This paper deals with the overall stability of an embankment foundation failure that lies at km 40+700 of the new Irbid-Amman Highway in Jordan. Slope stability back analysis was carried out for the slope to assess the conditions at time of failure, and estimate most representative shear strength parameters of foundation materials. Slope stability analysis was also carried out for proposed remedies. Probabilistic seismic hazard analysis was carried out for the landslide site. Peak Ground Acceleration (PGA) value of 0.2 g was estimated for design. This corresponds to a 90% probability of non-exceedence in a 50 year design life of the highway. Pseudo-static slope stability analysis was also carried out. The study concluded that the landslide movement occurred within the foundation colluvium material. It resulted primarily from the excessive load of the embankment and excess piezometric pressures generated within the slope. The most feasible remedial measure to stabilize the landslide area was removal of existing failed embankment down to the top of sandstone layer, and reconstruction (using imported free-drainage rockfill) of a split level embankment together with the construction of surface and subsurface drainage system. These measures were successfully implemented in the field.

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The paper presents the results from a series of tests in Shanghai, PRC on laterally loaded single piles in a medium stiff clay. The diameter of the piles varied from 0.09 m to 0.60 m. The piles were instrumented with strain gauges to determine the moment distribution along the piles and the lateral deflections. The test results from the static load tests have been analyzed assuming that the load-displacement relationship of the soil is hyperbolic. The assumed p-y curves could be related to the stress-strain curves as determined by triaxial tests. Numerical values on the coefficients, R_f, A, k and ε₅₀ used in the analysis of the test results are discussed in the paper. However, a reduced shear strength had to be used when the clay is overconsolidated.

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In this paper, an elasto-viscoplastic constitutive model with strain softening is proposed based on Adachi-Oka's model. In the model, a time measure, instead of strain measure adopted in a previous model, is introduced as an internal variable to account for not only stress history but also time change. The yielding function is defined in the way that the structural deterioration of geologic materials with time is considered. The application of the model to the experimental results for soft sedimentary rock indicates that the model can not only describe the time dependency, such as strain rate dependency, creep and stress relaxation to some extent, but also the strain softening behavior of geologic materials.

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The mechanism of wave-induced instability in a permeable seabed have been studied for more than two decades. The distinction between shear failure and liquefaction, however, has not been clearly defined. This paper presents a fundamental study on the differences in two failure modes for a fully saturated seabed of both finite and infinite thickness. The wave-induced effective stresses and pore pressure, obtained from an analytical solution of Biot's pore-elastic consolidation theory, were employed to examine the failure modes under a two-dimensional plane strain condition. A case study is presented to examine the failure modes with respect to several parameters, such as excess pore pressure, seepage flow, seepage force, failure areas and stress path in the seabed. The conclusions obtained from this study were as follows ; (1) the thickness of a permeable seabed affects the pore pressure and effective stress response to ocean waves and the failure mode of the seabed, (2) either a liquefaction or shear failure, or both, occur in the seabed, even in the saturated seabed, (3) the Mohr-Coulomb's failure criterion, when combined with elastic stresses, can not be employed to estimate the liquefaction failure in the seabed, (4) the liquefaction can be evaluated by a criterion in terms of the excess pore pressure, (5) The liquefied zone in the seabed is significantly different from the shear failure zone. The shape beneath the seabed surface for the former is almost identical to the contour where the upward seepage flow is concentrated.

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The group effect which causes different downdrag distribution in individual piles within the group was investigated by using a numerical analysis and an analytical study. The interaction factors due to group spacing, the total number of piles in a group and the relative position of a pile within the group were estimated by using a three dimensional nonlinear finite element approach. An approximate closed form solution was also developed for the single pile case. It was shown that the interaction factor for pile groups varies extensively according to the group spacing, a major parameter influencing the group effect. Based on the results obtained, interaction factors were proposed quantitatively for 9 to 25 piles with spacing to diameter ratios varying from 2.5 to 5.0 for downdrag loads.

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The behavior of natural clays during one dimensional consolidation is influenced strongly by strain rate as well as temperature. This is evidenced, in particular, by the series of Constant Rate of Strain (CRS) oedometer tests performed on clay from Berthierville, Canada. The preconsolidation pressure is a function of both strain rate and temperature. The viscous behavior of the natural clay skeleton as well as the characteristics of the permeability are discussed in this paper, based on the experimental results obtained on Berthierville clay. An elasto-thermo-viscoplastic constitutive model is also developed to reproduce the one dimensional behavior of natural clays at different strain rates and temperatures. An effective stress based finite element method is applied to the experimental results of consolidation. The simulated results were found to agree well with the experimental ones.

