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.
The resonant-column method, a relatively nondestructive test employing wave propagation in cylindrical specimens, is used to obtain modulus and damping of soils as functions of vibratory strain amplitude and other factors such as ambient confining stress and void ratio. Descriptions of the apparatus, calibration procedures, testing procedures, and aids for data reduction are given for apparatus which propagate either rod compression waves or shear waves or both. Data reduction aids include graphs for a wide range of apparatus conditions and include a computer program that covers all admissable boundary conditions.
The resonant-column test is a relatively nondestructive test employing wave propagation in cylindrical specimens of soil and rock. Test results are usually quite accurate, but in some cases insufficient coupling exists between specimen and apparatus or specimens are too stiff for a given apparatus, or both. A criterion is given to evaluate whether a coupling problem exists and solutions are suggested. Procedures for evaluating limiting specimen stiffness and maximum strain amplitude capabilities are given. Solutions for reducing air migration problems during long-term tests are presented. Finally, a simple method for estimating strain amplitudes during a test is demonstrated for both shear and axial compression.
Among the available procedures for obtaining reconstituted laboratory sand specimens, pluvial compaction appears to best simulate the natural processes leading to formation of sand deposits. Although widely used for a long period of time, effects of some components of the specimen preparation equipment (sand rainer) on the relative density of the specimen formed have not been comprehensively studied. This paper presents the results of an investigation aimed at studying these effects. The results obtained are used to provide a guide-line for design of a sand rainer.
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