Foundations: Proceedings of the Second BGA International Conference on Foundations, ICOF2008. Brown M. J., Bransby M. F., Brennan A. J. and Knappett J. A. (Editors). IHS BRE Press, 2008. EP93, ISBN 978-1-84806-044-9. www.ihsbrepress.com 30 EXPERIMENTAL EVALUATION OF SOIL DEFORMATION PATTERNS AROUND LATERALLY LOADED PILES M. HAJIALILUE-BONAB and Y. SOJOUDI Faculty of Civil Engineering, University of Tabriz, Tabriz, Iran hajialilue@tabrizu.ac.ir SUMMARY: An experimental study on the behaviour of soil around laterally loaded piles was undertaken. Digital images were captured during the lateral loading of the pile. The PIV method was applied and the deformation of the soil around the pile was obtained in each test. The effect of pile length on soil deformation pattern was investigated. The effect of pile stiffness and diameter on soil deformation pattern was also studied. A rigid pile was used in order to study the soil deformation and compared with a flexible pile. Keywords: digital imaging, flexible piles, lateral loading, PIV, soil deformation pattern. INTRODUCTION Deep foundations must often support substantial lateral loads as well as axial loads. While axially loaded, deep foundation elements may be adequately designed by simple static methods, the design methodology for lateral loads is more complex. The solution must ensure that equilibrium and soil-structure-interaction compatibility are satisfied 1 . In the analysis of soil-pile interaction problem under horizontal load, the behaviour of soil in front of piles is one of the important phenomena. A vertical pile resists lateral loads by mobilising passive pressure in the soil surrounding it. The degree of distribution of the soil reaction depends on soil and pile properties. The previous detailed observation, for example, the distribution of earth pressure around piles measured 2 and the behaviour of sand immediately adjacent to pile observed with X-ray system were carried out by model piles 3 . Strain wedge (SW) model are extended to predicting of pile reaction under lateral loads. In this method the (SW) properties depend on three-dimensional passive strain wedge extension in front of piles and defined by angles (β m ), (φ m ) and strain wedge depth 4 . An important objective of this research is to determine the effect of pile properties on soil deformation around piles and mobilized passive strain wedge depth and angle, using the “PIV” method.