1 00:00:01,840 --> 00:00:07,640 Speaker 1: Welcome to Brainstuff, a production of iHeartRadio. Hey brain Stuff 2 00:00:07,680 --> 00:00:12,400 Speaker 1: Lauren Vogebon Here. With winter coming on fast here in 3 00:00:12,440 --> 00:00:16,320 Speaker 1: the Northern Hemisphere, I've been thinking about travel, but not 4 00:00:16,480 --> 00:00:19,959 Speaker 1: travel through the cold, wet weather. What if we could 5 00:00:19,960 --> 00:00:26,840 Speaker 1: reach a beautiful destination via underwater tunnel. Unfortunately, contrary to 6 00:00:26,960 --> 00:00:30,320 Speaker 1: what supervillains and Moleman would have you believe, it takes 7 00:00:30,400 --> 00:00:33,400 Speaker 1: more than some giant machine to build an underwater tunnel. 8 00:00:34,960 --> 00:00:37,960 Speaker 1: Even so, for most of human history we've been pretty 9 00:00:37,960 --> 00:00:41,640 Speaker 1: tunnel savvy. Humans have tunneled since the first cave dwellers 10 00:00:41,680 --> 00:00:45,360 Speaker 1: decided to excavate a spare bedroom, and the essentials of 11 00:00:45,479 --> 00:00:48,520 Speaker 1: dig support and advance were well refined by the time 12 00:00:48,520 --> 00:00:51,760 Speaker 1: the ancient Greeks used tunnels to irrigate and drain their farmland. 13 00:00:53,320 --> 00:00:58,760 Speaker 1: Even underwater tunneling is old. Sometime around twenty one seventy BCE, 14 00:00:59,320 --> 00:01:02,120 Speaker 1: the Babylonia built one of the first known examples by 15 00:01:02,120 --> 00:01:06,679 Speaker 1: diverting the Euphrates River. The bricklined and arch supported tunnel 16 00:01:06,760 --> 00:01:10,080 Speaker 1: measured twelve feet high by fifteen feet wide that's four 17 00:01:10,120 --> 00:01:13,679 Speaker 1: by five meters, and provided passage for pedestrians and chariots 18 00:01:13,720 --> 00:01:16,520 Speaker 1: alike between the royal palace and a temple some three 19 00:01:16,560 --> 00:01:21,360 Speaker 1: thousand feet or nine hundred meters away. For centuries, tunnels 20 00:01:21,360 --> 00:01:25,240 Speaker 1: were employed mainly by miners and medieval sappers, who dug 21 00:01:25,319 --> 00:01:30,440 Speaker 1: under castle walls to collapse them, hence the term undermine. 22 00:01:30,720 --> 00:01:35,120 Speaker 1: But the advent of canal transport and later railroads gave 23 00:01:35,200 --> 00:01:39,120 Speaker 1: workers something new to sink their shovels into. The eighteenth 24 00:01:39,200 --> 00:01:42,680 Speaker 1: thirty twentieth centuries saw a succession of ever more challenging 25 00:01:42,720 --> 00:01:46,920 Speaker 1: tunnel projects, made possible by vast improvements in surveying and 26 00:01:47,000 --> 00:01:51,840 Speaker 1: ventilation techniques. Even so, a danger and expense delayed attempts 27 00:01:51,840 --> 00:01:56,880 Speaker 1: at underwater tunneling until the mid eighteen hundreds, which raises 28 00:01:56,920 --> 00:02:00,840 Speaker 1: the question if underwater tunneling risks in your own grave, 29 00:02:01,240 --> 00:02:06,520 Speaker 1: literally and financially, why bother. Many city planners agree turning 30 00:02:06,560 --> 00:02:10,800 Speaker 1: to tunnels only when congested bridges reach choking capacity. But 31 00:02:11,000 --> 00:02:14,919 Speaker 1: bridges are problematic too. They interfere with shipping traffic, take 32 00:02:15,000 --> 00:02:18,920 Speaker 1: up valuable riverfront property, and block scenic views. From a 33 