Water sealing and dropping design and comprehensive construction technology of over-deep permanent foundation pit

The common support for deep foundation pits belongs to the temporary support structures, namely when the basement is completed and the earthwork is filled back, the support for the deep foundation pits will be removed. As to the common civil buildings or the municipal buildings, when the underground continuous walls are used as the external structural walls as well as the support of the foundation pits, in common sense, the floor slab will be used as the support of the continuous walls, namely during the period of adopting the external walls of the basement, the calculative span or height is similar to the one of the proper working condition of the deep foundation pits. Besides the above-mentioned cases, the case that the great difference in the calculative span or height exists between the use stage of the foundation pits and the excavation stage, such as the main platform where the lifting stage is located. Therefore, the concept of over-deep permanent foundation pits was put forward.