In the construction process of tunnels and underground projects, initial support is a key link to ensure the safety and stable progress of the project. It not only provides safety for subsequent construction, but also directly affects the quality and progress of the entire project. This article will discuss in detail the general process flow of initial support construction and the importance of each step.

　　I. Initial spraying of concrete after excavation

　　After the excavation of the tunnel is completed, the first step is to carry out the initial spraying of concrete. This link aims to quickly close the rock surface, prevent the loosening of the surrounding rock and soil erosion, and provide a stable working surface for subsequent support work. Initial spraying of concrete usually adopts wet spraying to ensure the density and strength of the concrete, thereby effectively resisting the initial stress release of the surrounding rock.

　　II. System support construction

　　System support construction is the core link of initial support, mainly including the installation of anchor rods, steel mesh and steel frame. This process ensures the safety of the tunnel in the subsequent construction process by enhancing the stability of the surrounding rock.

　　1. Anchor construction: Anchors penetrate deep into the rock layer to tightly combine the surrounding rock with the support structure, thereby improving the self-stabilizing ability of the rock mass. The arrangement of anchors should be carried out according to geological conditions and design requirements to ensure that they can effectively resist the deformation of the surrounding rock.

　　2. Laying of steel mesh: The laying of steel mesh can enhance the crack resistance of shotcrete and improve the integrity of the support structure. Combined with anchors and steel frames, the steel mesh can form a complete support system to effectively control the displacement of the surrounding rock.

　　3. Steel frame installation: As the skeleton of the support structure, the steel frame can provide rigidity and support. Especially in areas with complex geological conditions and poor surrounding rock stability, the installation of the steel frame is particularly important.

　　III. Re-spraying concrete to the designed thickness

　　After completing the system support construction, re-spraying concrete is required to achieve the support thickness required by the design. This link can not only further enhance the strength of the support structure, but also ensure the integrity and waterproof performance of the support structure, providing guarantee for the long-term stable operation of the tunnel.

　　Key points:

　　Ensure that the concrete is sprayed evenly to avoid weak points.

　　The thickness of the re-sprayed concrete should be strictly controlled according to the design specifications to ensure the long-term stability of the tunnel.

　　The initial support construction is a key step in the tunnel project. It builds the "first line of defense" for tunnel safety through a series of processes such as initial spraying of concrete after excavation, system support construction (including the installation of anchor rods, steel mesh, and steel frames), and re-spraying of concrete to the designed thickness. Each link needs to be carefully designed and constructed to ensure the safety and quality of the entire project. Through scientific and reasonable initial support construction, the deformation of the surrounding rock can be effectively controlled, creating favorable conditions for subsequent construction and ensuring the smooth progress of the tunnel project.