At 23:00pm, June 10, 2014, Huayuan Company successfullycompleted pulling back the prefabricated pipeline through the HDD borehole underneaththe Yellow river in Zhengzhou city for the Boai- Zhengzhou- Xuedian Natural GasPipeline Project, which was actually Huayuan’s 8th time of successful YellowRiver Crossing.
Theφ610mm×σ12.5mm pipeline of the Yellow river crossing section was2621.76m length, whose crossing strata was mainly medium sand layer. The entrypoint was located at eastern side of Lupo hill, Wancun Town, Xingyang City,Henan Province; daylight point was located nearby Chenjiagou (which is thebirthplace of Chinese traditional Kung Fu, Chen’s Shadowboxing), Wen County,Jiaozuo City, Henan Province. Most of the crossing route passed throughunsteady sand layers, which was very permeable, giving rise to the difficultyof the HDD construction works.
In view of avoiding such problems as insufficient torqueof drill rig, deficient stiffness of drill string, positioning difficulty ofdrill bit, which are usually caused by too much length of the pilot holedrilling, Huayuan gave up the traditional one-shot pilot hole drilling method. Twosets of drill rigs were respectively deployed at the entry-site and daylightsite, drilling forward simultaneously to the intersection point in the midwayunder the steering of downhole surveying device, DX-I, which was self-developedby Huayuan company, exclusively used for downhole survey and downholeinterception. The drill bits, with Huayuan’s lately-developed Mag-Target Probeand sensor mounted in the rear, can conquer such difficulties as disturbance toposition the drill bit due to too much length of pilot drilling and/or river waveswhen crossing a river. Finally, Huayuan successfully intercepted the two drillbits under the borehole, making a single consecutive pilot hole strictlycomplying with the designed trajectory. At the reaming stage, two drill rigswere synchronously maneuvered to make the borehole larger, resolving theproblems of insufficient working torque and deficient drill-string stiffness ifonly one rig were used.
Because ofthe risks of borehole contraction initiated by the unstable sand layer and the ensuingunanticipated resistance, the pipeline being pulled back was very probably beenlocked in the very long borehole; moreover, under this circumstance, if onlyone rig was used to forcibly pull back the pipeline, the drill string was veryprobably been broken off, making the pulling back work fail. In view of this,at the pipeline back pulling stage, Huayuan used the self-developed 500tpipeline thrusting device to assist pushing the pipeline from the oppositesite. At last, under the cooperation of the pulling rig at one end and thethrusting device at the other, the pipeline was successfully installed into theborehole.