This paper presents the development of a rational design method for determining the formation thickness of a railroad track. The design method is based on keeping the maximum deviator stress induced on the subgrade surface due to traffic loading below the threshold stress of the subgrade soil by providing a suitable formation thickness. The design method is intended to achieve a stable deformation behavior of the subgrade soil under repeated loading, limiting plastic deformation. The new method has significant advantages over existing methods. The new method is applicable to various soil types, and different ballast and subballast qualities. The effect of the rail size and the tie spacing is separated from the formation quality and design charts for different values of rail size and tie spacing can be readily prepared. A simple laboratory test procedure for quick evaluation of the threshold stress of the subgrade soil is suggested. A flow chart is given for systematic formation design along with a suitable design example. The importance of drainage condition for the success of this approach is emphasized. The design method is evaluated by observing the performance of an actual track under repeated load applications.

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This paper describes the results of two instrumented axial loading tests on large scale model stone columns, constructed similarly to the prototypes with a technique which employs ordinary pile driving equipment. Kaolin was used to simulate natural soil conditions. Pressure cells and electric piezometers were used to monitor lateral stresses and pore pressures respectively, during loading. A factual report of the data and a direct evaluation with respect to the load-deformation response and the mode of failure of the stone columns is provided. Two deformation models are examined : a triaxial specimen expanding laterally under compression and a skin friction pile. Furthermore, a trilinear load-settlement relation is proposed for design purposes, based directly upon the results of the model tests.

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Earth pressures are generated on the abutment wall of an integral bridge as a result of thermal expansion of the bridge deck. This provides an example of soil : structure interaction where a rational result can only be obtained if the relative stiffiness of the fill and the structure is taken into account. The problem must be understood and analysed as a whole. A numerical case study is described in which analyses of a typical integral bridge are used to show that, for the flexible abutment wall being considered, the development of earth pressure is primarily controlled by the stiffness of the fill and is hardly influenced by its strength. Comparisons are given between computed earth pressures and those proposed by design guides. The fill is described as an elastic-Mohr Coulomb perfectly plastic material. Typical stress paths for elements behind the wall indicate that the nature of the loading is dominated by compression rather than shearing. The selection of stiffiness properties-for which very little reliable information will usually be available-is discussed and a possible range of values is proposed.

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Geotechnical centrifuges enable prototype-magnitude effective stresses to be generated in small-scale soil models, a necessary condition for using them to predict prototype behaviour. The paper presents a thorough dimensional analysis of the modelling process. The general relationships between soil-particle size, pore-fluid viscosity and time-scaling processes which are necessary (in addition to effective-stress consistency), to ensure correct Reynolds Number modelling are presented in detail. The conditions for valid modelling of consolidation and accelerating-particle processes are also defined and discussed. Some historical errors are noted together with an analysis of the shortcomings of the use of 'prototype soil' in the model and oversimplified fluid viscosity scaling. A new pseudo-prototype concept is also introduced. This defines the prototype soil which is actually being modelled in a centrifuge test, enabling it to be compared with the one intended.

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Very few attempts have been made to evaluate the liquefaction resistance from a ductility viewpoint. The authors propose a new method to evaluate the ductility of soils against liquefaction, based on the energy dissipation capacity obtained from stress-strain loops of the constant-strain-controlled cyclic triaxial test. The method makes it possible to evaluate the liquefaction resistance against large earthquakes like the 1995 Hyogoken-Nambu earthquake. The effectiveness of the proposed method is explained using the test results of various soils. To confirm its effectiveness, a comparison was made of the energy dissipation capacity for Masado soil on Kobe Port Island obtained from the cyclic triaxial test, the array observation data and the seismic response analysis. The energy dissipation capacity obtained from the above three procedures shows very consistent results.

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The objective of this article is to propose and evaluate a sliding-block model to deal with very large displacements of slopes when a horizontal earthquake is applied. The slip surface consists of two inclinations on which full shear resistance is mobilized. Internal shearing exists along a sub-plane that intersects the angle between the two sub-planes that form the external slip surface. The ratio of the distance moved along the two external sub-planes depends on the inclination of the internal sub-plane. If there is a water table line, undrained conditions are assumed during motion and total stress analysis is performed. The governing equations of motion are formulated, analytical solutions are obtained for some cases, and back-analysis of four well-documented slides is performed.

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Man-made islands have recently been considered as possible new construction sites for a variety of facilities. The performance of the seawalls bounding these islands when subjected to seismic loading is an important aspect of design. To obtain data on the performance of such structures when founded on a medium dense sand seabed and supported by an armored embankment, a series of large scale centrifuge models were tested at the University of California, Davis. The concrete caisson within the seawall was found to settle, displace laterally and rotate slightly away from the backfill. However, the deformations were limited, and global failure of the structure did not occur despite base accelerations of up to 0.6 g. The model accelerations were amplified up through the substratum and caisson during relatively small events, but were strongly attenuated during the larger events. Zones containing high excess pore pressures were generally located towards the top of the sand fill forming the island, and in the seabed below the toe of the armored embankment. These zones grew progressively larger as the event magnitude increased, and accordingly the times for pore pressure dissipation to occur lengthened with increasing event magnitude.

