1, pro-course and anti-course
The construction methods of foundation pit engineering are usually divided into two types: the forward construction and the reverse construction. In foundation pit engineering, earthwork excavation is carried out after slope excavation or foundation pit supporting structure is set up, and underground structure construction is carried out layer by layer from bottom to bottom by laying underground structure foundation plate, which is called forward construction. Using uni-axial, step by step down on the underground structure construction, the construction of underground continuous wall around the foundation pit or first row pile as underground structure walls or supporting structure of foundation pit engineering, at the same time in the middle of the pit according to the need to play a supporting column and bearing pile, vertical bearing system of underground structures during construction, and then start top-down construction of the underground structure from the ground floor, The structural beam plate is used as the horizontal support of the support structure, and then a layer of earthwork is dug from top to bottom, that is, a layer of underground structure beam plate is poured until the bottom sealing. At the same time, since the ground floor structure has been completed, when conditions are available, the upper structure can be constructed layer by layer at the same time, until the project is completed. This kind of construction method which uses the whole or part of the main permanent structure as the supporting structure and alternates the underground structure and the foundation pit excavation from top to bottom is called the reverse method.
2, foundation pit supporting structure and underground main structure-The body is changed
In the design of foundation pit engineering, the integration design of foundation pit supporting structure and underground structure is an important characteristic of reverse construction. Under normal circumstances, the supporting structure in underground structure after the construction completion, the demolition, uni-axial structure integration design, supporting structure in the supporting role of underground structures during construction, and in normal use of underground structure, also as part of the structure of wall body, namely the wall with the underground structure lining wall two wall one, common as enclosure wall of underground structures. Therefore, when the reverse construction method is adopted, the supporting structure mostly adopts the diaphragm wall structure as the outer wall of the underground structure at the same time, which is also called the integration design of the supporting structure and the underground main structure. This combination can reduce the thickness of the exterior wall of the basement, realize the design of foundation pit retaining structure for building energy saving and sustainable development, and has great social and economic benefits.
3, shorten the overall construction period
One of the characteristics of the reverse method is that it can shorten the construction time, especially under the conditions of simultaneous construction. The comparison of the construction time between the reverse method and the forward method is shown in the figure.
4Control the deformation of the surrounding ground to ensure environmental safety
Because THE DESIGN METHOD OF combining SUPPORTING STRUCTURE and underground main structure CAN be adopted IN the design of foundation pit, without setting temporary support and eliminating the construction condition of demolition and bracing, it is very powerful to control the deformation of supporting structure. In addition, as the horizontal support system of the supporting structure, the structural floor has large supporting stiffness, high retaining safety, small deformation of the supporting structure and little impact on the surrounding environment, which is very advantageous when the environmental protection requirements are strict.
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