Subway construction is mostly carried out in urban central areas, involving deep foundation pit excavation, underground tunnel construction and station structure construction, with narrow construction space, complex surrounding environment (close to existing buildings, underground pipelines and traffic lines), high groundwater level and large lateral soil pressure. As the core temporary load-bearing component in subway construction, steel props not only need to bear the weight of concrete, formwork and construction personnel, but also need to resist lateral soil pressure, water pressure and structural deformation, and even bear the impact of train operation vibration in some scenarios. Therefore, compared with ordinary building construction, subway construction has more special and strict requirements for steel props, which must be strictly implemented in accordance with relevant standards and engineering actual needs.
First of all, there are special requirements for the material performance of steel props in subway construction. Due to the complex stress state of steel props in subway construction, they need to have high strength, good toughness, excellent welding performance and low-temperature resistance. The main material of steel props is usually high-strength low-alloy steel such as Q355, and some heavy-load scenarios even use higher-strength steel materials. The yield strength of the steel should not be less than 355MPa, and the tensile strength should not be less than 470MPa, which can ensure that the steel props have sufficient load-bearing capacity and anti-deformation ability under large axial pressure and lateral force. At the same time, the steel should have good low-temperature toughness to adapt to the construction environment of cold regions, avoiding brittle fracture under low-temperature conditions. In addition, the steel material must pass strict quality inspection, and the chemical composition and mechanical properties must meet the requirements of national standards such as GB/T 1591-2018, and relevant inspection reports must be provided to ensure the reliability of the material. For steel props used in subway projects, the material must also have good fatigue resistance to withstand the cyclic vibration generated by subway construction and subsequent train operation.
Secondly, the structural design of steel props in subway construction has special requirements, focusing on stability, adjustability and connection reliability. The structural type of steel props for subway construction is mainly telescopic thread type and pin type, and disk buckle type steel props are also widely used in large-span foundation pit support. The cross-sectional shape is mainly circular, because the circular cross-section has equal moment of inertia in all directions, excellent compression stability and bending stiffness, which can effectively prevent the support from buckling under pressure. The tube diameter and wall thickness of steel props are significantly larger than those used in ordinary building construction: the common outer tube diameter is 609mm, 800mm, etc., and the wall thickness is not less than 16mm, such as the common specification φ800×16, which can ensure sufficient structural strength and stability under heavy load conditions. The adjustable range of steel props should be flexibly designed according to the depth of the foundation pit and the height of the tunnel, and the adjustment accuracy should be controlled within 1-3mm to meet the precise control requirements of subway construction for structural elevation. The locking mechanism must be reinforced, and the thread engagement length should not be less than 8 buckles for thread-locked props to avoid loosening under vibration. For pin-locked props, the pin should be made of high-strength alloy steel, and the insertion depth should be sufficient to ensure reliable connection. In addition, the connection between steel props and steel purlins, bases and top plates should adopt flange connection or high-strength bolt connection, and the welding quality should be strictly controlled to avoid welding defects such as cracks and incomplete penetration, ensuring that the force is evenly transmitted between components.
Thirdly, the load-bearing capacity requirements of steel props in subway construction are more stringent, and they need to have sufficient safety reserves. Subway deep foundation pit excavation will break the original stress balance of the stratum, and the lateral soil pressure and water pressure acting on the retaining structure will be transmitted to the steel props, requiring the steel props to have strong axial compression capacity and lateral anti-deformation capacity. The rated load-bearing capacity of steel props for subway construction is generally not less than 100kN, and heavy-duty steel props can reach 200kN-300kN to meet the load requirements of deep foundation pit and large-span tunnel support. In addition, steel props need to bear dynamic loads such as construction vibration and train operation vibration, so the fatigue resistance of the props must be strictly tested to ensure that they will not be damaged due to fatigue under long-term cyclic loads. The design of steel props should also consider the impact of load redistribution, and set up a reasonable number of props and spacing to ensure uniform load distribution. The spacing of steel props is usually 1.5m-2.5m, and the specific spacing is determined according to the calculation of soil pressure and load-bearing capacity. At the same time, active prestress must be applied to the steel props after installation, which is usually 50% to 70% of the design axial force, so as to pre-offset part of the deformation of the retaining structure and reduce the actual displacement during foundation pit excavation.
