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Box Tunnel is a railway tunnel in Western England, between Bath and Chippenham, dug through Box Hill, and is one of the most significant structures on the Great Western Main Line. It was originally built for the Great Western Railway under the direction of the GWR's engineer Isambard Kingdom Brunel. The tunnel is 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 which includes service to Bristol Temple Meads, scheduled for completion around 2016. ==Geology== Proposed in the 1835 Great Western Railway Act, due to its length and the difficult underlying strata, the construction of a tunnel through Box Hill was considered an impossible and dangerous engineering project. However, the project did have one advantage. The strata through which it would pass had already been proven to be tunnellable, the sequence being Great Oolite on top with Fuller's Earth, Inferior Oolite and Bridport Sand beneath. The Great Oolite limestone formed about 160 million years ago when the area was a shallow, warm sea. Ooliths form by strong currents moving tiny grains back and forth; calcium carbonate is precipitated around the grains in concentric rings until the ooliths becomes too big for the currents to support. They fall to the sea bed and over time are cemented by calcium carbonate to form the distinctive rock known as oolitic limestone, or locally as ''Bath Stone''. Easily worked, this had been mined for construction purposes since Roman times, and particularly during the 17th and 18th centuries to build many of the buildings in Bath, Somerset, extracted by the "room and pillar" method. To assess the strata more accurately, between 1836 and 1837 Brunel sank eight shafts at intervals through the hill and along the projected alignment to establish the nature of the underlying rock.〔(【引用サイトリンク】title=Box Tunnel )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Box Tunnel」の詳細全文を読む スポンサード リンク
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