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A series of consolidated-undrained torsion shear tests was performed on large, hollow cylindrical specimens of undisturbed San Francisco Bay Mud to investigate the influence of stress rotation and changes in b-values on the stress-strain, pore pressure, and strength characteristics of a cross-anisotropic, natural clay. The specimens were first K₀-consolidated and then sheared along various undrained stress paths to study the clay behavior in the full range of stress rotation from 0° to 90° relative to vertical. For this cross-anisotropic clay, the test results indicate that the major principal strain increment directions in physical space do not coincide with the directions of major principal stress at failure. The deviation between these two directions varied continuously and the maximum deviation was measured at approximately 20°. The normalized, undrained shear strength decreases systematically with inclination of the major principal stress at failure, ψ, from triaxial compression with ψ=0° and b=0 to triaxial extension with ψ=90° and b=1. The effective friction angle remains constant at approx. 35° in the range of ψ from 0° to 30° after which increases gradually to almost 50° at ψ=90°. These results are unlike those obtained for a laboratory prepared deposit of kaolin, which tended to behave more like an isotropic material despite the initial K₀-consolidation. Thus, effects of aging are very important in the behavior of clays, and it may not be possible to simulate such effects with sufficient accuracy and reliability with laboratory prepared clay deposits.

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Large diameter bored piers have a shaft diameter of more than 0.8 m, are man-bored and are cast in-situ. The piered raft foundation, a combination of a raft foundation with piers, has recently generated much interest and discussion as a foundation system for high-rise buildings on complicated soil conditions. This paper presents the performance of a piered raft foundation observed in-situ. The contact pressure and its distribution, the load sharing between the piers and the raft are monitored using earth pressure cells installed at the pier base-soil and raft-soil interfaces. Observation results show that the raft appears to support 20% of the building load. The substructure and superstructure have a stiffening effect on the foundation stiffness, resulting in redistribution in settlement and hence load of the piers. As a trial of the application of the research results, another piered raft foundation was successfully designed and practised for a 14-storeyed building in Shenyang, China.

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This study was performed to clarify which factors affected damage to tame-ike (small embankment dams for irrigation) in Hokudan Town as a result of the January 17, 1995 Hyogoken-Nambu earthquake. Factors were assumed to be : Location (e.g., Distance to Epicenter, etc.), Structure (e.g., Angle to Nearest Fault, Embankment Volume, etc.), Soil Properties of Embankment, Geology of Dam Site and History (Era of Construction, Repaired, etc.). Multivariate statistical analyses were performed for documentary data (damaged : 181, undamaged : 328). Ordinary statistical analyses were conducted for the data investigated in situ for soil properties of the embankment. The results show that the factors causing damage to dam are : (1) Nearest Fault (Nojima, Mizukoshi and D2), (2) Distance to Nearest Fault (less than 500 m), (3) Distance to Epicenter (approximately 8 to 14 km, which almost agrees with the location of seismic intensity 7 JMA), (4) Elevation of Dam Site (higher than 100 m), (5) Embankment Volume (the greater the volume the more damage was caused), (6) Direction of Dam Axis (normal or diagonal to the epicenter or to nearest the fault), (7) Plan View of Dam Axis (3 or 4 axes), (8) Surface Geology of Dam Site (non-cohesive soil type ground), (9) Era of Construction (prior to 1891) and (10) Soil Properties of Embankment (sand, not silty sand or gravel, penetration resistance that is 10% smaller than the undamaged dams).

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This paper examines a recently proposed work equation which accounts for energy dissipated in particle fracture and frictional rearrangement. A simple approach is adopted whereby the relative proportion of plastic work dissipated in fracture and friction is a simple function of stress ratio, and the normality principle is applied to generate a new family of yield loci. The derived family of yield loci requires the specification of a single parameter in addition to the critical state friction dissipation constant, and the original Cam clay yield locus is shown to be a special member of this family. By selecting an appropriate value of the new parameter, it is possible to model many of yield surfaces commonly encountered for isotropically consolidated clays and sands. The method also provides a convenient way of rounding off the corner of the Cam clay yield locus, if that is all that is required. The approach is useful in that it warns against use of the new yield loci on the dry side of critical states : for this purpose a non-continuum approach should be used. Care should also be taken in applying the normality principle : for sands at high stress ratios, extensive particle rearrangement occurs, in which case a non-associated flow rule could be adopted with the new family of loci.

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