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The standard of practice when assessing the liquefaction susceptibility of geosystems uses an empirical case history database that was primarily developed for clean, poorly graded sands. However, many geosystems in the built environment are either constructed with or founded on well graded soils, creating a disconnect between the sand encountered in practice and the sand used as the basis of knowledge. Using the 9-m centrifuge at the University of California Davis’s Center for Geotechnical Modeling a centrifuge experiment was designed to test the dynamic response of embankments constructed poorly graded and well graded sands at the system level scale. The experiment consisted of two 10-degree slopes, one constructed with a poorly graded sand and the other with a well graded sand positioned side by side in the same model container. Each slope was dry pluviated to the same relative density of Dr=63%, while the absolute densities were different. The slopes were instrumented with dense arrays of pore pressure transducers and accelerometers in the level ground at the head of the slope. The stress-strain behavior between accelerometers was calculated using inverse analysis techniques, providing a 1-D shear-beam soil response at the sensor array location. Liquefaction was triggered, as defined by an excess porewater pressure ratio (ru) of 1.0, but the shear strains at triggering in the well graded sand were significantly less than the strains in the poorly graded sand. During cyclic mobility, strain accumulation in the well graded sand occurred at a slower rate. This study demonstrates that liquefaction triggering and the post-triggering response for saturated sands needs to consider gradation characteristics and clean poorly graded sands cannot act as a single predictor of dynamic response for all sand gradations.
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The Effects of Soil Gradation on System Level Dynamic Response
Recent studies have focused on how the dynamic response of a clean sand changes with increasing fines content; however, there remains a limited understanding regarding the effects of increasing coarse content. This study aims to elucidate these effects at a system level via centrifuge testing of two uniformly-graded and one well-graded soil mixture which range in mean grain diameter (D50) from 0.18 to 2.58 mm and in coefficient of uniformity (CU) from 1.53 to 7.44. Models of each soil mixture were prepared to approximately 50% relative density (DR) and subjected to uniform cycles of sinusoidal acceleration at various Arias intensities (Ia). The high hydraulic conductivity (k) of the coarsest, uniformly-graded mixture prevented significant excess pore pressure generation; however, liquefaction was induced in the other two mixtures. Furthermore, the well-graded mixture exhibited a stronger dilative tendency than the clean sand. The centrifuge results were compared to cyclic direct simple shear (DSS) results in order to consider the complementary perspectives that centrifuge and element testing can provide.
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- Award ID(s):
- 1916152
- PAR ID:
- 10158291
- Date Published:
- Journal Name:
- GeoCongress 2020
- Page Range / eLocation ID:
- 357 to 366
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1061/9780784482810.038
