Yellow River Project, China
A tunnel to supply three major cities with water as part of the world’s largest construction project.
Words by Rudy Marognoli – CMC on Lot 5, TaiYuan, PRC site.
Shan Xi WanJiaZhai Yellow River Diversion Project (YRDP) is located in the northwest of ShanXi Province. The Project will transfer the water from the Yellow River at the intake at WanJiaZhai Dam Complex to three industrial cities of Tai Yuan, DaTong, and PingSuo.
The project consists of General Mainline, South, Mainline and North mainline. The total length ofthe three mainlines is approximately 313.2 Km and CMC. Ravenna (ITALY) is active in all the stretches executed by Tunnel Boring Machins and all the machines use ZED guidance systems.In particular, on tunnel 7, where CMC is the only one contract worker, it use a TBM Robbins with 4.82 m diameter advancing every day using a ZED Guidance System 261.
The length of the tunnel is 13,520 metres, with the relative lining by concrete segments.
Surveyors are present in all the TBM activities to guarantee a constant monitoring of TBM and ZED System. The Survey department is composed of 1 Italian supervisor and 10 Chinese people working in these shifts:
7 a.m. to 10-12 a.m. : Maintenance Time – 1 Surveyor + 3 helpers
10-12 a.m. to 7 p.m. : 1st boring shift – 1 Assistant surveyor + 2 Helpers
From 7 p.m. to 7 a.m. : 2nd boring shift – 1 Assistant surveyor + 2 Helpers
The most important shift for surveyors is the maintenance one. During this time, surveyors are busy checking length of the bored tunnel during the past night shift, the TBM vertical and horizontal offset, replacement of laser position and any queries involving the ZED System.
The tunnel 7 alignment is on a straight line without any vertical or horizontal curve but the tolerance is narrow enough (50 mm vertically and 100 mm horizontally) to made CMC provide a very accurate guidance system like ZED 261. The kind of laser adopted is a “LASERLINE LR 2020D”. It is able to show to the surveyor the horizontal and vertical angle of the laser beam. The daily bore length is about 60 metres and every maintenance time the surveyor and his helpers move ahead the laser position basing the coordinates on a “inside traverse”. After this, using the Portable terminal, the surveyor input the new Laser data in the Control Unit and the TBM is ready to bore again.
The system is very easy to use and we never overtake the project tolerance, which means the system is also very accurate. The geological condition of the rock, obligate the survey dpt., to make very stable brackets to support the weight and the vibrations of the Inclinometer, Target and Distribution box. ZED Instruments also provide a perfect kind of Anti-vibration system for the bases of the units.