A jacking force study based on interpretation of box jacking records: A case study of curved rectangular box jacking in soft soil in Saitama, Japan

Abstract

Box-jacking as a tunnelling method has gained popularity in recent years for locating underground utilities and infrastructure. Nevertheless, the employment of this technique still poses challenges, particularly in predicting the jacking force of long drives. Accurate prediction of jacking force is highly desirable for anomaly detection, avoiding thrust overload limits, and protecting the box culverts and launch shafts from damage. However, such a prediction entails accounting for numerous factors, including site geology, lubricated overcut, work stoppages, deviations in alignment, and the driving style of the tunnel boring machine. In this paper, technical details of a Japan box-jacking project totalling over 220 m in length are discussed, with a focus on elucidating the relationship between tunnelling parameters and jacking force. Then, calculating approaches for forecasting jacking force during curved box-jacking are introduced. The modified Box-soil-lubricant contact model based on the analysis of tunnelling parameters is adopted for this purpose which can improve the accuracy of forecasts. Forecasts determined by the proposed approach are appraised through comparisons to predictions obtained using the PBK method currently utilized in industry. The results show that the proposed approach provides better forecasts of the monitored field data and highlight the significance of interpreting field data as a valuable tool for assimilating the experience with box-jacking in various ground conditions.