Dynamic Centrifuge Tests to Evaluate Reinforcing Mechanisms of Soil-Cement Columns in Liquefiable Sand

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“…Most recent numerical method verifications (Rayamajhi, et al, 2014;and Rayamajhi, et al, 2016) as well as dynamic centrifugal testing results (Rayamajhi, et al, 2015) supported Goughnour and Pestana (1998) arguments. Based on comparing the ground response of the improved and unimproved soil, the ratio of seismic shear stress in improved and unimproved sand, R rd , is (Rayamajhi, 2014): (1) where G r is the shear modulus ratio of the inclusion and sand (= G pc/sc /G s ), A r is the ratio of the inclusion area to the total area (= A pc/sc /A), g r is the ratio of shear strain in the inclusion to the strain in the sand (= g pc/sc /g s ), and C G is a shear factor (= 1.0 for circular inclusions, and ~ 0.5 for rectangular grids).…”

“…As the shear modulus in the sand will be reduced due to pore pressure increase, the reduced shear stress, may or may not increase the shear strain. In centrifugal tests, Rayamajhi et al (2015) observed that there was a slight delay in the initiation of liquefaction, when stiff column inclusion was provided. In addition to the results of the response spectra analysis and the post construction v s measurements, as well as considering the results of vibroseis test as reported by Wissmann (2015), the contribution of the reinforcement mechanism in the recently proposed methods is likely somewhat underestimated.…”

Performance of Driven Displacement Pile–Improved Ground in Controlled Blasting Field Tests

“…Nearest to the epicenter, the body wave amplitudes are greatest and most distinguishable, but decay with distance so that the ground motions become dominated by Rayleigh waves. The displacement amplitude of body waves decay with the inverse of the radial distance squared, whereas surface waves decay in correspondence to the inverse of the square root of radial distance (Richart et al 1970). Triaxial geophones used to observe the ground motions during blasting were positioned at epicentral distances ranging from 24 to 120 m from the center of the blasted areas, and allowed observation of longitudinal (P wave dominant), transverse (S wave dominant) and vertical motions.…”

“…(1) for much stiffer reinforcement elements such as deep soil mixing columns, jet grouted columns, drilled displacement piles, continuous flight auger piles, and other ground reinforcement techniques. However, questions regarding the applicability of the SSC assumption have developed as a result of numerical and analytical studies by Olgun and Martin (2008), Gueguin et al (2013), and Rayamajhi et al (2014), and centrifuge tests by Rayamajhi et al (2015). These studies have suggested that flexure of reinforcing elements decreases the magnitude of cyclic shear stresses reduction; however, these findings have not been confirmed at full-scale.…”

“…Fresh cracking around the soil-pile interface was noted in the field following blasting, and this pointed to possible cyclic gapping between the soil and the pile during the blast-induced ground motions, which would have limited a composite or strain-compatible response. Based on numerical and analytical models (Olgun and Martin 2008;Gueguin et al 2013;Rayamajhi et al 2014), centrifuge model tests (Rayamajhi et al 2015), and the field tests described in this paper, the use of the shear strain compatibility assumption and corresponding design approach for relatively stiff reinforcement liquefaction mitigation ground improvement may not be appropriate.…”