Name: 海灘洞為何如此致命？ (Why Are Beach Holes So Deadly?)
Uploaded: 2025-04-04T04:03:56.000Z
Duration: 16 min 11 s

情態副詞

Even though it's a favorite vacation destination, the beach is surprisingly dangerous.

儘管海灘是人們最喜愛的度假勝地，但它的危險性卻出人意料。

There aren't that many recreational activities in our lives that have explicit staff whose only job is to keep an eye on us, make sure we stay safe, and rescue us if we get into trouble.

在我們的生活中，沒有多少娛樂活動有明確的工作人員，他們唯一的工作就是照看我們，確保我們的安全，並在我們陷入困境時營救我們。

There are just a lot of hazards on the beach.

Heavy waves, rip currents, heat stress, sunburn, jellyfish stings, sharks, and even algae can threaten the safety of beach goers.

大浪、激流、熱應力、晒傷、水母蜇傷、鯊魚甚至海藻都會威脅到海灘遊客的安全。

But there's a whole other hazard, this one usually self-inflicted, that doesn't make the list of warnings, even though it takes, on average, two to three lives per year just in the United States.

但還有另外一種危險，這種危險通常是自己造成的，雖然它在美國平均每年奪去兩到三條人命，但卻沒有被列入警告名單。

If you know me, you know I would never discourage the act of playing with soil and sand.

如果你瞭解我，就會知道我從不阻止玩泥土和沙子的行為。

It's basically what I was put on this earth to do.

這基本上就是我來到這個世界的目的。

Because just about every year, the news reports that someone was buried when a hole they dug collapsed on top of them.

因為幾乎每年都有新聞報道說，有人因為挖的坑塌方而被埋。

There's no central database of sand hole collapse incidents, but from the numbers we do have, about twice as many people die this way than from shark attacks in the US.

雖然沒有關於沙洞坍塌事故的中央數據庫，但從我們掌握的數據來看，在美國，死於沙洞坍塌事故的人數大約是死於鯊魚襲擊的人數的兩倍。

It might seem like common sense not to dig a big, unsupported hole at the beach and then go inside it, but sand has some really interesting geotechnical properties that can provide a false sense of security.

不要在海灘上挖一個沒有支撐的大洞，然後再鑽進去，這似乎是一種常識，但沙子具有一些非常有趣的岩土特性，可以提供一種虛假的安全感。

So let's use some engineering and garage demonstrations to explain why.

是以，讓我們用一些工程和車庫演示來解釋原因。

I'm Grady and this is Practical Engineering.

我是格雷迪，這裡是實用工程。

In some ways, geotechnical engineering might as well be called slope engineering because it's a huge part of what they do.

在某些方面，岩土工程也可以稱為邊坡工程，因為這是他們工作的重要組成部分。

So many aspects of our built environment rely on the stability of sloped earth.

我們建築環境的許多方面都依賴於坡土的穩定性。

Many dams are built from soil or rock fill using embankments.

許多水壩都是用土壤或岩石填料築成的堤壩。

Roads, highways, and bridges rely on embankments to ascend or descend smoothly.

道路、高速公路和橋樑都要依靠路堤才能順利上升或下降。

Excavations for foundations, tunnels, and other structures have to be stable for the people working inside.

地基、隧道和其他結構的挖掘工作必須保證內部工作人員的安全。

Mines carefully monitor slopes to make sure their workers are safe.

礦山仔細監測斜坡，確保工人安全。

Even protecting against natural hazards like landslides requires a strong understanding of geotechnical engineering.

即使是防範山體滑坡等自然災害，也需要對岩土工程有深入的瞭解。

Because of all that, the science of slope stability is really deeply understood.

正因為如此，人們對邊坡穩定性的科學認識才真正深入。

There's a well-developed professional consensus around the science of soil, how it behaves, and how to design around its limitations as a construction material.

關於土壤的科學、土壤的特性以及如何利用土壤作為建築材料的侷限性進行設計等問題，已經形成了廣泛的專業共識。

And I think a peek into that world will really help us understand this hazard of digging holes on the beach.

我認為，窺探那個世界將真正幫助我們理解在海灘上挖洞的危險。

Like many parts of engineering, analyzing the stability of a slope has two basic parts, the strength and the loads.

與工程學的許多部分一樣，對斜坡穩定性的分析包括兩個基本部分，即強度和荷載。

The job of a geotechnical engineer is to compare the two.

岩土工程師的工作就是對兩者進行比較。

The load, in this case, is kind of obvious.

在這種情況下，負荷是顯而易見的。

We can complicate that a bit by adding loads at the top of a slope called surcharges.

我們可以通過在坡頂增加稱為附加荷載的載荷來使情況變得複雜一些。

And no doubt, surcharged loads have contributed to at least a few of these dangerous collapses from people standing at the edge of a hole.

