A jacking force study of curved steel pipe roof in Gongbei tunnel: Calculation review and monitoring data analysis

Jacking force is one of the crucial parameters for pipe structure design, selection of pipe jacking machine and shaft structure design during jacking process. To predict the jacking force more accurately, this paper summarizes four calculation methods of curved jacking force. The Japan Micro Tunneling Association (JMTA) Method is based on Terzaghi arching theory with full contact between pipe and soil. However, according to the elastic contact theories, Hertz contact method, Shimada method and Persson contact method assume that pipe and soil contact partially in stable excavation cavity. The three methods are considering the influences of frictional resistance of pipe-soil and pipe-mud concurrently. By field monitoring of jacking force data in different types of soil and cover depth in the curved pipe jacking roof of Gongbei tunnel, the cutterhead resistance, dynamic and static frictional resistance have been analyzed. Also, the additional frictional resistance caused by stoppage effect has been presented. The results show that the mud pressure is more convenient to calculate the cutterhead resistance than active soil pressure. The Persson contact model is applicable to calculate the friction in stable condition of excavation cavity while the Shimada model is capable of predicting frictional resistance values for unstable condition.