Box culverts in small-scale urban utility tunnel areas are an innovative form of urban infrastructure construction, specifically referring to the underground tunnel-like structural units carefully designed and constructed to meet the unique needs of small cities or specific areas within a city. Such box culverts are characterized by their relatively small cross-sectional dimensions and flexible length specifications, and are mainly manufactured using precast concrete technology. Their core function is to integrate, accommodate, and effectively protect various crucial municipal pipeline facilities in the city, such as water supply systems, drainage systems, power cables, communication optical cables, and gas pipelines.

This article will take you to understand the structural design and installation of small

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1. Structural Design and Material Selection of Small Box Culverts

1.1 Analysis of Structural Forms and Applicable Scenarios

In the design of box culverts in small-scale urban utility tunnel areas, the common structural forms are mainly rectangular and circular. These two forms each have unique characteristics and applicable scenarios. Their internal space layout is adaptable and flexible, allowing efficient utilization of underground space and facilitating the installation, arrangement, and maintenance of various pipelines of different types and sizes. In narrow urban areas or densely populated urban centers with extensive pipe networks, the advantages of rectangular box culverts are more prominent. They can effectively fit into the space beneath the existing roads and achieve seamless docking with other underground structures such as subway tunnels and drainage facilities. Due to their uniform stress distribution around the body, they possess good compressive performance and stability, and are particularly suitable for complex geological conditions or situations where greater external pressure needs to be withstood, such as quicksand strata, areas with high groundwater levels, and regions with frequent seismic activities. Furthermore, the circular structure has less impact on water flow, which improves the smooth operation of the drainage system and reduces the safety hazards caused by water erosion.

1.2 Research on Material Properties 

In terms of material selection for small box culvert structures, reinforced concrete and prestressed concrete have become the mainstream choices due to their excellent mechanical properties, construction convenience, and cost-effectiveness. Composed of high-strength steel and reinforced concrete, making them strong enough to handle loads, including self-weight, pipeline weight, soil pressure, and accidental loads. Meanwhile, through reasonable proportioning and anti-corrosion measures, their durability and resistance to environmental erosion can be improved. On this basis, structural strength and stability are further improved. By applying prestress in advance to offset most of the tensile stress that may occur during the use process, the possibility of crack occurrence is reduced, the service life of the box culvert is extended, thinner wall thicknesses and larger spans can be designed, saving material costs while enhancing the integrity and aesthetics of the structure. With the progress of science and technology and the improvement of environmental protection requirements, new composite materials (such as GFRP and CFRP) have emerged and have been tried and applied in specific small box culvert projects. These new materials not only have the characteristics of being lightweight, high-strength, and corrosion-resistant, but also help to reduce the impact of construction on the surrounding environment and lower maintenance costs, aligning with the concept of sustainable development. 

1.3 Design Principles and Key Technical Indicators

Ensure that the box culvert can safely and stably bear loads from all directions under normal operating conditions, including but not limited to self-weight, soil pressure, pipeline load, traffic load, and other sudden loads. Designers must accurately calculate and reserve sufficient safety factors based on actual working conditions.

Select materials with strong durability and good anti-corrosion performance, and incorporate detailed structural design details, such as setting reasonable waterproof layers, strengthening joint treatment, and using high-quality sealing materials, to minimize the impact of water penetration on the box culvert structure and extend the service life of the facilities. In addition to the design of the structure, a comprehensive waterproof and anti-seepage system should also be considered to ensure that there is no leakage on the inner and outer walls of the box culvert, guarantee the normal operation of the pipelines, and avoid adverse effects on the surrounding soil environment. During the design phase, consider the future inspection and replacement needs of the pipelines, provide sufficient inspection ports and passages, and simplify the internal structure to make daily maintenance and emergency repair work more convenient and efficient.

2. In-depth Analysis of On-site Installation Technology of Small Box Culverts

2.1 Selection of Installation Methods

For situations where the geological conditions permit and the impact on the surrounding environment is relatively small, the precast box culvert units are gradually pushed forward according to the design requirements by pre-digging guide grooves on the ground or underground. This method has a fast construction speed and minimal impact on traffic and residents' lives, but requires precise control of the pushing speed and direction to avoid damage to the surrounding structures.

When the engineering conditions are complex or the box culvert size is large, excavation is usually adopted for installation. First, the foundation pit is excavated, and then the precast box culvert components are hoisted to their predetermined positions and spliced and fixed. Although the excavation method has a relatively large impact on the surrounding environment, it can adapt to various complex geological conditions and construction requirements and has high flexibility.

2.2 Installation Process and Key Steps

Operation Process of the Direct Pushing Method:

Accurately excavate the guide grooves according to the design drawings and ensure their straightness and flatness. Pre-assemble each part of the box culvert in the designated area, and complete the installation of the internal pipelines and external waterproof treatment. Use professional equipment to push the box culvert into the guide grooves and monitor its pushing speed and direction in real time. Make fine adjustments and corrections when necessary. Ensure the connection of adjacent box culvert sections is tight and leak-free, and implement necessary reinforcement measures for the connecting parts. 

Operation Process of the Excavation Method:

Excavate the foundation pit according to the design requirements, and take effective temporary support measures such as herringbone supports, screw pile supports, or precast concrete supports simultaneously. Use cranes or other lifting equipment to hoist the precast box culverts into the foundation pit section by section, accurately position them, and temporarily fix them. Complete the welding or bolting of the interface between the box culverts and the internal and external waterproof treatment. In the end, the box culverts are installed and pass the acceptance inspection, carry out the backfilling operation of the foundation pit, and do a good job in restoring the bearing capacity of the foundation and ensuring its stability.

2.3 Support Technologies during the Installation Process

Herringbone Support Method: This method uses steel-structured Herringbone brackets as temporary support structures, which are simple to use and relatively low in cost. The advantages include fast construction speed and convenient flexible adjustment. The drawbacks include a limited depth of the foundation pit and relatively high requirements for geological conditions, and it is not applicable to sites with soft soil or high groundwater levels.

Screw Pile Support Method: Use screw drills to drive into the soil layer to form screw piles to provide stable and reliable temporary support. This method is suitable for various soil conditions, especially having a good effect on sandy soil layers. The advantages are significant support effect and high construction efficiency, but the cost is relatively high and it has a strong dependence on equipment.

Precast Concrete Support Method: Precast concrete support members such as I-beams and H beams have the characteristics of high strength and high rigidity, which can effectively prevent the deformation and collapse of the foundation pit. The advantages are strong stability, durability, and reliability. However, the transportation and installation are relatively complex, the construction period is longer, and the one-time investment is relatively large.

The in-depth research on the construction technology of small box culverts in urban utility tunnel areas is of far-reaching significance for improving the utilization efficiency of urban underground space resources, optimizing the layout of municipal facilities, and ensuring the normal operation of urban functions. In the future, with continuous technological innovation and the accumulation of practical experience, the construction technology of small box culverts will move towards a more green, intelligent, and efficient sustainable development direction, further promoting urban modernization construction and high-quality development.