Study On The Influence Of The Relative Density Of Foundation Soil On Size Effects In Bearing Capacity Test

In 1941, Golder found that the bearing capacity coefficient Nγobtained in bearing capacity model tests decreased with the foundation scales increasing, in other words, it means that the foundation bearing capacity tested is nonlinear with the foundation scale. De Beer defined this phenomenon to scale effect, which is a popular problem in the capacity test. As a result, a safety coefficient much bigger should be applied because Nγin the small scale model test is smaller than that used in the archetype foundation. Therefore, much more money should be used in order to satisfy the safety requirement. Centrifuge model tests turned to be a powerful tool in solving soil engineering problems with the development of centrifuge modeling technology. In centrifuge model test, stresses of archetype could be simulated to research the process of stability, distortion, and destruction of the structures in engineering such as soil architecture, hydraulic and hydroelectric projects, offshore, transportation, exploration etc, testify the designed engineering whether credible and reasonable or not, and provide evidence for other analysis methods.In this paper, the relationship between the scale effect and the density of sand foundation is studied through centrifuge model tests based on the size effect of sand grain ignored at the beginning. Then the scale effect in the bearing capacity tests is rectified according to the results of centrifuge model tests. At last, the scale of the bearing plate in the plate loading tests is rectified in based Design Criterion of Construction Foundation (GB50007-2002) in order to eliminate the influence of the scale effect and the size inconsistence of the bearing plate.As for the scale effect in the bearing capacity test, it is solved using the centrifuge model test based on the ignorance of the size effect of the sand grain. The bound of the foundation width B₀, smaller than which the scale effect would appear, could calculated with relative density of foundation soil (B₀=0.0137Dr). The scale effect would turn smaller and smaller following the foundation expanded, and the effect would be ignored when the foundation width B exceeds B₀. As a result, B₀ could reflect the extent of the scale effect. When the value of B is big, the scale effect is obvious and influences fargoingly; and when the value B is small relatively, the scale effect is faint and influences incomprehensively. At the same time,β(the dependency of the bearing capacity factor on the confining stress level) could calculated with relative density of foundation soil by functionβ=0.0027Dr. Andβcould represent the extent of the scale effect of foundation, in other words, the scale effect increases following the density of sand foundation increasing.As for the plate loading tests of sand foundation, the scale effect does not existed when the bearing plate diameter B is bigger than the bound width B₀ of scale effect based on test results. And when B id smaller than B₀, which means scale effect exists, the bearing capacity of foundation should be rectified based on scale effect.In the plate loading tests, the results could just be rectified based on scale effect of loading plate if the scale effect of foundation does not exist; however, if the foundation scale effect can't be avoided, the test results should be rectified based on the foundation scale effect, and then the rectified results should be rectified again based on the scale effect of loading plate. In the regular dimension range (56⁸0cm) of loading plate diameter in Design Criterion Of Construction Foundation, the scale effect of foundation could be avoided for the loose and a little dense sand foundation; And as for foundation of relatively dense and dense in mid sort sand, Bsp=110cm is chosen as a standard diameter, and the test results using bearing plates of other scales could be calculated based on the standard scale.