Horizontal Bearing Characteristics of Ultralong Composite Steel Tube Concrete Variable-Section Piles

In order to consider the comprehensive effects of steel casings in addition to the construction method in engineering projects, this study investigates the influence of steel casing length, thickness, mud skin, and shear rings on the horizontal load–bearing characteristics of composite steel piles. Based on the practical project of the Anluo Expressway Yellow River Bridge, nine sets of model pile experimental tests were conducted, with the aforementioned four influencing factors as variables. The test results were used to calibrate the variables of soil properties in the theoretical calculations used in the finite difference method and to obtain p−y curves and the initial modulus of soil resistance k that is applicable to this project. Using the calibrated parameters, the horizontal bearing characteristics of the piles were predicted. The results show that increasing the steel casing length can improve the horizontal bearing capacity and the soil resistance transfer depth of piles and can reduce displacement and cause a downward shift in the location of the bending moment peak. Furthermore, boundary effects were observed. It is recommended that the steel casing length below the mud surface may be set to be 0.4–0.5 times the critical pile length. It is for the first time that the critical pile length is used to estimate the length at the variable section to provide new insights for the study of variable-section piles. These results may have guiding significance for predicting the horizontal characteristics and engineering application of ultralong composite steel tube piles.