Reliability Analysis of Vertical Capacity for Necking Piles Assisted with Support Vector Machine

Since commonly used first order reliability method (FORM) often yields inaccurate reliability index of pile bearing capacity, support vector machine (SVM) is combined with FORM to calculate the reliability index of bearing capacity of defective piles in this paper. Taking the reduced-diameter defective pile as an example, the vertical loading test of one complete pile and five reduced-diameter piles was carried out. The random weighting method is used to estimate the mean value of the bearing capacity reduction coefficient of the defective piles. The example shows that the shrinkage is filled with soil, which converts the lateral friction resistance of the pile here into the friction of the soil interface, and weakens the bearing capacity of the pile. The larger the shrinkage length, the larger the area filled by the soil at the shrinkage, and the smaller the pile bearing capacity reduction coefficient and reliability index. The closer the shrinkage position is to the top of the pile, the greater the degree to which the shrinkage limits the resistance of the side friction. The pile end resistance compensates for part of the loss of lateral friction resistance, so that when the shrinkage diameter is located in the shallow and middle parts of the pile body, the pile bearing capacity reduction coefficient and reliability index are roughly the same; when located deep, the bearing capacity loss is minimal and the reliability index is the largest.