Experimental study on multi-bench retaining foundation pit

In deep excavations with a large area of soft soil, the multi-bench retaining method, which has a short construction period and doesn’t need any horizontal reinforced concrete struts, can be used to replace the method with reinforced concrete struts. This method has been used in some regions of China. Because of the lack of researches on the multi-bench retaining method, a serious of model tests are designed to learn its work and failure mechanism. The main parameters, width of the bench between retaining piles B and length of the second retaining pile L₂, are studied. The test results show that the multi-bench retaining structure has three kinds of failure modes, the overall overturning failure, the mutual-effect failure and the separate failure, according to different widths of the bench between retaining piles. The main differences of these failure mechanisms are the range of the slip surface and the stress condition of the soil between retaining piles. As the width of the bench increases, the deformation and moment of the retaining piles decease and have better stability. The second retaining pile will become the main retaining structure, which means that the second retaining pile bears a larger moment than the first one, with a long second retaining pile. The increase of L₂ can also decrease the displacement of the first retaining pile and improve the stability.