Why Go Underground? / 为什么要去地下？

Why Go Underground? / 为什么要去地下？

Imagine you are standing in the middle of a great city. Above you, there are no more empty plots of land. The streets are clogged with carriages and carts, the sidewalks are packed shoulder-to-shoulder with people, and the smell of rotting garbage drifts from every alley. The rivers are polluted, the wells are dry, and there is no place left to put anything new. Where do you go when the top is full?

想象一下，你正站在一座大城市的中央。抬头看，再也没有空地可以使用了。街道被马车和推车堵得水泄不通，人行道被人们挤得肩并肩，每条小巷都飘着腐烂垃圾的气味。河流被污染了，井水干涸了，没有地方可以再放任何新东西。当地面已经满了，你会去哪里？

You go down.

你会去地下。

For thousands of years, human beings have dug into the earth. We have built caves, cellars, tunnels, mines, aqueducts, catacombs, sewers, and subways. We did not dig because we enjoyed dirt under our fingernails. We dug because the surface of the Earth could no longer hold everything we needed to live, work, eat, drink, and travel. Underground space became the only place left to grow.

几千年来，人类一直在向地下挖掘。我们建造了洞穴、地窖、隧道、矿井、水道、地下墓穴、下水道和地铁。我们挖洞不是因为喜欢指甲缝里的泥土，而是因为地球的表面再也无法容纳我们生活、工作、吃饭、喝水和出行所需的一切。地下空间成了唯一可以继续发展的地方。

This book is about a particular city—Paris, the City of Light—and the three great underground systems that lie beneath it: the Métro (the subway), the Égouts (the sewers), and the Carrières (the old limestone quarries). But before we descend into the Parisian underground, we need to ask the most basic question of all: why did humans ever start building downward in the first place?

这本书讲的是一座特定的城市——光之城巴黎，以及它脚下三大地下系统：地铁（Métro）、下水道（Égouts）和采石场（Carrières）。但在我们潜入巴黎地下之前，我们需要先问一个最基本的问题：人类究竟为什么一开始就要向地下建造？

In this chapter, we will answer that question in three steps. First, we will look at the four main functions that underground space can serve. Second, we will travel back in time to see how ancient people learned to dig. Third, we will examine the specific crisis that struck Paris in the 1800s and forced its engineers to become the world's first true masters of the underground.

在本章中，我们将分三步回答这个问题。首先，我们会看看地下空间可以承担的四大功能。其次，我们会回到过去，看看古代人是如何学会挖掘的。第三，我们会考察 19 世纪巴黎所遭遇的那场特殊危机，正是这场危机迫使巴黎工程师成为世界上第一批真正的地下工程大师。

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The City Above Is Full: A Story About Pressure / 地上已经满了：一个关于压力的故事

The Physics of Crowding / 拥挤的物理学

Imagine you have a small toy box. At first, you can fit a few toys inside easily. As you add more and more toys, the box gets heavier and heavier, until finally it cannot hold any more. If you try to force in one more toy, something has to give: either the box breaks, or a toy falls out, or the lid will not close.

想象你有一个小玩具盒。刚开始的时候，你可以轻松地装下几个玩具。随着你不断增加玩具，盒子越来越重，直到最后再也装不下了。如果你硬要塞进一个玩具，就必须有东西让步：要么盒子破了，要么一个玩具掉出来，要么盖子合不上。

Cities work the same way. A city is a box that holds people, buildings, roads, pipes, wires, markets, factories, garbage, and water. When the city becomes too full, something has to give. In the worst cases, people get sick because waste has nowhere to go, fires spread because streets are too narrow, and businesses fail because goods cannot be delivered.

城市的运作方式完全相同。一座城市就是一个盒子，里面装着人、建筑物、道路、管道、电线、市场、工厂、垃圾和水。当城市装得太满时，就必须有东西让步。在最糟糕的情况下，人们因为废物无处可去而生病，街道太窄导致火灾蔓延，货物无法送达导致商业崩溃。

Engineers use a special word for this problem: pressure. The pressure inside a city comes in many forms:

工程师用一个专门的词来描述这个问题：压力。城市内部的压力有多种形式：

• **Population pressure** / 人口压力: more people want to live in the same area.
• **Sanitation pressure** / 卫生压力: more people produce more waste that must go somewhere.
• **Transportation pressure** / 交通压力: more people need to move from place to place.
• **Storage pressure** / 储存压力: more goods must be kept safe until they are needed.
• **Defense pressure** / 防御压力: more people need protection from enemies and weather.

When surface space runs out, the pressure does not vanish. It looks for somewhere else to go. Underground space is one of the most powerful places to relieve this pressure, because the volume of the Earth below our feet is enormous compared to the thin layer we live on.

