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While design methods of deep foundations are mainly developed for homogenous soil deposits, the presence of highly cemented layers could lead to underestimation of resistance and overestimation of settlement of pile foundations. This study presents a novel approach using competent caliche layers bonded to the top and bottom of a continuous flight auger (CFA) pile as a new composite foundation system named caliche stiffened pile (CSP). The key objective is to optimize the required pile length in a cost-effective approach without ameliorating soil properties. Settlements of the CSP foundation for a high-rise building were monitored and full-scale tests were conducted to measure piles' capacity. Finite element back analyses were performed to avoid adverse effect of sample disturbance in settlement calculations. A back calculation of a test fill embankment was performed to determine soil stiffness parameters by simulating an unscheduled imposed load to the structure. Impacts of the CSP on controlling the settlement of pile foundation and optimizing the required pile length are investigated using finite element analysis and a parametric study. The proposed CSP foundation can reduce the CFA pile settlement significantly in the presence of caliche layers with thickness equal or greater than a pile diameter at CFA pile head and toe, where the CSP is located. Key words: cemented soil layers, pile capacity, pile foundation, soil-pile interaction, foundation settlement, 1. Introduction Existence of highly cemented deposits in the soil strata enhances side resistance and end bearing capacity of piles while reduces the settlement of deep foundations (Stone 2009; Afsharhasani [...]

The re-liquefaction resistance of cemented sands under multiple liquefaction events such as pre-shock, main-shock, and after-shock earthquakes is a complex phenomenon because the response may alter due to bond breakage. A series of multistage liquefaction-re-consolidation soil element tests under undrained stress-controlled cyclic loading condition using cyclic triaxial were carried out to assess the liquefaction and re-liquefaction resistance of cemented sands with varying degrees of cementation. Lightly cemented specimens were reconstituted using Sydney sand and high early strength Portland cement with cement content ranging from 0.25% to 1% and unconfined compression strength from 15 to 80 kPa. The results showed that the re-liquefaction resistance of cemented sands with different amounts of cement decreased after the first liquefaction event and then increased for succeeding liquefaction events. While the trend of residual excess pore water pressure ratio and cyclic stiffness degradation index of untreated sand under successive liquefaction events remained consistent, the corresponding responses for cemented sands altered for the second to the fifth liquefaction events. In fact, the residual excess pore water pressure ratio and cyclic stiffness of cemented sand increased and degraded faster during the early cycles of loading for the second to fifth liquefaction events. Key words: liquefaction, re-liquefaction, post-liquefaction behaviour, lightly cemented sand, multistage soil element tests La resistance a la re-liquefaction des sables cimentes sous de multiples evenements de liquefaction tels que les tremblements de terre pre-choc, choc principal et post-choc est un phenomene complexe, car la reponse peut changer en raison de la rupture des liens. Une serie d'essais par elements de sol de liquefaction-reconsolidation en plusieurs etapes dans des conditions de chargement cyclique controlees par des contraintes non drainees en utilisant le triaxial cyclique a ete realisee pour evaluer la resistance a la liquefaction et a la re-liquefaction des sables cimentes avec differents degres de cimentation. Des specimens legerement cimentes ont ete reconstitues a l'aide de sable de Sydney et de ciment Portland a haute resistance initiale, avec une teneur en ciment allant de 0,25 % a 1 %, pour une resistance a la compression non confinee de 15 a 80 kPa. Les resultats montrent que la resistance a la re-liquefaction des sables cimentes avec differentes quantites de ciment diminue apres le premier evenement de liquefaction et augmente ensuite pour les evenements de liquefaction successifs. Alors que la tendance du rapport de l'exces de pression d'eau interstitielle residuelle et de l'indice de degradation de la rigidite cyclique du sable non traite lors d'evenements de liquefaction successifs est restee coherente, les reponses correspondantes pour les sables cimentes ont change du deuxieme au cinquieme evenement de liquefaction. En fait, le rapport residuel d'exces de pression d'eau interstitielle et la rigidite cyclique du sable cimente ont augmente et se sont degrades plus rapidement pendant les premiers cycles de chargement pour les deuxiemes a cinquiemes evenements de liquefaction. [Traduit par la Redaction] Mots-cles : liquefaction, re-liquefaction, comportement post-liquefaction, sable legerement cimente, essais par elements de sol a plusieurs niveaux, Introduction The liquefaction phenomenon that occurs during an earthquake is the main cause of damage to manmade structures or for natural disasters such as landslides (Brandenberg et al. 2007; Haskell [...]