5.4　Waterproof and Drainage of Open-pit Mine

5.4.1　Open pit threatened by flood shall be provided with ground flood control project.

5.4.2　When groundwater poses severe threats to the safety and normal production of open pit，water control measures such as drainage or interception should be taken.

5.4.3　Water drainage method for open pit shall meet the following requirements:

1　Free drainage method shall be taken for sidehill open pit.

2　The water drainage methods taken for deep open pit is as follows:

1）For the open pit with small catchment area and small underground water inflow，the pit bottom central drainage method may be adopted.

2）When there is large catchment area and large underground water inflow，shaft drainage method may be taken.

3）When catchment area，underground water inflow and exploitation depth are all large，sublevel relay or shaft sublevel drainage method may be adopted.

4）When the application of single drainage method is unreasonable in economy and infeasible in technology，the combined drainage method may be adopted.

5.4.4　Allowed flooding time for open pit may be determined based on the number of benches mined at the same time.Allowed flooding time should be 1d to 7d；when shaft drainage method is adopted，the allowed flooding time should be 1d-5d.