当地面空间耗尽时，压力不会消失。它会寻找别的地方释放。地下空间是缓解这种压力最有力的场所之一，因为与我们脚下薄薄的一层生活空间相比，地球下方的体积是巨大的。

Let us put this in numbers. The average European city in the 1800s stood about 10 to 15 meters tall above the ground—the height of a four- or five-story building. But the rock and soil beneath a city can extend hundreds or even thousands of meters deep. If we think of the city as an iceberg, the part we see is only the tip. The rest is hidden, and it is mostly empty.

让我们用数字来说明。19 世纪欧洲城市的平均建筑高度约为10 到 15 米——也就是四五层楼的高度。但城市下方的岩石和土壤可以延伸到数百甚至数千米深。如果把城市比作一座冰山，我们看到的部分只是冰山尖。剩下的大部分都被隐藏起来，而且大部分是空的。

This hidden volume is the underground resource of every great city. Some cities have hard rock, which is difficult to dig. Some cities have soft clay or sand, which is easy to dig but can collapse. Some cities sit on solid limestone, which is both strong and easy to carve. Paris sits on limestone, and that is one reason its underground story is so special. We will see why in Chapter 2.

这些隐藏的体积就是每座伟大城市的地下资源。有些城市的地下是坚硬的岩石，难以挖掘；有些城市的地下是松软的黏土或沙子，容易挖掘但容易塌方；有些城市的地下是坚固的石灰岩，既结实又易于开凿。巴黎就坐落在石灰岩之上，这也是它的地下故事如此特别的原因之一。我们将在第二章中详细介绍。

A Pressure Example from Real History / 一个真实历史中的压力案例

To make this idea concrete, let us take one real moment from history. In the year 1878, Paris was preparing for the Exposition Universelle—a huge World's Fair that would show off the best inventions, art, and engineering from around the world. Millions of visitors were expected to arrive.

为了让这个想法具体化，让我们回到历史中的某个真实瞬间。1878 年，巴黎正在筹备万国博览会——一个展示世界各地最好发明、艺术和工程的巨型世博会。预计将有数百万游客到来。

City engineers at the time wrote a private report that has become famous among urban historians. They were worried about three specific problems:

当时的城市工程师们写了一份在城市规划史学界非常著名的内部报告。他们担心三个具体问题：

1. Street crowding / 街道拥挤：Paris streets in 1878 were already narrow, many only 5 to 8 meters wide, designed in medieval times for horses and carts. They could not hold the new carriages, omnibuses, and crowds of the modern age. 2. Sewage overflow / 下水道溢流：Paris had only a partial sewer network, much of it still medieval. Sewage often backed up into the streets and even into the river Seine, creating terrible smells and disease. 3. Building collapse / 建筑倒塌：Many buildings were sinking because they were built on top of old, empty quarries that had been forgotten. The ground beneath them was hollow.

This report is a perfect example of the city crisis that drives underground engineering. When surface space is exhausted and surface systems fail, engineers must look down.

这份报告是推动地下工程的城市危机的完美例证。当地面空间耗尽、地面系统失灵时，工程师们就必须向地下寻找答案。

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The Four Hidden Functions of Underground Space / 地下空间的四大隐藏功能

Now we come to a powerful idea. Underground space is not used for just one thing. Throughout history, engineers have used the underground for four main functions. Every great underground project in history fits into one of these four categories.

现在我们来讲一个非常重要的概念。地下空间并不只用于一个目的。纵观历史，工程师们把地下空间用于四大功能。历史上每一个伟大的地下工程都属于这四大类别之一。

1. Movement: Moving People and Goods Underground / 1. 交通：在地下运送人与货物

The most famous use of underground space is for transportation. Humans need to move from one place to another. On the surface, this is hard because streets are crowded, and every car, carriage, or person takes up space. Underground, you can build a tunnel that goes straight from Point A to Point B, with no intersections, no traffic lights, and no pedestrians in the way.

地下空间最著名的用途是交通。人类需要从一个地方移动到另一个地方。在地面上，这很难，因为街道拥挤，每一辆汽车、马车或行人都占用空间。在地下，你可以建造一条隧道，从 A 点直线到达 B 点，没有十字路口，没有红绿灯，也没有挡路的行人。

Examples of underground movement systems include: 地下交通系统的例子包括：

• **Subway systems** (Métro, Underground, U-Bahn) / **地铁系统**（Métro、Underground、U-Bahn）
• **Railway tunnels** through mountains / **穿山铁路隧道**
• **Underwater tunnels** beneath rivers and seas / **河底和海底的水下隧道**
• **Pedestrian passages** beneath busy inte