00:02:18,960 --> 00:02:23,120 Speaker 1: defense standpoint, bridges make easy airstrike targets and can constitute 34 00:02:23,160 --> 00:02:28,880 Speaker 1: hazards if they collapse. Tunnels conversely, withstand tides currents and 35 00:02:28,919 --> 00:02:32,680 Speaker 1: storms better than bridges, can reach longer distances and have 36 00:02:32,840 --> 00:02:37,799 Speaker 1: virtually unlimited weight carrying capacity. In addition, a tunnel's per 37 00:02:37,919 --> 00:02:41,840 Speaker 1: length cost drops as it gets longer, whereas for bridges 38 00:02:41,880 --> 00:02:45,560 Speaker 1: the opposite is true, and while tunnels require a larger 39 00:02:45,600 --> 00:02:49,239 Speaker 1: initial investment, bridges make up the difference in maintenance costs. 40 00:02:51,040 --> 00:02:55,359 Speaker 1: But let's not get tunnel vision. Tunneling faces particular security 41 00:02:55,440 --> 00:02:59,960 Speaker 1: vulnerabilities and safety issues of fires and accidents post die 42 00:03:00,280 --> 00:03:03,519 Speaker 1: threats in tunnels, which is why rail tunnels include crossover 43 00:03:03,560 --> 00:03:07,120 Speaker 1: passages where trains can switch tracks, along with service tunnels 44 00:03:07,160 --> 00:03:11,600 Speaker 1: that can serve as emergencies scape routes. Yet today underwater 45 00:03:11,680 --> 00:03:14,480 Speaker 1: tunnels are so commonplace that we rarely think of them 46 00:03:14,600 --> 00:03:18,840 Speaker 1: as the modern wonders that they are. Take the Seikan 47 00:03:18,960 --> 00:03:22,520 Speaker 1: Tunnel in Japan, a connecting the islands of Honshu and Hokkaido, 48 00:03:22,880 --> 00:03:26,160 Speaker 1: which holds the record for the longest and deepest underwater 49 00:03:26,240 --> 00:03:28,919 Speaker 1: rail tunnel at thirty three and a half miles that's 50 00:03:28,960 --> 00:03:32,200 Speaker 1: fifty four kilometers, reaching a depth of seven hundred and 51 00:03:32,280 --> 00:03:36,720 Speaker 1: ninety feet or two hundred and forty meters. Japan began 52 00:03:36,800 --> 00:03:39,680 Speaker 1: planning it in the nineteen fifties after a typhoon caused 53 00:03:39,720 --> 00:03:43,280 Speaker 1: a deadly disaster in the strait between the islands. It 54 00:03:43,320 --> 00:03:46,240 Speaker 1: took thirty years to complete, and pumps keep it clear 55 00:03:46,240 --> 00:03:49,400 Speaker 1: of water at the rate of twenty tons per minute. 56 00:03:51,160 --> 00:03:54,920 Speaker 1: As impressive as the Seikon Tunnel is, only about fourteen 57 00:03:54,960 --> 00:03:58,280 Speaker 1: of its miles or twenty three of its kilometers run underwater, 58 00:03:58,880 --> 00:04:01,600 Speaker 1: meaning that the Channel Tip or chunnel that connects the 59 00:04:01,720 --> 00:04:05,840 Speaker 1: United Kingdom in France beats it. There. The channel only 60 00:04:05,880 --> 00:04:08,640 Speaker 1: goes a third is deep, but its underwater portion runs 61 00:04:08,680 --> 00:04:10,960 Speaker 1: for twenty four miles or about thirty eight and a 62 00:04:11,000 --> 00:04:16,040 Speaker 1: half kilometers. It was finished in nineteen ninety four, but okay, 63 00:04:16,200 --> 00:04:19,840 Speaker 1: the Sekan and Channel tunnels respectively blasted and bored their 64 00:04:19,880 --> 00:04:24,279 Speaker 1: passages through solid rock. The longest and deepest immersion tunnel 65 00:04:24,400 --> 00:04:27,719 Speaker 1: is the Marmarai, which connects the Asian and