How Engineers Straightened the Leaning Tower of Pisa

One of my favorite civil engineering projects!
🌌Get Nebula using my link for 40% off an annual subscription: go.nebula.tv/Practical-Engine...
🚆Watch "The Logistics of X": nebula.tv/thelogisticsofx?ref...
The lean isn’t just a fascinating oddity; it is integral to the historical character of the tower. It’s a big part of why we care. Unlike the millions of photos of tourists pretending to hold the Pisa tower up, the contractors, restoration experts, and engineers actually did it (for the next few centuries, at least).
Sources: The script is primarily based on the papers linked below.
www.tandfonline.com/doi/abs/1...
associazionegeotecnica.it/art...
www.issmge.org/publications/p...
Watch this video ad-free on Nebula: nebula.tv/videos/practical-en...
Signed copies of my book (plus other cool stuff) are available here: store.practical.engineering/
Practical Engineering is a KZbin channel about infrastructure and the human-made world around us. It is hosted, written, and produced by Grady Hillhouse. We have new videos posted regularly, so please subscribe for updates. If you enjoyed the video, hit that ‘like’ button, give us a comment, or watch another of our videos!
CONNECT WITH ME
____________________________________
Website: practical.engineering
Twitter: / hillhousegrady
Instagram: / practicalengineering
Reddit: / practicalengineering
Facebook: / practicalengineergrady​
Patreon: / practicalengineering
SPONSORSHIP INQUIRIES
____________________________________
Please email my agent at [e-mail]
DISCLAIMER
____________________________________
This is not engineering advice. Everything here is for informational and entertainment purposes only. Contact an engineer licensed to practice in your area if you need professional advice or services. All non-licensed clips used for fair use commentary, criticism, and educational purposes.
SPECIAL THANKS
____________________________________
This video is sponsored by Nebula.
Stock video and imagery provided by Getty Images, Shutterstock, and Videoblocks.
Music by Epidemic Sound: epidemicsound.com/creator
Tonic and Energy by Elexive is licensed under a Creative Commons Attribution License
Source: • Elexive - Tonic and En...
Video by Grady Hillhouse
Edited by Wesley Crump
Produced by Ralph Crewe
Graphics by Nebula Studios

[@mfaizsyahmi]

I find it very amusing that the sidewalks are actually load bearing, not just for pedestrians but the entire tower.

[@nw4042]

It's kind of brilliant. They built what amounts to a float foundation/spread footing that is likely the main reason the tower stayed up as long as it has while tilted.

[@eternaldrunk]

amerifats are getting heavier

[@nekomimicatears]

​@@eternaldrunkoh no not the "amerifats"! Whatever shall we do!

[@travisk5589]

Uh. That's not what he said nor described.

[@AethelwulfBretwalda]

​@@eternaldrunk "You're not going up there. It's all winding stairs."

[@DrRadula]

There's just something extremely joyful about a guy being able to say "recreational geology" with a straight face and a genuine smile

[@jonslg240]

I remember when they were doing this.. we watched an hour (whole first period) of Channel One news once a week in school during home period(the first class).. Other days we had to watch 15 minutes of it, instead of whatever class we were in. Everyone liked it because it was far more fun to watch TV than be bored being re-taught things we've learned before. Channel One news covered plenty of interesting things.. But they also only covered anything political from 1 side of the spectrum.. which is pretty underhanded. I'm sure it's great to feed propaganda to kids when it's from the side you agree with.. But how would you feel if it was coming from the side you didn't agree with, and all adolescents were being forced to watch it in school? That's a very dangerous precedent to set. Feeding 12-17 year-olds very select news in a VERY politically biased way. Being presented by "cool kids" who are 18-21 and meant to be interpreted as role models. Talk about having no shame.

[@Naruto5471]

As a geologist, I laughed so hard....

[@jhandle4196]

Sounds like he has rocks in his head.

[@Someone-sc2hk]

@@Naruto5471 you wanna look at my obsidian knife?

[@mvmlego1212]

I thought the same thing when I heard the phrase "stellar seismology" on PBS Space Time earlier this week.

[@magimix2000]

The tower is *curved*?! That is amazing. I can't believe I never knew that.

