The effects of temperature cycling on the volume change behavior of soil is examined during isotropic consolidation tests in the laboratory. Tests are performed on six different natural marine samples which vary from a sand to a clay of high plasticity. Samples are subjected to a heating and cooling cycle of 25 °C at constant confining stress in both normally consolidated and overconsolidated stress ranges. Results of this investigation indicate that the permanent reduction in void ratio due to a temperature cycle of 25 °C is independent of the effective confining stress for a normally consolidated soil. This permanent void ratio reduction is shown to be a unique value for a given normally consolidated soil and is directly related to soil plasticity. For overconsolidated soil, the effect of temperature cycling on volume change behavior is shown to be a function of the magnitude of effective stress decrement or overconsolidation ratio.
This study examines the individual particles comprising a typical deep-sea calcareous clay as a means of explaining their unique engineering properties and compression behavior. The scanning electron microscope is used to determine calcareous particle geometry, size, and packing, and the effect of one-dimensional compression on microstructure and particle fracture. The sediments examined in this study have carbonate contents of 40 to 90 percent, including 5 to 10 percent of sand-sized Foraminifera, the remainder being fine, silt-sized nannofossils. The Foraminifera and nannofossils are hollow and capable of storing large quantities of intraparticle water. When subjected to moderate compression stresses, the Foraminifera particles are susceptable to fracture and release intraparticle water, whereas the nannofossils exhibit minor fracturing or chipping at particle contact points. Carbonate contents should be routinely performed as an index property on deep-sea sediment specimens to determine the presence of hollow nannofossil and foram particles.
Processed waste tires mixed with soils are applicable in lightweight fills for slopes, retaining walls, and embankments that may be subjected to seismic loads. Rubber's high damping capacity permits consideration of granulated rubber/soil mixtures as part of a damping system to reduce vibration. The dynamic properties of granulated rubber/soil mixtures are essential for the design of such systems. This research investigates the shear modulus and damping ratio of granulated rubber/sand mixtures using a torsional resonant column. Specimens were constructed using different percentages of granulated tire rubber and Ottawa sand at several different percentages. The maximum shear modulus and minimum damping ratio are presented with the percentage of granulated rubber. It is shown that reference strain can be used to normalize the shear modulus into a less scattered band for granulated rubber/sand mixtures. The normalized shear modulus reduction for 50% granulated rubber (by volumme) is close to a typical saturated cohesive soil. Empirical estimation of maximum shear modulus of soil/rubber mixtures can be achieved by treating the volume of rubber as voids.
A laboratory apparatus for measuring the chemicoosmotic efficiency coefficient, , for clay soils in the presence of electrolyte solutions is described. A chemico-osmotic experiment is conducted by establishing and maintaining a constant difference in electrolyte concentration across a soil specimen while preventing the flow of solution through the specimen. The chemico-osmotic efficiency coefficient is derived from a measured pressure difference induced across the specimen in response to the applied concentration difference. The effective diffusion coefficient (D*) and retardation factor ( R d ) of the electrolytes (solutes) also can be determined simultaneously by measuring the diffusive solute mass flux through the specimen until steady-state diffusion is achieved. Experimental results using specimens of a geosynthetic clay liner subjected to potassium chloride solutions indicate that the measurement of may be affected by soil-solution interactions, as well as by changes in the induced chemico-osmotic pressure difference due to solute diffusion. As a result, should be evaluated using the induced pressure difference at steady state. The time required to achieve a steady-state response in induced pressure difference is related to the time required to achieve steady-state diffusion of all solutes, and may be affected by the circulation rate at the specimen boundaries. The circulation rate should be sufficiently rapid to minimize changes in the boundary concentrations due to diffusion, but sufficiently slow to allow measurement of solute mass flux at the lower concentration boundary for evaluating D* and R d . FIG. 1-Measured head differences (⌬H) across a kaolinite specimen as a function of externally imposed flow rates (Q/t) and the ratio of NaCl concentrations at the specimen boundaries (C B /C T ) (replotted after Olsen 1969).
A study is presented of potential errors in, and methods of interpreting, the results of cantilever-type, piezoceramic bender element tests for measuring the shear wave velocity of laboratory soil specimens. Interpretations based on the first direct arrival in the output signal are often masked by near-field effects and may be difficult to define reliably. Interpretations based on characteristic points or cross-correlation between the input and output signals are shown to be theoretically incorrect in most cases because of: (1) the effects of wave interference at the boundaries; (2) the phase lag between the physical wave forms and the measured electrical signals; and (3) non-one-dimensional wave travel and near-field effects. Interpretations based on the second arrival in the output signal are theoretically subject to errors from non-one-dimensional wave travel and near-field effects. Differences in Vs values obtained by the different interpretation methods are illustrated analytically and experimentally.
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