Vulnerability assessment of power transmission towers affected by land subsidence via interferometric synthetic aperture radar technique and finite element method analysis: a case study of Zanjan and Qazvin provinces

Subsidence induced by groundwater (GW) in the plains of Zanjan and Qazvin provinces in northwestern parts of Iran has impacted various infrastructures. Hence, investigating the study area to identify the risky zones and identifying the vulnerable members of power transmission towers (PTTs) are required by policy-makers. This study investigated the impact of GW depletion on land subsidence and its effect on PTTs in the Zanjan and Qazvin provinces. Subsidence maps were acquired via time series analysis by performing a small baseline subset on Sentinel-1 (2017-02-23 till 2019-02-25) satellite data. Results indicate maxima values of 132 mm/years and 80 mm/years subsidence rates in line-of-sight direction for Qazvin and Zanjan provinces, respectively. Observed GW shows a rapid decline of piezometric head of 13.2 m for Qazvin province. Furthermore, GW head drop, coupled with the dominance of fine-grained soils in Qazvin province, increases the probability of plain-wide subsidence. Employing a finite element method analysis on two commonly utilized PTTs in the region illustrated such vulnerable members (bottom legs and first transverse plane) under support settlement conditions. However, the T-30 tower, by mitigating the stress to more members of the tower, performed superior in most subsidence scenarios. It is recommended to implement new policies such as avoiding risky zones for developing PTTs, installing T-30 towers instead of DC towers in obstructed routes, and continuous monitoring of threatened PTTs.