Method for calculating frictional resistance of long-distance pipejacking in deeply buried rock strata

The pipe jacking method has the advantages of high efficiency, safety, environmental protection and reliable quality, and is widely used in soil strata. In order to meet the demand for rapid construction of water conservancy projects and municipal projects, pipe jacking is also used in rocky strata, but there is a lack of research on the calculation of the frictional resistance of long-distance pipe jacking in deeply buried rock. Based on the first long-distance pipe jacking case in rock in China, Guanjingkou water conservancy project of Chongqing, through the field tests on jacking force it is found that the pipe- rock friction resistance is mainly affected by the filling of over-excavation gap and the injected lubricating mud, and the former has a greater impact. According to different degrees of the filling of the over-excavated gap with sediment, three mechanical models for the contact between pipe and rock are proposed, and based on the elastic-plasticity theory and the coordinated deformation between the pipe and the filling, the formulae for calculating the frictional resistance of the pipe are derived for each mechanical model. The applicability of the formulae for the frictional resistance in deeply buried rock strata is verified by comparing the calculated values of the frictional resistance with the measured ones.