1. Before the installation of the steel arch support , check the contour, center line and elevation of the excavation section.
2. The installation of the steel arch support shall ensure that the arch feet on both sides shall be placed on a firm foundation. Before installation, the scum and other sundries at the bottom of the foot should be thoroughly removed. Shotcrete should be used to fill in the underfoot when the elevation of overdug or arch foot is insufficient. The height of the arch foot should be 15 ~ 20cm lower than the bottom line of the upper half section. When the bearing capacity of the surrounding rock at the arch foot is insufficient, steel backing plates and beams or concrete with strength not less than C20 should be added to the direction of the surrounding rock to increase the contact area of the arch foot.
3. The steel arch support shall be installed in sections, and the sections shall be connected to each other according to the design requirements. The connecting plate plane shall be perpendicular to the axis of the steel frame.
4. Longitudinal rebar shall be used to connect the two adjacent trusses of steel frames. The diameter of the rebar shall not be less than 18mm, and the spacing of the rebar shall not be greater than 1.0m.
5. After the steel arch support is erected, correct it to the correct position according to the center line and level, then fix it with positioning bars, and connect it firmly with the adjacent steel frames with longitudinal connecting bars. The steel frame shall be installed perpendicular to the center line of the tunnel, without inclination or distortion. Upper, lower, left and right allowable deviation ±50mm, the inclination of steel frame should be less than 2°.
6. The steel arch support is installed after the initial shotcrete. It should be closely pasted with the surrounding rock or the initial shotcrete as far as possible.
7. The steel arch support shall be erected in strict accordance with the design, the spacing shall meet the design requirements, and the installation position of the arch frame shall be marked with red paint and coded.
