Experimental Analysis on Deformation Law of Inclined Pile Composite Foundation Under Vertical Repeated Loading and Unloading

Improper construction, lateral surcharge, or excavation often leads to the tilting of pile bodies and causes problems of centralizability; however, the deformation characteristics of inclined pile composite foundation is not fully understood and may lead to new engineering diseases. A model box and loading device were designed to study the deformation law of inclined pile composite foundation under vertical repeated loading and unloading. The results are as follows: During the process of cyclic loading, the settlement and lateral displacement of the inclined pile top and its composite foundation increase as the load increases. Moreover, its growth rate increases as the load increases and decreases as the loading time increases. During the process of cyclic unloading, the settlement and lateral displacement of the inclined pile top and its composite foundation at the initial stage of unloading are not apparent, and elastic deformation occurs only during the last one or two stages of low pressure. Under the same load, the settlement of the pile top increases with the increase in the tilt angle. The inclined pile has a "critical inclination angle for settlement (6° during one to three loading and unloading cycles for the test)" that decreases with the increase in soil compactness. When the inclination is less than the critical value, the settlement of the pile has negligible effect and the settlement increases rapidly with the increase in the angle of inclination when it is greater than the critical value. The inclined pile has a "critical inclination angle for lateral displacement (9° for the test)" that corresponds to the peak value of lateral displacement. When the tilt angle is less than the critical value, the pile top lateral displacement increases with the increase in tilt angle. When the angle of tilt is larger than the critical value, the pile top lateral displacement decreases with the increase in tilt angle. The "critical inclination angle for lateral displacement" is greater than the "critical inclination angle for settlement". Under the same load, the lateral displacement of the composite foundation with an inclined pile is larger than that of the 6° pile and smaller than that of the 12° pile, and the settlement is larger than that of any inclined pile. When the pile is inclined, the lateral displacement of both the inclined pile and the composite foundation is considerably smaller than the settlement, but the lateral displacement is more sensitive than the settlement. In engineering, the inclination angle of the pile should be reduced as far as possible, and the settlement and lateral displacement of the inclined pile and its composite foundation should be reduced. © 2019, Editorial Department of China Journal of Highway and Transport. All right reserved.