The commonly used cast-in-place method for construction of underground municipal pipelines in China has many drawbacks. In recent years, the development of large-scale prefabricated concrete culverts has been rapid, and on-site assembly construction is adopted. Applied in projects such as the Shanghai World Expo underground comprehensive pipe gallery, it has the advantages of good quality, short construction period, low cost, and environmental protection. It can be used for both slotting method construction and top pipe method construction, and has great significance for the construction of urban underground comprehensive pipe galleries..

The current construction methods for underground pipelines and comprehensive pipe galleries mainly include cast-in-place and prefabricated assembly. The differences between the two methods are compared as follows:.

The box and arch concrete culverts constructed by on-site pouring method in China have been widely used in railways, transportation, water conservancy engineering, and urban underground municipal comprehensive pipe galleries for many years. The disadvantages of cast-in-place concrete are:.

(1) Only the slotting method can be used for construction, which cannot meet the needs of pipe jacking..

⑵ Long construction time, heavy on-site wet work workload, long concrete curing and reinforcement time, and inability to backfill for a long time after slotting are not conducive to road construction, shortening construction period, and meeting the requirements of fast traffic release in cities..

During on-site production, groundwater has a significant impact on construction. It is necessary to lower the groundwater below the bottom plate elevation before pouring concrete foundations, which increases construction costs and is not conducive to the protection of the ecological environment..

The impermeability performance of concrete produced on site is not as good as that of concrete produced in the factory, which is prone to local leakage and affects the functionality of the pipeline..

The cast-in-place concrete culvert pipe is prone to cracks (such as through cracks on the side walls of the culvert body). Cracks can cause leakage and affect the stress state of the structure; If the environment in which the structure is located has corrosive media, the media can penetrate the structure through cracks, causing corrosion of steel bars, affecting the load-bearing capacity and durability of the structure, and shortening the service life of underground pipelines and comprehensive pipe galleries..

The concrete culvert pipes made on site are divided into sections of a certain length (about 20m), and rubber waterstops are used to connect the sections. The disadvantages are:.

① The interface of rubber waterstop has poor resistance to uneven settlement of the foundation. Under the action of top soil compaction and additional loads, the culvert pipe causes displacement and warping deformation of the culvert pipe interface, resulting in deformation of the waterstop at the culvert pipe interface. Cracks are formed between the concrete and rubber waterstop at the culvert pipe interface, and in severe cases, the waterstop is pulled apart..

② Rubber waterstops have poor pressure resistance. When transporting liquid media, they can only work under low pressure and are generally only used in non pressure pipelines, which are prone to breakdown in pressurized pipelines..

③ The construction quality of the concrete culvert pipe waterstop joint is not easy to ensure, often due to the lack of compaction of the concrete at the waterstop part, hidden leakage channels are left, causing leakage at the culvert pipe joint..

The segmented length of the pipeline produced on site is large, and if the foundation has uneven settlement or is subjected to external loads (such as earthquakes), it is easy to break. Therefore, it is required to improve the longitudinal bearing capacity of the pipeline foundation and increase the longitudinal reinforcement of the culvert pipe..

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The on-site production conditions are poor (as shown in pictures 1 and 2), which affects the quality. In structural calculations, safety should be increased and material usage should be increased..

The overall cost of cast-in-place construction method is roughly equivalent to that of prefabricated assembly construction method..

Domestic report on the comparison between prefabricated construction method and cast-in-place construction method.

(1) The cast-in-place construction method for the underground comprehensive pipe gallery of the Shanghai World Expo《.