Despite COVID-19, flood and other obstacles, on July 27, 2020, the hard rock slurry balance pipe jacking machine (DN4000), named Zhengxian (which translates to “try to be the first”), successfully broke through on the Mingzhu Avenue utility tunnel in Huanggang City, Hubei Province, China. The machine is suitable for complex geology and independently developed by China Railway Engineering Equipment Group Co. Ltd. (CREG). At present, this project is the largest diameter utility tunnel project using a circular pipe jacking machine in China.
With the continuous development of China’s economy and society, the demand for underground space development projects such as urban municipal pipe network construction and renovation, mechanized construction of subway cross passages, and large-span tunnels construction with the pipe-roofing method are increasing rapidly. Since China is known as for its diverse geology and complex hydrogeology, the tunnel alignment usually comprises variable geologies. Therefore, the construction of small diameter tunnels in complex strata with diverse geology and variable ground hardness puts forward very high requirements for the overall performance of pipe jacking machine.
In May 2015, CREG successfully developed China’s first small diameter slurry balance pipe jacking machine (DN2800), which has completely independent intellectual property rights and is suitable for composite strata. Major breakthroughs and innovations have been achieved in core technologies such as adaptable cutterhead, miniaturization technology, micro-drive technology, and cutting tool changing technology for mixed ground. This machine has been successfully applied in Nanning’s municipal sewage pipeline project. The tunnel alignment is staggered with upper soft and lower hard full-face red clay and hard rock, along with karst caves. The saturated uniaxial compressive strength of limestone exceeds 110 MPa at most. The tunneling length is about 3.5 km and the maximum daily advance rate reaches 20 m.
In October 2017, the Scientific Research Consortium constituted by CREG, Shanghai Civil Engineering Co. Ltd. of CREC, Shanghai Tunnel Engineering & Rail Transit Design and Research Institute, and Ningbo University successfully developed China’s first pipe jacking machine for cross passages. It achieved four technical innovations, including high mobility and high integration, new-type curved cutterhead, movable pipe joint prestress safety support system and mechanized construction method for cross passages. This machine has successfully been applied to more than 10 projects such as Ningbo Metro and Wuxi Metro.
Zhengxian has a diameter of 4.86 m and is one of the large hard rock slurry balance pipe jacking machines for complex strata globally. There are several breakthroughs and innovations in key technologies, such as new-type tapered secondary crushing technique by displacement shear, new-type machine and pipe joint anti-entrapment design, high-efficient slurry flushing technology for preventing filter cake, micro disturbance advance and self-adaptive attitude control technique. In addition, CREG successfully overcame difficulties such as cutterhead abrasion, rock fragmentation, ground settlement and local karst caves while achieving rapid advance rate, low energy consumption, and minimal disturbance to the surrounding area, which won the owner’s high praise.
At present, all kinds of hard rock pipe jacking machines for complex strata in diameterd ranging from 0.3 m to 5 m designed and manufactured by CREG have been applied to many projects, including sewage, power, water diversion, utility tunnel, pipe roofing and cross passage, which sets a good example for promotion and application of pipe jacking method in hard rock and complex strata.