Grey Prediction Of Ultimate Bearing Capacity Of Cast-in-place Pile And Finite Element Analysis

The cast-in-place pile is one of the piles common used in civil engineering, The vertical ultimate bearing capacity, a key parameter for the design of piled foundation, usually can be ascertained by pile static loading test. However, due to the high price and the equipment limitation of the pile test, the ultimate bearing capacity cannot be achieved, and its load-settlement curve is not complete.Because of the difference of some factors such as geological conditions, the load-settlement curves which obtained by pile static loading test can be roughly divided into two categories, the "gradually fall-type" and "steep fall-type". In order to predict the ultimate bearing capacity of a single pile according to the data already available, grey system forecasting model and finite element analysis are used this article to analyze the date got by grey system forecasting model and finite element analysis to improve the prediction accuracy.But single grey system forecasting model has its limitation, and the forecast precision of single model is directly related to the type of the pile's load–settlement curve as described in. So the applicability of the non-same step GM(1,1) model, the new information GM(1,1) model, the model GM(1,1) with residual error correction and the self-modifying GM(1,1) model on the vertical ultimate bearing capability forecast in soft soil are compared and analyzed in this paper by means of combining the experiment data in soft soil in Tianjin area. The self-modifying GM(1,1) model is has the highest accuracy for piles whose load-settlement curves present "gradually fall-type". But the accuracy is lower when the load-settlement curves present "steep fall-type". So based on the self-modifying GM(1,1) model, this article averaged three data which is extrapolated for the vertical ultimate bearing capacity of the cast-in-place pile. And the data proved that the method this article used has higher accuracy and reliability, and the grey system forecasting model which fits Tianjin soft soil best was proposed, providing a new method on the prediction of the pile's ultimate bearing capability in soft soil area.In addition to the grey system theory, this article used finite element analysis method to analyze the vertical ultimate bearing capacity of the cast-in-place piles. With ABAQUS software, the data of the vertical ultimate bearing capacity was analyzed and the load-settlement curves were obtained. Analysis of the ultimate bearing capacity values compared with the actual data show that the use of finite element to simulate the vertical ultimate bearing capacity of the cast-in-place piles is possible, and the accuracy can be meet requirements of the project in Tianjin soft area.