Model test on compression characteristics of composite foundation with defective piles

Composite foundation is more and more widely used in soft foundation treatment, but the pile defect is difficult to avoid. The engineering properties of composite foundation with defective piles under compression and its reinforcement technology are widely concerned. Model tests were carried out to investigate the engineering properties of the composite foundation with defect piles to provide basis for its reinforcement design. The results show that for the same defect position and under the same loading condition, the broke pile has the largest settlement, followed by the shrinking pile and the normal pile, while the expanding pile has the smallest settlement; the expanding pile has the largest top stress and pile-soil stress ratio, followed by the normal pile, the shrinking pile and the broken pile. In terms of engineering effect, the expanding pile is better than the shrinking pile, while the broken pile is the worst. For the three kinds of defect, the closer the defect position is to the top of pile, the worse the pile's property is. The axial force at the defect position has an abrupt change and the defect position becomes a neutral point. The axial force of the shrinking part is significantly reduced resulting in a minimum value. The shrinkage of the upper half section of the pile causes the position of peak axial force and the neutral point of the lower half section to move down. The shrinkage of the lower half section of the pile causes the position of peak axial force and the neutral point of the upper half section to move up. The shrinkage of middle part of defective pile causes two peaks and two neutral points at the upper part and the lower part respectively. The axial force at broken surface becomes smaller. The peak axial force of middle broken pile is still in the central part. The position of peak axial force of the upper broken pile moves down. The axial force of the expanding part has a peak value. If the pile body is defective, the bearing capacity should be tested, the settlement and stability of composite foundation with defective piles should be checked, and if necessary, an additional pile body is suggested according to the principle of composite pile foundation. © 2020, Editorial Office of Journal of Building Structures. All right reserved.