Why It's Unique: With a 76-foot diameter, Yerba BuenaIsland Tunnel is the world's widest single-bore tunnel, an impressivefeat considering it opened in November of 1936.

独特之处： 直径达76英尺的耶尔瓦布埃纳岛隧道是世界上最宽的单孔隧道，1936年11月，这项令人印象深刻的工程落成开通。

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This year, a huge circular bore is to be lowered into a layer of sand deep beneath the city, where it will drill a tunnel to link them.

今年，就要在城市地下深处的砂层打通一个巨大的圆形隧道，把地铁站连起来。

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After 15 years of construction work, the 9.5-meter (31-foot) wide drilling machine will bore through the remaining 1.5 meters of rock to join two ends of the tunnel some 2,000 meters under a mountain.

经过15年的施工，9.5米宽的钻孔机将会钻穿最后剩下的1.5米的岩层，联通了位于山体下2000米的隧道两端。

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Construction began on the twin-bore tunnel in January 2007.

BBC: Hindhead Tunnel

The twin-bore Sasago tunnel is an estimated 4.3km (2.7 miles) long and is on one of the major highways out of Tokyo.

BBC: Japan Sasago tunnel: Collapse traps cars