Application of Geophysical Methods to Supplement Geotechnical Site Characterization of a Small-Scale Land-Slide Event
Date
2024-09-25
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0009-0004-2687-6374
Type
Thesis
Degree Level
Masters
Abstract
Characterization of subsurface geometries and material properties along urban riverbanks are essential steps in determining slope stability. Geophysical methods offer a non-invasive solution to mapping the subsurface geometries and infrastructure while also facilitating the opportunity to qualitatively monitor elastic parameters of the in-situ soils and materials present. This thesis presents the application and results of multiple geophysical methods, including high resolution three dimensional (3-D) direct current (DC) resistivity, seismic refraction, and multi-channel analysis of surface waves (MASW) along an urban riverbank that has experienced ongoing slope failure within the last decade.
Application of a high resolution 3-D DC resistivity survey was successful in imaging the electrical resistivity material property contrast between the surficial clays and underlying glacial till throughout the research area. This analysis provided the location of the contact between the differing material bodies, which has been defined as the failure plane for nearly all local slope failures within the last 100 years in numerous geotechnical studies.
Results of the seismic refraction field measurements and analysis successfully defined the compressional wave velocity contrasts between the surficial clayey soils and the underlying glacial till. Further, the refraction analysis was able to map the boundary between the unsaturated and saturated glacial till, highlighting the presence and location of the water table, an important metric in proper geotechnical analysis.
Interpretation of the collected data sets places the location of the contact between the surficial clays and underlying glacial till at an elevation of approximately 486 meters above sea level, with local variations up to one meter. The location of the water table remained consistent between the seismic collections at an elevation of approximately 484 meters above sea level, with local variations of approximately 0.5 meters.
Application of coincident refraction and MASW surveys over the research area provided the means to successfully measure the shear wave velocities and estimate elastic parameters of the soil units in an undisturbed setting. By collecting coincident refraction and MASW surveys in a time lapse manner, in-situ elastic properties were compared between the 2021 and 2022 summer collection seasons. Results of the coincident seismic collections indicate that both the bulk modulus and Poisson’s ratio remained relatively stable, while the shear modulus and Young’s modulus both experienced slight increases over the research period.
Description
Keywords
Geophysics, Geo-technical, Land-slide, River bank
Citation
Degree
Master of Science (M.Sc.)
Department
Geological Sciences
Program
Geology