9 Tunnels are round

What are houses made from? Most houses are made from bricks, but they can be built out of almost anything—as long as it's strong and it keeps out the weather. Builders like to use materials they can get hold of easily bricks or stone, wood, reeds or mud. Bricklayers put mortar between the bricks. Mortar is a mixture of water, sand and cement, and it glues the bricks together. Houses protect us from the heat in the summer, and the cold and rain in the winter. There are about 12,000 bricks in the outside walls of a two-storey house. Some birds use mud to build their homes, but it's not shaped into little bricks! There aren't any bricks in the middle of a forest, but there is plenty of wood for building cabins. For thousands of years in the marshes of southern Iraq, the East, people used bundles of river reeds to build beautiful homes. In hot places such as Africa, people often built with mud and straw, which dries hard in the sunshine.

房子是用什么做的？ 大多数房子都是用砖砌成的，但它们几乎可以用任何东西来建造——只要它坚固并且能抵挡风雨。 建筑者喜欢使用容易获得的材料砖或石头、木材、芦苇或泥土。 泥瓦匠在砖之间涂灰浆。 砂浆是水、沙子和水泥的混合物，它能把砖粘合在一起。 房子在夏天保护我们免受炎热，在冬天保护我们免受寒冷和雨水。 一座两层楼房的外墙大约有12000块砖。 一些鸟用泥来建造它们的家，但它不是被塑造成小砖！森林中央没有砖头，但有足够的木材来建造小屋。 几千年来，在东部伊拉克南部的沼泽地里，人们用一捆捆的河芦苇建造美丽的家园。 在像非洲这样炎热的地方，人们经常用泥土和稻草建造房屋，这些泥土和稻草在阳光下会变干。

What holds up the ceiling? The weight of ceilings and floors is carried by strong wooden beams called joists. There are joists hidden away under the floorboards and above the ceiling of every room. What's behind the walls? Among other things, there's usually a lot of air! That's because most brick houses have double outer walls, with a gap between the walls. Pipes and electrical wiring are tucked away in this gap. What's under the floor? There are pipes under the floor. Some carry clean water around the house. Others take dirty water away. Some aren't for water at all-they carry gas, which is burned to heat ovens for cooking and water for washing. The roof is held up by thick wooden tufters. Tiles keep out the rain. Sometimes uninvited visitors live under the floor, such as the wood-eating grubs of the woodworm beetle. Building a house is teamwork. A plumber lays all the pipes, an electrician does the wiring, and a carpenter puts in the windows, doors and cupboards.

是什么支撑着天花板？ 天花板和地板的重量由称为托梁的坚固木梁承载。 每个房间的地板下面和天花板上面都有托梁。 墙后面是什么？除此之外，通常有很多空气！这是因为大多数砖房都有双层外墙，墙壁之间有空隙。 管子和电线都藏在这个缝隙里。 地板下面是什么？地板下面有管道。 有些人在房子里带着干净的水。 其他人把脏水带走。 有些根本不是用来装水的——它们携带气体，燃烧后可以加热烤箱做饭，也可以用来洗衣服。 屋顶是由厚厚的木片支撑着的。 瓷砖可以挡雨。有时不请自来的客人住在地板下，比如食木虫甲虫的蛴螬。 盖房子是团队合作。 水管工负责铺设所有的管道，电工负责布线，木匠负责安装门窗和橱柜。

What do bulldozers do? Bulldozers clear building sites and make the land flat enough to build on. The huge steel blade at the front shifts great mounds of soil, brick or anything else that's in the way. Bulldozers are incredibly powerful machines—just the job for pushing and shoving things around. Why don't bulldozers get stuck? Instead of a tyre on each wheel, a bulldozer has a crawler track around each pair of front and back wheels. Crawler tracks grip the ground well and stop the bulldozer from getting bogged down in the mud. At the back of some bulldozers there's an arm with large metal spikes called rippers. These are used to break up hard rock and to tear out tree stumps. Guess what a small bulldozer is called- a calfdozer! There are even special under- water bulldozers which flatten riverbeds or the seafloor so that bridges can be built on them. A bulldozer once won a tug-of-war contest against 150 people! Bulldozers can be as much as 500 times heavier than you. But their tracks spread the weight so evenly that they are much less likely to sink in the mud!

推土机是做什么的？推土机清理建筑工地，使土地平整到可以盖房子。 前方巨大的钢刃会移动挡在路上的土堆、砖块或其他任何东西。 推土机是一种非常强大的机器——就是用来推东西的。 为什么推土机不会被卡住？ 推土机不是每个轮子上都有一个轮胎，而是在每一对前后轮周围都有履带。 履带式履带能很好地抓住地面，防止推土机陷进泥里。 在一些推土机的后面，有一个带有大型金属钉的机械臂，叫做“开膛手”。 这些都是用来打碎坚硬的岩石和撕下树桩的。 猜猜一种小型推土机叫什么——calfdozer！甚至还有专门的水下推土机，可以把河床或海底削平，以便在上面建桥。 一台推土机曾经在一场拔河比赛中战胜了150人！推土机可能比你重500倍。 但是它们的足迹均匀地分散了重量，所以它们不太可能陷进泥里！

