The polarization and conduction of clay-water-electrolyte systems in a low-frequency electric field can be presented in terms of the Dukhin-Shilov double-layer polarization model and a resistor-in-series model. In an experimental program, the permittivity and conductivity of two natural Leda clays were measured at a frequency of 60 Hz. The results of permittivity measurements were in good agreement with the Dukhin-Shilov theory. The surface conductivity of clay particles was estimated through the measurements to clay mass and pore fluid based on the resistor-in-series model.

The Berkeley trigger criterion for evaluating the potential for earthquake-induced phenomena in sandy soils is reviewed in this paper. The historical database comprising the criterion is reconsidered using a consistent “weakest-link-in-the-chain” approach. Revised plots of average cyclic stress ratio (CSR) versus ( N₁ ) ₆₀ are presented using the new minimum values of ( N₁ ) ₆₀ . Lower-bound state lines, in terms of ( N₁ ) ₆₀ , are applied to the nonliquefied data and upper-bound state lines are applied to the liquefied data. It is found that these lines do not coincide, forming a single trigger line in either clean sand or sand with fines; instead, they define a zone in which liquefaction may or may not occur. An additional zone is defined in which earthquake-induced phenomena are likely to consist of only sand boils. This supports the necessity of site-specific investigations to determine liquefaction potential. The results of this study demonstrate the effect of fines content on liquefaction potential, but not to the same extent as found in original interpretations of the field data.

The initial state of a sand, defined by the void ratio and effective mean normal stress, can be used to predict its large-strain response. Laboratory studies have shown that the shear-wave velocity of a sand is controlled primarily by the effective confining stresses and void ratio. Since shear-wave velocity can be measured both in the field and in the laboratory, there is an increasing interest in using shear-wave velocity to define the state of a sand. This paper presents an experimental study of shear-wave velocity interpretation for clean Ottawa sand based on steady/critical state concepts. The results show that the large-strain behavior of Ottawa sand can be estimated using shear-wave velocity measurements combined with a knowledge of the in-situ effective stress. Knowledge of the state of a sand makes it possible to estimate the boundary between either a contractant or dilatant sand at large strains. Based on these findings, a preliminary method to evaluate the potential for flow liquefaction using shear-wave velocity measurements is presented.

By means of scaled modeling on a geotechnical centrifuge, a systematic experimental investigation was conducted to examine the vertical dynamic response of surface foundations on granular soils. From the results of more than 100 tests, it was found that the dynamic characteristics of such foundations can be well represented in the frequency domain by the homogeneous half-space analytical solution despite the gravity- and load-induced spatial variations of the soil's modulus. However, it was also revealed that the foundation response has a significant nonlinear dependence on the soil bearing pressure and footing dimension. To capture such aspects, a set of equivalent-homogeneous elastic parameters was determined from the physical measurements for a wide range of soil-foundation configurations. Through an analytical synthesis, it was found that the equivalent-homogeneous Poisson's ratio of the soil can be taken as 0.25 while the equivalent-homogeneous shear modulus of the soil can be related through a power law to the soil's void ratio, footing radius, and average foundation bearing pressure. The practical relevance and potential applications of the resulting semiempirical formula for the dynamic foundation compliance are discussed.

To quantify the effect of gravel content on the liquefaction resistance of sand-gravel composites, a series of undrained cyclic triaxial tests was performed on sand-gravel composite specimens with gravel contents of 0%, 20%, 40%, 60%, and 100%. Test results show that the liquefaction resistance of sand-gravel composites may increase significantly with increasing gravel content. This increase was observed even for composite specimens tested at the same relative density. It was found that at 40% gravel content, a 40% relative density composite with 40% gravel will behave like a 65% relative density sand for the soils tested in this study. A methodology is described to estimate the cyclic strength of the composite soil by testing the finer fraction soil alone. Scalping oversized particles from gap-graded soils may result in significantly underestimated prototype cyclic strength when the scalped soil is tested at the same relative density as either the total composite or the finer fraction of the composite. For loose composite specimens with a small percentage of gravel particles, a more reasonable estimate of the prototype cyclic strength may be obtained by testing the fine material at an equivalent relative density. An equivalent density of the finer fraction is proposed to account for the effect of gravel inclusions on the liquefaction behavior of the composite.

The seismic bearing capacity of a strip-surface foundation resting on a Mohr-Coulomb material is evaluated. The upper-bound theorem of the yield design theory is used to obtain an estimate of the ultimate load. The loading parameters consist of a normal and tangential force applied to the foundation and of inertia forces developed within the soil volume. The classical Prandtl-like mechanism is used to show that the reduction in the bearing capacity is mainly caused by the load inclination; the consideration of inertia forces within the soil is only responsible for a decrease in the bearing capacity that is at least an order of magnitude smaller than the one caused by the load inclination. It is therefore concluded that, from a practical engineering standpoint, the soil-inertia forces can be neglected.