[@1pcfred]

The walls of old brick buildings are always curved. You just can't see it from the ground. But when you get on top of one and look down the wall you can see it then. You can see every brick. Makes it look taller. Modern brick faced buildings are different. The brick is just a siding. It's held up by the inner structure of the building which is blocks and steel. There's wavy metal straps called ties that hold the brick to the real wall.

[@robertheinkel6225]

I have seen the tower in person. It is not curved. It was built straight, but as it started to tilt, they readjusted the next section so it would be straight up, with a tilted base. They made three corrections to correct for the tilt.

[@greenidguy9292]

@@robertheinkel6225It is “essentially curved”, no not a true curve, but similar.

[@greensteve9307]

Ditto!

[@Lipi19821]

​@@robertheinkel6225 if not curved, explain how one side has 2 stairs more than the other😮

[@certiPHIer]

I was there in 1987, 3 years before the tower was closed for repairs. It is a terribly disorienting building to climb the stairs to the top, not only because of the lean that causes you to (correctly) feel like you are leaning in every direction in sequence, like someone terribly drunk, but also because the centuries of foot traffic on the steps have caused them to wear out unevenly, so they are dished out where the feet have trafficked the most. Plus the single narrow spiral stair has both people climbing up and people climbing down at the same time. It was also ver scary when you got to the top, because from the lowest side of the platform, you could not see the base of the tower beneath you, the lean was so great. But I'm glad I had the opportunity and really glad it did not collapse while I was in the tower. I'm so happy it has been stabilized now and future generations will have a chance to experience it themselves.

[@rhouser1280]

“If you’re into recreational geology & heavy construction!” 😂 I really wasn’t until I started watching your channel! Now I think about it driving down the road looking at anything that was built.

[@richardred15]

Nah, you were the whole time, just didn't know it yet :)

[@Cheezed_]

This was my exact thought. I wasn't until you did this to me.

[@SliceofLifeHousewife]

Me too!

[@roryoconnor1411]

Same

[@dmacpher]

It’s legal in Canada now!

[@kenchilton]

A couple other ideas that were rejected were installing a tube system under the foundation to freeze the water in the subsoil, controlling the temperature according to the lean, or using hydraulically injected foam to correct the lean in conjunction with injecting a water-cured polymer to harden the subsoil.

[@davidschoon8254]

Compensation grouting (aka compaction or hydrofracture grouting) with cement is what I would have done since I'm a grouting engineer but honestly it would've been similar in cost and schedule to what they did. I've lifted a penstock at a power generating station using cement and sodium silicate. 3 months to lift 3/4" with a goal of 1". With steady gradual progress, its possible to react to geoinstrument feedback to target specific points to lift and others to leave alone. The structures took weeks to react to the initial consolidation and kept moving upward for weeks after I completed the work to reach the 1" total lift target. Compensation grouting with water reactive polyurethane is hard to control because polyurethane expands so much and doesn't necessarily find water to react with at the time of injection, especially in clay. The soil and foundation may take weeks to react to injection (as measured on geoinstruments), so the rate and location of lifting is unpredictable, and differential and overrcompensation happens. People do compensation with polyurethane successfully, but it carries risk.

[@1pcfred]

I heard they did pump grout into the ground to harden it up and stabilize it. Whatever they did it worked.

[@gregculverwell]

I had thought that they actually did try that as a temporary measure, but it was a long time ago.

[@cornrichard]

I was thinking that they should just mud jack it. I suspect my home brew sidewalk repair experiance is not adequate for this scale of project. @@davidschoon8254

[@Yvolve]

The freezing concept was used in Amsterdam during the construction of the Noord-Zuid Lijn (North-South Line). It runs underneath the historic city center and everything is built on wooden poles as it was originally a marsh. Some huge, historic buildings risked collapse, so they froze a massive section to drill through safely.

[@chrissistrunk]

I love the nod to Mitch Hedberg at the beginning. "A river used to run into the Ligurian Sea, It still does...but it did back then too"

[@willpowerfpv3246]

Best. 😂👌🏻

[@dewilew2137]

He died right across the street from where I lived at the time. Well, rt. 10 isn’t really a street, per se, but this is true.

[@glfporsche1]

Came here for this comment. Lol

[@beardysam2052]

Fun fact: The engineers from Imperial College London that assisted this project had already stabilised the Queens Tower at their university in London, and later stabilised Big Ben with the same methods.

[@stinew358]

It's absolutely wonderful that the engineers locked the leaning side into the sidewalk to support it. Medieval architects were something else.

