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This paper presents the results from a study of the role of soil fabric on the cyclic response of silty soil samples retrieved from two different sites from a series of sites investigated as a part of a larger study: one along the Willamette River (Site B) and one along the Columbia River (Site D). The soils investigated in this study were retrieved from Site B and exhibited an average 𝑃𝐼=13, and from Site D which were characterized with an average 𝑃𝐼=28. The cyclic response of the soils was evaluated by performing several constant-volume, stress-controlled, cyclic direct simple shear tests (CDSS) with varying cyclic stress ratios, CSRs, on natural, intact specimens and their reconstituted counterparts. Despite the lower void ratios of the reconstituted specimens, the cyclic resistance of the intact specimens for Sites B and D at 15 loading cycles were 19% and 37% greater than their reconstituted counterparts, respectively. For the given loading conditions, the rate of excess pore pressure development, single amplitude shear strain (𝛾) accumulation, and shear stiffness degradation in reconstituted specimens were greater than the natural intact specimens, emphasizing the role of soil fabric, as confirmed by the lower shear wave velocity (𝑉𝑠) of reconstituted specimens compared to their intact counterparts. 

Current best practices for the assessment of the cyclic response of plastic silts are centered on the careful sampling and cyclic testing of natural, intact specimens. Side-by-side evaluation of in-situ and laboratory element test responses are severely limited, despite the need to establish similarities and differences in their characteristics. In this paper, a coordinated laboratory and field-testing campaign that was undertaken to compare the strain-controlled cyclic response of a plastic silt deposit at the Port of Longview, Longview, WA is described. Following a discussion of the subsurface conditions at one of several test panels, the responses of laboratory test specimens to resonant column and cyclic torsional shear testing, and constant-volume, strain-controlled cyclic direct simple shear testing are described in terms of shear modulus nonlinearity and degradation, and excess pore pressure generation with shear strain. Several months earlier, the in-situ cyclic response of the same deposit was investigated by applying a range of shear strain amplitudes using a large mobile shaker. The in-situ response is presented and compared to the laboratory test results, highlighting similarities and differences arising from differences in mechanical (e.g., constant-volume shearing; strain rate-effects) and hydraulic (e.g., local drainage) boundary conditions and the spatial variability of natural soil deposits. 

Coastal dunes often present the first line of defense for the built environment during extreme wave surge and storm events. In order to protect inland infrastructure, dunes must resist erosion in the face of these incidents. Microbial induced carbonate precipitation (MICP), or more commonly bio-cementation, can be used to increase the critical shear strength of sand and mitigate erosion. To evaluate the performance of bio-cemented dunes, prototypical dunes consisting of clean poorly graded sand collected from the Oregon coast were constructed within the Large Wave Flume at the O.H. Hinsdale Wave Research Laboratory at Oregon State University. The bio-cementation treatment was sprayed onto the surface of the unsaturated dune. The level of cementation was monitored using shear wave velocity measurements throughout the duration of the treatments. The treated and control dunes were subjected to 19 trials of approximately 300 waves each, with each trial increasing in water depth, wave height, and wave period. The performance of the dune was evaluated using lidar scans between each wave trial. The results indicate that the surface spraying treatment technique produced consistent levels of bio-cementation throughout the treated length of the dune and demonstrated significant resistance to erosion from the wave trails.