An investigation was undertaken to evaluate the integrity of a geogrid-reinforced steep slope subjected to significant differential settlements and seismic loading. The reinforced soil structure under investigation was constructed in 1987 in order to enhance the stability of steep landfill slopes at the Operating Industries, Inc. (OII) Superfund site, a hazardous waste site in southern California. The site is in an area of high seismicity. The 4.60 m high, 460 m long geogrid-reinforced structure was founded, along most of its length, on concrete piers located towards the front of the structure. However, as the back of the reinforced slope was founded on waste, the structure experienced more than 600 mm of differential settlements ten years after its construction. A geogrid experimental testing program was implemented to evaluate the performance of the reinforcements when loaded rapidly after a period of constant load. A finite element numerical simulation was performed to assess the integrity of the geogrid reinforcements when subjected to 30 years of additional differential settlements followed by the design earthquake. The maximum geogrid strains predicted for a sequence of expected static and extreme seismic loadings were found to be well below the geogrid allowable strain values, indicating that the integrity of the structure should be maintained even when subjected to large differential settlements and severe earthquake loads. The numerical results show that the critical reinforced zone (i.e., the reinforcement layers that are strained the most) that corresponds to different loading mechanisms (construction, differential settlement, seismic loading) occurs at different elevations within the reinforced soil structure.

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This study aims to verify whether there is a relationship between the fractal dimension (D_tot) and the internal friction angle (ψ) of sandy materials while also considering the mineralogical composition of these materials. Geotechnical and morphometric tests were therefore carried out on both natural and artifical samples which differed markedly from one another in terms of shape and roundness and yet all the samples fell within the granulometric band ranging from 177 to 710 μm. A linear relationship was found between the internal friction angle and fractal dimension that can be expressed by the equation : ψ=237.89D_tot-218.2. In addition, a relationship was also found between the internal friction angle and the textural fractal dimension (D₁), as well as the structural fractal dimension (D₂) of the analysed samples. In the first case, the two parameters are linked by the linear equation ψ=399.47D₁-381.28 ; in the second case, the general relationship that links the friction angle and structural fractal dimension is ψ=109.83D₂-89.362.

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Based on the methods previously presented by the authors (Yasuhara et al., 1992, 1994, 1996) for predicting the degradation in strength and stiffness of soft clays in the course of cyclic loading, a methodology has been developed to estimate the cyclic loading-induced settlements. The method also includes not only immediate settlements but also post-cyclic long-term settlements due to dissipation of cyclically induced excess pore pressures in soft soils. The simplified formulae included in the proposed methodology are given as functions of the amplitude of cyclic-induced excess pore pressure normalized by the confining pressure, u/p'_c, plasticity index I_p and factor of safety against bearing capacity failure, F_s. The calculations of cyclic-induced settlements were conducted for soft soil deposits with different index and geotechnical properties. The results calculated using the proposed methodology are presented in the form of a design chart to give the settlement versus normalized excess pore pressure ratio relations including the effects of the plasticity index and safety factor for bearing capacity. An example of the calculated results using the proposed procedure for the earthquake-induced settlements of embankments founded on soft clay, is presented to demonstrate the practicality of the method for design at fields.

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In Hong Kong large diameter long bored piles and barrettes are often used to support tall buildings to resist both vertical and horizontal loads. These piles penetrate through and may be founded in saprolitic soils or rocks. Generally, the design for side shear resistance (often called skin friction) of large diameter bored piles (drilled caissons or shafts) in saprolites involves considerable uncertainty and design parameters must usually be verified by field tests. In this paper, 28 full-scale load tests on large diameter machine bored piles constructed in various saprolitic soils were reviewed in detail, in particular the degree of mobilization of side shear resistance using a mobilization rating factor. The diameter of these floating piles ranges from 1.0 m to 1.5 m and the depth from 22 m to 75 m. The authors were heavily involved in the recent construction and testing of 12 of these piles. For bored piles constructed under water, 90% ultimate side shear resistance was mobilized at an average local pile displacement of 1.9% of the pile diameter with a 95% confidence range of 0.9% to 3.0%. For piles constructed under bentonite, ultimate side shear resistance was achieved at a local pile displacement of 1% of the pile diameter. For non-grouted bored piles constructed under water, the mobilized side shear resistance lies between 0.5N^^- and 2.0N^^- (kPa) and β^^- values fall within 0.1 and 0.5, with average values of 1.2N^^- (kPa) and 0.3 respectively. Post-grouting improves the capacity of side shear resistance by a factor of about 2 as compared with the non-grouted piles constructed under water. On the contrary, piles constructed under bentonite show a reduction of capacity of side shear resistance between 50% and 70% depending on the method of analysis.

