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  3. No one quite knows how many tunnels have been dug under London. Some of the city’s many underground channels have been subject t

No one quite knows how many tunnels have been dug under London. Some of the city’s many underground channels have been subject t

admin2022-09-18  107
问题     No one quite knows how many tunnels have been dug under London. Some of the city’s many underground channels have been subject to the Official Secrets Act. Others are so old they have fallen into disuse and been forgotten. Nonetheless, anyone walking through central London can reckon that the busy streets around them are mirrored in criss-crossing (十字交叉) tunnels below. The world’s first subterranean (地下的) railway, the London Underground, opened in the city 150 years ago. Last month the first tunnel for Crossrail, an ambitious 15 billion ($24 billion) new railway project running across London, was completed. It lies 40 meters below the surface of the city, a wonder of engineering. Why does London do so much tunneling?
    London has evolved tightly packed, with narrow streets and alleyways spreading out across it like arteries. Between 1801 and 1851 its population grew from around 960,000 to over 2.5 million. Railway lines terminated at the edges of the city, as it was then defined, at Paddington and Victoria. As visitors and workers flocked to the city, its central roads became increasingly congested. Underground railways were built in 1863 to relieve the choked streets. Not everyone liked the early metro system, particularly as the trains still ran on sooty (煤烟熏黑的) steam engines. "I had my first experience of Hades today," spluttered R.D. Blumenfeld, an American journalist, in 1887, "and if the real thing is to be like that I shall never do anything wrong. " As the wealthiest city in the world at the time, London’s private investors could afford to sink money into the tunneling schemes.
    London’s congestion created the need for tunnels and its booming economy provided the financing. But what made them feasible was the city’s location. The clay on which most of the city is built provided an excellent tunneling medium. It is soft enough to be excavated easily, but impermeable (防渗透的) enough to stay dry. Once it is dug through it will not crumble. It has a "stand-up time", says Roger Bridge of the British Tunneling Society—when the first Crossrail tunnel was being built, parts of the section could be bored out and then explored as the clay stayed in place. Harder rock would require more powerful machines or explosives to dig through it. In contrast, cities such as Dublin are built on a mixture of sandstone and boulder clay. The boulders make it difficult to mine through, while the sand absorbs water, making it less sturdy. Before the development of better technology, such as pressure-balance machines, such conditions made tunneling tricky. Indeed, parts of south London have fewer tunnels than the centre because fewer of its neighborhoods are built on clay.
What made it easier to build tunnels in London than in Dublin?
选项 A、There were not so many buildings in London as in Dublin.
B、The clay of London is easier to be dug and waterproof.
C、London had more advanced machine and technology than Dublin.
D、London’s clay is sturdier and harder.
答案B
解析 细节题。根据题干中的made it easier to build tunnels in London than in Dublin。定位于本文最后一段第四句It is soft enough to be excavated easily, but impermeable enough to stay dry和第八句In contrast, cities such as Dublin are built on a mixture of sandstone and boulder clay. 前一句提到伦敦的泥土软硬适中，适合挖掘，且不渗水，后一句提到都柏林的泥土是砂砾和泥砾的混合。可见伦敦的泥土比都柏林的更适宜修隧道。四个选项中只有B涉及泥土的特性，故选B。
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