Technical content of 1
Common ditch, also known as "common ditch", refers to the comprehensive corridor of urban underground pipelines, which is a municipal public facility built under the city to lay municipal public pipelines and carry out unified planning, design, construction and maintenance. By adopting common ditch, all kinds of pipelines can be laid centrally, and urban underground space resources can be comprehensively utilized.
The construction methods of comprehensive pipe trench are mainly divided into cut and cover method and underground excavation method.
Open cut construction methods mainly include: slope excavation construction; Retaining structure of cement-soil mixing pile; Sheet pile wall envelope and SMW construction method. The construction of open-cut pipe gallery can adopt cast-in-place construction method and prefabricated assembly construction method. Cast-in-place construction method can work in a large area, divide the whole project into several construction sections and speed up the construction progress. Prefabrication and assembly construction method requires large-scale prefabrication plant and large-tonnage transportation and hoisting equipment, which has high construction technology requirements and strict requirements for joint construction treatment.
The main construction methods of underground excavation are shield method and pipe jacking method. Shield method and pipe jacking method are both underground excavation construction methods using special machinery to build tunnels. A shaft or foundation pit is built at one end of a certain section of the tunnel, and the machinery is installed in place. Starting from the hole in the wall of a shaft or foundation pit, the machine pushes the tunnel to the design hole of another shaft or foundation pit along the design axis, effectively controlling the ground heave. Shield method and pipe jacking method have the characteristics of high automation, little environmental impact, safe construction, reliable quality and fast construction progress.
2 technical indicators
(1) cut and cover
1) foundation engineering
Before the excavation of the foundation pit (trough) of the common ditch project, the construction scheme should be made according to the type of retaining structure, engineering hydrogeological conditions, construction technology and ground load.
Backfilling of foundation pit shall be carried out after the acceptance of common ditch structure and waterproof engineering. Backfill materials shall meet the design requirements and the relevant provisions of the current national standards. Backfill on both sides of the pipe gallery shall be symmetrical, layered and even. Backfill materials within the range of 1000mm at the top of pipe gallery shall be compacted by manual layers, and large rollers shall not be directly constructed at the top of pipe gallery. Backfilling and tamping of common trench shall meet the design requirements.
The construction and quality acceptance of common ditch foundation shall comply with the relevant provisions of Code for Quality Acceptance of Building Foundation Engineering (GB50202).
2) Cast-in-place structure
Before the common ditch formwork construction, the formwork and support shall be designed according to the structural form, construction technology, equipment and material supply. The strength, rigidity and stability of formwork and support should meet the stress requirements.
Concrete pouring shall be carried out after the formwork and support have passed the inspection. Segregation should be prevented when entering the mold; During continuous casting, the casting height of each layer should meet the requirements of vibrating compaction; When pouring concrete around reserved holes, embedded pipes, embedded parts and water stop, it should be supplemented by manual tamping.
Concrete floors and roofs shall be continuously poured, and no construction joints shall be left. When designing deformation joints, they should be poured in different warehouses according to the deformation joints.
The acceptance of concrete construction quality shall conform to the current national standard "Code for Acceptance of Construction Quality of Concrete Structure Engineering" GB50204.
3) Prefabricated structure
Formwork for prefabricated assembled reinforced concrete members shall be finished steel formwork.
Component stacking area should be flat and compacted, and have good drainage measures. When transporting and hoisting components, the concrete strength should meet the design requirements. When the design has no requirements, it should not be less than 75% of the design strength.
Before installation, the appearance and cracks of precast members should be checked according to the design requirements and the relevant provisions of the current national standard "Code for Quality Acceptance of Concrete Structure Engineering" GB50204. When there is a crack on the component and the width exceeds 0.2mm, it should be identified.
The connection between precast members and cast-in-place members and between precast members shall be constructed according to the design requirements. When the pre-assembled common ditch structure is connected by prestressed tendons or bolts, the bending bearing capacity of flat-fell joints should meet the design requirements.
The material, specification and tightening torque of bolts shall meet the design requirements and the relevant provisions of Code for Design of Steel Structures (GB500 17) and Code for Acceptance of Construction Quality of Steel Structures (GB50205).
(2) Undercut method
1) shielding method
The technical indexes of shield construction shall conform to the relevant provisions of Code for Construction and Acceptance of Shield Tunnels (GB50446).
2) Pipe jacking method
When calculating the construction jacking force, the pipe joint material, the allowable maximum load of the back wall structure of the jacking working well, the jacking equipment capacity, construction technical measures and other factors should be comprehensively considered. The maximum jacking force in construction should be greater than the jacking resistance, but it should not exceed the allowable jacking force of the pipeline or the back wall of the working well.
When a jacking distance is greater than 100m, relay technology should be adopted.
The technical index of pipe jacking method shall conform to the relevant provisions of Code for Construction and Acceptance of Water Supply and Drainage Pipeline Engineering (GB50268).
3 Scope of application
Common ditch is a municipal public project mainly used for unified urban planning, design, construction and maintenance. It is built underground and used for laying municipal public pipelines.
.4 engineering case
The common ditch of Tiananmen Square in Beijing, Tonggou of Zhang Yang Road in Pudong New Area in Shanghai, Common ditch of Guangzhou University Town, Common ditch of Guangfu Road and Cai Yun Road in Kunming, Common ditch of Zhongguancun (West Area), Common ditch of Shanghai World Expo Park, Common ditch of Wuhan Optical Valley, Common ditch around Hengqin New Area in Zhuhai, Common ditch of Shanghai Anting New City and utility tunnel of Shanghai Songjiang New City.
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