Why doesn’t the Leaning Tower of Pisa fall over? - Alex Gendler

翻译人员: 彬琳 张 校对人员: Tingting Zhao

In 1990, the Italian government enlisted top engineers

1990 年，意大利政府招募了 一批顶尖工程师

to stabilize Pisa’s famous Leaning Tower.

来维护著名的比萨斜塔。

There’d been many attempts to right the tower during its 800 year history,

在过去的八百年中 有过许多次修正斜塔的尝试，

but this team’s computer models revealed the urgency of their situation.

但计算机模型向这只团队 揭示了他们面临的严峻考验。

They projected the tower would topple if it reached an angle of 5.44 degrees—

他们预测这座塔将在 倾斜角度超过 5.44 度的时候倒塌——

and it was currently leaning at 5.5.

现在它的倾斜角度是 5.5。

No one knew how the tower was still standing, but the crisis was clear:

没有人知道为什么斜搭仍旧屹立， 但危机就摆在眼前：

they had to solve a problem that stumped centuries of engineers,

他们需要解决这个困扰了 无数代工程师的问题，

and they needed to do it fast.

并且是迅速解决。

To understand their situation,

为了更好的理解他们的处境，

it’s helpful to understand why the tower tilted in the first place.

让我们先来了解比萨塔倾斜的原因。

In the 12th century, the wealthy maritime republic of Pisa

在 12 世纪，富有的比萨海上共和国

set about turning its cathedral square into a magnificent landmark.

着手将主教座堂广场 变成它宏伟的地标建筑。

Workers embellished and enlarged the existing church,

工人们扩大并装饰了原有的教堂，

and added a massive domed baptistry to the plaza.

并在广场上加盖了带穹顶的洗礼堂。

In 1173, construction began on a free-standing campanile, or bell tower.

1173 年，独立式钟楼的修建也开始了。

The engineers and architects of the time were masters of their craft.

参与建造的工程师与建筑师 都是那个时代的大师，

But for all their engineering knowledge,

然而相对工程知识，

they knew far less about the ground they stood on.

他们对脚下的这片土地知之甚少。

Pisa’s name comes from a Greek word for “marshy land,"

“比萨”一词起源于 古希腊词汇“沼泽之地”，

which perfectly describes the clay, mud, and wet sand below the city’s surface.

恰好完美描述了藏在这座城市 地表之下的黏土、淤泥和湿砂岩。

Ancient Romans counteracted similar conditions with massive stone pillars

相似的条件下， 古罗马人将大理石柱立在地表岩床上

called piles which rest on Earth’s stable bedrock.

以增加建筑的稳定性。

However, the tower’s architects believed a three-meter foundation would suffice

然而，塔的建筑设计师认为三米的地基

足以支撑这个相对较矮的建筑。

for their relatively short structure.

Unfortunately for them, less than five years later,

不幸的是，不到五年，

the tower’s southern side was already underground.

塔的南侧已经陷入地下。

Such a shifting foundation would normally have been a fatal flaw.

通常情况下地基的倾移 将成为致命的缺陷。

If workers added more weight,

如果继续增加重量，

the pressure from upper stories would sink the structure

来自上层的压力将使建筑下沉，

and fatally increase the lean.

从而导致更严重的倾斜。

But construction halted at the fourth story for nearly a century

由于比萨陷入长久的战争时期，

as Pisa descended into prolonged warfare.

工程在第四层停滞了将近一个世纪。

This long pause allowed the soil to settle,

在这期间，土壤沉降

and when construction began again in 1272,

等到 1272 年工程再次开始时，

the foundation was on slightly more stable footing.

地基的基脚变得相对稳定。

Under the direction of architect Giovanni di Simone,

在建筑师乔瓦尼 · 迪 · 西蒙尼 （Giovanni di Simone）的指导下，

workers compensated for the tower’s minor tilt

接下来几层的建造中

by making the next few floors taller on the southern side.

钟楼南侧略高于北侧， 以此来修正塔的微小倾斜。

But the weight of the extra masonry made that side sink even deeper.

然而额外的砖石结构加速了塔楼南侧的下沉。

By the time they completed the seventh floor and bell chamber,

等到第七层及钟室竣工时，

the angle of the tilt was 1.6 degrees.

塔已经倾斜了 1.6 度。

For centuries, engineers tried numerous strategies to address the lean.

数个世纪以来，工程师们 无数次尝试修正它。

In 1838, they dug a walkway around the base to examine the sunken foundation.

1838 年，为了探究下沉的地基， 他们围绕地基挖掘出一条走道，

But removing the supporting sand only worsened the tilt.

然而挖走支撑的沙土 导致了更严重的倾斜。

In 1935, the Italian Corps of Engineers injected mortar to strengthen the base.

1935 年，为了加固塔基， 意大利工程军向基底灌注砂浆，

However, the mortar wasn’t evenly distributed throughout the foundation,

然而砂浆灌注不均匀

resulting in another sudden drop.

引发了又一次下沉。

All these failed attempts, along with the ever-sinking foundation,

所有失败的尝试， 伴随沉降的地基

moved the tower closer to its tipping point.

使得倒塌一触即发。

And without definitive knowledge of the soil composition,

由于缺乏对土壤构成的认知，

engineers couldn’t pinpoint the tower’s fatal angle

人们无法计算出塔何时会倒

or devise a way to stop its fall.

也无法阻止它发生。

In the years following WWII,

第二次世界大战结束后，

researchers developed tests to identify those missing variables.

学者们尝试确定这些缺失的变量。

And in the 1970’s, engineers calculated the curved tower’s center of gravity.

20 世纪 80 年代， 工程师们计算出塔的重心曲线，

With this data and new computing technology,

再加上新的计算机技术，

engineers could model how stiff the soil was, the tower’s trajectory,

土质硬度，塔的轨迹

and the exact amount of excavation needed for the tower to remain standing.

以及精确的挖掘量才得以确定。

In 1992, the team drilled diagonal tunnels

1992 年，施工队挖出倾斜的隧道，

to remove 38 cubic meters of soil from under the tower’s north end.

从北端的塔基挖走 38 立方米的土壤。

Then, they temporarily counterbalanced the structure with 600 tons of lead ingots

随后，他们用 600 吨铅锭 来过渡性的平衡塔身，

before anchoring the base with steel cables.

最后用钢索来固定地基。

More than six centuries after its construction,

在竣工的六个世纪之后，

the tower was finally straightened… to a tilt of about four degrees.

塔的倾斜角终于被修正到 4 度左右。

No one wanted the tower to fall,

没有人希望它倒塌，

but they also didn’t want to lose the landmark’s most famous feature.

但他们也不想失去 这个地标建筑最出名的特征。

Today the tower stands at 55– or 56– meters tall,

如今，塔高约 55 到 56 米，

and it should remain stable for at least 300 years

作为缺陷之美的里程碑，

as a monument to the beauty of imperfection.

它将至少屹立 300 年。