The buried depth of the bottom plate is 47.17~65.51m, the thickness of the water-resisting layer is 2.32~40.90m, and the average thickness is 19.14m m. It is mainly composed of brown yellow, grayish yellow and grayish green sandy clay with 0~4 layers of sand. The top of the bottom plate is rich in sand roller blocks and ferromanganese nodules. The clay is stable in distribution, strong in plasticity and good in water isolation.