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In order to investigate the effects of different consolidation conditions on liquefaction characteristics of sands containing fines, a series of undrained cyclic triaxial liquefaction tests was performed on artificial samples prepared by mixing Toyoura sand and bentonite at a ratio of 95% to 5% by dry weight. Some specimens were isotropically consolidated for 1, 20 or 100 days at a regular temperature, while the others were consolidated for 2 or 5 days while heating the cell water up to 60 degrees centigrade. Over-consolidated specimens with OCR of 2 and 4 were also prepared at a regular temperature. During consolidation and cyclic triaxial shearing of several specimens, their quasi-elastic deformation properties were measured while applying very small amplitude cyclic axial loads. Longer consolidation time, higher temperature during consolidation or higher ratio of over-consolidation resulted in an increase in the liquefaction resistance, with the exception that the liquefaction resistance of specimens consolidated for 100 days was not larger than that of specimens consolidated for 20 days. On the other hand, such different consolidation conditions affected the change in the quasi-elastic deformation properties in different manners. Development of cementation was suggested to have occurred during consolidation under high temperature. Reduction in the extent of anisotropy was suggested to have occurred during over-consolidation, which was accompanied by a decrease in the negative dilatancy at the initial part of shearing.

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Centrifuge research conducted at Rensselaer Polytechnic Institute (RPI) is summarized focusing on the effect of sand permeability and of weak aftershocks on earthquake-induced lateral spreading. One-dimensional shaking tests were conducted in a laminar box at a centrifugal acceleration of 50 g, simulating a 10 m thick homogeneous layer of clean Nevada sand of relative density 40-45% inclined a few degrees to the horizontal. Seven centrifuge experiments were done using either water or a viscous pore fluid fifty times more viscous than water, thus varying the soil permeability by a factor of fifty and simulating either a coarse prototype sand or a fine sand in the field. These seven tests were subjected to the same shape of base input excitation but with peak input accelerations ranging from 0.18 g to 0.46 g between tests. An additional special centrifuge test of a similar model with viscous pore fluid was subjected to a strong base "main shock", followed after a few seconds by two "weak aftershocks". Excess pore pressures, accelerations, settlements and lateral ground deformations were measured. The results are discussed in detail and several correlations are presented between testing and measured parameters such as thickness of liquefied soil, ground surface settlement, lateral ground displacement and input peak acceleration. The results of the special test, together with other evidence, provide strong support to the hypothesis that reported continued ground deformations from lateral spreads in the field are often caused by continued weak vibration or aftershocks occurring after the main shock.

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In this paper, centrifuge shaking table tests were conducted in order to understand the performance of seawalls during a seismic event. The model tests showed that the displacement of the caisson was much affected by the seaward shear deformation of the sand seabed beneath it during shaking. It was also confirmed that an armored embankment played an important role in the displacement of the caisson during shaking. Based on these test results, a two-dimensional DEM-FEM coupled analysis method was newly developed to numerically predict the deformation of seawalls covered with armored embankments during earthquakes. The movements of the armor units were calculated by DE analysis and deformations of the caisson, rubble mound, sand seabed and backfill were calculated by FE analysis considering the non-linearity of the soil materials based on the effective stress. Dynamic interaction was taken into account by delivering the nodal displacements of the finite elements or the nodal forces converted from the contact forces through the imaginary distinct elements defined at the boundaries between the DE and FE domain. The applicability of this method to the prediction of the deformation of seawalls was verified through numerical simulations of the centrifuge model test.

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There are many cases in which ground is subjected to stress history not only via artificial actions but also by tectonic movement. The effects of stress history under three dimensional stress conditions are one of the important phenomena which have to be evaluated for the accurate prediction of ground deformation. The purpose of this study is to supply the fundamental data relating to stress history which can be incorporated in prediction or design techniques. To achieve this objective, a series of hollow-cylindrical torsional shear tests was conducted on saturated cohesive specimens which were subjected to shear history under constant p', various directions and three dimensional stress conditions. From the experimental results, it was seen that the magnitude of the ultimate strength was the same for a given p' and not related to the shear history. On the other hand, the deformation characteristics (the elastic locus) behaved differently with respect to the shear history. The elastic locus developed by the stress history has directional and stress condition effects. Finally, taking into account the experimental results of the present study, the predominant parameters-the difference in the direction of shear, and the stress condition between the shear history and the shear-were selected. Using these parameters, the elastic boundary space due to the stress history was confirmed to evaluate the effects of the shear history under three dimensional stress conditions.

