Title

Development of a Portable Surface Wave Inversion System for Near-Surface Soil Characterization

Date of Award

2015

Degree Type

Thesis

Degree Name

Master of Science in Civil and Environmental Engineering

Department

Civil and Environmental Engineering

First Advisor

Aaron S. Bradshaw

Abstract

Currently there is a need for a portable, lightweight, and reliable site investigation tool for characterizing near-surface soil properties for assessing airfield capacity in remote locations around the globe. The objective of this study was to develop a new small-scale surface wave inversion system to characterize the near-surface soil properties needed to assess airfield capacity. The near surface wave inversion system was developed using six accelerometers, six cables, six sensor signal conditioners and a recording unit. Initial field testing was performed to determine the best arrangement for the system as well as how to tie the accelerometers to the ground and diminish noise. The field testing showed that the accelerometers should be coupled to the ground using 10.16 cm (4 in) stakes. A sand bag also helped to diminish noise measured by the accelerometer. A small-scale soil test tank was constructed to test the inversion system hardware and data analysis methods. Bender elements were placed at various depths within the test tank to make direct measurements of shear wave velocity. The near surface wave inversion system was then deployed in the soil test tank and measurements of surface waves produced from various sources were recorded. The phase velocities of the Rayleigh waves were used to get a quick estimate of the shear speed using an empirical approach. An inversion technique was then used on the data measured by the system to determine the average shear wave velocities for the layers of soil in the tank. These shear wave velocities were then compared those measured by the bender element systems in the tank. The results from each system agreed reasonably well given the errors associated with the testing performed.

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