This paper develops a new numerical procedure for the slope stability analysis, by combining the slice method in the limit equilibrium method with the lower-bound approach in the limit analysis method. The procedure provides an appropriate lower-bound solution subject to the collapse mechanism represented by a potential slip surface. First, the safety factor for the shear strength is calculated for the case in which the position of the slip surface is known beforehand. The problem is formulated as an optimization problem for finding a stress field which minimizes the safety factor within the limitations of satisfying the lower-bound conditions. The formulated problem is solved numerically by the mathematical programming technique. The obtained stress field appears physically reasonable. Several case studies have shown that the simplified Janbu method based on the critical slip surface tends to underestimate the safety factor on the safety side, compared with the lower-bound solution by the proposed procedure. Subsequently, the assumption used in each of the representative slice methods, which are necessary to render the stability problem to a statically determinate, is verified by the use of the stress field determined by the proposed procedure. Finally, a procedure for locating the critical noncircular slip surface which minimizes the safety factor within the lower-bound conditions is developed. Many important properties in the slope stability analysis are clarified through the development of this procedure.

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A piezocone data base is compiled from 36 well-documented clay sites with known stress histories. Only transducer readings on the cone tip or just behind the tip were considered. The normalized excess pore pressure to effective overburden ratio (Δu/σ_vο') indicated better trends with overconsolidation ratio (OCR) than the parameters (u/q_c) and B_q=Δu/(q_c-σ_vο). A direct relationship was also observed between the measured excess pore pressure (Δu) and effective preconsolidation pressure (σ_p'). Positive or negative values of pore pressure can apparently be measured behind the tip in heavily overconsolidated clays, while only positive values can occur at the tip. For the sake of consistency and simplicity of evaluation, this study suggests that standardization of piezocones place the porous element on the cone face. Alternatively, two transducers should be used.

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In order to investigate the change in undrained shear strength characteristics corresponding to the change in the test condition and soil type, four different types of consolidated undrained triaxial tests were performed on some natural marine clays in Japan, and the test result was compared with that previously obtained for artificially mixed soils. The following conclusions were obtained. i) Relationship between the undrained shear strength characteristics and the plasticity index obtained for the natural marine clays was practically identical to that obtained for the artificially mixed soils. ii) Angle of shear resistance and pore pressure coefficient at failure were found to be approximately in linear relation with the plasticity index corresponding to the type of triaxial tests. iii) Calculated value of the ratio of the undrained shear strength to consolidation pressure, based on the experimentally obtained relationship between the strength parameters and the plasticity index, compared well to the value measured in each of four different types of triaxial tests. iv) Relationship between undrained shear strength characteristics and the plasticity index obtained in the present study may be used, as the first approximation, for some of marine clays in coastal area of Japan.

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A methodology to assess the permanent deformation of earth fills such as dams and embankments subjected to a shaking of an earthquake is presented. The method consists of a hybrid use of the static and dynamic response analyses and the laboratory soil tests by means of the triaxial torsion shear test apparatus. The static as well as dynamic analysis are made first using the finite element method to obtain the initially applied static stresses and also the time histories of shear stress during an earthquake. The tests are performed by applying the time histories of three components of dynamic stress plus the static state of stress thus obtained to the representative samples placed in the test apparatus. The residual strain potential obtained from the tests is incorporated into the static analysis to evaluate the final configuration of the earth fills deformed by the earthquake shaking. This methodology was applied to assess the seismic behavior of an earth dam in Japan.

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The boundary element method expanded in frequency domains is presented to analyze the dynamic interaction between an embedded flexible rectangular foundation and soil with consideration of the obliquely incident waves. Numerical results describing the influence of the flexibility of the foundation on the dynamic responses of the foundation due to obliquely incident waves indicate that the flexibility of actual foundations can diminish the reduction of translation responses and increase the rotational responses in the high frequency range. These phenomena are more conspicuous as the embedment ratio is larger and the value of the wave velocity ratio of the soil and the foundation approaches to unity. When the high frequency components of the input ground motion are important and the basement has higher flexibility (for example ₂v_s/₁v_s >0.4), the analysis method which considers the basement as a rigid foundation may lead to unsafety estimations and the estimation of the flexibility of the foundation is necessary as analysing the effective input motion with consideration of the incident waves.

