Acta Polytechnica Hungarica Vol. 7, No. 2, 2010 – 119 – Liquefaction Resistance of Chlef River Silty Sand: Effect of Low Plastic Fines and other Parameters Mostefa Belkhatir, Ahmed Arab, Noureddine Della Civil Engineering Department Hassiba Benbouali University of Chlef Chlef, Algeria E-mail: abelkhatir@yahoo.com, ah_arab@yahoo.fr, nour_della@yahoo.fr Hanifi Missoum Civil Engineering Department University of Mostaganem Mostaganem, Algeria E-mail: hanifimissoum@yahoo.fr Tom Schanz Laboratory of Foundation Engineering, Soil and Rock Mechanics Ruhr University Bochum, Germany E-mail: tom.schanz@ruhr-uni-bochum.de Abstract: Silty sands are the most common type of soil that could be involved in both static and earthquake-induced liquefaction. Most of the recent earthquakes have revealed the liquefaction of silty sands. Therefore, the selection of the appropriate undrained residual shear strength of liquefied soils to be used in the assessment of the post-liquefaction stability of earth dams and other earth structures is becoming a major challenge. A series of undrained monotonic and cyclic triaxial tests were carried out on reconstituted saturated samples of sand with variation in the fines content ranging from 0 to 50% for the monotonic tests and from 0 to 40% for the cyclic ones, in order to study the influence of fines fraction and other parameters on the undrained residual shear strength and liquefaction potential of loose, medium dense and dense silty sand samples (Dr = 12%, 50%, 60% and 90%). The results of the monotonic tests show that the stress-strain response and shear strength behaviour is controlled by the percentage of fines fraction and the samples become contractive for the studied relative densities (Dr = 12% and 90%). The