The Application Of Supporting Techniques For Deep Foundation Pit To Water Conservancy Engineering

Many buildings are laid in deeper underground where foundation pit excavation is needed. But in many cases, there is no sufficient space for side-sloping setting-out outside the foundation pit or side-sloping setting-out can not be carried out if other buildings, underground pipeline or transport roads exist in this space. Therefore, the design and construction of vertical excavation under the protection of supporting structures, namely, supporting technique for deep foundation pit, is the only way to be used. The construction of underground cellars of high-layer and multilayer buildings, underground shopping mall, underground garage and subway station will be confronted with the problem of deep foundation pit. In the field of water conservancy and hydropower engineering, the constructions of hydropower stations, pumping stations for water supply and drainage, navigation locks and sluices are often faced with the problem of deep foundation pit. The problem of this kind will be settled by supporting technique for deep foundation pit. It is necessary to understand the characters of the supporting structures of various types and to choose the suitable scheme for foundation pit support based on its geological conditions and local conditions. The inner forces and deformation of supporting structures can be calculated by classical mechanical method, analytical or numerical method, FEM or a simplified method, so as to determine the size or dimensions of supporting structures. By certain construction method, foundation pit excavation and the constructions of permanent structures will be completed under the protection of the supporting structures.The power house of Xixi (Western Brook) Electric Power Plant of Chaozhou Water Supply Project, Guangdong Province, is an underground structure. The geological composition of its foundation is silt and the maximum dept of its foundation pit is 18 m. In order to meet the requirement of construction, the original design in which the supporting structure was continuous walls plus steel bearing pipes, had to be changed into a new one in which the supporting structure was continuous walls plus reinforced concrete bearing beams of expanded horizontal intervals. Hence, the stability of the foundation pit should be recalculated. The internal forces of the supporting structure were calculated by a simplified and practical method of Beam on Elastic Foundation, and the results show that the substituting scheme can satisfy the requirements for safety. During theconstruction of foundation pit of this power house, confined groundwater of high water head was met, which was not taken into consideration in the original design, thus the stability against floating of the bed of foundation pit was very serious. After comparison, the scheme of the bed strengthening of foundation pit by rotating spouting plus drainage by relief wells was adopted, and the stability against floating was satisfied after calculation. The problem of the potential floating of bed of foundation pit during construction was solved. The problem of the stability of foundation pit was successfully settled by supporting techniques for deep foundation pit, according to the process and results of construction.