Publication Date

12-2016

Date of Final Oral Examination (Defense)

10-24-2016

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Civil Engineering

Department

Civil Engineering

Major Advisor

Arvin Farid, Ph.D.

Advisor

Bhaskar Chittoori, Ph.D.

Advisor

Jim Browning, Ph.D.

Abstract

Electromagnetic (EM) waves of various power levels and frequencies can be used to alter the hydraulic conductivity of soil with minimal heat generation. The result can lead to a number of potential applications such as contamination remediation and liquefaction mitigation. In this research, the possibility of radio-frequency (RF) waves’ effect on the excess pore-water pressure (EPWP) generation and hydraulic conductivity of coarse-grained soils has been investigated.

Impact tests were performed on glass beads to examine the effect on the generation of EPWP due to RF waves. These tests were performed on a rigid box made of Plexiglas. The impacts were produced by shaking the box with periodic impact, and the generated EPWP was measured using a pore-water pressure (PWP) transducer. A loop antenna was installed inside the specimen to launch RF-waves. The RF-stimulated impact tests were performed at a constant frequency of 498 MHz and input power levels of 10, 25, 40, and 50 Watts. There were no noticeable changes observed in the EPWP generation within the glass-bead sample due to the application of RF waves.

In order to better understand the above-mentioned potential of using RF waves to mitigate liquefaction, a different set of experiments, hydraulic-conductivity measurements, were performed on two types of samples: (i) glass beads and (ii) natural sand. These tests were conducted using a customized, rigid-wall, cylindrical permeameter placed inside a box made of Plexiglas. Constant-head (D2434, ASTM, 2010) tests were performed to measure the hydraulic conductivity of these samples. The soil samples were placed within a cavity made of Plexiglas covered with transparent conductive film (resonant cavity). A chlorinated polyvinyl chloride (CPVC)-cased monopole antenna sharing the same electric ground as that of the cavity was placed within the soil sample at its center and used to launch RF waves. Various sets of tests were conducted to evaluate the effect of the power of RF waves on the change in the hydraulic conductivity. For both samples, the tests were conducted at a constant frequency of 726 MHz and input power levels of 10, 25, and 40 Watts. The hydraulic conductivity of both natural sand and glass-bead samples increased with the RF stimulation, and the increase was larger at higher RF power. At the input power of 40 Watts, the hydraulic conductivity of glass-bead sample increased by 8.7% of the unstimulated value, whereas the increase in natural-sand sample was only measured to be 25.4%.

Measurement of the electric-field component of RF waves was performed and plotted to verify the pattern of the electric field to evaluate both the impact and the hydraulic-conductivity tests. The electric field was simulated using COMSOL Multiphysics and validated against the experimentally measured electric field. In the case of the hydraulic-conductivity tests, a finite-difference numerical model was developed in MATLAB interface to analyze the seepage flow. This numerical model was also validated against experimentally measured hydraulic conductivity. This numerical model was then used to find the spatial variation of the hydraulic head within the soil specimen.

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