毫無疑問，至少有幾次站在洞口邊緣的人因荷載過大而造成危險的坍塌。

But for now, let's keep it simple with just the soil's own weight.

但現在，我們還是簡單地用土壤自身的重量來表示吧。

On a flat surface, soils are generally stable.

在平坦的地面上，土壤通常是穩定的。

But when you introduce a slope, the weight of the soil above can create a shear failure.

但是，當引入斜坡時，上方土壤的重量會造成剪切破壞。

These failures often happen along a circular arc because an arc minimizes the resisting forces in the soil while maximizing the driving forces.

這些故障通常沿著圓弧發生，因為圓弧可以將土壤中的阻力減到最小，同時將驅動力增到最大。

We can manually solve for the shear forces at any point in a soil mass, but that would be a fairly tedious engineering exercise, so most slope stability analyses use software.

我們可以手動求解土體中任意一點的剪力，但這將是一項相當繁瑣的工程工作，是以大多數邊坡穩定性分析都使用軟件。

One of the simplest methods is just to let the software draw hundreds of circular arcs that represent failure planes, compute the stresses along each plane based on the weight of the soil, and then figure out if the strength of the soil is enough to withstand the stress.

最簡單的方法之一就是讓軟件繪製數百個代表破壞平面的圓弧，根據土壤重量計算每個平面的應力，然後計算土壤強度是否足以承受應力。

But what does it really mean for a soil to have strength?

但是，土壤擁有力量的真正含義是什麼？

If you can imagine a sample of soil floating in space and you apply a shear stress, those particles are going to slide apart from each other in the direction of the stress.

如果你能想象一個漂浮在太空中的土壤樣本，並施加一個剪切應力，那麼這些顆粒就會沿著應力的方向相互滑開。

The amount of force required to do it is usually expressed as an angle, and I can show you why.

所需的力通常用角度來表示，我可以告訴你為什麼。

You may have done this simple experiment in high school physics where you drag a block along a flat surface and measure the force required to overcome the friction.

您可能在高中物理中做過這樣一個簡單的實驗：在平面上拖動一個木塊，並測量克服摩擦力所需的力。

If you add weight, you increase the force between the surfaces, called the normal force, which creates additional friction.

如果增加重量，就會增加表面之間的力，即法向力，從而產生額外的摩擦力。

The harder you press the particles of soil together, the better they are at resisting a shear force.

將土壤顆粒壓在一起的力度越大，它們抵抗剪切力的能力就越強。

In a simplified force diagram, we can draw a normal force and the resulting friction, or shear strength, that results.

在簡化力圖中，我們可以畫出法向力和由此產生的摩擦力或剪切力。

And the angle that hypotenuse makes with the normal force is what we call the friction angle.

斜邊與法向力的夾角就是我們所說的摩擦角。

Under certain conditions, it's equal to the angle of repose, the steepest angle that a soil will naturally stand.

在某些條件下，它等於傾斜角，即土壤自然形成的最陡峭的角度。

If I let sand pour out of this funnel onto the table, you can see, even as the pile gets higher, the angle of the slope of the sides never really changes.

如果我讓沙子從這個漏斗裡倒到桌面上，你可以看到，即使沙子堆越堆越高，兩邊的傾斜角度也從未真正改變過。

And this illustrates the complexity of slope stability really nicely.

這很好地說明了斜坡穩定性的複雜性。

Gravity is what holds the particles together, creating friction, but it's also what pulls them apart.

萬有引力將粒子聚集在一起，產生摩擦力，但同時也將粒子拉開。

And the angle of repose is kind of a line between gravity's stabilizing and destabilizing effects on the soil.

休止角是重力對土壤的穩定和破壞作用的分界線。

But things get more complicated when you add water to the mix.

但如果再加上水，情況就變得複雜了。

Soil particles, like all things that take up space, have buoyancy.

土壤顆粒和所有佔據空間的物體一樣，都有浮力。

Just like lifting a weight underwater is easier, soil particles seem to weigh less when they're saturated, so they have less friction between them.

就像在水下舉重更容易一樣，土壤顆粒在飽和時重量似乎更輕，是以它們之間的摩擦力也更小。

I can demonstrate this pretty easily by just moving my angle of repose setup to a water tank.

我只需將我的仰角裝置移到水箱上，就能很容易地演示這一點。

It's a subtle difference, but the angle of repose has gone down underwater.

這是一個微妙的差別，但水下的仰角已經變小了。

It's just because the particle's effective weight goes down, so the shear strength of the soil mass goes down too.

這只是因為顆粒的有效重量降低了，所以土塊的抗剪強度也降低了。

And this doesn't just happen under lakes and oceans.

這種情況不僅發生在湖泊和海洋下面。

I've covered a lot of topics on groundwater if you want to learn more.

