Discussion of “Experimental Study on the Pipe-Soil Interface under the Influence of Pipe Jacking Stagnation Time” by Tianliang Li a , Wen Zhao a , Run Liu a , Jianyong Han a and Cheng Cheng a

Jacking forces which exceed expectations constitute a risk for tunnelling contractors. One scenario in which high forces may arise is when jacking of lubricated pipes is temporarily halted, which was considered by Li et al. using a programme of direct shear testing. While recognising the importance of the topic to the profession, the purpose of this Discussion piece is to highlight some of the limitations of the study.