Recently, with the continuous deepening of urban underground space development and utilization, underground passages, as important infrastructure connecting urban commercial districts, transportation hubs, and residential areas, play an increasingly important role in alleviating surface traffic pressure, improving urban traffic efficiency, and enhancing urban functions. The excavation and support construction of underground passages is the core link of underground engineering construction, which directly affects construction safety, engineering quality, and the stability of the surrounding environment. Due to the complex underground construction environment, which is greatly affected by geological conditions, surrounding buildings, underground pipelines, and other factors, inadequate support measures can easily lead to safety hazards such as rock collapse and ground subsidence, posing a threat to the safety of construction personnel and the normal operation of surrounding facilities.
The excavation and support construction of underground passages follows the core principle of "support first, excavation later, layered and segmented, and gradual progress". Based on the cross-sectional size, burial depth, geological conditions, and surrounding environment of the underground passage, appropriate excavation and support technology types are selected in a targeted manner to achieve coordinated progress of excavation and support, ensuring the safety and controllability of the construction process. Industry experts suggest that the selection of excavation and support technologies for underground passages should take into account safety, economy, and applicability. Different types of technologies have their specific application scenarios, and construction units need to scientifically select them based on the actual engineering situation to avoid blind construction.
According to the classification of excavation methods, underground tunnel excavation and support technologies are mainly divided into three categories: open excavation support technology, hidden excavation support technology, and cover excavation support technology. Each category of technology includes multiple specific support forms, which are suitable for different engineering scenarios and geological conditions.
The open cut method support technology is a widely used technique in the excavation and support of underground passages, suitable for areas with shallow burial depth (usually less than 10 meters) and no important buildings or underground pipelines around, such as shallow buried underground passages under urban main roads, subway station entrance and exit passages, etc. This technology first excavates the surrounding soil of the underground passage to the design elevation, then carries out support construction, and finally completes the pouring of the main structure of the passage. Its core support forms include slope support, soil nail wall support, row pile support, and steel sheet pile support.
Slope support is the simplest and most economical form of support in open excavation method, suitable for scenarios with good soil quality and shallow excavation depth. By making the excavation slope surface a certain slope and utilizing the stability of the soil itself, support can be achieved. During construction, geotextile and sprayed concrete need to be laid on the slope surface to prevent soil weathering and collapse. Soil nail wall support is suitable for medium strength soil layers such as silty soil and sandy soil. By planting soil nails on the excavation slope and spraying concrete surface layer, the soil and soil nails are connected as a whole to enhance slope stability. It is widely used in the open excavation construction of underground passages. For example, in a certain city's underground pedestrian passage project, soil nail wall support technology was adopted to effectively control soil deformation during excavation and ensure construction safety. Pile support is suitable for scenarios with large excavation depths and surrounding buildings or underground pipelines. By setting up reinforced concrete cast-in-place piles or prefabricated piles around the channel, a continuous support barrier is formed to prevent soil collapse. During construction, anchor rods and cables can be used to enhance the support effect. Steel sheet pile support adopts steel sheet piles driven underground to form a closed support structure, which has the characteristics of convenient construction, short construction period, and recyclability. It is suitable for open excavation projects in soft soil layers and high groundwater levels, and can effectively prevent foundation pit seepage and soil collapse.
The underground excavation support technology is suitable for areas with deep burial, important buildings in the surrounding area, dense underground pipelines, or unsuitable for open excavation construction, such as urban core commercial districts, underground passages in old urban areas, etc. This technology does not require extensive excavation of the ground and only completes channel excavation and support through underground operations, with minimal interference to the surrounding environment. Its core support forms include shield tunneling support, shallow buried excavation support, and pipe jacking support.