Fourthly, the anti-corrosion performance requirements of steel props in subway construction are extremely high due to the harsh environmental conditions. Subway construction is mostly carried out in underground or semi-underground environments, with high humidity (relative humidity up to 90%), high groundwater level, and even corrosive media such as salt fog (coastal areas) and stray current, which are easy to cause corrosion of steel props. Corrosion will reduce the cross-sectional area and load-bearing capacity of steel props, and even lead to structural failure in severe cases. Therefore, steel props for subway construction must adopt high-standard anti-corrosion treatment. The preferred anti-corrosion method is hot-dip galvanizing, and the thickness of the zinc layer should not be less than 80 microns, which can form a dense protective layer to effectively isolate corrosive media. For some special scenarios with strong corrosion, a double anti-corrosion treatment of hot-dip galvanizing plus epoxy spraying is adopted, and the total thickness of the anti-corrosion layer is not less than 150 microns. The anti-corrosion treatment must comply with the requirements of GB/T 2518-2019 and ISO 1461 standards, and the neutral salt spray test time should not be less than 1000 hours to ensure that the anti-corrosion life of steel props is not less than 15 years. In addition, regular anti-corrosion inspection and maintenance should be carried out during the use of steel props, and the damaged anti-corrosion layer should be repaired in time to avoid corrosion expansion.
Fifthly, the installation and construction of steel props in subway construction have strict special requirements, focusing on standardization, precision and safety. The installation of steel props must follow the principle of "support first, excavation later, layered excavation and layered support" to avoid excessive deformation of the foundation pit caused by premature excavation without support. Before installation, the installation position, spacing and elevation of steel props must be accurately positioned according to the design drawings, and the error should not exceed ±5mm. The steel props must be installed vertically, and the verticality deviation should not exceed 1/1500 of the prop length to ensure uniform stress. The base of the prop must be placed on a solid concrete cushion or steel plate to avoid uneven settlement. For steel props used in foundation pit support, horizontal bracings and diagonal bracings should be installed at intervals of 1.5m-2.0m to form an integral support system, enhancing the overall stability and resistance to horizontal loads. The installation of steel props must be operated by professional personnel who have received special training and are familiar with subway construction specifications. During the installation process, personal protective equipment must be worn, and construction must not be carried out in harsh weather such as strong winds and heavy rains. In addition, the disassembly of steel props must follow the specified sequence, and can only be disassembled after the lower structure (such as the foundation slab) is poured and reaches the design strength, so as to avoid stress sudden release leading to structural deformation.
Finally, steel props in subway construction must be equipped with a complete monitoring system to realize real-time dynamic monitoring. The stress state of steel props in subway construction changes dynamically with the progress of foundation pit excavation, stratum creep and temperature changes, so real-time monitoring of the axial force, deformation and displacement of steel props is essential. Each main steel prop should be equipped with an axial force gauge, which can continuously transmit monitoring data to the control center. The monitoring frequency should be not less than once a day during normal construction, and the monitoring frequency should be increased to once every 2-4 hours during key construction links such as deep foundation pit excavation. When the monitoring data shows that the axial force or deformation exceeds the early warning value, construction should be stopped immediately, and measures such as adjusting the prestress or adding steel props should be taken to ensure safety. For large-scale subway projects, an axial force servo system can be adopted, which can automatically drive the hydraulic pump station to dynamically adjust the axial force of the support according to the preset threshold, realizing intelligent closed-loop control and controlling the deformation within the millimeter-level precision. The monitoring data should be recorded and sorted out in detail to provide a basis for project acceptance and subsequent maintenance.
It should be noted that the special requirements of steel props in subway construction must comply with relevant national and industry standards, such as GB 50157-2013 《Code for Design of Metro》, GB/T 50299-2018 《Standard for Construction Quality Acceptance of Metro Engineering》 and JGJ130-2011 《Technical Specification for Steel Pipe Scaffold and Formwork Support in Construction》. For international subway projects, relevant international standards such as EN 1065 and ASTM A123 should be followed. In addition, steel props for subway construction must pass strict factory inspection and on-site acceptance, including material inspection, structural size inspection, load-bearing performance test and anti-corrosion performance test, and only products that pass the inspection can be put into use. Customized steel props for special subway scenarios must be designed and produced by professional manufacturers with relevant qualifications, and the design plan must be reviewed and confirmed by the design unit to ensure that they meet the special requirements of subway construction.
References
1. GB/T 7714 Format
China Railway Tunnel Bureau Group Co., Ltd. Special Requirements for Steel Props in Subway Construction[EB/OL]. [2026-04-17].
2. MLA Format
American Galvanizers Association. "Special Performance Requirements of Steel Props for Subway and Tunnel Construction." American Galvanizers Association, 2026. Accessed 17 Apr. 2026.
3. APA Format
Xinfa Yijian Engineering Co., Ltd. (2026). Technical Requirements and Quality Control of Steel Props for Subway Deep Foundation Pit Construction.