Abstract: Based on gray theory, an unequal step length gray differential equation was presented to describe bearing capacity of overlength piles, and obtain its accurate solution. Error objective function was created based on optimization theory, further used least squares method to get the system parameters of the differential equation. In order to improve the accuracy of model, according to Markov theory, dividing the test value of gray optimizing model into n kinds of states based on predicating fitting curve, and getting one-step transfer matrix to forecast bearing capacity of overlength piles. The predication results show that the gray optimizing -Markov model based on the load-settlement curve can improve the precision of prediction compared with GM(1,1) model and gray optimizing model. A new way is provided for the predication of bearing capacity of overlength piles.

Key words: overlength piles, load-settlement curve, gray optimizing-Markov model, prediction