By Lynda Myer
Completing a 946m single drive, and setting a record for the longest pipe jacking in complex geology and high water pressure stratum in China, a CRCHI pipe jacking machine has dug on the Jiaoliu River headrace tunnel for the Chaoer-Xiliao River diversion project.
With a single crossing distance of 946m and a maximum overburden of 26m, the diameter of this pipe is 4.3m, whereas the water pressure throughout construction was over than 2 bar and the geology comprised rock, mud gravel and clay.
Considering that the pipe jacking machine was equipped with a hard rock heavy-duty main bearing, high power density main drive, intelligent monitoring and control system, as well as independent man lock, allows it to cope with complex working conditions.
According to CRCHI: “The construction team repeatedly used the independent man lock to carry out hyperbaric cutterhead intervention in the unstable formation.”
Also the maximum progress of this team was 15m per day and it had a maximum monthly advance of 219m.
While China’s first EPBM was exported to South America by CRCHI in September2023, the intended machine was 105m long, with an excavation diameter of 9.8m and is due to be deployed on Lot 1 of the Santiago Metro Line 7 project in Chile.
With almost 7.9km, Lot 1’s 6.7km will be dug by TBM and the line travels beneath the Mapocho River for 60m, with an overburden of 10m.
The geology of the path of this tunnel will be fine-grained soil, silt, clay, sand, gravel, pumice, and volcanic rock formation, whereas the minimum turning radius of the alignment is 250m.
The features that CRCHI equipped the TBM with them were independent technologies. The cutterhead has a composite design of six spokes and six panels, with a central support. Disc cutters, drag bits, and gauge scrapers are dressed on the cutterhead for full-face excavation, and all detachable cutting tools can be replaced from the back of the cutterhead. It is capable of bidirectional rotation for muck discharge. When the TBM needs to turn, the stroke difference of each group of propulsion cylinders is adjusted to meet the minimum turning demand of the alignment.
Crossing through seven urban areas in the capital, the 26km-long Santiago Metro Line 7 has a construction period of six years and is slated to include seven stations and construction shafts.
