Collapsible soils undergo considerable reduction of shear strength and deformation modulus due to water wetting. This paper investigates the effects of leak induced sub base soil settlement on deformation and stability of buried flexible pipes. Nonlinear finite element program (Z-Soil 2007) is used to model progressively increased wetting zone around buried HDPE pipes. Wet to dry ratios of deformation modulus, shear strength friction angle, and cohesion of collapsible soil were evaluated using oedometer, direct shear and plate load tests. HDPE pipes of 200 mm diameter and 25 mm thickness with sand bed and cover in the pipe zone and soil backfill up to ground surface were considered. Effects of progressively increasing wetting zone of 0.0 to 70.0 cm depth under the pipe sand bed were investigated. Staged backfill and surface pressure were considered. Results show increasing pipe invert vertical displacement and pipe deformation amplification with increased wetting zone in collapsible soil due to pipe water leak.
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