Investigation on Causes of Destruction of Concrete Lining of Irrigation Canals Constructed on Gypsiferrous Soils (A Case Study for Shabankareh Irrigation Network)

In this research, the reasons of failures in concrete linings in Shabankareh irrigation project were studied. In this context, a detailed field survey was performed and all concerning technical reports were studied. In the second stage, several test pits were dug along the canal embankment and soil samples were taken from different depths. All samples were tested for their chemical, physical and mechanical properties. The results of grain size analysis and Atterberg Limits tests showed that most samples werer coarse grained soils with classification of GP, GM, GP-GM and SM according to USCS standards. The results of Pin Hole tests showed that some samples were of medium to highly dispersive type. The results of the chemical tests indicated that the gypsum content of the soils varied from 2 to 70 percent. Based on the overall results of the field and laboratory investigations, the main causes of the damages to the lining were related to geotechnical properties of the foundation soil. Also, it was concluded that the existence of gypsum particles in the bed materials was mainly responsible for the failures. Finally it was observed that Gypsiferrous soil layers under the lining were easily dissolved and eroded by seepage flow and surface runoff and cavities were formed extensively, which in turn caused lack of support of the concrete slabs, and general failure of the lining.