Due to the environmental temperature changes or current change caused by contact rail operation to produce can cause contact rail temperature change, make contact rail produce length change for heat expansion and cold shrink. Therefore, when contact rail is laying, every one anchor section will install one expansion joint device to compensate length change due to heat expansion cold shrink of contact rail, and ensure the current to continue good
         According to the environment temperature: inside tunnel is 0 ℃ ~ + 40 ℃, outdoors is - 27.4 ℃ ~ + 42.6 ℃, Suggest the largest anchorage length outside tunnel 76.8 m, the largest anchorage length inside tunnel 106.8 m lay one expansion joint, consider temperature change of contact rail outside tunnel 112.4 ℃, in tunnel 85 ℃, expansion joint compensation distance outside tunnel is 176.9 mm, inside tunnel is 186.1 mm. Stroke of expansion joints is 200mm, completely meet the needs.