This paper presents centrifuge model test data of the behaviour of a circular spudcan footing on drained saturated silica sand subjected to combined vertical, horizontal, and moment loading. The data are compared with predictions of a numerical model, and with relevant aspects of the recent code of recommended practice by SNAME (1994).

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This paper examines a method of numerical simulation of 3-leg jackup response to horizontal load. The method assumes variable rotational (moment) fixity, variable horizontal fixity, and complete vertical fixity. Numerical results are compared with centrifuge model test data. Consistently with Wong et al. (1993), it is shown that moment fixity increases with increasing spudcan rotational stiffness, increasing leg length, and decreasing leg flexural rigidity. It is further shown that fixity degrades with increasing horizontal load. Fixity with a longer leg under high horizontal load may become smaller than fixity with a shorter leg length under low horizontal load.

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A rational method of calculating the van der Waals attractive force between two clay particles is presented. The classical London, Hamaker and De Boer theories, and the more recent Lifshitz theory are combined to obtain closed form solutions for the force between clay particles. Special attention is given to nonparallel nature of particles, and the influence of the interstitial pore fluid. With the aid of equations developed, the influence of geometrical parameters such as the particle length, thickness, orientation and spacing, and the influence of pore fluid properties are illustrated. The study presented herein, along with the study presented recently on repulsive forces, should provide a more quantitative means of evaluating the physico-chemical interparticle forces in cohesive soils. In addition, the results in the present paper should make possible the consideration of van der Waals attractive force in micromechanical numerical studies such as the discrete element method of analysis.

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The behaviour of pile groups when adjacent surcharge loads are applied to a clay layer was studied using centrifuge model tests. Lateral soil movements due to the surcharge loading cause passive lateral pile pressures and traction under the pile cap. These loadings induce pile group displacement and rotation away from the surcharge load. This 3-d soil-structure interaction is complex and requires data upon which design rules can be based. Short-term loading was found to be the most critical case for design. Results are presented together with investigation of the long-term behaviour and the new 'buttonhole' foundation technique designed to reduce passive lateral pile pressures. Soil contact beneath the pile cap increased pile group loadings and enlarged the region of soil deformation compared to previously investigated geometries in which the pile cap was above the top surface of the deforming soil.

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A new formulation is presented for realistically modeling the mobilized maximum stress and phase-transformation stress states of saturated sands subjected to cyclic undrained shear on the basis of analysis of laboratory tests. It was found that, with the development of induced shear strain, the effective stress path associated with positive dilatancy asymptotically moves in parallel with and tends toward the critical stress state line. Such a material response is quantitatively described as a Moving Critical Stress state Line (MCSL) and a Moving Phase-Transformation Line (MPTL). It has been shown that 1) MCSL and MPTL are two straight lines fixed in the moving stress space whose coordinate origin is shifted along the normal stress axis by a "reference stress" p_r; 2) the reference stress p_r is a hyperbolic function of an "accountable shear strain increment" Δγ_a, and is dependent on the initial density; and 3) the slope of MCSL depends mainly on the initial relative density, while that of MPTL is independent of the density for a given sand. This formulation is further confirmed to be also suitable for irregular cyclic loading conditions.

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A detailed laboratory investigation was undertaken to study the settlement and deflection behavior of open ended caissons on sandy soil. Effect of embedment depth, diameter, and point of lateral load application were studied due to combination of vertical and lateral loads. Results indicate that load shared by the skin friction is greater than the base resistance for higher embedment depth / diameter ratios. Hence, the long-term safety of the caissons depends on the unused part of the tip loads, as the skin friction is mobilized at low settlements. Load-settlement curves indicate that the soil behaves linearly elastic up to very small settlements and deflections (2 to 4% of diameter). For better comparison with numerical methods, elasto-plastic constitutive laws are a must. Observed results agree well with those available in the literature. It was found that neglecting the base resistance is uneconomical for caissons with predominantly vertical loads, but it is recommended in estimating ultimate lateral load capacity. These results also indicate that small scale laboratory tests conducted in controlled conditions allow rapid and reliable information on field performance of caissons.

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A new mechanism of large post-liquefaction shear deformation in saturated sand was established on the physical basis that the shear deformation is governed by two types of volumetric strains due to dilatancy, i.e., an irreversible dilatancy component, ε_υ.ir, and a reversible dilatancy component, ε_υ.re. It was found that : 1) the shear strain is composed of a shear strain component depending on change in effective stress γ_d, and a shear strain component independent of effective stress γ_o; 2) post-liquefaction γ_o-value is triggered principally in the state of zero effective confining stress, and its current magnitude has a nearly unique relationship with the preceding maximum shear strain γ_max for sand of a given density; and 3) γ_d is determined by a good correlation existing between dε_υ.re/ dγ_d and deviator-isotropic stress ratio, q/p'. Based on the formulation for the above experimental findings and stress-dilatancy concept, a new approach is proposed to evaluate the large post-liquefaction shear strain γ=(γ_o+γ_d) in saturated sand. The results predicted by the proposed method compared favorably with experimental observation.

