| Title | Investigating the low-strain dynamic properties of late-glacial silts and clays in the lab and the field |
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| Author | Crow, H L ;
Cascante, G; Leboeuf, D; Sivathayalan, S; Motazedian, D |
| Source | SSA 2017 Annual Meeting announcement and program; Seismological Research Letters vol. 88, no. 2B, 2017 p. 567, https://doi.org/10.1785/0220170035  Open Access |
| Image |  |
| Year | 2017 |
| Alt Series | Earth Sciences Sector, Contribution Series 20160349 |
| Publisher | Seismological Society of America (United States of America) |
| Meeting | Seismological Society of America 2017 Annual Meeting; Denver, CO; US; April 18-20, 2017 |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Province | Ontario |
| NTS | 31G/05 |
| Area | Ottawa; Ottawa River |
| Lat/Long WENS | -76.0000 -75.5000 45.5000 45.2500 |
| Subjects | surficial geology/geomorphology; engineering geology; geophysics; Nature and Environment; Science and Technology; glacial deposits; silts; clays; landslides; landslide deposits; earthquakes; earthquake
risk; earthquake damage; strain analysis; seismic waves; seismic velocities; boreholes; glaciomarine sediments; cumulative effects |
| Program | Public Safety Geoscience Western Canada Geohazards Project |
| Released | 2017 03 01 |
| Abstract | Late-glacial marine silt and clay sediments found along the highly populated St Lawrence and Ottawa River valleys are known to amplify ground motions during weak shaking, but knowledge of the dynamic
properties governing their behaviour at higher strain levels is limited. A joint study is investigating the frequency and strain-dependence of material damping, shear wave velocity (Vs), and cyclic shear strength properties at a site near Ottawa,
Ontario, Canada. Accordingly, one theme within this project is examining low strain comparisons between field and lab measurements of Vs and damping. A thin-walled Osterberg hydraulic piston sampler was used to collect 127mm-diameter samples at a
test site adjacent to a 95m borehole cased for geophysical testing. A new technique for a modified Stokoe-type resonant column is used to measure the transfer function and dynamic properties of the samples as a function of frequency at constant
strain levels. These lab tests will be compared to downhole measurements conducted using a mono-frequency approach to the spectral ratio technique. A vibratory source generating signals between 10 and 100Hz, and two identical downhole 3-component
geophones were used for the field tests. Field results indicate a very low-loss material (damping<0.5%, strain<10-6%) with negligible frequency dependence in massive muds, although layering can produce some scattering effects at higher
frequencies.
The integrated field and lab results are indicating that a more complete understanding of site response is provided by surface and downhole geophysical investigations to image the 'large scale' geological features at a site (e.g.
seismically distinct deposits, bedrock topography) which provide a better context for the laboratory-analyzed samples. |
| Summary | (Plain Language Summary, not published)
Late-glacial marine silt and clay sediments found along the highly populated St Lawrence and Ottawa River valleys are known to amplify ground motions
during weak shaking, but knowledge of the dynamic properties governing their behaviour at higher strain levels is limited. A joint University-GSC study is investigating the frequency- and strain-dependence of damping, shear wave velocity (Vs), and
cyclic shear strength properties at a site near Ottawa, ON. Accordingly, one theme within this project is examining low strain comparisons between field and lab measurements. The integrated field and lab results are indicating that a more complete
understanding of site response is provided by surface and downhole geophysical investigations to image the large scale geological features at a site (e.g. seismically distinct deposits (layers), bedrock topography) which provide a better context for
the laboratory-analyzed samples. |
| GEOSCAN ID | 299713 |
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