In the above image, one of the huge tunnel-boringmachines is shown just as it breaks through to one of the completed sections of the tunnel.
上图显示的是一台巨型隧道掘进机在工作，两条隧道正在贯通。
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Theregion's unpredictable geology and its volcanic rock prevented engineers from using boringmachines, forcing them to blast and dig their way under the Tsugaru Strait.