Liquefaction Potential of Silty Sand in Simple Shear ZAHEER AHMED ALMANI *, KAMRAN ANSARI*, AND NAEEM AZIZ MEMON* RECEIVED ON 16.02.2012 ACCEPTED ON 18.09.2012 ABSTRACT In this paper, the liquefaction potential of medium dense and dense sand layers was studied by performing constant volume (undrained) cyclic simple shear tests using cyclic simple shear apparatus. Strain- controlled approach was adopted. The liquefaction potential of two layers of a silty sand soil profile consisting of surface medium dense layer and underlying dense sand layers were studied. A medium dense sand surface layer exhibited flow type total liquefaction in cyclic loading in few cycles after initial liquefaction. An underlying dense sand base layer showed initial liquefaction in relatively more number of cycles and then cyclic mobility due to which pore pressure increases and decreases with cycles that is the characteristics of dense sand. The pore pressure increase and decrease is directly related to decrease and increase of effective stress. Key Words: Strain-Controlled, Medium Dense Sand, Dense Sand, Liquefaction, Cyclic Mobility, Shear Strength. * Assistant Professor, Department of Civil Engineering, Mehran University of Engineering & Technology, Jamshoro. 1. INTRODUCTION stress-controlled tests may not be suitable and strains may exceed the measured range before the stresses reach the specified amplitude for relatively loose sand subjected to higher stress amplitude. On the other hand, strain- controlled cyclic simple loading directly relate pore pressure and consequent liquefaction with the amplitude of shear strains [9]. Further, these types of tests more closely simulate the earthquake loading. From literature review [7-8] it is evident that study on liquefaction potential of silty sand using strain-controlled cyclic simple loading is at primary stage and comprehensive data is not available in literature. Much work is still needed to better understand the liquefaction potential of silty sand. T he buildings on shallow foundations which are constructed over liquefiable loose or medium dense sand deposits in coastal areas or where water is high, suffer significant damage due to lique- faction-induced settlements and tilting. These large settlements are caused due to, bearing capacity failure (shear failure) when the soil loses stiffness as a result of liquefaction. This behaviour of shallow foundations have been reported during earthquakes such as Niigata, Japan, [1], Dagupan City, Philippines, [2], Chi-Chi, Taiwan, [3] and Kocaeli, Turkey, [4-5]. Many researchers have carried out stress-controlled [6] and strain-controlled tests [7-8] to study the liquefaction potential of loose and medium dense sand. However, Mehran University Research Journal of Engineering & Technology, Volume 32, No. 1, January, 2013 [ISSN 0254-7821] 85