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Non-linear consolidation deformation behavior of saturated clays under embankment loading (plane strain) has been investigated using numerical analysis. The governing equations are based on the finite deformation theory which considers both geometric non-linearity and material non-linearity and the finite element method is used for the solution procedure. The subloading surface Cam-clay model for finite deformation is employed for the non-linear material behavior of lightly/heavily overconsolidated clays. The clay foundation response to embankment construction under both the non-linearities is discussed within the Critical State Soil Mechanics framework. For overconsolidated soils, both the hardening and softening behavior above the critical state line (p'-q stress space) occur with plastic volume expansion. The area under the embankment slope reaches the normally consolidated state first during load application. In a lightly overconsolidated clay foundation, this area undergoes strong strain localization which can lead to physical failure of the structure. The embankment toe area of a heavily overconsolidated clay foundation exhibits a softening behavior with net volume dilatation at the end of the consolidation. The drained loading of a heavily overconsolidated clay foundation tends to give higher load bearing capacity than for undrained loading as in the case of lightly overconsolidated soils.

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This study evaluates the scale effect observed in the behavior of a shallow anchor in dense sand, by comparing a conventional 1 g model test with a finite element analysis. The model tests were performed in h/D=1, 2 and 3 (h : depth, D : anchor diameter). Flat circular 0.5 cm thick steel plates with D of 3 cm, 5 cm, 10 cm and 20 cm were used as circular anchors. The finite element analysis employed a constitutive model in which non-associated strain hardeningsoftening elasto-plastic material was assumed and the effect of shear band thickness was introduced. The finite element analysis was available to predict the anchor uplift capacity. The scale effect was observed by both theoretical and experimental results. The scale effect was remarkable with increase in h/D. The cause of the scale effect was considered due to progressive failure with shear banding. Comparing with the results of centrifugal tests, scale effect was remarkable on a conventional 1 g test in case of h/D=3. The propagation of shear band and the domain attaining the residual strength condition in the sand mass with increase in D were remarkable at h/D=3. The different trend of the scale effect observed in the conventional 1 g test and the centrifugal test was attributed to a particle size effect due to progressive failure.

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A new estimation method is proposed for the relationship of the point bearing loads and point settlements of bored precast piles installed in sandy supporting strata by preboring or inner excavation. The method is derived using analyses by finite element method, back-analyses by neural network and regression analyses. The piles have widened holes at the pile points which are filled with cement milk. Nomographs are prepred and, if the diameter of the widened part, embedded length of the part into the supporting stratum, N-value and effective overburden pressure on the surface of the stratum are given, we can estimate the relations by manual calculation.

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In order to investigate the undrained deformation behaviour of sand subjected to principal stress rotation, two series of tests were performed using a torsional cylinder shear apparatus. The following conclusions were obtained from the tests. Pore pressures and strains in excess of 5% were accumulated under the cyclic rotation of principal stresses despite the deviatoric stress remaining constant. The form of deformation could be classified into non-flow, limited flow or full flow deformation. Flow deformation occurred when the effective stress state of samples reached a critical stress ratio. If the effective stress reached the steady state line after the critical stress ratio was reached, samples demonstrated full flow deformation. If on the other hand, the effective stress reached the phase transformation line after the critical stress ratio was attained, samples demonstrated limited flow deformation. The critical stress ratio was defined as the stress ratio at which strain softening commenced, and was obtained from undrained shear tests at various relative densities and principal stress directions. It was observed that the existence of a critical stress ratio was a function of both relative density and principal stress direction. The test results in this paper demonstrate the importance of investigating the effects not only of the density and confining pressure, but also of the principal stress direction and its rotation on the flow deformation of sand.

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This paper discusses the factors used to determine the point bearing capacity of non-displacement piles in hard clay, and proposes a new approach based on a failure mechanism for estimating settlement of a non-displacement pile with tip in hard clay. Model tests were performed in which void ratios as well as undrained shear strength, confining pressure, pile diameters and settlement rates were adopted as the factors determining the point bearing capacity of non-displacement piles in hard clay. The results of the model tests led to the following conclusions : (1) The point bearing pressure-settlement behavior can be divided into three phases. In the first phase, it is linear elastic and can be expressed by the elastic solution for a rigid punch. In the second phase, the hard clay under the pile tip failed in punching shear and in the third phase, it is practically defined to be ultimate ; (2) Void ratio as well as undrained shear strength is one of the factors determining the point bearing capacity because it seriously affects point bearing capacity in the second and third phases. Point bearing capacity doesn't vary significantly however with confining pressure, pile diameters and settlement rates ; and (3) The proposed approach for estimating the settlement of the tip of a non-displacement pile in hard clay is generally consistent with the results of the model tests.

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Based on the concept "intermediate soil wedge" which is dependent on mobilized frictional resistance, a new theory has been developed for evaluating the seismic earth pressures against retaining walls under any condition between the active and passive states. For this theory, the seismic earth pressure is separated into four components according to their formation. New equations are proposed to determine the distribution, resultant and point of application for each component. An equivalent seismic coefficient is introduced to take into account non-uniform seismic acceleration distribution with depth. The equations place special emphasis on dependence of the seismic earth pressure on mode and level of wall movement. The equations can be reduced to the Mononobe-Okabe equation for the limiting conditions. Their applicability was confirmed by comparing the predictions with a number of previous model test results.

