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Research Activities: 2001
Determination of Shear-wave Velocity Profiles from Surface (Rayleigh) Seismic Waves: Wahite Ditch and St. Francis River Bridge Sites, Southeast Missouri
Matching Research Agency
|Missouri Department of Transportation (MoDOT)|
|Graduate students will participate|
|Assess utility of surface wave technique as a tool for determining shear wave velocity profile of shallow sediment|
|UMR will acquire multi-channel surface-wave (Rayleigh wave) seismic data in the vicinity of the Wahite Ditch Bridge and St. Francis River Bridge test sites. These Rayleigh wave data will be processed and analyzed, and used to construct subsurface shear-wave velocity profiles to depths on the order of 100 feet. These Rayleigh wave data will be compared to borehole seismic and seismic CPT data previously acquired at the test sites. The objective is to determine if the multi-channel surface-wave seismic tool is a cost-effective and accurate means of determining shear-wave velocity profiles for the shallow subsurface. |
This proposed project supports MoDOT's Research Focus Plan in that the evaluation of developing Rayleigh wave technology was identified as a priority for the Geotechnical RDT TAG during the MOTREC/MODOT biennial meeting (8/7/01). If the Rayleigh wave tool provides accurate and cost-effective results, this methodology could be used to acquire shallow velocity control in areas where CPT tool cannot be used (site accessibility, potential for tool damage, cost considerations, depth of investigation, etc.). The Rayleigh wave methodology also has other applications including determination of depth to bedrock, identification of karst features, etc. These will be discussed in the report prepared by the investigators.
Wahite Ditch Bridge and St. Francis River Bridge test sites: Two deep (200 foot), air-filled, PVC-cased boreholes were completed at Wahite Ditch Bridge site (1) and St. Francis River Bridge site (1) during the course of the MoDOT-funded study entitled "Earthquake Hazard Assessment Along Designated Emergency Vehicle Priority Access Routes". Shear-wave interval-velocity profiles (0" 200 ft) were generated at the Wahite Ditch Bridge site (only) by lowering an arm-locking triaxial geophone into the cased borehole, and determining shear-wave travel times from the surface sources to predetermined borehole geophone locations. Shear-wave cone-penetrometer.
Analysis of Rayleigh wave data: Rayleigh waves are dispersive meaning that different frequency components travel at different maximum depths and with different phase velocities (Bullen, 1963). Rayleigh wave phase velocities are a function of subsurface in-situ shear-wave velocity profile (and Poisson's Ratio). Rayleigh wave data can be recorded at each test site and analyzed with a view to determining phase velocities and constructing shear-wave velocity profiles (Park et al, Xia et al., 1999). UMR has the capability of generating and recording Rayleigh wave data at the test sites. Acquired surface-wave data will be analyzed using state-of-the-art software recently developed by the Kansas Geologic Survey and the Perm Mining Institute.
Methodology: We will acquire multi-channel surface-wave (Rayleigh wave) seismic data in the vicinity of the Wahite Ditch Bridge and St. Francis River Bridge test sites (cased borehole and CPT locations) using a weight-drop impulse source and an array of low-frequency geophones. These Rayleigh wave data will be processed and analyzed, and shear-wave velocity profile will be generated for each site studied.
|Rayleigh wave technology has bored potential applications (e.g., detection of voids, depth to bedrock, pavement thickness, etc.). The proposed study will give UMR researchers the opportunity to evaluate the overall utility of the Rayleigh wave tool, including accuracy of interpretations, cost-effectiveness (relative to CPT and borehole seismic method), site suitability requirements, and potential applications.|
|Non-destructive/and non-invasive imaging.|
Relationship to other Research/Projects
|UMR faculties are engaged in a number of externally-funded projects that involve the non-destructive imaging of engineered structures and non-invasive site characterization (including studies at Fort Leonard Wood).|
Technology Transfer Activities
|Expertise with respect to acquisition, processing, interpretation and application of geophysical technologies will be shared with MoDOT, FHWA and the public (as published literature).|
Transportation Research Board Keywords
|Non-destructive imaging, technology transfer, Rayleigh waves, shears waves.|