Experimental Study on the Shear Characteristics of the Interface between Marine Soft Clay and Jacked Pile

Marine soft clay is widely distributed in coastal areas. Aiming at the characteristics of low strength and stress level of marine soft clay, the effects of normal stress, water content, and resting time on the pile–soil interface shear characteristics of marine soft clay–jacked piles were investigated using improved direct shear test equipment. On this basis, a practical interface shear strength prediction model considering the above factors is proposed. The test results show that the relationship between shear stress and shear displacement at the pile–soil interface can be divided into three stages—initial, transitional, and stable—and the relationship is in accordance with the hyperbolic model. Under the same water content and resting time, the interface peak shear stress increases linearly with the increase in normal stress. The interface peak shear displacement decreased with the increase in normal stress. Under different water content conditions, the peak shear stress decreases with increasing water content, while the corresponding peak shear displacement increases. The internal friction angle and adhesion at the pile–soil interface decreased rapidly and exponentially with increasing water content of the soil around the pile. The interfacial adhesion varies in the range of 1.07–13.76 kPa and the internal friction angle in the range of 1.8–6.1°. The change in water content when the water content of marine soft clay is less than the liquid limit has a great influence on the interface shear strength. The peak shear stress increases with increasing resting time, while the corresponding peak shear displacement decreases for different resting times. The Internal friction angle and adhesion at the pile–soil interface increases exponentially with the resting time. Interfacial adhesion changes in the range of 1.8–4.9 kP, and the internal friction angle is 2.8–4.7°. The strength of the pile–soil interface grows with the advancement of the resting time, and the bearing performance of the jacked pile is improved, with the most significant effect in 14 days. Based on multiple linear regression analyses, the effects of normal stress and water content on interfacial shear strength are comparable and the effect of normal stress on the shear strength is more significant compared with the resting time. The test results provide valuable reference for the design and construction of jacked piles in marine soft ground.