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Assessment of earthquake-induced liquefaction is an important topic in geotechnical engineering due to the significant potential for damage to infrastructure. Some of the most significant infrastructure damage occurs due to differential settlement of the ground, including due to liquefaction. Postliquefaction deformations commonly are assessed using one-dimensional empirical models, which inherently assume laterally homogeneous soil layers. Numerical models offer the potential to examine the effects of ground motion variability and spatially variable soil properties on liquefaction-induced deformations. This study explored the postliquefaction reconsolidation settlement for a site in Hollywood, South Carolina, which was characterized using a three-dimensional (3D) geostatistical model and simulated using the numerical platform FLAC and constitutive model PM4Sand. The effects of ground motion characteristics on mean and maximum differential settlements were investigated. The physical mechanisms associated with postliquefaction responses such as excess pore pressures, shear strains, and volumetric strains also were examined. The efficacy of uniform models assuming representative percentile soil properties to represent the stochastic mean settlement was investigated. The inherent inability of uniform models to capture differential settlements and therefore the need for using stochastic models is discussed. [ABSTRACT FROM AUTHOR]

Regression models are presented to estimate the cyclic resistance of transitional silts as an alternative to semiempirical case history and stress history and normalized engineering parameter-based models using a database of cyclic laboratory tests on intact specimens. Expressions for the plasticity index (PI) dependent semilogarithmic slope, exponent b , of the curve describing the variation of cyclic resistance ratio (CRR) and number of loading cycles and the variation of number of equivalent loading cycles with b are developed for subduction zone earthquakes alongside corresponding magnitude scaling factors for use in cyclic failure assessments (i.e., liquefaction triggering and cyclic softening) within the simplified method framework. A PI, overconsolidation ratio, and shear strain-dependent model for the variation of CRR with N is presented to estimate cyclic resistance as a function of cyclic shear strain failure criteria ranging from 1% to 10%. The suite of models can be used together or separately to facilitate assessments of cyclic failure of, or plan cyclic laboratory test programs and/or calibrate constitutive models for, transitional silts in the absence of site-specific laboratory tests. [ABSTRACT FROM AUTHOR]

Thus, the HT ht computed for HT ht should not be relied on. The statistical distributions of HT ht for the Yes and No cases were found to be nearly identical. As pointed out in the following, the shape of the triggering curve can impact HT ht for low HT ht . Nonetheless, the cyclic strain-based approach may be able to help screen sites for large deformation potential in conjunction with other available models, without reliance on the specific magnitude of HT ht calculated. [Extracted from the article]

In this paper, efforts to characterize and compare the full-scale in situ three-dimensional (3D) dynamic response of a low-plasticity silt deposit to multidirectional loading from two different sources, a vibroseis shaker named T-Rex and controlled blasting, are presented. Horizontal vibroseis shaking at a frequency, f , of 10 Hz, produced dynamic responses in the silt that ranged from linear-elastic to nonlinear-inelastic, inducing maximum equivalent direct simple shear (DSS) shear strains, γDSS,max , up to 0.15% and residual excess pore pressure ratios, ru,r , of 14.1%. Blast-induced shear waves with predominant frequencies ranging from 9.6 to 14.6 Hz excited nonlinear-elastic and nonlinear-inelastic responses in the silt deposit, with γDSS,max of 1.14% and maximum ru,r of 61%. Importantly, these responses were observed to be minimally influenced by high frequency compression waves. Multidirectional loading, and excess pore pressure, ue , migration and impedance were identified as the predominant factors for achieving the large ru,r in the silt deposit from these two in situ testing techniques. The cyclic threshold shear strain, γtp , to trigger ru,r observed from the T-Rex shaking equaled 0.007% to 0.011% and varied with the initial soil stiffness. The two testing techniques demonstrated that the in-situ shear modulus, G , reduced to 90% of the maximum shear modulus, Gmax , at γDSS,max≈γtp , whereas by γDSS,max≈1% , G further reduced to 10 to 30% of Gmax corresponding to ru,r of ∼60%. Changes in soil fabric were quantified using small-strain shear-wave velocity measurements performed before and/or upon initiation and after each stage of dynamic testing, and were linked to the observed increase and decrease in γtp for the shallower and deeper 3D elements, respectively, following T-Rex shaking. The side-by-side comparison of the dynamic responses and soil properties derived from these two distinctly different field-testing techniques validate the use of controlled blasting for quantifying in situ dynamic soil properties and responses. [ABSTRACT FROM AUTHOR]