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Subsidence and tilting of such structures as oil storage tanks and buildings which are not supported by deep foundations are an important kind of damage induced by seismic soil liquefaction. The present paper describes the results of case-history studies conducted in Dagupan City in the Philippines, where substantial damage occurred to buildings during an earthquake in 1990. Relationships of size and shape of buildings with the extent of subsidence were found, while a better correlation was detected by using soil stratification. This correlation appears helpful for quick assessment of the liquefaction-related risk of buildings. To investigate further the mechanism of subsidence, shaking table tests were conducted. Thereafter, an analytical method for predicting the subsidence of a building was developed by considering liquefied subsoil as a viscous fluid. It was accordingly possible to obtain reasonable matching between calculated and observed subsidence when the extent of damage was significant. On the other hand, a relatively poor matching when the damage extent was light suggests that liquefied sand was not so soft as supposed in the analysis. Combining the aforementioned correlation with stratification, this analytical measure will help carry out the risk assessment of liquefaction-prone buildings.

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This paper describes the development of a continuous intrusion miniature cone penetration test system (CIMCPT) for shallow to semi-deep subsurface investigations. A novel feature of this new in situ testing system is the chain driven caterpillar-type continuous push device powered by a hydraulic motor to advance the cone penetrometer, which greatly increases productivity and serviceability. The system is housed in an environmentally controlled van body that is mounted on a one-ton, four-wheel drive, all-terrain vehicle. A new state-of-the-art data acquisition system using interface modules and a global positioning system, for real-time monitoring, acquiring, storing, and displaying data in real time on a computer screen in graphic form was developed and implemented. The miniature cone penetrometer has a projected cone area of 2 cm² and a friction sleeve surface area equal to 40 cm². It gives finer detailed soil profiles compared to the standard 10 cm² cross-sectional area reference cone penetrometer. In situ calibration of the CIMCPT system with the standard 10 cm² cone penetrometer indicated that the average tip resistance of the CIMCPT was 11 percent higher than that of the standard cone penetrometer. The average CIMCPT sleeve friction was 11 percent lower than that of the standard cone penetrometer.

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The inherent/induced anisotropy of soils was described concisely by the concept of the rotation of the yield surface around the origin of stress space, called the rotational hardening by Hashiguchi (1977), whilst the description of the inherent anisotropy of natural grounds by the rotation of the yield surface was advocated by Sekiguchi and Ohta (1977). In this article the interpretation of the evolution rule for the rotation of the yield surface, i.e. the rotational hardening rule for soils is given on the pertinent physical background, revealing the similarity to the nonlinear kinematic hardening rule for metals. The rotational hardening variable is the second-order tensor and thus the material-time derivative does not obey the ordinary transformation of a second-order tensor losing objectivity. Some comments for its pertinent integration are given in brief.

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This paper presents a review of the stress dependence for soil stiffness at very small strains. Previously published data for sands and clays are presented, and it is shown that in all cases, provided voids ratio is kept approximately constant, then the very small strain stiffness of soils is found to vary with mean effective stress p as p^1/2. The p^1/2 dependence of stiffness has long been established for more idealised aggregates comprising regular arrays of spherical particles, and published micro mechanical explanations for this behaviour are presented. A simple mean field approach based on Hertzian contact theory predicts that the dependence should be p^1/3, but highlights two possible reasons for the apparent discrepancy comparing with available data : (i) contacts may not be Hertzian and (ii) the number of contacts may increase with increasing stress level at approximately constant voids ratio. Two alternative previously published explanations for the p^1/2 dependence relate to conical contacts between particles and particle chain buckling mechanisms. These mechanisms are presented and discussed, and the paper shows that the p^1/2 dependence could arise due to one or other of these mechanisms, but not both simultaneously. It seems possible that in densely compacted or overconsolidated soils where voids ratio is approximately constant until yield occurs, contacts may be aspherical and the number of contacts may simultaneously increase with increasing confining stress. In this case the conical contact and particle chain buckling mechanisms are not viable : a more rigorous analysis based on the contact of rough particles is required. It is proposed that such an analysis should allow for the simultaneous elastic squeeze down of surface asperities and increase in the number of asperity contacts under increasing confining stress.

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The main objective of this paper is to point out limitations of a coupled finite element analysis involving saturated soils subjected to fluctuating load. For this purpose an experimental program has been carried out in which a sample of medium dense sand was subjected to a cyclic loading history under free-draining conditions. The results showed that, in spite of the high permeability of the material, the consolidation settlements were insignificant. The mechanical response of this sample was then simulated using coupled finite element analysis based on Biot's formulation. The analysis predicted high settlement amplitudes, which were inconsistent with the experimental data. This indicates that the applicability of Darcy's law, which governs the transient flow, is restricted to the case when the hydraulic heads undergo a slow monotonic change, whereas under a typical scenario involving fluctuating load (e.g. an earthquake excitation) the conditions remain essentially undrained.

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