The paper studies the soil-dependent calibration constants used for determining water content and density of soil using time domain reflectometry (TDR), specifically, to establish the typical soil calibration values and study the extent of the uncertainty in calibration factors on measurement accuracy. The TDR method described here makes use of a calibration equation normalized by soil dry density, which involves two soil-dependent constants, a and b. Both a and b have physical significance, with the value of a related to the apparent dielectric constant of the dry density – normalized dry soil solids and the value of b related to the apparent dielectric constant of the pore fluid. From theoretical predictions, typical values of a are around 1.0, and typical values of b are around 9. Practically, the constants a and b are obtained through calibration tests performed in conjunction with standard compaction tests. Experimental study shows that calibration constants fall within the ranges from theoretical predictions. Tests on five soil mixtures provided average values of a = 0.945 and b = 8.76, while 11 clean sands resulted in average values of a = 1.0 and b = 8.5. The study also shows that there are no significant effects of compaction energy on the measured values of a and b. Sensitivity analyses indicate that variations in a and b both cause variations in TDR-determined water content and density, but the variations are typically within acceptable limits for engineering application purpose. Results from TDR tests on simulated field experiments are consistent with the sensitivity analyses.Key words: time domain reflectometry, TDR, calibration constants, water content, dry density, sensitivity.
A new technique is described to quantify particle shape and angularity using an image analyser. The method relies on discretising the two-dimensional projection of the particle and comparing the projected outline with that of a standard geometric shape, namely a circle. Two new parameters for particle shape and angularity were formulated and their values were determined for various materials. The relationship between the new parameters and large-strain (steady-state) internal friction angle as well as pluviated void ratio was examined. Overall, the results indicate that as shape and angularity parameters increase, the drained friction angle and pluviated void ratio increase. In addition, shape and angularity were found to influence the measured maximum void ratio and, to a lesser extent, the minimum void ratio.
Short- and long-term exposure to inorganic solutions can cause significant degradation of the hydraulic properties of bentonite clay used in geosynthetic clay liners (GCLs). In particular, the increase in hydraulic conductivity due to cation exchange when Na-montmorillonite is subjected to leachates rich in Ca and Mg has caused problems in incinerator ash landfill liners located in wet environments, where large quantities of leachates are generated. Experimental results are presented to evaluate the immediate change in hydraulic conductivity of seven types of GCL clays upon permeation with leachate generated from three ash landfills. The composition of the ash, which is a by-product of the incineration of municipal solid waste (MSW), in turn influences the composition of the resulting leachate. Falling head permeability tests were performed on flexible-wall permeameter specimens, with back-pressure saturation. Chemical analysis shows that the three leachate products contain high, medium, and low concentration Ca and Mg cations. The clay component of GCL materials tested in this study consists of regular and polymer-treated bentonite. Polymer treatment is believed to render the clay non-reactive to many organic and inorganic chemicals. The results of this study indicate that: (1) polymer treatment is generally more beneficial if the clay is first saturated with water and not directly with the leachate; (2) high swell potential of the bentonite is more advantageous than polymer treatment, especially when low hydraulic conductivity is required in the short term and if the clay is pre-hydrated. Experiment setup and special specimen preparation procedures are also discussed.
Many types of geosynthetic-reinforced soil are subjected to repeated or cyclic loading. In transportation infrastructures such loading conditions occur in pavements supported by reinforced soil retaining walls, reinforced soil bridge abutments, reinforced roadways, or railway foundations. Insufficient knowledge on the mid- and long-term performance of geosynthetics and on soil-reinforcement interaction under such conditions might be considered a hurdle to their use as reinforcement in permanent earth structures. In this paper, information on the performance of geosynthetic-reinforced soil structures and the durability of geosynthetic materials under repeated or cyclic loading is summarized. Semi-empirical methods are currently available to design geosynthetic-reinforced unpaved roads under traffic loading. A spreadsheet program was used in order to perform sensitivity analyses on three widely used design methods for unpaved roads. Based on the analytical results, the limitations of the currently available experimental database are discussed and research needs identified.
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