Shield tunneling support technology is a highly automated and efficient type of technology in underground excavation, suitable for long-distance and large section underground passage construction, such as urban subway section passages, cross river underground passages, etc. This technology uses a shield tunneling machine to excavate underground. The cutterhead at the front end of the shield tunneling machine cuts the soil, while the pipe segments are assembled at the tail end of the machine to form a channel support structure. The pipe segments are made of reinforced concrete prefabricated parts, which have high strength and good impermeability, and can be directly used as part of the main structure of the channel. The underground passage project of a certain city crossing the river adopts shield tunneling method for construction. The shield tunneling machine accurately excavates under complex geological conditions at the bottom of the river, and the pipe assembly and excavation are carried out synchronously, effectively reducing the impact on river navigation and surrounding environment, and greatly shortening the construction period. The shallow buried excavation method support technology is suitable for underground passages with shallow burial depth and small cross-section, such as underground pedestrian passages, underground pipeline passages, etc. This technology adopts the construction principle of "pipe ahead, strict grouting, short excavation, strong support, fast closure, and frequent measurement". Common support forms include grid arch support, shotcrete support, anchor rod support, etc. During construction, the surrounding rock is first reinforced by advanced small pipe grouting, and then layered and segmented excavation is carried out. Grid arch support is timely erected and shotcrete is sprayed to form a joint support system to control the deformation of the surrounding rock.
The top pipe support technology is suitable for underground passages crossing roads, rivers, buildings, and other scenarios, without the need to excavate the ground. Prefabricated pipe sections are pushed into the ground through top pipe equipment to form a channel structure, and support and excavation are completed synchronously. The commonly used form of support is pipe section self support, combined with grouting reinforcement of surrounding soil to enhance pipe section stability. This technology has high construction accuracy and minimal interference with the surrounding environment, and is widely used in underground passage construction in urban core areas.
The cover excavation method support technology is a hybrid support technology that combines the advantages of open excavation and underground excavation methods. It is suitable for areas with heavy ground traffic and unsuitable for long-term road closures, such as underground passages on urban main roads and transfer passages at subway stations. This technology first lays a cover plate on the ground to maintain normal traffic flow, and then excavates and supports underground passages below the cover plate. According to the different laying times of the cover plate, it is divided into two forms of support: the cover excavation method and the cover excavation method.
The cover excavation method first excavates the foundation pit to the design elevation, lays the cover plate, and then carries out the construction of the main structure of the channel. The support form is similar to the open excavation method, using support structures such as row piles and steel sheet piles; The reverse excavation method involves laying the cover plate first, and then excavating layer by layer from below the cover plate to complete the construction of the main structure of the channel simultaneously. The combination of the support structure and the main structure reduces the amount of support work and shortens the construction period, making it suitable for the construction of large section and deeply buried underground channels. The underground passage project of a certain city's main road adopts the cover excavation reverse method support technology, which successfully completes the excavation and support construction of the underground passage without interrupting ground traffic, minimizing the impact on citizens' travel.
The reporter learned that the technical selection for excavation and support construction of underground passages needs to fully consider factors such as geological conditions, project scale, and surrounding environment, while also conducting monitoring work during the construction process. Before construction, it is necessary to clarify the underground geological conditions and the distribution of surrounding facilities through geological drilling, underground pipeline exploration, and other methods, in order to provide a basis for technical selection; During the construction process, it is necessary to strengthen real-time monitoring of indicators such as surrounding rock deformation, ground settlement, and support structure stress, adjust construction parameters and support measures in a timely manner, and ensure construction safety; After the construction is completed, quality inspection of the supporting structure is required to ensure compliance with design requirements and provide guarantees for the long-term safe operation of the underground passage.
Industry experts remind that the excavation and support construction technology for underground passages is developing towards refinement and intelligence. With the continuous emergence of new support materials and construction equipment, such as high-strength prefabricated pipe segments, intelligent monitoring equipment, and small shield machines, not only has the construction efficiency and support quality been improved, but the construction safety risks have also been reduced. In the future, with the continuous deepening of urban underground space development, more new excavation and support technologies will be applied to underground passage construction. Combined with BIM technology and intelligent control methods, the construction process will be further optimized to reduce interference with the surrounding environment, providing strong support for the high-quality development of urban underground infrastructure and helping to create a more convenient, safe, and efficient urban underground transportation system.
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