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By employing a dozen of irregular time histories of motions obtained during the recent major earthquakes, two series of simple shear tests, one in uni-directional and the other in multi-directional loading conditions, were carried out on saturated loose, medium dense and dense samples of Fuji river sand. Following the undrained application of irregular loads, the generated pore water pressures were made to dissipate and the volumetric strains measured. The amount of reconsolidation volumetric strains thus determined is regarded as representing the settlement characteristics of sand which takes place in-situ deposits following the liquefaction during earthquakes. The test results indicated that the magnitude of maximum shear strain induced during the irregular loading is uniquely correlated with the volumetric strains during the reconsolidation. The test results also indicated that if the sand is deformed largely during the irregular load application, the subsequent volumetric strains during the reconsolidation could amount to as much as about 4.O%, 2.5% and 1.2% for the sand sample prepared with relative densities of 47%, 73% and 93%, respectively.

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The elasto-plastic finite element method based on the modified Cam-clay theory was used in numerical experiments to investigate the settlement behavior of an improved ground where vertical drains had been installed in a portion of the ground area. The numerical experiments were performed taking into account the effect of changes in the loading width and the width of the area improved by vertical drains. As a result, the authors have clarified the following facts : the rate of settlement of a ground which is partially improved by installation of vertical drains lags behind the rate predicted by design theory ; the degree of lag becomes more noticeable in the areas closer to the edges' of the improved area and in the later stage of consolidation due to the influence of the adjacent non-improved area. In order for any ground improvement work to be completely effective within a limited period of time, it is necessary to install drains over an area somewhat larger than the designated improvement area. In this paper, a method for the determination of the size of the additional drain-installation area required to properly complete the improvement process is proposed using the results of the numerical experiments.

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A laboratory investigation has been carried out into the effects of initial anisotropic fabric and b=(σ₂'-σ₃')/(σ₁'-σ₃') on the strength and deformation characteristics of air-pluviated Toyoura sand. Drained tests in triaxial compression (b=0.0), in plane strain compression (b≒0.2∼0.5) and in triaxial extension (b=1.0) were performed at different directions of principal stresses with respect to the deposition direction. The strength in triaxial extension was found to be strongly influenced by failure modes. The inherent anisotropy in strength and the effects of both the parameter b and the failure mode on strength are portrayed in the form of a three dimensional surface having the axes of φ, b and the angles ω and ξ;ω and ξ represent the deposition direction with respect to the directions of σ₁', σ₂' and σ₃'. It was found that φ is rather insensitive to the change in b when the one of the planes of the maximum stress obliquity is in parallel with the bedding plane. The deformation characteristics including the stress-dilatancy relation are discussed in a similar way as for φ.

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This paper describes a method for observing the particle behavior near the interface in sand-steel friction tests. A friction testing apparatus was modified to allow the observation of sand particles. Close-up photographs were taken of the sand particles at specified timing in sand-steel friction tests. The change in particle coordinates gives the displacement of particles during the friction test. The sand-steel interface showed a small amount of sliding before the peak in the frictional resistance. The sand on a smooth steel surface slid without large shear deformation. The sand particles on a rough steel surface rolled as well as slipped along the interface. These movements caused the formation of a shear zone within the sand along a rough interface. The displacement of stacked aluminum frames provides approximate displacement of the sand particles. The relative displacement between the bottom frame and the steel specimen gives the sliding displacement at the sand-steel interface.

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Using two kinds of sands, a series of cyclic undrained triaxial tests was performed on loose and dense specimens subjected to different periods between O.1 hour and 68 days of sustained pressure. At the same time, tests on specimens over-consolidated with an OCR of two or four were performed in order to compare the effects of long-term consolidation and over-consolidation. For each sand, the strength increase after 68 days under sustained pressure was found to be equivalent to that due to over-consolidation with an OCR of about two. It was further found that for each sand the strength increase due to long-term consolidation and over-consolidation was found to be a similar function of the plastic axial strain which had occurred during each consolidation history. This result suggests that the strength increase by these different consolidation histories is due to a similar mechanism. It was also found that strength increase due to either long-term consolidation or over-consolidation was larger for the sand including some fines than the other clean sand.

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