This study presents the results of a laboratory test program that serves to improve the understanding of the liquefaction susceptibility and cyclic response of intact silts that span sand- and clay-like behaviors. Specimens were prepared from samples characterized with a plasticity index (PI) ranging from 0 to 39, fines content (FC) ranging from 29% to 100%, and overconsolidation ratio (OCR) ranging from 1.0 to 4.2, retrieved from five silt deposits in Western Oregon and Southwest Washington. The roles of PI, FC, and OCR on the 1D compression and monotonic and cyclic strength of nonplastic to plastic silts are identified. Hysteretic metrics proposed to quantify cyclic behavior provided an objective means to distinguish between qualitative judgments of sand-like, intermediate, and clay-like behavior. Prior soil index test-based liquefaction susceptibility criteria exhibited good to poor accuracy; modifications to existing criteria aligned with quantified hysteretic behavior, which together indicate that sand- and clay-like behavior is subject to the intensity and duration of cyclic loading. The variation of cyclic resistance ratio (CRR) and cyclic strength ratio, τcyc/su,DSS , with the number of loading cycles, N , to reach single amplitude shear strain, γ , of 3% and 3.75% is presented. The τcyc/su,DSS for Nγ=3%=10 and 30 appeared constant for PI≤11 and PI≥18 and equal to 0.63 and 0.54, and 0.82 and 0.76, respectively, with an apparent linear trend for 11

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This study presents a comprehensive investigation into the monotonic, cyclic, and postcyclic response of a medium stiff, plastic, lightly-overconsolidated, alluvial clayey silt deposit. The laboratory investigation is performed on natural, intact, and reconstituted specimens derived from high-quality samples to establish the role of the stress history and soil fabric on cyclic resistance, excess pore pressure generation, and postcyclic behavior. The results of cone penetration tests (CPTs), vane shear tests (VSTs), and downhole and crosshole geophysical tests are used to compare the monotonic, stress-controlled direct simple shear (DSS) test data and interpret differences in the cyclic response of natural and reconstituted specimens. Constant-volume, stress-controlled cyclic tests indicate that the naturally-overconsolidated (OC), artificially normally-consolidated (NC), and reconstituted OC silt exhibit the cyclic mobility-type failure mechanism. The cyclic resistance of the intact, natural silt was determined to be sensitive to overconsolidation, with greater pore pressure generation potential observed in the NC silt for the same loading conditions. Despite significantly denser conditions, the reconstituted OC silt specimens exhibited a cyclic resistance approximately 44% lower than the natural, intact OC specimens at the cyclic resistance ratio corresponding to 15 cycles of loading. The magnitudes of postcyclic volumetric strain in the natural, intact specimens were independent of the overconsolidation ratio (OCR) and depended on the maximum excess pore pressure generated during cyclic shear. Strain-controlled cyclic DSS tests were used to identify the cyclic threshold shear strain, γtp , to generate residual excess pore pressure, which is approximately 0.012% in the naturally OC silt, and the cyclic degradation indices for various shear strain amplitudes. The various stress- and strain-controlled cyclic response of this natural silt deposit are compared to similar plastic soils reported in the literature to provide a well-characterized soil deposit for reference by geotechnical practitioners. [ABSTRACT FROM AUTHOR]