European halves 66 00:04:27,720 --> 00:04:31,040 Speaker 1: of Istanbul Turkey across the floor of the Bosporus Sea. 67 00:04:31,640 --> 00:04:35,880 Speaker 1: It employs pre assembled sections connected by thick, flexible rubber 68 00:04:35,960 --> 00:04:40,200 Speaker 1: reinforced steel plates to better contend with regional seismic activity, 69 00:04:40,600 --> 00:04:44,000 Speaker 1: and stretches a total of eight miles or thirteen kilometers, 70 00:04:45,880 --> 00:04:48,039 Speaker 1: but let's back up a bit and get into some 71 00:04:48,200 --> 00:04:53,760 Speaker 1: technical but important definitions. A tunnel is technically a passage 72 00:04:53,839 --> 00:04:57,919 Speaker 1: dug entirely underground, and many of the subterranean tubes that 73 00:04:57,960 --> 00:05:01,599 Speaker 1: we consider tunnels, like subway and sewage and water lines, 74 00:05:01,880 --> 00:05:05,919 Speaker 1: are technically conduits because to build them we temporarily remove 75 00:05:05,960 --> 00:05:09,200 Speaker 1: ground material, place the line, then cover it back up, 76 00:05:09,960 --> 00:05:12,920 Speaker 1: which is generally much cheaper and easier, especially if you're 77 00:05:12,920 --> 00:05:17,719 Speaker 1: dealing with loose dirt and shallow projects. But to tunnel 78 00:05:17,720 --> 00:05:20,120 Speaker 1: in the earth under a body of water, the classic 79 00:05:20,120 --> 00:05:23,640 Speaker 1: approach is to use a tunneling shield. Shields let you 80 00:05:23,680 --> 00:05:26,839 Speaker 1: dig a long tunnel through soft earth without its bleeding 81 00:05:26,960 --> 00:05:32,680 Speaker 1: edge collapsing. Here's how it works, okay, Imagine you take 82 00:05:32,720 --> 00:05:35,799 Speaker 1: a coffee can and take off the lid, then sharpen 83 00:05:35,839 --> 00:05:38,400 Speaker 1: the edge around the bottom and punch a few holes 84 00:05:38,440 --> 00:05:41,719 Speaker 1: in the bottom. If you took that tin by the 85 00:05:41,720 --> 00:05:45,159 Speaker 1: open end and pushed the bottom into soft earth, some 86 00:05:45,279 --> 00:05:48,520 Speaker 1: dirt would squeeze up through the holes. You could remove 87 00:05:48,560 --> 00:05:52,599 Speaker 1: the dirt and then push the can in further. On 88 00:05:52,640 --> 00:05:55,520 Speaker 1: the scale of a real shield. Several humans as sometimes 89 00:05:55,600 --> 00:06:00,039 Speaker 1: nicknamed muckers or sandhogs, would stand inside compartments within the 90 00:06:00,120 --> 00:06:04,800 Speaker 1: can and remove the clayer sand. Hydraulic jacks would gradually 91 00:06:04,880 --> 00:06:07,960 Speaker 1: move the shield forward while crews behind it installed metal 92 00:06:07,960 --> 00:06:12,560 Speaker 1: supporting rings, then lined them with concrete or masonry. In 93 00:06:12,640 --> 00:06:15,200 Speaker 1: order to hold back water seepage from the tunnel walls. 94 00:06:15,400 --> 00:06:18,240 Speaker 1: The front of the tunnel or shield is sometimes pressurized 95 00:06:18,279 --> 00:06:22,679 Speaker 1: with compressed air. Workers who can only withstand short periods 96 00:06:22,720 --> 00:06:25,560 Speaker 1: in such conditions must pass through one or more air 97 00:06:25,600 --> 00:06:31,560 Speaker 1: locks and take precautions against pressure related sickness. Shields are 98 00:06:31,560 --> 00:06:35,520 Speaker 1: still used in tunnel construction, especially when installing utility conduits 99 00:06:35,600 --> 00:06:40,080 Speaker 1: or larger water or sewage pipes. Although labor intensive, they 100 00:06:40,120 --> 00:06:43,080 Speaker 1: cost only a fraction as much as their mammoth cousins. 