Seal design investigations for omerler underground coal mine in Turkey

Western Lignite's Enterprises (GLI) under the branch of Turkish Coal Enterprises (TKI) located in Tuncbilek, Kutahya has been operated since 1940's. According to the current reserve estimation, the site has around 170 million tons of lignite. Annual production of the site reaches 4.2 million tons while 20% of that amount is met from underground mining. Omerler underground lignite mine produces around 1.000.000 tons of lignite from fully mechanized longwalls. Average thickness of lignite seams is 8 m to 9 m. Top caving system is used to produce 6-m thickness coal from the backside of hydraulic support system while the initial 3-m thickness of lignite produced from shearer. Seals are used to form a barrier to isolate abandoned working areas from the current production sites. 29 seals were constructed up to date for the underground mine. In this study, 29 seals were firstly classified based on construction material and cross-section area, and then classified seals were also evaluated based on seal thickness. 4 different types of seals were found in the underground mine while seal thicknesses were also changed as 45 cm, 50 cm, 70 cm, 100 cm. Reinforced concrete, brick, and aerated concrete blocks were used as construction materials. Engineering properties of construction materials as well as surrounding rock mass of the seals were also determined from the existing studies to evaluate the sufficiency of seals against collapse caused by explosion and/or in-situ stress-strain conditions. The following reasons are summarized to the requirement of re-design and evaluation of the existing permanent seals to protect the underground mine against any type of accidents. Excessive number of abandoned mining panels increases the stress over seals as well as the effect of depth that is around 250 m. The geological materials around the seals are mostly classified as poor or very poor. Space behind the seals were not filled up to 100 m for 21 number of seals and that increases the risk of gas explosion or flood. The quality control of construction materials was not documented in the mine. Because of these, permanent seals designs were evaluated and re-designed in this study to protect the underground mine. The current design procedures proposed as per USA, UK, and German systems discussed in this study were applied to evaluate the sufficiency of existing seals as well. As a result of this study, new designs of permanent seals are proposed after evaluating and re-designing the existing permanent seals of Omerler Underground Lignite Mine.