ORIGINAL PAPER A laboratory study of the initial structure and the overconsolidation effects on the undrained monotonic behavior of sandy soil from Chlef region in northern Algeria Noureddine Della & Ahmed Arab & Mostefa Belkhatir Received: 3 May 2010 / Accepted: 4 July 2010 / Published online: 24 July 2010 # Saudi Society for Geosciences 2010 Abstract The effects of initial state of the samples and the overconsolidation ratio (OCR) on the behavior of Chlef sand were studied in this article. For this purpose, the results of two series of undrained monotonic triaxial compression tests on medium dense sand are presented. In the first test series, the influence of the specimen's fabric and confining pressure has been studied. The tests were conducted at initial confining pressure of 50, 100, and 200 kPa. Two methods of sample preparation, which included the dry funnel pluviation and the wet deposition, were utilized. All the samples were subjected to a monotonic loading after consolidation phase. The results of the tests demonstrate that an increase in initial confining pressure leads to an increase in the resistance to liquefac- tion. The results also show that the samples prepared with the dry funnel pluviation method exhibit a greater resis- tance to liquefaction than those prepared with the wet deposition method. In the second series of tests, the overconsolidation influence on the resistance to the sand liquefaction has been realized on samples at an effective stress of 100 kPa for OCR varying between 1 and 8. The tests show that the increase of OCR improves the stiffness of sand and accelerates the appearance of dilatancy. Keywords Liquefaction . Undrained . Monotonic . Sand . Dry funnel pluviation . Wet deposition . Confinement . Overconsolidation Introduction The region of Chlef situated to the north of Algeria about 200 km to the west of the capital Algiers, by its proximity of the contact of the continental European and African plates as it is shown by Fig. 1, is constantly a very unstable zone subjected to an intense seismic activity. During the last centuries, it underwent destructive earthquakes (ex. Orléansville, El-Asnam) in 1922, 1934, and 1954. This last earthquake of magnitude 6.7 which have been described enough well by Rothé (1955), Thevenin (1955) and Mckenzie (1972), had caused the death of 1,340 people and important damages on the different civil engineering structures and the apparition of the soils sliding and liquefaction phenomenon. October 10th, 1980, at 13h25 (local hour), the region was the theater of a strong earthquake of a magnitude of 7.3 according to the calculations of Papastamatiou (1980), followed by two important jolts of magnitudes 6 and 6.1 to some hours of interval and numerous retorts appeared during several months (Ouyed 1981). The main shock generated an important inverse fault of about 40 km long appeared in surface (Ambraseys 1981). The disaster of October 10, 1980 provoked numerous losses in human lives (about 3,000 deaths), the destructions of buildings in high number, and the important damages to the linking infrastructures and to public equipment. The seismic vibration also generated a certain number of geodynamic phenomena to the surface of the soil: move- ments of ground of varied nature and size, and especially the liquefaction of the sandy soils following a loss of shearing resistance. According to Durville and Méneroud (1982), the phenom- enon of liquefaction appeared on a vast alluvial valley N. Della (*) : A. Arab : M. Belkhatir Laboratory of Material Sciences and Environment, Civil Engineering Department, University of Chlef, Sendjas Street, PO Box 151, Chlef 02000, Algeria e-mail: nour_della@yahoo.fr Arab J Geosci (2011) 4:983–991 DOI 10.1007/s12517-010-0178-2