The stiffness of axial pipe-soil springs and axial joint springs tested by artificial earthquakes

This study proposes an experimental method to obtain the stiffness of axial pipe-soil and axial joint springs in time and frequency domains. The proposed method can determine axial pipe-soil spring stiffness by using the pipe strains and slippages between pipes and soil. It can also determine axial joint spring stiffness by utilizing pipe strains and joint deformations. The pipe-soil spring stiffness values of ductile cast iron (DCI) and welded steel (WS) pipes are obtained and analyzed through artificial earthquake tests on a 24 m × 24 m buried pipe network. Artificial earthquakes are produced with trinitrotoluene explosives. Three theoretical models are discussed, and their results are compared with the test results. The comparisons indicate that the proposed experimental method is valid to obtain the stiffness of axial pipe-soil and axial joint springs. The stiffness values can be a benchmark to study the pipe-soil interaction and flexible joints. The effects of axial pipe-soil spring stiffness on the joint deformations of DCI pipes and pipe strains of WS pipes are also discussed.