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Many cranes were damaged in the Kobe docks in the January 1995 earthquake. In particular, repeated impact marks on the concrete pavement of the wharf indicated that one crane rocked on its wheels, at the same time as the earthquake shaking and the pressure of liquefied backfill was pushing out the sea wall caissons and attached front rail. Analysis of the crane motion was performed to provide a time scale for dock movement, and in addition supplied interesting information on the crane's response.

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In this paper the angle of repose of sands is investigated; the slope angle of conical heaps of granular materials formed statically on a flat plate were observed as a typical angle of repose. The relationship of the angle of repose with the angle of internal friction is explained with regard of the deformation mechanism for the sliding layer of the heap on a thin surface. Some series of tests were conducted on plates with different roughness, and the factors influencing the measurement of the angle of repose were examined, including : the size, material pouring rate and boundary friction effects. In order to avoid the effects of the unfavorable influence factors, a rational method of measurement was proposed and the device for using this method is introduced.

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Marine clays are present in many parts of the world and these deposits are characterized by poor engineering properties such as low strength and high compressibility. These deposits are sensitive to changes in the stress system and the system chemistry of the pore fluid, and the use of a lime stabilization technique for such problematic clays is not new. In the present investigation an attempt was made to examine the diffusion of lime in the lime treated marine clay from the lime column or lime injection points and the changes which occurred in the engineering behavior of the soil system. The formation of new reaction products due to soil-lime reactions has resulted in particle growth of soil particles and the same has been confirmed using scanning electron microscopy. The test results indicated that the presence of excessive sodium ions in sea water do not retard the effective penetration of lime into the soil and that there is significant improvement in the engineering behavior of the soil system. The lime column and lime injection techniques can therefore be conveniently used to improve the behavior of soft marine clay deposits.

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Soft marine clay deposits are present in many coastal regions of the world and they are usually enriched with chlorides and occasionally with sulphates. The use of lime to improve the properties of soft clay deposits is not new. A test program was carried out to study the changes in the particle level of soil systems attributed to lime in a marine environment. The formation of various new reaction products due to soil-lime reactions were identified by X-Ray Diffraction (XRD) and the same was investigated using Scanning Electron Microscope (SEM). The test results indicate that the presence of chlorides encourage the efficiency of lime stabilization, but the presence of monovalent sulphates affect the improvement of the soil system due to the formation of the swelling compound, etttringite. It is suggested, that the lime injection technique can be conveniently used to improve the behavior of soft marine clay deposits.

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This paper describes a case study in which undrained cyclic deformation properties of a recent sand deposit in use for seismic response analysis was investigated through a comprehensive site investigation, coupled with cyclic loading tests in the laboratory. The test site comprised a loose sand deposit in Tokyo Bay which was reclaimed in 1960'. The objective of this investigation was to examine the applicability of profiling small-strain shear modulus and damping characteristics of the recently reclaimed sand deposit by performing undrained cyclic triaxial and / or torsional shear tests on disturbed sand samples retrieved by ordinary tube samplers, and also on fully reconstituted samples prepared with a void ratio similar to the in-situ subsoil. Two types of sand sample with high and low quality were obtained by means of in-situ ground freezing technique and by ordinary tube samplers, respectively. The quality of the samples was evaluated by comparing the pseudo-elastic shear modulus, G_max, from the laboratory cyclic loading tests to G_f from an in-situ downhole seismic cone test, which was involved with little disturbance to the original subsoil. On the basis of the test results, it was concluded that for this loose sand deposited only thirty years ago, the aging and structural effects were not significant with respect to the undrained cyclic deformation properties at small strains. It was also demonstrated that the undrained cyclic deformation properties can be evaluated with laboratory tests on isotropically consolidated specimens using disturbed or even fully reconstituted samples when the density profile with depth is pre-determined by means of appropriate in-situ tests.

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Experimental results for sand, gravel, sedimentary soft rock and stiff clay are presented which show that even at small strain levels (less than about 0.001%), these geomaterials exhibit nearly linear elastic behavior, but creep deformation and stress relaxation are not negligible. In cyclic loading tests, at these small strain levels, damping values are not negligible, and with a decrease in the loading frequency from a certain limit, the peak-to-peak secant modulus decreases and the damping values are not constant. These test results for the small strain domain, which show the existence of viscous effects, are successfully simulated by a rheological model called the Simple Asymptotic Body. It consists of a linear spring connected to a set of another linear spring parallel with a linear dashpot. According to this model, the peak-to-peak secant modulus has maximum and minimum values at very high and low loading frequencies where the damping value is zero, while the damping has the maximum value at an intermediate loading frequency. Some keys to answer the questions concerning i) the existence of difference in dynamic and static moduli and ii) "quasi-linear domain" for geomaterials are also given.

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