Process flow:. ①Considering that the tunnel requires 5~10mm gravel for shotcrete, the gravel is designed in 3 grading, with sizes of 5~10mm, 10~20mm, 16~31.5mm, and machine-made sand less than 4mm. The mesh sizes are 4mm (steel mesh screen), 6mm (nylon mesh screen), 12mm (nylon mesh screen), 21mm (nylon mesh …