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A critical state testing round robin programme was carried out on sandy silt gold tailings. This involved 15 laboratories around the world testing a sandy silt tailings to infer its critical state line (CSL). Methods to be used were intentionally not supplied to participants, to enable the current methods being employed in industry and academia to be obtained in an unbiased manner. All but one of the laboratories involved in the study used the moist tamping sample preparation technique, generally to produce loose, contractive specimens. Void ratio was measured using a variety of means, including cell calibration, end-of-test water content and end-of-test soil freezing (EOTSF) to assist in measuring the final water content. Of the 15 entries, four were excluded from the primary comparison owing to various issues that appear to have led to their divergence from most of the entries received. Of the remaining entries, the best reproducibility was produced by laboratories that used EOTSF to measure void ratio. Most other test procedure variations appeared to have a negligible effect, with the exception of fixing of the top platen and possibly sample size. A CSL elevation range of 0·04 void ratio for laboratories using EOTSF was observed.

The paper examines the effect of the presence of small percentages (1-5%) by dry mass of the sand of laponite - a synthetic nanoclay with plasticity index exceeding 1000% - on the cyclic response of sand with relative density in the 15-25% range. The work is based on cyclic triaxial tests performed on specimens prepared pluviating sand and laponite under dry conditions and then permeated with water. 1% laponite impacts all stages of the cyclic tests, from the response during the first loading cycle to liquefaction, increasing the cyclic resistance. Further benefits are observed with a longer pre-shear aging period or higher dosages (3-5%) of laponite. The observed behavior is associated with reduced mobility of the sand particles during cyclic loading, which can be ascribed to two mechanisms: (1) bonding/bridging at the particle contacts due to the charged laponite fines which are attracted to the sand grains; and (2) formation of a pore fluid with solid like properties. The first appears to control the behavior with 1% laponite, while it is proposed that the second is responsible for the response with higher dosages of laponite. The results presented provide new insight into the effects of high plastic fines on the cyclic response of sands, the "extreme" effects of the plasticity of the fines, and are significant in light of the possible use of laponite for liquefaction mitigation, an idea first put forth by the authors. (C) 2016 Elsevier Ltd. All rights reserved

Few moderate-to-strong earthquakes associated with active and capable geological faults have been documented for the southern coastal region of Ecuador. The seismic record of Ecuador initiates with the Guayaquil earthquake in 1787 (Mw 6.5), followed by the 1943 (Mw 6.2), and the most recent one in 1980 (Mw 6.1). The available data is insufficient to evaluate the seismic hazards associated with faults capable of generating seismic events of magnitude Mw≥6.0 in the region. Also, earthquakes of minor magnitudes can be disregarded as they do not induce significant ground coseismic effects. In this context, this study presents a catalog of geological faults, delineating 40 segments of capable and active faults on the sea floor of the Gulf of Guayaquil and inland segments of Guayas, Santa Elena, and El Oro provinces. This methodological approach estimates a variety of seismicity levels ranging between Mw 6.2 and Mw 7.2, with rock peak ground accelerations between 0.24 g and 0.41 g. These values have been obtained from empirical regression equations applied to the length of capable geological faults. The F-40 seismogenic structure located in the accretionary prism, close to the subduction zone, is capable of generating Mw 8.2 earthquakes and potentially causing coseismic ground damage to the city of Guayaquil located ca. 177 km to the NE. Furthermore, local tsunami hazards may affect severely areas that are densely populated, with developing industrial areas, on the coast of the Gulf of Guayaquil. This structural geological analysis provides useful new data for seismic hazard assessment.

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