[@wobblysauce]

Knew it was an issue and making the footing on that side wider eases the issue

[@nasonguy]

Too bad they operated a bit too much like modern engineers. Implemented a field fix and then didn't bother to document it in the as-builts, lol.

[@KaitouKaiju]

Hey, even if it's leaning it's lasted 600 years That has to count for something

[@stephenfry-gdot]

@@nasonguy You mean "resident construction engineers?" As-builts are the responsibility of the resident engineers, at least for transportation projects. Design engineers (such as myself) are required to issue "Use-on-Construction" revisions.

[@crispy-k]

Not very smart to start digging on that side though, clearly weakens the wrong side. Had they done it on the "high side" of the tower foundation it would have straightened instead of risking to tilt even more and risk collapse.

[@MinneapolisRaven]

Grady, your channel is my favorite example of why KZbin channels are so much better than regular TV. So many old cable shows would breeze over topics and say "amazing, right?" Those shows were dumbed down and insulting; while your videos are deeply interesting and, by inspiring young people to pursue an engineering career, literally making the world a better place. Thank You!

[@a3b36a04]

Lots of this stuff you won't even get in university.

[@AnirudhTammireddy]

your niche audience on YT can come and go as they please. TV is made for the masses and thus has it's flaws associated with its reach. If the TV (edu content) was indeed insulting, you wouldn't have Grady who was probably "to pursue an engineering career" from watching TV

[@gmdille]

"So many old cable shows would breeze over topics and say "amazing, right?" Yes, but you have to remember a lot of those older shows were for children, so some simplification was needed. I agree overall that the quality here can get much better than some of those old shows though

[@eily_b]

And the most annoying thing I noticed lately is that they stretch a 15 minute topic to 1 hour (plus commercials).

[@Vaasref]

TV shows would have "experts" saying how incredible those "ancien builders" were as leaning a single degree more would have brought the tower down, then they would have make 30 more minutes saying that "we had to use computer simulation to get to that level of precision" with at least 3 people saying the same thing including an civil engineer that either isn't worth is salt or with directed questions and editing would have said that "such precision is barely attainable with the most modern techniques".

[@maxcactus7]

5:23 - 5:48 Sneaky, sneaky Grady!!! The Tower was increasinig in it's tilt that entire 25 seconds and I only noticed the difference when I did a quick rewind of the 20 seconds prior to 5:48 to show the stark difference once the catino was removed. Very subtle and VERY well done in your graphics - bravo!! And overall, this video was beautiful and a wonderful illustration of the tremendous, positive real world impact engineer's have on the world!!

[@kenbrown2808]

I'm reminded of the stories a friend of mine tells. he worked construction on housing developments in Florida, and in many places, the slab foundations for houses floated on wet sand until the house was built and slowly compacted the water out. if the house was built asymmetrically, the foundation would tilt under the unbalanced load, so they had to be careful how they loaded the material onto the slab.

[@pizzaivlife]

that is one nice thing of living in a northern climate- Michigan requires 42" of footings so that solves a lot of floating issues. not all mind you, but a lot

[@kenbrown2808]

@@pizzaivlife here, the terrain is so varied that there is no one size fits all rule. my brother's beach house is on bedrock. there are other houses I know of, where they drove 30 foot pilings flush to the ground and poured footings on top of them.

[@sandy1653]

@@pizzaivlife where grew up in Florida, ground water aquifer started at around six feet deep. You couldn’t put footings down that deep if you wanted to.

[@pizzaivlife]

@@kenbrown2808 right, we have those issues too. It is just nice that even in good soil you have to have those 42" of footing. you can need more for structural reasons of course, but that is the starting point for anything you don't want to pop out of the ground

[@kenbrown2808]

@@sandy1653 we can hit ground water in just inches. I've seen a below ground garage with tides.

[@PaulSerious]

At the moment in Italy we're having a very similar situation in Bologna, where one of the two towers is leaning so much they had to close part of the town center. From what I understood, the real issue is that in this case the motivation for such lean are unclear, hence there's no idea of how to act.

[@kskdtr]

as far as i know bologna's ground is really muddy, and can't withstand the weight (that's why Bologna can't have a metro).... add up the traffic just driving by... stay strong Garisenda!

