Effect of Soil Structure on Penetration Response of Jacked Piles: Model Tests in Structured Clays

Laboratory model tests were conducted on artificially structured clays using self-developed equipment to better understand the penetration mechanism of jacked piles in structured clays. Two artificially structured clays with the same initial void ratio but different structured strengths, along with one unstructured clay, served as foundation soils for model tests. Cement and salt were selected to simulate the bonding force and macroporous fabric between soil particles in artificially structured clays. The microstructure and mechanical behavior of artificially structured clay samples were analyzed using a scanning electron microscope and a triaxial apparatus. This analysis aimed to evaluate the efficacy of the current method utilized in preparing structured clays and elucidate the evolution mechanism of pile response in structured clays in relation to soil cells. The findings showed that increased confining pressures lead to a more pronounced impact of soil structure on pile jacking force. Unlike the pile shaft, soil structure played a more crucial role in influencing the pile end during jacking, primarily due to the shear-induced structure degradation of clays close to the pile shaft. The axial force and shaft resistance of piles significantly increased with higher cement content. Simultaneously, the mobilization of the increased pile shaft resistance enhanced the nonlinearity in the distribution of axial force along the pile shaft. The pore-water pressure and total radial stress at the pile–soil interface, located 150 mm from the pile toe, experienced respective increases of 1.27 and 1.38 times as the cement content of model soils increased from 0% to 4%.