Hazard Evaluation of Qanat in the West of Mashhad by plaxis software

Khorasan Razavi province is one of the areas with many chains of Qanat and Mashhad city in the center of this province has developed on areas with Qanat in the west direction. Loads caused by tall buildings and structures that built on old Qanats can make Qanats unstable and consequently Qanat collapse can lead to ground settlement. This paper deals with identifying the exact locations of Qanat chains by aerial photographs and evaluating the main factors that cause Qanat collapsing. Moreover the stability of Qanat was evaluated in numerical modeling by Plaxis software. The geotechnical data، Qanat depth، Qanat lining system and vertical load was used in modeling and after that، the extension of plastic zone around the Qanat underground tunnel was analyzed. The results of this research show that the rate of plastic zone extension and the influence of lining in Qanat stability decreases by increasing in the Qanat depth. As it is estimated while Qanat depth increases as much as one meter، it can tolerate more pressure as much as loads induced by a one-storey building.