[@absalomdraconis]

If it's the tower I'm thinking of, then the correct first step is probably to disassemble the tower so a new foundation can be built. Less intrusive measures may be possible, but from what I've heard the towers in the area in general were probably never on foundations fit for their size, so if the thing is to really last it needs a good foundation to be engineered, preferably with the neighboring tower getting the same treatment as soon as the first one is finished up.

[@Sashazur]

The tower in Bologna also leans a lot, it’s just as noticeable as the one in Pisa. It’s just not as famous because it’s not as pretty.

[@sonorangaming4450]

​@@Sashazur Yeah, it's definitely ugly.

[@iMertin]

Get Lewis Ferguson to stand up against it

[@danielbarreiro8228]

I saw the bracing of the tower when visiting Italy in the late 90s, however, I didn't get to see the actual fix being done at ground level since the work area was boarded all around. The cables clearly looked temporary, as they were not fixed permanently to the tower rather they embraced the exterior with wood planks to shield the stone from the cable. For everything I saw above the edge of the fence, I guessed they were pumping some sort of cement mix under it, not taking out soil. They did a nice trick there. Thanks for telling the story.

[@dewilew2137]

I was there in ‘99 and I remember this too! I was a Kid, but I still have those corny photos that my dad had me pose for, standing in the foreground with one arm up, as if I’m holding up the tower. 😅

[@joekrusec9066]

Ditto, I was there in 2000 with my wife, and confirm the upper was strapped and tied back with cables. Great to see more info to add to the placarded info provided at site by the engineers (in English!).

[@GaddarKerim1]

I would do jet grouting method. This is soil liquifaction.

[@TheLastTater]

I just visited the leaning tower of Pisa a month ago on my honeymoon and it’s amazing thing to see in person. I learned all about its lean and foundation changes. So awesome you made a video on it! I loved it

[@PatrickKQ4HBD]

Congratulations on your marriage! May you be a happy couple and pillars of your community!

[@TheRealPOTUSDavidByrd]

The ending monologue about the team working to continue an 800 year old project was oddly touching. Kudos!

[@MajoraZ]

Another video like this you could do on a many-centuries-long engineering project, albeit one that ended in failure, could be the Aztec capital/Mexico City's water and soil issues: Tenochtitlan was a giant city with Venice-like canals built on both a natural island and expanded with a grid of artificial islands over time, with a complex series of levees, aqueducts, and other systems to intake fresh water and to avoid flooding. When the city was sieged by Conquistadors and armies from other local city-states, much of that infrastructure was destroyed and Mexico City, built on the ruins, had regular issues with flooding. Eventually in the 1700s intensive draining efforts to drain the series of 5 lakes in the valley got underway (after previous management attempts) and continued to the 20th century, which backfired as it ended up almost entirely depleting the aquafer and led to the liquefaction and compaction of the loose lakebed sediment, especially as Mexico City's urban sprawl has spread over much of the former lakebed and added (millions) of tons of weight. As a result, today, Mexico City is sinking... rapidly. Some parts of the city as fast as 50 centimeters/20 inches a year, and it's not predicted to stop for many decades, and recent reports have found that it's past the point of no return already. There's constant issues with sewage lines, subways, etc breaking as a result of this, and it's renewing flooding issues while the lakes are mostly gone (save some surviving Aztec period canal systems in Xochimilco, which too are threatened by this), now it's worsening issues with retaining rainwater. Some other channels have covered this already, but I find many of the videos don't delve into the specific engineering details or all the historical context: We know the specifics of how many of the Aztec aqueducts worked (the main aqueduct which sourced water from Chapultepec for example had dual ceramic pipes with a switching mechanism) and with the specific drainage projects, yet neither has really been covered with detailed diagrams and like yet like you did here. I also find people only mention Tenochtitlan, sometimes even mistakenly showing the valley being empty aside from Teno. with it only urbanizing as Mexico City grew, despite there being hundreds of other Aztec cities in the Valley some of which had their own lake infrastructure/engineering efforts (like Texcoco's Texcotzingo waterworks system) some of which played a role in these events; and there being significant urbanization there for thousands of years before the Aztec period, like with Tlatilco, Cuicuilco, Teotihuacan, etc. So I think there's still room for you or the Wendover team you mentioned you work with to contribute to the topic in a way other people haven't done so yet. I actually work with history and archeology channels with researching and fact checking their Mesoamerican stuff and would be down to help out if you ever wanted to cover it!

