Abstract: According to pile foundation, a closed diaphragm wall has a relatively large stiffness. Because of the great stiffness difference between ferroconcrete and soil, under horizontal load, two types of failure form. Their mechanism can be found via numerical emulation and in-situ test. One is rotary failure, which is associated with rigid short piles. The other is flexible failure, which is associated with elastic long piles. Inside certain buried depth of a diaphragm wall, the buried depth of diaphragm wall notably affects the horizontal load-carrying capability of closed diaphragm wall foundation. Under the same geological condition, when the buried depth of diaphragm wall exceeds 30 m, the buried depth does not notably control the horizontal load-carrying capability of the foundation.