Vertical tunneling in China-A case study of a hydraulic tunnel in Beihai

Abstract The vertical tunneling (lifting) method was invented in China to build hydraulic tunnels efficiently, safely, and conveniently. This paper presents a case study of a hydraulic tunnel in Beihai, China. In this study, the jacking force of five standpipes is analyzed and a back analysis principle of the average frictional coefficient is proposed. The jacking force is mainly composed of the face resistance and the frictional resistance, and the local variation is mainly ascribed to the face resistance. Slightly after the jacking force reaches the maximum value, the deviation starts to increase to the maximum value. The back-analyzed value of μavg for number 9 standpipe is 0.39, indicating that number 9 standpipe is well lubricated, and μavg = 0.55 is suggested in the poorly graded sand. By moving from the poorly graded sand to the silty sand or silty clay, the jacking force decreases. Additionally, the average jacking speed is higher in the poorly graded sand than in the other soil layers.