如果您想了解更多，我已經介紹了很多關於地下水的話題。

There's this concept of the water table, below which the soils are saturated.

有一個地下水位的概念，在地下水位以下，土壤處於飽和狀態。

And they behave in the same way as my little demonstration.

他們的行為方式與我的小演示如出一轍。

The water between the particles, called pore water, exerts pressure, pushing them away from one another and reducing the friction between them.

顆粒之間的水被稱為孔隙水，會產生壓力，將顆粒相互推開，減少顆粒之間的摩擦力。

Shear strength usually goes down for saturated soils.

飽和土壤的抗剪強度通常會降低。

But if you've played with sand, you might be thinking, this doesn't really track with my intuitions.

但如果你玩過沙子，你可能會想，這與我的直覺不太相符。

When you build a sandcastle, you know, the dry sand falls apart and the wet sand holds together.

堆沙堡時，幹沙會散開，溼沙會粘在一起。

Friction actually isn't the only factor that contributes to shear strength in a soil.

實際上，摩擦力並不是影響土壤剪切強度的唯一因素。

For example, I can try to shear this clay and there's some resistance there, even though there's no confining force pushing the particles together.

例如，我可以嘗試剪切這種粘土，儘管沒有約束力將顆粒推到一起，但還是會有一些阻力。

In finer-grained soils like clay, the particles themselves have molecular-level attractions that make them basically sticky.

在粘土等顆粒較細的土壤中，顆粒本身具有分子級的吸引力，使其基本具有粘性。

Geotechnical engineers call this cohesion.

And it's where sand gets a little sneaky.

這就是沙子變得有點狡猾的地方。

Water pressure in the pores between particles can push them away from each other, but it can also do the opposite.

微粒間孔隙中的水壓可以將微粒相互推開，但也可以起到相反的作用。

In this demo, I have some dry sand in a container with a riser pipe to show the water table connected to the side.

在這個演示中，我在一個容器中放了一些幹沙，並用一根立管顯示連接到一側的地下水位。

And I've dyed my water black to make it easier to see.

我還把水染成了黑色，這樣就更容易看到了。

When I pour the water into the riser, what do you think's going to happen?

當我把水倒入立管時，你認為會發生什麼？

Will the water table in the soil be higher, lower, or exactly the same as the level in the riser?

土壤中的地下水位會比立管中的水位高、低還是完全相同？

Pretty much right away, you can see what happens.

The sand essentially sucks the water out of the riser, lifting it higher than the level outside the sand.

沙子基本上會把水從立管中吸走，使其高於沙子外的水位。

If I let this settle out for a while, you can see there's a pretty big difference in levels.

如果我讓它沉澱一段時間，你就會發現它們在水準上有很大的不同。

And this is largely due to capillary action.

Just like a paper towel, water wicks up into the sand against the force of gravity.

就像紙巾一樣，水會在重力的作用下吸進沙子裡。

This capillary action actually creates negative pressure within the soil, compared to the ambient air pressure.

與環境氣壓相比，這種毛細作用實際上會在土壤中產生負壓。

In other words, it pulls the particles against each other, increasing the strength of the soil.

換句話說，它能將顆粒相互拉扯，增加土壤的強度。

It basically gives the sand cohesion, additional shear strength that doesn't require any confining pressure.

它基本上賦予沙子內聚力和額外的剪切強度，而不需要任何約束壓力。

And again, if you've played with sand, you know there's a sweet spot when it comes to water.

再說一遍，如果你玩過沙子，你就會知道，水是有甜點的。

But if there's just enough water, you get this strengthening effect.

但如果有足夠的水，就會產生這種強化效果。

However, unlike clay that has real cohesion, that suction pressure can be temporary.

然而，與具有真正內聚力的粘土不同，這種吸力可能是暫時的。

And it's not the only factor that makes sand tricky.

讓沙子變得棘手的因素還不止這些。

The shear strength of sand also depends on how well-packed those particles are.

沙子的剪切強度還取決於這些顆粒的堆積程度。

Beach sand is usually well-consolidated because of the constant crashing waves.

由於海浪的不斷衝擊，海灘上的沙子通常都很堅固。

If the particles are packed tight, they essentially lock together.

如果顆粒擠得很緊，它們基本上就會鎖在一起。

You can see that to shear them apart doesn't just look like sliding motion, but also a slight expansion in volume.

你可以看到，將它們剪切開不僅看起來像滑動運動，而且體積也在輕微膨脹。

And you don't need a microscope to see it.

In fact, you probably notice this walking around on the beach, especially when the water table is close to the surface.

事實上，您在海灘上走動時可能會注意到這一點，尤其是當地下水位接近水面時。

Even a small amount of movement causes the sand to expand.

即使是很小的移動也會導致沙子膨脹。

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海灘洞為何如此致命？ (Why Are Beach Holes So Deadly?)

essentially

material

basically

practical