[@paulhaynes8045]

Very interesting. I only knew the outline of this. This topic is a must for this channel. Although I think it will take more than one video!

[@MikeV8652]

That sounds fascinating!

[@RowanHawkins]

How do the massive sinkholes which open from time to time come about?

[@GabrielHarper]

This!

[@Kenionatus]

An entire channel dedicated to infrastructure history and archaeology would be fascinating.

[@tomypreach]

I've had many teachers throughout my life. This channel continues to be on the top ten list of most influential.

[@georgiabelle3717]

I saw the title and thought, “What? Again?” I’m glad I didn’t miss anything as big as a second stabilization, and I’m happy to finally hear the story of how it was done.

[@Harborman1691]

Back in the early 80s I lived in Egypt and met some Italian engineers that lived in the same hotel that I was staying. I told them what I would do to fix the tower and this is exactly what I told them to do. Two years ago the History channel showed what they did. That really made my day.

[@epiphgd4302]

Armchair-architect alert 😂

[@gab_v250]

2:05 *by neighbouring cities. Tuscany has a long history of city rivalries. The main ones are Pisa vs Livorno, Siena vs Firenze... But in general each city hates each other, even the smaller ones.

[@aaACEa]

...was in Larderello (Tuscany) two days ago👌. The people can 'rival' one another but not the food/drinks, natural landscapes, cultures. 💯

[@Boretheory]

Ah also the whole region specifically hate one of its cities: Pisa itself so the tower is the symbol of their evil nature, the PISANS.

[@gab_v250]

@@Boretheory it's summed up in one sentence: "pisa merda"

[@Boretheory]

@@gab_v250 sempre 🥹 ( always )

[@zbarba]

The Garisenda tower in Bologna has a similar problem. The degrees of tilt are even greater, and very recently it has been deemed dangerous after some instruments detected too much vibration

[@eragonpower2397]

Yep, the city has closed near road access to try to minimize vibrations

[@StefanoBorini]

The problem is that they can't pull this trick with the Garisenda. I suspect the soil situation is similar, but the tower is embedded in a very narrow urban setting.

[@davideastham]

When in the Chicago area, I always love to visit the Leaning Tower of Niles. It opened in 1934 and it is a half size replica of the one in Pisa.

[@1pcfred]

Somewhere out in the desert we have the real London Bridge too. Some screwball bought it and shipped it over block by block. They spray painted numbers on every block so they could put it back together just the way it was. I think it's in front of some housing development? They built an artificial waterway under it so it's not just sitting in the desert. But it's really sitting in the desert now. It is rather charming. I've seen pictures of it. How many bridges get to retire and enjoy their autumn years?

[@davideastham]

@@1pcfred Yep, if I remember correctly, it's somewhere in Arizona?

[@alessandro7805]

Americans only know how to copy

[@1pcfred]

@@davideastham that sounds right. It's in either Arizona or Nevada. One of those Godforsaken desert states. I think they got the bridge just as an attraction. Like look it's something other than barren desert. We have a famous bridge. The Brits were going to demolish it anyways. They needed a bigger bridge. So they happily sold it to the loon.

[@OldManDoom]

I always love a good Mitch Hedberg reference. Nice!

[@travisolander4749]

I love that the erstwhile builders curved the tower. Basically made sure it couldn’t be straightened - if they did straighten it, it’d just look like a vertical banana.

[@joebesko5592]

i remember all the work that went into saving the tower, it was definitely a great engineering feat to save the tower. There is definitely a lot more monitoring in place and there are limits on how many people can be in the tower too. Thanks for doing a story on this

[@chrisrnz]

One of my favourite Practical Engineering videos for a while. Absolutely fascinating & total genius, really.

[@1pcfred]

I watched a documentary on the Tower and in it they said there's wedges in the base and by measuring those wedges they were able to track the lean over time. They even plotted the data on a computer and showed how the tower's been moving over time. It was hilarious. It's been doing a dance back and forth.

[@RyanPaton]

Another amazing video Grady! Thanks for being awesome! ❤

[@GarageSupra]

Tourist note. I went there about 10 years ago with my wife, the place surrounding the tower is a massive tourist trap. We got endlessly harassed from the second we got out of our car in the nearby car park. I nearly ended up in fights with multiple street sellers and scammers (high crime area also). I can not speak for what it is like now but i would not return there. However other places I went in Italy that are not on the big tourist icons were awesome and people were super friendly.

