Scale effects of uplift capacity of circular anchors in dense sand

The scale effects of uplift capacity of circular anchors in dense sand are studied by means of the model tests and finite element method. The pullout tests on the circular anchors with the diameters of 20, 50 and 400 mm as well as the embedment ratios of 2~6 are carried out, where the curves of uplift resistance and displacement and ultimate uplift capacity are obtained. It is seen from the test results that the breakout factor decreases with the increase in anchor diameter under the same embedment ratio, and the phenomenon is more obvious with larger embedment ratio. Numerical analysis for the pullout tests is performed based on the modified Mohr-Coulomb model which can reflect the strain softening of dense sand, and the results are compared with those based on the elastic-perfectly plastic Mohr-Coulomb model. It is shown that the numerical results based on elastic-perfectly plastic model overestimate the uplift capacity of anchors remarkably, while the simulations based on the modified Mohr-Coulomb model can reveal the process of mobilizing soil strength to the peak value, and thus the numerical results agree well with the test ones. The reasons causing the scale effects are the soil strength dependent on stress level and the progressive failure during pullout. The process that the soils surrounding the anchors reach failure step by step becomes more and more obvious with the increase of anchor diameter when the embedment ratio is relatively large.