Behaviour of segmental pipeline protective vaults subjected to fault offset

Abstract

The San Francisco Public Utilities Commission is currently undertaking a seismic upgrade of Bay Division Pipelines (BDPLs) Nos. 3 and 4 located in Fremont, California. To improve the reliability of the pipelines at a crossing of the Hayward Fault, a new pipeline (BDPL No. 3X) will be constructed in a segmental reinforced concrete vault with flexible connection joints that can accommodate lateral offsets and compressive deformations during a significant fault rupture. FLAC 3D finite difference analysis was performed to enhance the understanding of the soil–structure interaction behaviour of this special design. The analysis focused on the behaviour of the segmental concrete vault when subjected to up to 2.0 m (6.5 ft) lateral fault movement. The effects of fault intersection angle, fault location, soil strength, backfill type and connection joint size on the performance of the segmental concrete vault were also evaluated. Numerical results show that the movement of the vault developed gradually without sudden or concentrated deformation in response to the increasing fault displacement. Hence, the articulated vault design can withstand significant lateral offset and compressive deformation during fault rupture through the relative slip and rotation of the flexible connection joints.