关键词: 上拔扩底基础, 黄土地基, 荷载位移规律, 抗拔承载力, 承载特性的差异性

Abstract: The uplift bearing capacity of spread footing can be obtained through the footing uplift static loading test. At present, the load-displacement curves at the top of footing are usually used as the basis in this process. However, the deformation and failure behaviors of the soil around footing are ignored frequently, which often occurred in footing projects. Aiming at this problem, the difference of the uplift resistance characteristics between the spread footing and the foundation soil are studied. The uplift static loading tests of nine full-size spread footings are carried out. And the load-displacement curves at the top of footing and the ground surface are obtained. The comparative studies are carried out through analyzing the changing features of the load-displacement curves and the values of the uplift bearing capacity. The results show that both the load-displacement curves at the top of footing and the ground surface vary gradually. Under the same load, the displacement at the ground surface is less than that at the top of footing. And the difference between them is most significant at the elastic stage. Moreover, the values of the elastic limit load QL1 obtained from the curves at the two positions show the obvious difference. With the transition from the initial straight line to the final curve, the difference will decrease gradually. Finally, they get the same values of the plastic limit load QL2. Based on the analysis of the failure behavior of spread footing, the incompatible deformation between the footings and the ground soil is regarded as the main reason for this discrepancy. At the beginning of the tests, the footing displacement value is the sum of the soil compression quantity and the pulling out amount of the footing, and when the soil upon the enlarged head of the footing is compacted completely, the footing together the soil form a whole and the displacements for the footing and the ground soil tend to coordinate.

Key words: uplift spread footing, loess foundation, load-displacement law, uplift bearing capacity, difference of uplift resistance characteristics