EXPERIMENTAL STUDY FOR LATERAL CYCLIC RESPONSE OF PILED-RAFT FOUNDATION IN MULTI-LAYER SOIL

Abstract

In piled raft foundation, the load-sharing system between the raft and piles are occurring to transfer the load coming from the superstructure to the soil. This foundation is usually supporting bridge piers, offshore platforms, marine structures and others that are required to resist not only static loading, but also lateral cyclic loading that developed from different sources of loadings such as wind and seismic loads. Therefore, this complex system in layered soil with different load combination needs more laboratory and numerical studies to improve the knowledge regarding the performance of such a problem. This study offers an experimental study which is carried out to investigate the behaviour of laterally loaded pile raft models with three configurations (1×2, 2×1, and 2×2) where slenderness ratio is 40. Furthermore, three layers soil are used with different percentage of saturation. In addition, many other parameters are selected; such as spacing between piles 3D, 5D, and 7D (D is a diameter of pile) and cross-sectional shape of the pile (i.e. square and circle). To simulate the loading to be as much close as possible to the real cases, different loading conditions are used such as number of cycles, level of the cyclic load ratio (CLR) and influence of axial load. VIII The results of the study indicated that deflection and bending moment profiles behaviour increase with an increasing number of cycles for all spacing of piled raft foundation models. Correspondingly, in case of pure lateral cyclic load (without vertical loads) where spacing to diameter ratio is 3, the results illustrated that at the critical cyclic load level CLR=60% for 100 cycles, the lateral deflection is about 42%, 31%, and 44% more than at CLR= 40% of piled raft models (1×2), (2×1) and (2×2) respectively. Furthermore, it found that the presence of vertical loads has reduced the lateral displacement and bending moment profiles in all cases. For circular pile shape group, the reduction in lateral displacement at 100 cycles was approximately 19%, 14% and 44% for models 1×2 , 2×1 and 2×2 respectively, whereas for square shape, the percentage of the reduction were about 26%, 36%, and 34% respectively. The results also indicated that the increase in the lateral resistance in the group of square piles compared to a circular pile under pure lateral loading conditions within the group 1 × 2, 2 × 1 and 2 × 2 were about 16%, 20% and 23% respectively. The results demonstrated that lateral deflection and bending moment values of this model in saturated clay soil were less than in partially saturated clay soil and closer to the dry soil of about (35% and 13%) respectively. Finally, this study illustrated that maximum bending moment for trailing row was less than the leading row for circular piled raft models 1×2, 2×1, and 2×2 by about 16%, 17%, and 7% respectively, whereas the results for square model were about 22%, 13%, and 9% respectively.