Why a GRP Pipe of 800 mm dia is deshaped when buried at a depth of 2 meter. The dia reduces to 600 mm and it bulges after 1 years?

A GRP (Glass Reinforced Plastic) pipe of 800 mm diameter may become deshaped and reduce to 600 mm when buried at a depth of 2 meters due to factors such as insufficient soil support, external soil pressure, and inadequate pipe stiffness. Over time, the external loads combined with the pipe's material properties can lead to deformation and bulging, particularly if the backfill material is not properly compacted or if the installation did not account for environmental conditions. Additionally, prolonged exposure to stress and strain can weaken the pipe, exacerbating the deformation.