Recently, the "Shuiyuan" (Water Source), the smallest hard rock tunnel boring machine in China built by CRCHI (China Railway Construction Heavy Industry) in collaboration with China Railway 18th Bureau Group, broke through the rock, marking the successful completion of the Mabai branch water conveyance tunnel of the Shiyan City Central Urban Area Water Resources Allocation Project and laying the foundation for the smooth water supply of the project.

On-site breakthrough of the "Shuiyuan" TBM

As Shiyan City's No. 1 livelihood project, the Shiyan City Central Urban Area Water Resources Allocation Project takes the Pankou Reservoir in Zhushan as its water source and builds a new water diversion tunnel to the Majiahe Reservoir, with a total diversion route of more than 70 kilometers. Among these, the construction tasks of the 15.367-kilometer exit section of Tunnel No. 5 and the 4.155-kilometer branch line from Majiahe to the Bai'erhe Reservoir used two tunnel boring machines (TBMs), the "Wudang" and the "Shuiyuan," developed by CRCHI for simultaneous construction.

The Mabai branch water diversion tunnel has a total length of 4,155 meters. To avoid the impact of the traditional "one-way excavation drill-and-blast process" on the surrounding environment, the builders, based on actual conditions, innovatively manufactured the "Shuiyuan" TBM to perform "minor surgery" — the first attempt in a domestic tunnel to use an ultra-small-diameter tunnel boring machine.

As the smallest hard rock tunnel boring machine in China, this TBM is about 60 meters long with an excavation diameter of only 2.5 meters. It is equipped with an intelligent automatic excavation function, and the operator can remotely control the entire machine from outside the tunnel. The successful application of this equipment has greatly promoted the development of mechanized, automated and intelligent construction of small-section tunnels.

The "Shuiyuan" TBM

The "Shuiyuan" TBM arrived at the project construction site on September 15, 2021, and it took only more than 10 days to complete the TBM assembly and begin tunnel excavation. After being put into use, the equipment advanced about 10 meters per day, 3 to 6 times the efficiency of the drill-and-blast method. While accelerating the pace of project construction, it further reduced safety risks and improved the level of safety management, winning time for the early completion and water supply of the Bai'erhe ecological restoration project.

"Based on the long distance and small section of the Mabai branch tunnel of the Shiyan City Central Urban Area Water Resources Allocation Project, during excavation we overcame difficulties such as the design of the micro TBM cutterhead, the mucking of the main machine, the spatial layout of equipment, and long-distance rail transport, achieving an excellent average monthly advance of 200 meters and setting micro TBM construction records of 'a maximum daily advance of 23.68 meters and a maximum monthly advance of 343.38 meters,'" introduced the project manager.

Schematic diagram of the Shiyan Central Urban Area Water Resources Allocation Project

It is reported that the project mainly supplies water for urban domestic and industrial use in the central urban area of Shiyan City. By returning ecological water, it optimizes the water use conditions and water ecological environment of the receiving area, creates conditions for improving the ecological environment of the urban section of the Bai'erhe River, and will benefit 747,000 people.