101 00:06:43,400 --> 00:06:48,240 Speaker 1: The tunnel boring machines afar from dull. A tunnel boring 102 00:06:48,279 --> 00:06:51,920 Speaker 1: machine is a multi story tall engine of destruction capable 103 00:06:51,920 --> 00:06:55,640 Speaker 1: of chewing through solid rock at its front spins its 104 00:06:55,680 --> 00:06:59,200 Speaker 1: cutting head, which is a giant wheel that has bristles 105 00:06:59,200 --> 00:07:02,799 Speaker 1: of rock breaking discs, and incorporates a system of scoops 106 00:07:02,839 --> 00:07:05,039 Speaker 1: to lift the pummeled rock and drop it onto an 107 00:07:05,080 --> 00:07:09,400 Speaker 1: outbound conveyor belt. Behind the cutting head swings an erector, 108 00:07:09,920 --> 00:07:13,360 Speaker 1: which is a rotating assembly that builds the tunnel lining 109 00:07:13,440 --> 00:07:18,240 Speaker 1: in the machine's wave. In some large projects, like the Channel, 110 00:07:18,600 --> 00:07:21,800 Speaker 1: a separate tunnel boring machines begin on opposite ends and 111 00:07:21,880 --> 00:07:25,760 Speaker 1: drill toward a central point, using sophisticated surveying methods to 112 00:07:25,960 --> 00:07:31,520 Speaker 1: keep them on course. Drilling through solid rock creates largely 113 00:07:31,600 --> 00:07:36,160 Speaker 1: self supporting tunnels, and these machines drive forward quickly and relentlessly. 114 00:07:36,800 --> 00:07:39,640 Speaker 1: Some Channel machines could bore two hundred and fifty feet 115 00:07:39,640 --> 00:07:44,240 Speaker 1: a day, that's seventy six meters. On the downside, they 116 00:07:44,280 --> 00:07:48,000 Speaker 1: break often and deal poorly with rock that's worn, sheared, 117 00:07:48,120 --> 00:07:54,400 Speaker 1: or highly jointed, so they sometimes move much slower. Luckily, 118 00:07:54,560 --> 00:07:57,880 Speaker 1: tunnel boring machines and shields aren't the only games in town. 119 00:07:59,080 --> 00:08:03,600 Speaker 1: Enter these sunken two tube or immersed tube tunnel. These 120 00:08:03,920 --> 00:08:06,600 Speaker 1: entirely evade the problem of trying to dig through soft 121 00:08:06,640 --> 00:08:09,520 Speaker 1: earth or solid rock while preventing a whole ocean from 122 00:08:09,520 --> 00:08:13,040 Speaker 1: pouring into your tunnel by constructing the tunnel separately then 123 00:08:13,160 --> 00:08:18,360 Speaker 1: installing it under water. Immersion tunnels are assembled on site 124 00:08:18,440 --> 00:08:22,120 Speaker 1: from prefab pieces, each the size of a football field. 125 00:08:23,200 --> 00:08:26,760 Speaker 1: American engineer W. J. Wilgis pioneered the technique when he 126 00:08:26,800 --> 00:08:31,080 Speaker 1: built the Detroit River Railroad tunnel connecting Detroit, Michigan, and Windsor, Ontario, 127 00:08:31,440 --> 00:08:34,880 Speaker 1: in nineteen ten, and they've been the go to technique 128 00:08:34,880 --> 00:08:40,200 Speaker 1: for vehicle tunnels ever since. To make each segment, workers 129 00:08:40,240 --> 00:08:44,280 Speaker 1: assemble some thirty thousand tons of stealing concrete enough for 130 00:08:44,360 --> 00:08:47,480 Speaker 1: a ten story apartment building in a massive mold, then 131 00:08:47,520 --> 00:08:51,000 Speaker 1: allow the concrete to cure