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This paper presents the results of 24 centrifuge model tests of nailed soil slopes and vertical walls, constructed out of dry Leighton buzzard sand. The walls were initially supported by fluid pressure from flexible rubber bags against the face, and excavation was modelled by gradually draining the fluid from the bags. The finished model walls were 200 mm high and were initially tested at 30 g acceleration to correspond to a prototype structure 6.0 m high. If failure was not obtained, the acceleration was increased progressively to a maximum of 80 g. No surcharges were applied. The main parameters varied in the tests were the wall slope, nail length, nail surface roughness, nail inclination, facing stiffness and facing roughness. Observations were made of the mechanism of failure when it occurred, of soil pressures on the facing, and of pre-failure deformations. Failure was always by pull-out rather than breakage of the nails, and a series of pull-out tests of the model nails was conducted to aid interpretation of the results. Failure surfaces were seen to have the shape of logarithmic spirals, and limit equilibrium analyses based on these surfaces agreed well with experimental observations. Prior to failure, earth pressures on the facing compared reasonably well with those calculated by Coulomb's method, except at the base of the wall. One test set out to model a full-scale trial wall, and although the construction process could not be exactly modelled in the small-scale centrifuge tests, comparisons were sufficiently good to give confidence in the model test results.

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As an adjunct to a series of centrifuge model tests on nailed soil slopes, a comprehensive series of pull-out tests have been conducted on model nails. The objectives of the tests were to investigate the fundamental interaction mechanisms between nail and soil during pull-out, and to obtain basic data needed for the analysis of the centrifuge tests. Three different soil types were used, all dry sands, and the parameters varied in the tests were the nail length and diameter, nail stiffness, and surface roughness of the nail. Results of the tests are presented and considered in the context of a simplified theoretical model. The apparent coefficient of friction (bond) between stiff rough nails and soil is shown to be dependent on the friction angle of the soil, the rate of soil dilation during shear, the stiffness of the soil and the diameter of the nail in relation to the mean particle size of the soil. For smooth nails the bond resistance is much smaller, and such nails should not be used in practice. For relatively extensible nails the interaction mechanisms are complicated by the occurrence of progressive failure along the nail.

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A series of two-way cyclic tangential-displacement-controlled tests and cyclic rotational tests were carried out to study the behaviour of an interface between a dry silica sand and a rough steel plate. A recently developed interface apparatus, C3DSSI, was employed to perform the experiments. The sand container in C3DSSI is a simple shear box which allows the tangential displacements due to the shear deformation of the sand mass to be distinguished from the sliding displacements at the interface. The tangential forces are applied to the interface plane through an X-Y loading table by using two ball screw stepper motors. The elliptical and circular rotational paths on the interface plane are generated by combining the sinusoidal tangential-displacement-controlled cycles produced simultaneously in the x-and y-directions. A pneumatic actuator which is controlled by a motorized regulator induces the normal stress on the interface. The results of two-way displacement controlled cyclic tests indicated that the interface may fail and strength reduction may occur, even at tangential displacement amplitudes less than that required to mobilize the peak strength in a monotonic test. The results of cyclic rotational tangential displacement paths showed that by approaching a full circular path from an elliptical path the average compression of the sand mass increased for the same number of cycles. The peak and residual strengths, however, reduced as the displacement path became a circle.

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The present investigation aims at defining the normally consolidated drained failure envelope of a cohesive soil in the ultra-low stress range. The effective stress levels at hand are lower by three orders of magnitude or more than in traditional geotechnical practice. Drained shear strength measurements were conducted on freshly deposited Boston Blue Clay sediment beds of varying thickness using a specially designed Tilting Tank. The beds were prepared from a 550% water content slurry. The measured strength values were age dependent, and varied between 19 and 87 Pa for an effective normal stress range of 16.5 to 155 Pa. The failure envelope was linear at a given bed age, and the friction angle increased with bed age. However, all the failure envelopes converged at an effective stress of about 20 Pa, allowing the true cohesion of the soil to be estimated at approximately 10 Pa. For a given bed age and stress level, the drained strength was equal to or higher than the undrained strength measured with an automated fall cone device.

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Ariake clays have been widely deposited around Ariake Bay in Japan. The basic characteristics of Ariake clays are very soft and sensitive. How to assess quantitatively the quality of soil samples and correct the mechanical properties for sample disturbance is a well-known, but a not well-understood issue in geotechnical engineering. In this study, the undisturbed Ariake clays were deliberately disturbed to various levels of disturbance. A series of consolidation tests were then performed in order to investigate the effect of sample disturbance on the mechanical parameters. A simple index for providing a quantitative measure of the degree of sample disturbance is proposed in this paper. In addition, an approach of correcting the consolidation yield stress and the compression index for sample disturbance is also proposed based on the proposed index of sample disturbance. The existing data available are used to verify further the validity of the proposed method. The application of the proposed method is also discussed for a natural soil deposit.

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