allows to seek the unknown permeabilities which minimize the difference between calculated and measured time-histories of free surface position. The validity of the procedure is verified by calibrating the performance of the procedure being applied to hypothetical case studies.

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The angle of friction at the interface (or the skin friction) between cohesionless soil and another material is considered theoretically. It is pointed out that the angle of interface friction is upper-bounded by two different values. The first one is for the case when the interface is a velocity discontinuity between a mass of cohesionless soil and another material. In this case, the soil mass may or may not be at the limiting stress condition. This kind of friction angle may be independent of the strength and deformation properties of the cohesionless soil. The other one is for the case where a mass of cohesionless soil at the limiting stress condition moves solely due to its deformation along the interface without producing a velocity discontinuity. This kind of friction angle is a function of the strength and deformation properties of the cohesionless soil and the deformability of the material in contact with the cohesionless soil. Equations are given to evaluate the angle of soil interface friction from these properties as above.

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