for nearly a month. The 132 00:08:51,080 --> 00:08:54,600 Speaker 1: molds contain the tunnel's floor, walls, and ceiling and are 133 00:08:54,640 --> 00:08:57,199 Speaker 1: initially capped at the ends to keep them water tight 134 00:08:57,320 --> 00:09:01,880 Speaker 1: as they're transported out to sea. Immersion pontoons, which are 135 00:09:02,000 --> 00:09:04,920 Speaker 1: large ships resembling a cross between a gantry crane and 136 00:09:04,920 --> 00:09:09,839 Speaker 1: a pondtoon boat, do the hauling. Once they're over the 137 00:09:09,880 --> 00:09:13,040 Speaker 1: pre dug sea trench. Each tunnel section is weighted to 138 00:09:13,080 --> 00:09:16,559 Speaker 1: allow it to sink. A crane slowly lowers the section 139 00:09:16,640 --> 00:09:20,880 Speaker 1: into position while divers guide it precisely to its GPS coordinates. 140 00:09:21,800 --> 00:09:24,280 Speaker 1: Each new section is connected to its predecessor with a 141 00:09:24,320 --> 00:09:27,360 Speaker 1: massive flexible joint that can establish a seal on the 142 00:09:27,400 --> 00:09:30,960 Speaker 1: outside of the two tubes. Crews then pump out the 143 00:09:31,000 --> 00:09:34,000 Speaker 1: water between the two bulkhead seals on the inside of 144 00:09:34,040 --> 00:09:37,840 Speaker 1: the seal, and then can remove the bulkheads, at which 145 00:09:37,880 --> 00:09:40,440 Speaker 1: point you're ready to sink a new piece and connect 146 00:09:40,480 --> 00:09:44,000 Speaker 1: it the same way. Once the tunnel is built and 147 00:09:44,120 --> 00:09:47,520 Speaker 1: reinforced from the inside, it might be buried under backfill 148 00:09:47,679 --> 00:09:53,600 Speaker 1: or otherwise covered. Immersed tube construction can delve deeper than 149 00:09:53,640 --> 00:09:57,440 Speaker 1: other approaches. Because the technique doesn't require compressed air to 150 00:09:57,520 --> 00:10:01,000 Speaker 1: hold water at bay, A cruise can for work longer 151 00:10:01,000 --> 00:10:05,599 Speaker 1: in them and under more tolerable conditions. Moreover, sections of 152 00:10:05,600 --> 00:10:09,120 Speaker 1: an immersed tunnel can take any form, unlike a board tunnel, 153 00:10:09,160 --> 00:10:13,480 Speaker 1: which follows the shape of its shield or boring machine. However, 154 00:10:13,720 --> 00:10:17,360 Speaker 1: immersed tunnels do require additional tunneling methods to prepare the 155 00:10:17,360 --> 00:10:20,960 Speaker 1: bed and bore out their land based entrances and exits. 156 00:10:22,440 --> 00:10:26,000 Speaker 1: Researchers are working on developing submerged but floating tunnels that 157 00:10:26,040 --> 00:10:31,000 Speaker 1: would circumvent the need to bore at all. In underwater tunneling, 158 00:10:31,240 --> 00:10:39,000 Speaker 1: as in life, it takes all kinds. Today's episode is 159 00:10:39,000 --> 00:10:41,400 Speaker 1: based on the article how do you build an underwater tunnel? 160 00:10:41,440 --> 00:10:44,600 Speaker 1: On how stuffworks dot com, written by Nicholas Gerbis. Brain 161 00:10:44,600 --> 00:10:47,280 Speaker 1: Stuff is production by Heart Radio in partnership with HowStuffWorks 162 00:10:47,280 --> 00:10:49,959 Speaker 1: dot Com and is produced by Tyler Klang. For more 163 00:10:50,000 --> 00:10:53,599 Speaker 1: podcasts my Heart Radio, visit the iHeartRadio app, Apple Podcasts, 164 00:10:53,720 --> 00:11:05,439 Speaker 1: or wherever you listen to your favorite shows.