Study On Deformation Control And Construction Techniques Of Big & Deep Foundation Pit By Top-down Construction Method In Strata With Rock-soil Combination

Top down construction method was first introduced in Japan in 1935; it has developed for more than 70 years. Its principle is simple, economic and social benefits, those advantages making the top down construction method has been widely used in dense urban deep excavation; but there are also disadvantages such as higher require of the workers' technical quality, more construction organizations and complex processes, problems in the theoretical calculation and construction practices. Top down construction method was just first used in Qingdao, in consideration of the unique geological structure of soil and rock composition, it is necessary to systematic study the deep foundation operating technique for top down construction method, to smoothly guiding the project, and ensuring construction safety. This study has extremely important theoretical and practical value, and also can provide a reference for future similar projects.Based on the Qingdao's first top down foundation pit construction-Shelter pit excavation project of the East Sea road, this paper analyzed of measured deformation data and the actual construction project site conditions, simulated the differential settlement in construction process by finite element calculation method, and some of the deformation process technology for top down construction and related control measures have been studied. A number of conclusions can be used to guide the construction practice.1) When using top down method to excavate deep foundation pits in Qingdao rock area, because of the shallow depth of bedrock surface, fender post and column pile are embedded in rock, the relative settlement is very small.2) Foundation excavation followed in the "partition, layered, symmetrical, time-limited"principle, in special locations such as the external corner position in the pit, excavates according to the actual situation by the way of "small size, leaping", to reduce lateral deformation of the envelope as much as possible.3) When using top down method to excavate in Qingdao rock area, constructors should pay attention to bedrock fissure water. In the same time of drainage by open canal, recharge groundwater outside the pit to reduce the pit water level drop which may cause deformation of the surrounding environment.4) Strengthen the integration of design and construction, information construction is convenient to adjust the construction process and construction parameters, and has a better control of foundation and the surrounding environment the deformation.