Picture 1. The Headrace Tunnel 1# and 2#, Was Successfully Threaded Together

Picture 2.  Group Photo in Site for Celebration

On October 19, 2020, The Headrace Tunnel 1# and 2# (the downstream of the Headrace Branch 1# and the upstream of the Headrace Branch 2#) of CHMC Laos Nam Ngum 4 Hydropower Station, was successfully threaded together.

The control part of the Headrace Tunnel 1# and 2# is 3067 meters in length, and it is the longest control part of the headrace tunnel which have been threaded together. The surrounding rock of the Tunnel is dominated by type IV2 silty slate. The rock is some soft; the joints and fissures are developed; the rock mass is broken, and the stability of surrounding rock is poor. A fault structure is often encountered in the process of penetration, which is easy to cause local collapse and is very difficult to construct.

CHMC Project Department took several measurements to ensure the construction to move ahead in safety, as scheduled and as qualified. The first measurement is: according to the surrounding rock condition, suitable and effective support measures are taken in advance; the construction principle is “short range, weak blasting, strong support, frequent monitoring', as well as a flexible adjustment. The second measurement is: check the excavated tunnel in time to ensure no deviation of the axis of the tunnel. The third measurement is: establish a close communication between the two fore-fields in the last 100 meters, keep each fore-field informed of the construction situation at any time. The control part was successfully threaded together under the scientific management of the Project Department.

The successful threading of the control part of the Headrace Tunnel 1# and 2#, further encouraged the confidence of the Project participants, at the same time, created favorable conditions for concrete construction of the tunnel lining, laid a solid foundation for the scheduled completion of the Project.