[@MurasakiMonogatari]

Was there a year ago, hardly any tourists in January, great experience.

[@Alby_Torino]

That said, the Duomo square is an outstandingly wonderful place. The square has more art history and architectural masterpieces than entire Countries have.

[@midnightrider1827]

Was just there this Thanksgiving and had a great time. No issues and got to climb the staircase to the top and hear the bells ring the noon hr. Was really cool.

[@marisasob]

I went there with my school when I was 18 (12 years ago). It was always busy and there will always be street vendors (like in Paris). If they wanna sell you something, just offer such a ridiculous low price or say "I already bought".

[@DrPepperone]

Yeah, the Piss Tower is a pleb filter

[@falxonPSN]

That opening line was pure Mitch Hedberg goodness. Well played, Grady!

[@emilybjoerk]

I don't often comment but I feel like I have to: Practical Engineering is one of, if not the best, shows I've ever watched. The content turns what might at first appear as mundane and everyday things that everyone knows about or have some reference to (e.g. highway construction for example) into genuinely interesting and fascinating pieces with excellent infographics and the topics are explained in a way that I feel appeals to both laymen and engineers alike. All while being narrated by that very soothing voice. Please keep it up ❤

[@reilly6187]

Just imagine being having worked on this in the past and seeing the new and amazing ways that modern architects carried on your work, this is awe-inspiring. I wonder what similar situations we are in that will be corrected like this in the distant future.

[@icarus_flying1994]

This was an amazing video. I knew they had 'fixed' the tower but never the details. the graphics were very helpful in understanding the process. btw if you talk to the Nebula people, I would love a windows app. I have a subscription but never remember to use it.

[@NickMaurer]

This was such a great video! Incredible civil engineering history; really interesting problem-solving research and course correction, communicated in a digestible way.

[@thedevildick1]

My brain is so satisfied with this wonderful meal of knowledge. Thanks Grady!

[@c97f]

"If you're in to recreational geology and heavy construction. And who isn't?" Grady is a gift to humanity.

[@stephencahill7821]

For anyone wondering what an arcsecond is: It's 1/60th of an arcminute, which is 1/60th of a degree.

[@marcwilliams9824]

This wins the coveted Comment of the Day award.

[@ericlotze7724]

8:04 Like Lacroscopoc/Robotic Surgery…but for Foundations. Absolutely AMAZING.

[@barkebaat]

Hey, Grady! Just wanted to say that I really like your channel. Whenever I start watching one of your videos I find a smile on my face and that I'm learning and enjoying myself. You're obviously doing something right! Merry Christmas from a Norwegian woodworker :-)

[@peterlarkin762]

I live near a monastic roundtower called Kilmacduagh (west Ireland). It's been leaning for roughly 1000 years.

[@Zaphod-zj4mv]

I just finished a geotechnical engineering class that had a section on consolidation. One of the really interesting things we learned about electro-osmotic consolidation is that it is triangular so the soil between the electrodes is not consolidated equally. Another really interesting thing is that electro-osmotic consolidation not only consolidates the soil but also increases the strength of the soil due to particles from the electrodes being left behind during the process. I think that it is a fascinating process that deserves its own video.

[@craigmcdougall3693]

Surely this is only a temporary condition? Any zones of negative porewater pressure between electrodes should start the consolidation process in the surrounding soils due to the pressure gradient.

[@longiusaescius2537]

Interesting

[@Zaphod-zj4mv]

@@craigmcdougall3693 I just checked my notes again and I want to be clear I am not an expert in any of this but this is what I could find. The reason for the ununiform consolidation is that the voltage is highest at the anode which causes the water to flow towards the cathode. This results in the highest degree of consolidation occurring at the anode while the lowest consolidation occurs at the cathode as the water that flows out is immediately replaced. Once the power is turned off the pressure gradient dissipates but the ununiform consolidation remains. As for the permanent change in soil properties, studies showed that the Atterberg limits of the soil also changed in a triangular distribution with the highest increase occurring at the anode. The cause for this is that as the anode corrodes its ions flow into the soil in the direction of the water flow and react causing a change in soil properties.

