Behavior Of Composite Foundation Improved By Diving Dry-Vibrated Compacted And Anti-Pull Stone Columns

In this paper,based on the engineering practice of soft ground improved by diving dry-vibrated compacted and anti-pull stone columns,the calculations of settlement and bearing capacity for this kind of composite foundation are studied,and the behavior of anti-pullout and the calculation of pullout bearing capacity are analyzed. The yield of reinforcing steel bar under the press and the characteristics under the cyclic loading in the anti-pull stone columns are also studied.Failure modes of the stone columns are introduced first. Based on the failure modes,the bearing capacity calculations of single pile and its composite foundation are analyzed. And combined with the practical project,the comparison analysis of the calculation is done. According to the analysis,bearing capacity calculation for composite foundation can use the computing formulas recommended by Technical Specifications for Ground Treatment of Building Foundation (JGJ79-91) and the improved computation formulas based on Brauns' Theory.The settlement is analyzed by using the settlement calculation theory already existed and the pile deformation modulus is researched under the different test conditions. It results in the different pile modulus of deformation that the pile side constraint is different because of the different testing conditions,so the settlement calculation for composite foundation of stone columns must use different computing modes based on the testing conditions. Factors affecting pile-soil stress ratio are discussed and the discussions show that pile-soil stress ratio is not a constant and varies with the change of influential factors.The failure mode and stress configuration of the anti-pull stone column are discussed briefly. And the computing formulas of the pullout bearing capacity are obtained. Based on the formulas and the experiment data,the calculating results compare with the experiment data. The results show that the formulas can meet the need of engineering practice.The mechanism of reinforcing steel bar under the press or pull is researched and the characteristics under the pull-press cyclic loading is studied in composite foundation. It shows that the stress concentrating on the reinforcing steel bar and the increasing stress can be seen with the increasing of cyclic times. Residual strain always exists after unloading without considering the size of pullout force and increases slowly with the cyclic times. The failure characteristics of anti-pullout stone column is very clear. The failure load of the anti-pullout stone column can be obtained specifically.