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1. Sand Particle Size Analysis by SedImaging in a Field Lab

   Horstmeier, G; Eykholt, J; Kempf, C; Ventola, A; Hryciw, R (June 2021, Western Dredging Association (WEDA))

   Hayes, Donald F (Ed.)

   SedImaging is an innovative alternative particle size analysis method developed to obtain high-resolution particle size distributions (PSDs) of sands. It was developed at the University of Michigan (UM) and is based on wet processing and digital image analyses of fine to medium sands. This work summarizes a variant of the SedImaging method, named FieldSed, which was first applied in a field lab setting for a sediments site by the authors and colleagues in October 2017. The goal of this work was to detect subtle variations in the fine sand and fines compositions as a pilot test at a field laboratory, without use of a sieve set or oven drying. The testing program included replicates, independent testing by UM, and other quality control measures. Sediment processing included wet-removal of fines and particles larger than coarse sand; preparation of the sample in a pre-sorter tube followed by sedimentation in a tall, water-filled column to sort the sands; and the collection and analysis of high-resolution digital imagery of the settled sand. The FieldSed method included variations to estimate mass percentages of oversized (> 2 millimeters [mm]) and undersized (< 0.075 mm) sediments, and throughput improvement. Wet sieving and air drying were used to separate and prepare oversized sediments for weighing. Multiple decants of sediment-water mixtures were used to wash out more dispersive fines. Decanted fines contents were estimated by differences in wet weights and by specific gravity approximations. Digital images were analyzed and used to generate highresolution PSDs, which typically included more than 80 size bins from 2 mm to less than 0.050 mm. The FieldSed method was successful in clearly distinguishing coarse and fine material, as well as defining the gradient between medium sands, fine sands, and coarse silts. Color, angularity, and other grain characteristics from the digital imagery were noted. With further testing to improve processing rates and efficiencies, the method could be applied to provide same-day field decisions. More efficient and faster processing could be achieved for characterization of cleaner sands, and applications could be expanded further, such as to assess suitability of post-dredge sand cover materials in the field. 

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2. The effect of gradation on the response of saturated sands when subjected to seismic loading: A centrifuge test

   Trevor J. Carey; Anna Chiaradonna; Nathan Love; Jason T. DeJong; Katerina Ziotopoulou (October 2021, GeoNiagara 2021)

   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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3. Triaxial compression behavior of 3D printed and natural sands

   https://doi.org/10.1007/s10035-021-01143-0  

   Ahmed, Sheikh_Sharif; Martinez, Alejandro (September 2021, Granular Matter)

   Abstract Different particle properties, such as shape, size, surface roughness, and constituent material stiffness, affect the mechanical behavior of coarse-grained soils. Systematic investigation of the individual effects of these properties requires careful control over other properties, which is a pervasive challenge in investigations with natural soils. The rapid advance of 3D printing technology provides the ability to produce analog particles with independent control over particle size and shape. This study examines the triaxial compression behavior of specimens of 3D printed sand particles and compares it to that of natural sand specimens. Drained and undrained isotropically-consolidated triaxial compression tests were performed on specimens composed of angular and rounded 3D printed and natural sands. The test results indicate that the 3D printed sands exhibit stress-dilatancy behavior that follows well-established flow rules, the angular 3D printed sand mobilizes greater critical state friction angle than that of rounded 3D printed sand, and analogous drained and undrained stress paths can be followed by 3D printed and natural sands with similar initial void ratios if the cell pressure is scaled. The results suggest that some of the fundamental behaviors of soils can be captured with 3D printed soils, and that the interpretation of their mechanical response can be captured with the critical state soil mechanics framework. However, important differences in response arise from the 3D printing process and the smaller stiffness of the printed polymeric material. Graphic abstract Artificial sand analogs were 3D printed from X-ray CT scans of sub-rounded and sub-angular natural sands. Triaxial compression tests were performed to characterize the strength and dilatancy behavior as well as critical staste parameters of the 3D printed sands and to compare it to that exhibited by the natural sands. 

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4. Experimental Study to Determine an EICP Application Method Feasible for Field Treatment for Soil Erosion Control

   https://doi.org/10.1061/9780784482834.023  

   Ossai, Rashidatu; Rivera, Lucas; Bandini, Paola (February 2020, Geo-Congress 2020: Biogeotechnics)

   null (Ed.)

   The end goal of this research is assessing the feasibility of using enzyme induced carbonate precipitation (EICP) to create a cemented top layer to control runoff erosion in sloping sandy soil. The paper presents the results of an experimental study of bench-scale tests on EICP-treated sands to determine a treatment method feasible for field placement for this application. The soils tested were two natural sands and Ottawa 20-30 sand used as control. The EICP application methods were percolation by gravity, one-step mix-compact, and two-step mix-compact. Other conditions considered were pre-rinsing the sand prior to treatment, adjusting soil pH prior to treatment, and changing the EICP solution concentration. Promising results for this field application were obtained using the two-step mix-compact when the soil was first mixed with the urease enzyme solution before compaction. Considering that the EICP reaction starts once all components are added, this method would ensure that the reaction does not take place before the protective layer of treated soil has been installed. The effect of pre-rinsing the natural sand was not consistent throughout the testing conditions and its role in improving soil cementation in natural sand needs further study. 

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5. Comparison of Liquefaction Constitutive Models for a Hypothetical Sand

   https://doi.org/10.1061/9780784480489.039  

   Carey, Trevor J.; Kutter, Bruce L. (March 2017, Geotechnical Frontiers 2017)

   This paper presents numerical liquefaction simulations of a hypothetical sand in cyclic direct simple shear tests for four different constitutive models. The four models are PM4Sand in FLAC, UBCSand in FLAC, Pressure Dependent Multi Yield 02 (PDMY02) in OpenSees, and the Manzari-Dafalias04 model in OpenSees. Parameters published by others for various sands were used for this work to avoid possible introduction of our bias into the calibration process. The material properties were determined by others for different uniformly graded sands, all with a relative density of approximately 50%. The simulations do not pertain to one sand or one set of laboratory data, so therefore, there is no right or wrong answer. Instead, the goal of this paper is compare a consistent set of results that show the implementations of each model behave as expected, and to illustrate basic differences in behavior of the different models. Cyclic strength curves (cyclic stress as a function of number of cycles) illustrate the behavior of the models over a range of cyclic stresses. Each model displays pore pressure build up, softening, and cyclic contraction-dilation cycles associated with cyclic mobility. Two of the models soften to a point, but then stabilize in a repeated hysteresis loop with no additional growth in the cyclic strain amplitude after some number of cycles. 

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