Jerry A. Yamamuro

Effects of Non-Plastic Fines on Minimum and Maximum Void Ratios of Sand

The role of non-plastic fines content on minimum and maximum void ratios, compressibility, and static liquefaction potential of sand and the relationships between these quantities are not well understood. This paper presents a study of the effects of non-plastic fines on the extreme void ratios of sand. Included in this paper is a review of previous theoretical and experimental studies of minimum and maximum void ratios of single spherical grains, packings of spheres of several discrete sizes, as well as optimum grain-size ratios to produce maximum densities. A systematic experimental study of the variation of minimum and maximum void ratios with contents of fines for sands with smoothly varying particle size curves and a large variety of size distributions is performed. It is shown that the fines content plays an important role in determining the sand structure and the consequent minimum and maximum void ratios. It is indicated how the fines content and sand structure affects the compressibility and the static liquefaction potential of the sand.

Evaluation of static liquefaction potential of silty sand slopes

The mechanism of instability in granular soils is explained and its requirement as a forerunner to the liquefaction of level or sloping ground is described. Case histories support the observation that it is silty sands that liquefy under static and a majority of earthquake-induced conditions. Recent experiments show that clean sands do not behave similarly to silty sands. Tests on loose, silty sand indicate a “reverse” behavior with respect to confining pressure and this violates the basic assumption that loose, silty sands behave similarly to loose, clean sands. Strong correlations between fines content, compressibility, and liquefaction potential are often found for these soils. A procedure for the analysis and evaluation of static liquefaction of slopes of fine sand and silt, such as submarine slopes, mine tailings, and spoil heaps, is presented. It involves determination of the region of instability in stress space in which potential liquefaction may be initiated and determination of the state of stre...

Experiments and modelling of silty sands susceptible to static liquefaction

Most historic cases of liquefaction have been found to occur in alluvial (water) deposited silty sands. Currently, the effect of non-plastic fines (particles smaller than No. 200 sieve) on the liquefaction behaviour of sands is viewed to be either negligible or its presence actually inhibits liquefaction. Undrained triaxial compression test results performed on silty sands clearly indicate a direct correlation between the quantity of finer, non-plastic constituents and the liquefaction potential of granular soils. Increasing the fines content increases the liquefaction potential, even though the density increases. Complete static liquefaction occurs at low confining pressures. As confining pressures increase, the liquefaction potential decreases resulting in increased stability. Thus, silty sands exhibit a ‘reverse’ pattern of soil behaviour with confining pressure. Drained tests indicate both a large contractive volume change and a suppressed friction angle at low confining pressures, and this explains the undrained behaviour. It is hypothesized that the mechanism underlying this behaviour is related to the formation of a particle structure between the large and small grains which creates a highly compressible soil fabric. This ‘reverse’ behaviour pattern makes predictions of static liquefaction of silty sands difficult. However, simple modifications to the Single Hardening Model yield surface formulation enables predictions of this behaviour pattern. Copyright

Physics and mechanics of soil liquefaction

The workshop aims to provide a fundamental understanding of the liquefaction process, necessary to the enhancement of liquefaction prediction. The contributions are divided into eight sections, which include: factors affecting liquefaction susceptibility and field studies of liquefaction.

Influence of time effects on instability of granular materials

Abstract Results of previously performed series of triaxial compression tests designed to expose the type of behavior displayed by granular materials have shown that materials that exhibit non-associated flow do not obey the stability postulates by Drucker and by Hill. Triaxial tests on fully and partly saturated specimens of sand have been performed under drained and undrained conditions to study the regions of stable and unstable behavior. Granular materials may become unstable inside the failure surface if the state of stress is located between the instability line and the failure surface for the material. Presented here are three series of experiments conducted on sands that compress during shear. In one series, experiments are performed to study the effect of strain rate on the location of the instability line. In the second series, the sand is allowed to creep under drained conditions resulting in outwards movement of the yield surface, and the sand consequently becomes suffer in the region above the stress point. Increasing amounts of creep therefore require increasingly high stress differences to render the sand unstable. In the third series of experiments, the saturated sand is allowed to creep under undrained conditions, and this results in increasing pore pressures and possible instability because the stresses may be brought into the region of potential instability. Thus, time effects play important roles in the stability of soils.

Experimental and data analysis techniques used for high strain rate tests on cohesionless soil

Experimental methods used to subject drained triaxial compression axisymmetric test specimens composed of cohesionless soils to very high strain rates and analyze the resulting data are presented. Included is the use of a custom gravity drop-frame loading system to generate the high strain rates and a custom square triaxial cell to minimize optical distortion. Methods to collect and analyze the experimental results are also presented. High-speed film photography, coupled with digital image analysis techniques, are used to capture specimen deformations. Experimental issues such as image analysis of specimens, optical corrections, time synchronization of photographic images with data acquisition, inertial effects, global versus local strain measurements, axisymmetric shape of the specimen during deformation, and membrane compliance are examined by analyzing test results that were performed at high strain rates.

Electrical tagging of cement composites for nondestructive integrity monitoring

The results of an investigation on the bulk electrical properties of carbon fiber cement composites (CFCC) with the prospect of developing a new nondestructive testing method are presented. The addition of carbon fibers to portland cement- based concrete or mortar improves the structural performance and at the same time significantly decreases the bulk electrical resistivity. This makes CFCC responsive to interrogation by electrical methods. This paper presents experimental data on the electrical behavior of CFCC as a multi-phase medium consisting of conducting and insulating phases. The volume electrical resistivity of CFCC samples was recorded as a function of curing time. The dependence of this electrical resistivity on the water-cement ratio, sand-cement ratio and volume fraction of carbon fibers in the mix was determined. Three different electrode configurations were investigated for their applicability in measuring electrical resistivity of CFCC samples.