Experimental study on the mechanical behaviors of rigid pile composite foundation in Yellow River alluvial plain upon ground water level fluctuations

In recent years, the increasingly frequent extreme weather conditions in Yellow River Alluvial Plain (YRAP) like heavy rains and drought have resulted in significant Ground Water Level (GWL) fluctuations. After long-distance transportation by Yellow River, the silt in this area gains characteristics of high particle roundness and poor grain gradation, which makes it sensitive to the changes of water content. Consequently, upon GWL fluctuations, the bearing behaviors of Rigid Pile Composite Foundation (RPCF) gradually deteriorate and result in additional settlement. In order to investigate the changing disciplines and inherent mechanisms of the RPCF bearing behaviors upon GWL fluctuations, a large-scale model test was performed and presented. The experimental results suggest that RPCF settlement experiences a sudden increase in the first GWL fluctuation cycle and then gradually stabilizes in the following cycles. Such phenomenon could be attributed to the soil structure rearrangement induced by matric suction reduction in the GWL rise process and growth of effective stress in the GWL drop process. Further, considering the soil stiffness deterioration in the GWL rise process, the traditional composite modulus method for RPCF settlement estimation was modified to extend its application in unsaturated YRAP. The changing disciplines, mechanisms and estimation method presented can facilitate practicing engineers to gain a more comprehensive understanding on the bearing behaviors of RPCF in YRAP upon GWL fluctuations.