The Tehlab plain is located in the Hamoun Mashkil catchment in the south of Mirjavah region and along the Iran-Pakistan border. In most of the rural areas of this plain, especially in the northern parts of the plain along the border of Iran and Pakistan, the effects of land subsidence in the form of cracks and fissures in buildings as well as collapse in sewage wells were observed. In order to evaluate these land subsidences, the Tehlab plain was first zoned in terms of subsidence risk. Based on the land subsidence risk zoning map, it can be seen that most of the areas of the Tahlab plain have a low risk of subsidence, except for the northern region, where there are many exploitation wells in this area. To study the collapse in sewage wells and its relationship with soil type in the northern regions of the plain, the collapsibility of soil samples was investigated. According to Jennings and Knight criteria in the oedometer device in the laboratory in the saturated state. the coefficient of collapsible of soil samples was measured between 0.21 to 7.3, which showed that the soil samples were collapsible in this area. Finally, to investigate the occurrence of collapse in sewage wells in the northern of the plain, an in-situ permeability test (ring) test was performed at different depths of a dug well. This test showed that a soil layer with high permeability rate (9.24 cm/hr) was located between low permeability layers. These low permeability layers caused an increasing the water level in the sewage wells. Moreover, the liquid limit of most surface soil samples was less than 30%. Therefore, the soil permeability and liquid limit were the most important factors controlling collapse in the sewage wells.
Type of Study:
Original Research |
Subject:
Hydrogeology Received: 2024/12/27 | Accepted: 2025/01/18 | Published: 2024/12/28