Box Tunnel

Box Tunnel is a railway tunnel in Western England, between Bath and Chippenham, dug through Box Hill, and is a significant structure on the Great Western Main Line (GWML). It was built between 1838-1841 for the Great Western Railway (GWR) under the direction of the railway's engineer Isambard Kingdom Brunel.DescriptionThe tunnel is 1.83mi in length, straight, and descends on a 1 in 100 gradient from the east.Box Tunnel is to be electrified with catenary as part of the GWML electrification scheme. In the summer of 2015 the track was lowered 600mm to allow for the electrification.The west portal is Grade II* listed and the east portal is Grade II listed.GeologyProposed in the 1835 Great Western Railway Act, the construction of a tunnel through Box Hill was considered an impossible and dangerous engineering project due to its length and the difficult underlying strata. The rocks through which it passes are Great Oolite on top with fuller's earth, Inferior Oolite and Bridport Sand beneath, a combination with which tunnellers at the time were already familiar.