Experimental modeling of far-field effects in buried pipelines subjected to reverse faulting

Abstract

Buried pipelines often traverse a broad geographical area and are subject to permanent ground deformations (PGDs) induced by fault movement, lateral spreading, or landslides. These PGDs distort the pipeline locally and mobilize the soil resistance along the pipe interface and outside of the affected area. This study primarily investigates the influence of far-field and transitional soil-pipe resistance on the response of pipelines crossing reverse fault regions. A series of 2.5 m long, one-tenth experimental-scale buried pipelines, representing 60 cm diameter steel pipe at 1.5 m depth prototype in cohesionless sandy soil was subjected to reverse faulting movement. The reverse faulting was simulated by a split-box apparatus under 1g conditions. The end-joint fixities should represent the far-field and transitional effects in full-scale pipes. Four scenarios of far-field and transitional effects were simulated using different pipe-end fixities: (1) free: movement of the pipe end is free in all three directions, (2) axially-free: pipe ends movement is axially free but radially fixed, (3) axially-fixed: pipe end movement is axially fixed and radially constrained by springs, and (4) spring-restrained: pipe end movements are axially and radially restrained by springs. For representing axial soil-spring forces in far-field and transitional zones, two methods were considered: a) the axial soil-spring forces recommended by ASCE (1984) guidelines; and b) an analytical-experimental method that is a combination of an analytical solution, proposed by Vazouras et al. (2015), and a series of pull-out tests, conducted in this study. The radial springs were designed based on ASCE (1984) guideline for both Scenarios of 3 and 4. The results show that the boundary conditions of the pipe have a significant effect on the mode of failure and required fault offset for occurrence of such failure mode. It is also indicated that the ASCE (1984) guideline recommendations on the axial soil-spring representation results in less soil resistance than analytical-experimental method in far-field zone, which may result in a non-conservative estimation of the pipeline performance in fault zones.