[@andrewnotRFAC]

Nice Mitch Hedburg reference at the beginning

[@effthegop]

This is fascinating! I've only gotten in as far as the stages of initial construction and I'm hooked. The details on the corrections were never very well publicized. Watched it and it didn't disappoint. This was one of the most interesting projects I had never really heard details about. I've found a new YT rabbit hole to explore :)

[@MatteoBurroni]

As an Italian who lives not so far from the tower (160km or 100mi), I've found this video amazing, I was a kid when this was done so I was not aware of how bad the things were at that time

[@sparkyfromel]

What I find absolutely stunning is that the tower could take so much leaning and didn't collapse

[@fukkitful]

It was built over a 200 year span which gave the foundation time to settle.

[@joesomebody3365]

Awesome story, great use of diagrams and models to visually show what you are explaining. Thanks for making and sharing this video.

[@alayneperrott9693]

Love your enthusiasm - it's really tefreshing!

[@seattlegrrlie]

As a budding young geologist at the time, I found this project fascinating

[@bartsanders1553]

nice Mitch Hedberg referrence😂

[@clearstream67]

My geotechnical design professor at UNH in the mid-1990s, Dr. Jean Benoit, was one of the engineers/researchers working on the stabilization project. For a work study, I helped on a few of his presentations he was giving in Italy. Nice to see it actually worked.

[@kaepsele0711]

Awesome video!!! Didn't know this tower rescue was so complex!

[@spiercephotography]

This is so fascinating and cool! I didn't even realize the builders were compensating for the lean originally until you just mentioned it. What weird (and neat) facts and info on what they did to save it, how much it was tilting, and so on!

[@mennomateo]

Starting with a Mitch Hedberg reference. I see what you did there

[@lev3k]

0:12 I appreciate the Mitch Hedberg

[@Moopeoplez]

I love this video as well as the others! I just received an early Christmas gift being a signed copy of engineering in plain sight from you. Despite any other gift I may revive that book is easily my favorite. You’re a true inspiration and mentor to me to be the best I can be in whatever I undertake. Keep up the great work.! Thankyou for such an amazing source of inspiration encouragement and knowledge.! 🙃🙃

[@Edison.m3806]

Doesn't matter what profession u come from, you have to tip your hat off to engineers. These guys are insane.

[@erikziak1249]

Somewhat similar was done to one bridge pier in Bratislava recently. It was sinking and leaning into the Danube. The bridge was being rebuilt, so they decided to inject concrete under high pressure under the pier as well as inside it to fill all cracks. Eventually the bridge pier from the year 1890 rose and tilted several centimeters, but I do not remember the numbers. It was also reinforced and extended, as two adjacent piers to one side were replaced by a single one to make the passage wider and the bridge is a bit higher above the water. Thus existing pier had to carry a higher load of the longer bridge "field" between the piers and shipping is now easier even during times with higher water levels of the Danube river. I thought they injected some concrete under pressure below the sinking side of the Tower of Pisa, but they did the opposite - they made the other side sink to compensate for the tilt. Until watching this video, I was completely ignorant, I just remember reading that the tower was somewhat "straightened" in the 1990s using modern technology.

[@Tim---]

Unexpected Mitch Hedberg in the first fifteen seconds. Thanks for that!

[@dan725]

I’ve learned more about the history of the Tower in the first 5 minutes than any other time in my life. It was always just there, and I would think about it from time to time when Superman would straighten it and then tilt it back again, angering the local craftsmen who made figurines of it. But now I realize that wouldn’t have been possible, especially since I never knew the tower was built curved. That’s so cool. This was insanely informative, but also incredibly entertaining! My family loves your content!!!

[@phoenix3231a]

The tallest leaning tower in the world is still the Olympic Stadium in Montreal. It's not fallign over but it's been a white elephant also. The cost of the stadium was exhorbitant and not there's talks to add a roof at a cost of 1 billion dollars! The old roof has been out of service for years after failing. It was a kevlar fabric roof hanging down from this massive leaning tower.

[@1nicube]

dont talk about that roof. Over her everyone want to tear down the Olympic stadium because of that roof 🤣

[@PatrickKQ4HBD]

​@@1nicubePolitics and religion are okay, but don't talk about the roof? 😅

[@jamesclarkson156]

It's the tallest intentionally leaning tower. The Millenium tower is likely the tallest unintentionally leaning tower. It is 32 meters taller.