Driven timber displacement piles are being increasingly used to densify and reinforce soils against earthquake-induced ground deformations. However, the role of timber piles to reinforce the soils and redistribute cyclic stresses to timber piles has not been established, despite their excellent flexural properties. This study presents a series of dynamic 3D, linear-elastic, numerical simulations set with the unit cell framework to evaluate the role of the tapered timber pile and design variables such as pile length, spacing and relative density on the amplification and stress redistribution possible with this ground improvement technique. The simulations indicate that the depth-dependent shear strain and shear stress redistribution variously depend on the pile length, spacing, relative density, and input motion frequency. Further, the previously-accepted shear strain compatibility assumption developed for stone columns served to greatly overestimate the magnitude in cyclic shear stress reduction. Due to the tapered pile geometry and the depth-varying soil properties implemented, the accuracy of a recently proposed approach to estimate shear stress redistribution to account for column flexure was found to depend on the flexibility of the composite soil-pile system: longer, more flexible piles and lower relative density were predicted more accurately than shorter, stiffer timber piles with higher relative density. In general, the average shear strain ratio between the improved and unimproved soil is most sensitive to pile length, moderately sensitive to relative density, and least sensitive to pile spacing, and the average ratio of shear stress reduction coefficients is most sensitive to pile spacing, moderately sensitive to pile length, and is least sensitive to relative density. • Driven displacement piles serve as ground improvements through densification and reinforcement of the surrounding soil. • Dynamic 3D numerical simulations are used to explore aspects of the reinforcement effect. • Timber piles are shown to reduce the average cyclic stresses acting on saturated soils. • Due to pile flexure, timber piles do not exhibit shear strain compatibility with the surrounding soil. [ABSTRACT FROM AUTHOR]

The effect of strain history on monotonic and cyclic response of intact and reconstituted, low and high plasticity silt deposits have been investigated through a series of constant-volume, staged, stress- and strain-controlled cyclic direct simple shear tests. In many cases the specimens subjected to stress-controlled loading exhibited a progressive increase in cyclic resistance due to beneficial effects of increased density following post-cyclic reconsolidation, apparent pseudo-overconsolidation and presumably increased lateral stresses. Such effects outweighed the detrimental effects of fabric destructing as a result of the prior strain history. However, some specimens exhibited an inconsistent evolution of cyclic resistance when assessed using different shear strain cyclic failure criteria. Symmetric accumulation of shear strains in earlier shearing stages did not consistently result in an increasing trend in the post-cyclic resistance; additionally, increases or decreases in cyclic resistance can occur in subsequent shearing stages depending on the amplitude of the maximum shear strain. Staged, strain-controlled tests were used to investigate the cyclic soil response to small and large shear strains, the latter of which caused a reduction in the cyclic resistance of overconsolidated (OC) silt specimens in the following loading event, confirmed using shear wave velocity, V s , measurements which indicated substantial fabric disturbance following the large strain event. In contrast, normally-consolidated (NC) and OC specimens subjected to multiple stages of small cyclic shear strain exhibited progressive increases in V s , the magnitude of which varied with stress history. The increase in cyclic resistance in the NC specimens was related to increased pseudo-overconsolidation following reconsolidation. The monotonic undrained shear strength of all silt specimens subjected to staged cyclic loading increased following post-cyclic reconsolidation; the increase in strength and changes in volumetric tendencies are governed by the magnitude of post-cyclic reconsolidation and changes in soil fabric inferred from V s , respectively. [ABSTRACT FROM AUTHOR]

Lightweight expanded clay aggregate (LECA) is a geomaterial that is low in density, porous, and has an enamel surface. A series of unconfined compression and resonant column tests were performed to understand the dynamic performance of LECA. Testing results show that the uncemented LECA is poorly graded but possesses a stable internal structure. The initial shear modulus, shear modulus reduction, and increase in damping with shear strain of uncemented LECA exhibits pressure-dependence. However, for cemented LECA, the increase in cement content and confining pressure leads to significant increases in the strength and stiffness, as well as greater nonlinearity in the dynamic shear modulus reduction. An empirical power law was recommended to describe the relationship between initial shear modulus and unconfined compressive strength. Cemented LECA exhibited larger damping characteristics than uncemented LECA for the range in strains investigated. The minimum damping ratio of LECA with a high cement content may exceed 5.0%, and generally increases with increasing confining pressure. Empirical equations were proposed to describe the modulus and damping ratio trends of LECA at low strains, and these relationships were compared to other geomaterials. The results were placed in the context of the application of LECA as an engineered backfill. • Dynamic properties of lightweight expanded clay aggregate (LECA) are explored. • The experimental dynamic test program considered cemented and uncemented LECA. • The effect of cement content and confining pressure on stiffness and damping is quantified. • Empirical models to estimate dynamic properties are presented. [ABSTRACT FROM AUTHOR]