Award Date

1-1-2006

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

First Committee Member

Barbara Luke

Number of Pages

248

Abstract

Soil profiles with an included carbonate-cemented layer, a high velocity layer (HVL), are commonly encountered in Las Vegas, Nevada and other arid settings. Knowledge of the presence, geometry and hardness of the carbonate-cemented inclusions is important for civil engineering site investigation. Active-source seismic surface wave methods were tested to detect this HVL. An optimization method consisting of simulated annealing followed by linearized inversion was applied to the data; The purpose of this study was to improve the ability to detect and delineate the HVL using surface wave methods. Two approaches are followed. One is inversion of the effective dispersion curve with the cylindrical wave forward model (EDC/CM). This corresponds to two-channel data acquisition followed by the phase spectral method for dispersion curve (DC) extraction. The other is simultaneous inversion of the first two modes of the DC with plane wave forward model (MDC/PM). This corresponds to multi-channel data acquisition followed by the frequency-slowness method for DC extraction. The applicability of the two approaches was tested with a normally dispersive (ND) profile and a HVL profile, which were solutions from forward models. Then it was tested through finite-difference (FD) simulation. Lastly, the approaches were applied to experimental datasets collected at a site known to have a carbonate-cemented layer; Both approaches achieved limited success. In the synthetic study, they were able to provide close-to-target results. The MDC/PM analysis showed significant improvement with respect to inversion of the fundamental mode alone. The FD simulation demonstrated that (1) for the MDC approach, accurate interpretation of the DC can be challenging for HVL systems; and (2) for the EDC approach, the EDC/CM analysis failed to resolve an HVL when a similar analysis using a plane wave forward model was successful. For the experimental study, the best results in both cases came from the less complex approach: modeling the fundamental-mode alone for the multi-channel measurement and modeling plane-wave propagation for the two-channel measurement. The simpler approaches succeed because the shape of the fundamental-mode DC carries the characteristics of the HVL.

Keywords

Anomalous; Anomalous Layers; Carbonate Cement; Delineating; High-velocity Layer; Layers; Method; Profiles; Seismic; Seismic Surface Wave; Soil; Surface; Wave

Controlled Subject

Geophysics; Geotechnology; Civil engineering

File Format

pdf

File Size

6307.84 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

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