The number of equivalent cycles (neq) concept plays an important role in geotechnical earthquake engineering and underlies the accounting for ground-motion duration in simplified liquefaction evaluation procedures, whether explicitly or implicitly. In this regard, several neq correlations have been proposed over the years that were developed using a similar variant of the Palmgren-Miner (P-M) fatigue theory. The correlations presented herein were developed using an alternative implementation of the P-M theory that better accounts for the nonlinear response of the soil and for multidirectional shaking. The proposed correlations are for shallow crustal earthquakes in both active tectonic and stable continental regimes. Additionally, two forms of the correlations are presented, one being expressed as a function of peak ground acceleration (a(max)). This relation shows a strong negative correlation between amax and neq, implying that motions with high amplitudes have short durations and vice versa. This negative correlation is not accounted for in most previously proposed neq correlations, which could result in the erroneous weighting of the unlikely scenarios of high amplitude-longer duration and low amplitude-short duration motions in liquefaction hazard studies. (C) 2016 American Society of Civil Engineers.

Since its inception in the early 1970s, the stress-based simplified procedure has become the standard of practice worldwide for evaluating liquefaction triggering potential. Central to this procedure is the stress reduction coefficient, rd, which allows the estimation of the seismically induced stresses at depth in a soil profile without the need to perform a numerical site response analysis. Proposed herein is a new rd relationship that was developed from equivalent-linear site response analyses performed on soil profiles representative of those in the liquefaction case history databases. The input motions used in the analyses are representative of those from shallow crustal earthquakes. Two variants of the rd relationship are presented that allow it to be used when the profile's shear-wave velocities are either known or unknown, with the former yielding values having less uncertainty. Additionally, calibration coefficients are provided for both active and stable continental tectonic regimes. In comparison with other rd relationships that are commonly used, the relationship proposed herein should yield values that have less bias and uncertainty.

Seismic compression is the accrual of volumetric strains in unsaturated soils caused by cyclic loading and has caused significant damages to buildings and other structures during earthquakes. To date, the available methods for predicting the severity of seismic compression have mainly been simplified procedures, in which a number of equivalent cycles are used to represent the duration of earthquake loading. Often, however, the number of equivalent cycles is computed inconsistently with the underlying mechanics of seismic compression. This paper proposes a non-simplified procedure for predicting the severity of seismic compression. The procedure is based on a modified version of the Richart-Newmark cumulative damage hypothesis, wherein volumetric strain is used as the damage metric. The proposed model was calibrated using data from 425 constant-amplitude sinusoidal strain-controlled cyclic simple shear tests performed on clean sand and validated using test data from samples subjected to variable-amplitude sinusoidal and earthquake loadings. In addition to predicting the severity of seismic compression, the proposed model can be used to compute number of equivalent shear-strain cycles for use in simplified models, consistent with the seismic compression phenomenon. In comparison with other proposed nonsimplified models for computing seismic compression, the proposed model gives good agreement with the measured seismic compression. (C) 2016 American Society of Civil Engineers.

The 12 January 2010 Haiti earthquake (M w 7.0) caused extensive damage to the Port-au-Prince region, including severe liquefaction failures along the Gulf of Gonâve coastline, along rivers north of Port-au-Prince draining into the Gulf, and a liquefaction-induced structural/bearing capacity failure of a three-story concrete hotel along the southern coast of the Gulf. During two reconnaissance missions, the authors documented ground conditions and performance at eight sites that liquefied and two sites that did not liquefy. Geotechnical characterization included surface mapping, dynamic cone penetration tests, hand auger borings, and laboratory index tests. The authors estimated median peak ground accelerations (PGAs) of approximately 0.17g to 0.48g at these sites using the Next Generation Attenuation (NGA) relations summarized by Power et. al. (2008) . These case histories are documented here so that they can be used to augment databases of level-ground/near level-ground liquefaction, lateral spreading, liquefaction flow failure, and liquefaction-induced bearing capacity failure.

Presented herein are the results of geotechnical investigations and subsequent laboratory and data analyses of the Port-au-Prince seaport following the Mw7.0 2010 Haiti earthquake. The earthquake caused catastrophic ground failures in calcareous-sand artificial fills at the seaport, including liquefaction, lateral spreads, differential settlements, and collapse of the pile-supported wharf and pier. The site characterization entailed geotechnical borings, hand-auger borings, standard penetration tests, and dynamic cone penetration tests. The laboratory tests included grain size and carbonate content tests. The observations and results presented herein add valuable field performance data for calcareous sands, which are relatively lacking in liquefaction case history databases, and the overall response of the artificial fills are consistent with predictions made using semi-empirical relations developed primarily from field data of silica sands.