7.1　Open channels

7.1.1　The construction of the open channels should not be carried out in rainy seasons or very cold seasons.

7.1.2　Prior to the excavation of the open channels，the dangerous rocks on the side slopes and front slopes shall be removed，and reinforcement，protection as well as construction of the water intercepting ditches above the open channels shall be carried out according to the requirements of the design.

7.1.3　Prior to the excavation of the open channel，the side lines and centerline of the open channel shall be laid out；during construction，they shall be checked at any time.

7.1.4　The excavation of the open channel shall comply with the following requirements:

1　The side slopes of the open channel shall be excavated from the top to the bottom layer by layer，and the excavated layer shall be protected before the next layer is excavated.The heights of the layers shall be determined according to factors such as the geological conditions，the design requirements，and the construction equipment.Excavation by cutting the bottom or vertical overlapping excavation shall be avoided.

2　The actual gradient of the side slope of the open channel shall not be greater than the designed slope gradient.The supporting and retaining structures shall be constructed as designed.

3　The construction shall be organized according to the approved blasting design.Loosening control blasting or smooth blasting should be adopted for the side slopes and front slopes.Blasting mode for caverns shall not be used for the side slopes and front slopes.

4　After blasting，the loose stones shall be removed before the next procedure is carried out.

7.1.5　Prior to open channel excavation，the side slopes shall be inspected and monitored.Reinforcement measures shall be taken if the side slopes are not stable.

7.1.6　If anti-slope drainage is adopted for the open channel，water collecting pits shall be provided and mechanical pumping shall be adopted.

7.1.7　The suppor of the side slopes and front slopes shall be constructed according to Chapter 10 of this code. ygTNlkbVvL/SQc6Ga1tmtdWhY4mmCFASZxaXZcgtVsCPXk+3HCJiZNmp5FSq5pZ+