1, planesupport Composition of the system
In general, the plane support system should be composed of waist beam and horizontalsupportThe horizontal support shall have strong integrity and plane stiffness, so that the force transmission of each part of the support is reliable.
The role of the waist beam is to strengthen the integrity of the retaining pile and transfer the horizontal force to the supporting members. Therefore, the waist beam is required to have larger plane stiffness and be connected with retaining pile reliably.
The function of the column is to ensure the longitudinal stability of the horizontal support and bear the dead weight of the horizontal support and other vertical loads. It requires better stiffness and smaller vertical displacement.
According to the specific situation of the project, the horizontal support can be used to brace, bevel brace and figure eight brace form of plane structure system.
2, planesupportArrangement of system
The number of horizontal support channels to be arranged in the vertical plane of foundation pit should be determined by calculation according to the construction requirements of foundation pit depth and earthwork excavation.
The upper and lower horizontal support axes should be arranged in the same vertical plane. The net vertical distance between adjacent horizontal supports should not be smaller than or equal to3m, should not be less than when using mechanical excavation and transportation4m; The set horizontal support elevation of each layer shall not interfere with the construction of the bottom plate and floor members of the underground structure of the main project.
In general, the horizontal cap beam at the top of retaining pile should be used as the waist beam of the first horizontal support.
3, the setting of the column
The column is the vertical supporting member of the horizontal support system in the pit. The column should be arranged at the intersection of the vertical and horizontal support, and should avoid the location of the main engineering beam, column and load-bearing wall. The spacing of the column should not exceed 15m. The lower end of the column should be supported on a better soil layer, and the length of the soil below the excavation face should meet the requirements of the supporting structure for the bearing capacity and deformation of the column.
The horizontal support of each layer forms a spatial structure through the columns, which strengthens the stiffness of the horizontal support and plays an effective role in controlling the displacement of the support structure. However, the subsidence of the column or the uplift due to the rebound of the soil at the bottom of the pit, as well as the differential settlement between adjacent columns and other factors will lead to secondary stress in the horizontal support, so the column should have enough depth of embedding. Usually, piles should be arranged under the column, and as far as possible combined with the main structure of the engineering pile setting, and the overall connection with the engineering pile, a pile.
4, planesupportSystematic material selection
Structural steel support is usually preferred. For the foundation pit with complex shape or high environmental protection requirements, cast-in-place concrete structure should be used for support.
(1)Steel structure support: In general, it is preferable to use mutually orthogonal and evenly arranged plane brace or brace truss system; For the long foundation pit, unidirectional arrangement of brace system can be adopted, and horizontal brace is set at the four corners of the foundation pit. When the horizontal distance between adjacent supports is large, a figure eight brace should be set at the end of the support. Figure eight support should be symmetrical, the length should not be greater than 9m, and the Angle between the waist beam should be60°.
(2Concrete structure support: the foundation pit with complex plane shape can adopt the plane support system composed of side truss and opposite brace or Angle brace. When large working space is needed in the support plane, the plane support system composed of edge truss, counterbrace truss or diagonal brace truss can be used; For regular square foundation pit, plane support system composed of diagonal truss or inner ring plane support system can be adopted.
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