Why do houses need holes? Most houses start with holes in the ground. The holes are filled with runny concrete, which hardens as it sets. The rest of the house is then built on top of this firm base, called the foundations. What do diggers do? A digger does much more than dig. Its wide front bucket is brilliant at scooping rubble into a truck. A scissor-like bucket can also be fitted to the front, to grab and lift logs and pipes. Many diggers have a wide front bucket, as well as the digging bucket at the back. A digger can dig a trench as fast as 20 people with spades. The biggest earth-scooping buckets can hold five large family cars. They are on huge mining machines called excavators, which are about ten times bigger than the average digger. Diggers also dig holes for swimming pools, rubbish heaps and top-secret underground hiding places! A huge hammer can be fitted to a digger, allowing it to smash up rocks.

为什么房子需要洞？大多数房子都是从地上挖洞开始的。 这些洞是用流动的混凝土填满的，混凝土凝固后会变硬。 房子的其余部分就建在这个牢固的基础上，称为地基。 挖掘机是做什么的？挖掘机不仅仅是挖掘。 它宽大的前斗在将碎石铲入卡车方面非常出色。 一个剪刀状的桶也可以安装在前面，以抓取和提升原木和管道。 许多挖掘机有一个宽的前斗，以及后面的挖掘斗。 一台挖掘机挖沟的速度相当于20个人用铲子挖沟的速度。 最大的挖土桶可以装下五辆大型家用汽车。 他们在一种叫做挖掘机的大型采矿机器上，这种机器比一般的挖掘机大十倍。 挖掘机也挖洞游泳池，垃圾堆和绝密的地下藏身之处！一个巨大的锤子可以安装在挖掘机上，使它能够粉碎岩石。

Do buildings have roots? Skyscraper foundations are called piles and they are made of steel or concrete. Piles do the same job for a skyscraper as roots do for a tree. They stop it blowing over in the wind, or sinking into the ground under its own weight. Which are the world's biggest hammers? To knock a nail into wood, you use a hammer. To drive a steel pile into the ground, builders use a huge hammer called a piledriver, A crane lifts up the piledriver, then drops it on to the pile with a deafening BANG! Which are the world's largest corkscrews? Sometimes, the holes for piles are drilled with an auger—a long tool which works like a giant corkscrew, twisting its way deep down into the ground. A steel rod is put into the hole, and then lots of concrete is poured down around it. The piles for some skyscrapers are well over 50 metres deep. That's the same as five houses buried one on top of the other! Using piledrivers at night is against the law in many towns and cities. They're much too noisy.

建筑有根吗？摩天大楼的基础被称为桩，它们由钢或混凝土制成。 桩对于摩天大楼的作用就像树根对于树木的作用一样。 它们可以防止它被风吹走，或者在自身重量的作用下沉入地下。 哪些是世界上最大的锤子？ 要把钉子敲进木头里，你得用锤子。 为了将钢桩打入地下，建筑工人们使用一种叫做打桩机的巨大锤子，起重机将打桩机抬起，然后发出震耳欲聋的巨响，把它扔到桩上！哪些是世界上最大的开瓶器？ 有时，钻孔是用螺旋钻钻成的，螺旋钻是一种长长的工具，它的工作原理就像一个巨大的开瓶器，扭曲着钻入地下深处。 把一根钢棒放进洞里，然后在洞周围浇上大量的混凝土。 一些摩天大楼的桩深超过50米。 这相当于五栋房子一幢盖在另一幢上！在许多城镇，夜间打桩机是违法的。 他们太吵了。

Do buildings have a skeleton? Nowadays, most big buildings have a strong steel framework inside them. This framework does a similar job to the bony skeleton inside your body. It props up the building and stops it from collapsing to the ground. Do buildings have a skin? The skin of a building is formed by its windows and walls. On modern skyscrapers these are made of glass or plastic panels, and thin concrete or stone sheets. These panels and sheets are called cladding. by big ncils called rivets. These are punched through holcs. Then their ends are flattened to stop them slipping out again. Other beams are joined by welding. The ends are heated until they melt and flow together like runny chocolate. When they cool down, the joined ends have hardened together. A skyscraper's framework is made from steel beams and tubes. The ends of one kind of beam look like the letters I or H. Beams this shape are stronger and lighter than square beams.

建筑物有骨架吗？ 如今，大多数大型建筑内部都有坚固的钢框架。 这个框架和你体内的骨骼起着类似的作用。 它支撑着大楼，防止它倒在地上。 建筑有皮肤吗？建筑的表皮是由窗户和墙壁构成的。 在现代摩天大楼上，这些都是由玻璃或塑料板，以及薄混凝土或石板制成的。 这些面板和薄板被称为包层。 被一种叫做铆钉的大钉钉住。 这些都是穿孔的。 然后将它们的末端压平以防止它们再次滑出。 其他横梁是通过焊接连接的。 末端被加热，直到它们融化，像巧克力一样流动。 当它们冷却下来时，连接的两端就硬化在一起了。 摩天大楼的框架是由钢梁和钢管构成的。 一种光束的末端看起来像字母I或H。 这种形状的梁比方形梁更坚固、更轻。