<p>A tunnel is relatively long and narrow; the length is often much greater than twice the diameter, although similar shorter excavations can be constructed, such as cross passages between tunnels. In this drawing give details of lagging. There were 25mm, 16mm, 20mm diameter bars are used. 75mm clear cover is used for all reinforcement bars. 500mm thick RCC lining of 25mm grade of concrete. 200mm backfill concrete of M15 grade of concrete with including lagging. For more information and details download drawing file.</p>