Assessment of pipe-jacking forces through direct shear tests on tunneling rock spoils

The continued growth of urban environments has brought about the advent of trenchless technology as the ideal installation method for buried infrastructure in densely populated urban areas, such as the city of Kuching. Kuching is the state capital of Sarawak, located on the Malaysian island of Borneo. For the construction of concrete sewer lines in the central business district of Kuching, Malaysia micro-tunneling by pipe-jacking was the utilized delivery method. Jacking forces are a critical component of planning for pipe-jacking works as jacking forces govern the drive span. Excessive jacking forces could also result in damaged jacked pipes. Thus, further understanding of pipe-soil jacking forces is necessary, and needs to be defined within the specific geology of Kuching. The low RQD values produced during rock core extraction created challenges in obtaining intact cores for rock strength testing. The Authors present a novel method for back-analysis of jacking forces by obtaining effective Mohr-Coulomb strength properties through direct shear tests on reconstituted tunneling rock spoils. Tunneling rock spoils were obtained from two pipe-jacking drives traversing phyllite and shale. Results from direct shear tests on reconstituted tunneling rock spoils were used in back-analysis of frictional coefficients, and in subsequent analysis o