An investigation on land subsidence and its effect on rupture of water well casings in Mashhad City area

Land subsidence due to excessive extraction of groundwater has been reported in different parts of the world and several plains and Iran. Mashhad Plain during the past 40 years has been faced with 60 m drawdown of water table. This drawdown caused land subsidence in some areas of the plain. Land subsidence effects appear as rupture and curvature of well casings and they cause destruction of subsurface structures in wells. Based on data available from three GPS stations in Mashhad plain، and with respect to geological parameters of the study area، effective factors on rupture of well casings which account for abundant damages every year، have been investigated in this paper for Toos area، northwest of Mashhad City. A deep grain size profile of underground layers has been provided for problematic area in the study area. Also، soil grain size profile in two levels، above and below the groundwater surface، has been provided using ArcGIS software for investigation of current situation and anticipation of continuity conditions of land subsidence and therefore its resulted destruction in the future.