It not only significantly improves the construction conditions of underground engineering, but also greatly reduces the construction period and cost of support structure installation, demolition, earth excavation and main structure construction.

Compared with conventional support methods, this support technology has the characteristics of low cost, short construction period and easy quality control, which greatly reduces energy consumption and construction waste, and has high social, economic and environmental benefits.

When the prestressed precast pile is used in the supporting structure, attention should be paid to prevent the brittle failure of the prestressed precast pile and ensure the construction quality of the joint.

This technology is a new technology which is relatively economical and has the advantages of cast-in-situ underground wall and precast underground wall.

Tool type combined internal support: (1) the span of standard combined support members is 8m, 9m, 12M, etc; (2) the height of vertical members is 3M, 4m, 5m, etc; (3) The slenderness ratio of compression rod shall not be greater than 150, and the slenderness ratio of tension rod shall not be greater than 200; (4) The number of internal force monitoring of members shall not be less than 15% of the total number of members; (5) The purlin members are 1.5m, 3M, 6m, 9m and 12m.

When the temperature difference is large, the influence of temperature stress should be considered.

It can be used in various geological conditions and complex surrounding environment.

When the precast pile is used as the foundation pit support structure, the conventional precast pile construction methods, such as static pressure or hammering method, can also be used to dismantle the cement soil mixing pile, TRD mixing wall or CSM double wheel milling mixing wall to form a continuous cement soil composite support structure.

After the groove is formed, the precast components are inserted, and the cast-in-place concrete is used between the components to connect them into a complete wall.

This technology can provide open construction space and make the excavation, soil transportation and underground structure construction convenient.

Prestressed fish web beam support: (1) the verticality of section steel column shall be controlled within 1 / 200; The section steel column and supporting beam bracket shall be connected with high-strength bolts; (2) During the construction of purlin, the flatness error of corbel shall be controlled within 2mm and shall not sag.

The flatness shall be checked with pull rope, long guiding ruler or steel ruler.

Prestressed fish web beam support is applicable to the foundation pits in areas with small temperature difference.

Main reference standards: Code for design of steel structures (GB50017) and technical code for building foundation pit support (jgj120).

This technology has the advantages of fast construction speed, various support forms, mature calculation theory, disassembly and reuse, saving investment and so on.

04 project case precast diaphragm wall technology has been successfully applied to Shanghai construction engineering activity center, Tomorrow Square, Da’an City single built underground garage, Ruijin Hospital single built underground garage, East China hospital parking garage and other projects..

03 scope of application: Precast diaphragm wall is generally only applicable to foundation pit within 9m, subway station and foundation pit engineering with complex surrounding environment; Prestressed fish web beam support is applicable to the foundation pits of subway stations, underground pipe trenches and various construction projects in municipal engineering.

At present, the more mature cast support structures in the market include: precast pile, precast diaphragm wall structure, prestressed fish web beam support structure, tool combined internal support, etc.

The precast underground continuous wall technology is that after the groove is formed according to the conventional construction method, the precast components such as precast wall section, precast pile, section steel or steel pipe are inserted into the mud, and then the self setting mud is replaced into the wall protection mud for the groove, or the self setting mud is directly inserted into the precast components, and the solidified body of the self setting mud is used to fill the gap behind the wall and prevent water seepage between the joints between the components to form the underground continuous wall.

The overall stiffness and stability of the support system are high.

The underground wall constructed by precast diaphragm wall technology has smooth surface, good wall quality and high strength, and can avoid making reinforcement cage, pouring concrete and treating waste slurry on site.

It mainly uses the characteristics of combined steel structure components, such as flexible and variable section, convenient processing and wide applicability.

01 technical content the cast support structure takes the formed precast components as the main body and is assembled into the support structure on site through various technical means.

In recent years, based on the conventional precast diaphragm wall technology, a new type of precast diaphragm wall has emerged, that is, instead of using expensive self setting slurry, the conventional slurry is still used to protect the wall into a groove.

If there is any error, it shall be corrected and fixed by welding after correction; (3) The supporting beam in the whole foundation pit must be horizontal, and the supporting beam must be able to bear the supporting self weight erected above it and other loads from the superstructure; (4) The removal of prestressed fish web beam support is the reverse order of installation.

The tool type combined internal support is suitable for deep and large foundation pits with dense surrounding buildings, narrow construction site, complex geotechnical conditions or soft foundation.

Tool type combined internal support technology is an internal support structure system developed on the basis of concrete internal support technology.

02 technical index precast diaphragm wall: (1) generally, the thickness of precast wall section is about 20mm less than that of grooving machine grab, and the commonly used wall thickness is 580mm and 780mm, which is generally suitable for foundation pit within 9m; (2) According to the capacity of transportation and lifting equipment, the road on the construction site and the conditions of stacking yard, the length of framing and precast parts shall be reasonably determined, and the width of wall framing shall meet the requirements of grooving stability; (3) In the sequence of grooving, the L-shaped groove section should be constructed first, and then the straight groove section should be constructed; (4) Adjacent groove sections shall be continuously grooved, and cast-in-situ joints shall be adopted for joints between frames.

Lifting Foot Anchor

Prestressed fishweb beam support technology consists of fishweb beam (high-strength and low relaxation steel strand as the upper chord member, H-shaped steel as the stress beam, composed of H-shaped steel support beams with different lengths), butt brace, corner brace, column, cross beam, pull rod, triangular joint, preloading jacking device and other standard components, which are combined and prestressed to form plane prestressed support system and three-dimensional structure system.