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7.3.1 The construction of the tunnel portal sections should not be carried out in rainy seasons or very cold seasons.
7.3.2 Before the construction of the tunnel portal section is started，the treatment of the surface water above the tunnel shall comply with the following requirements:
1 The drainage system of the side slopes and front slopes above the tunnel should be completed before the excavation of the side slopes and front slopes is started and the rainy season comes.
2 Water seepage prevention shall be carried out for the side slopes and front slopes of the tunnel portal according to the site terrain conditions.The slope surfaces should be covered with shotcrete or stones.The slope tops should be greened.
3 The streams or drainage ditches on top of the tunnel should be paved with mortar rubbles or concrete.
4 The pits at the ground surface above the tunnel portal shall be filled and water seepage prevention shall be carried out.
7.3.3 When the tunnel portal is located in weak，loose or accumulated strata，reinforcement shall be taken before excavation.Measures such as pipe roof，grouting，jet grouting，or well point dewatering may be taken before excavation，depending on the geological conditions and the groundwater seepage.The reinforcement quality shall comply with relevant current national standards and the design requirements.
7.3.4 The arrangement of the construction of the tunnel portal section shall comply with the following requirements:
1 Before the construction of the tunnel portal section is started，the stability of the mountain slopes above the side slopes and front slopes shall be checked and the dangerous rocks shall be removed.
2 During the construction of the tunnel portal section，uninterrupted monitoring and protection shall be implemented.
3 The protection of the side slopes and front slopes of the tunnel portal section shall comply with the design requirements，as well as relevant requirements in terms of environmental protection and water and soil conservation.
4 When the tunnel portal section is excavated to the designed elevation，the drainage facilities shall be costructed，and the construction of the drainage facilities shall be coordinated with that of the ground surface drainage system.