[@phoenix3231a]

@@jamesclarkson156The Millenium tower is leaning less and 1/60th of one degree. Pisa is about at 4 degree and olympic stadium at almost 45. Not the same scale

[@KevBoneT]

I didn't know "recreational geology" was a thing, but I've been into it for a while now. Thanks.

[@1pcfred]

They're called rock hounds. So they even have a nickname.

[@ELCobb83]

Your shows are always amazing!

[@crazyguy32100]

Most people think the failure point of the tower is it falling over but that's not the generally accepted scenario. The more likely outcome is the center of gravity will shift over far enough to cause overloading of the lower side. Since the shell of the tower is fairly thin in respect to its mass and the strength of the masonry that shift in loading will cause structural failure of the wall and the tower will just fall apart.

[@daleolson3506]

Watch silos being collapsed

[@catsupchutney]

Italy has so many ancient treasures. Their budget keeping them in repair must be immense!

[@stefa168]

Fun fact: we don't have enough money for everything, so a lot of buildings and other stuff doesn't get enough maintenance (if any)

[@furylatalpa]

I'm italian, yes we have the most unesco heritage sites and the estimated value of it all is in the bullpark of 10% of the yearly gdp; we did hit bad times during the pandemic though (turism is what makes possible to maintain everything in the first place) and we were and still are amongst the lowest spending countries for culture in the eu. So yeah the budget is a lot lower than you might think

[@davidhollywood3923]

So cool to think of the engineering process as a continuation of the natural progression of the lean. Great video!

[@Emppu_T.]

Loved seeing the tower for real. A very interesting piece of history and well done efforts on preservation.

[@chrismoody1342]

I’m sure the folks at Millennium Tower will be thrilled to learn that the leaning adds character and charm to the building.

[@andrewalexander9492]

Are you really admitting on an open forum that you don't grasp something as obvious as the fact that the Tower of Pisa has no residents, and serves no purpose other than a historical monument and tourist attraction? OR are you admitting that you're not intelligent enough to understand why that makes it different that the Millenium tower?

[@Self_Evident]

@@andrewalexander9492 Are *you* really admitting on an open form that you don't grasp simple sarcastic humor??

[@andrewalexander9492]

@@Self_Evident Nope, I grasp sarcasm just fine. But in order for your comment to actually BE sarcasm, there has to be equivalency between the Millennium tower and the tower of Pisa. Which of course, there is none. Without that, your comment isn't sarcasm, just inane nonsense.

[@alexanderSydneyOz]

@@andrewalexander9492 wow. the OP was making what is commonly known as "a joke". As you are plainly unfamiliar with the concept, I will say this: "jokes" are not required to be *literally* apt. For example, the fact that the LTP and the MT are centuries different in age, one is residential and the other not, is not inconsistent with the OP's comment being a "joke". Rather, the 'equivalency' is that they are both towers with an unintended lean, and both of which have been or are in the process of being unleant. I hope this helps, but as I will lay money you are an engineer, perhaps not.

[@procrastinator41]

😆

[@vasilikonstan]

I love your channel so much! Keep up the good work!

[@Multi_ToBi]

What a great video! The first time I went up the leaning tower was when I was 10 years old in 1970. Now, for my retirement, I am planning to stay half of the year in Pisa. That's a long lovestory. Thank you for enlightening me on my old love's health...!

[@michaelmcchesney6645]

As I recall, in 1983, Superman, after being exposed to Kryptonite that affected his personality, straightened the Leaning Tower of Pisa. But he did restore the tilt later that year after recovering from the Kryptonite effects. What effect did that have on the engineering plan to preserve the tower?

[@Yora21]

I've been up the tower three months ago. It's still really far leaning. I usually have no problems with climbing towers at all, but with the observation walkway at top being that far angled, it even made me pretty queasy.

[@donaldhollingsworth1123]

Amazing! I never knew that the tower curved. Wonderful video.

[@sheilam4964]

Merry Christmas and Happy Holidays. Thx for doing this, filming it and sharing it with us. 👍👍👍👍👍

[@petterlarsson7257]

i literally gasped when you said that it had a safety factor of *1.07*

[@MikkelHojbak]

When I design machines that carry people, it requires a safety factor of 5 or 6 to be CE-compliant. I don't know how it is for structures, but 1.07 is _definitely_ not enough to be safe.

[@Johnny-tt8zc]

Didn’t they issue warnings again this past summer about the tower?

[@eric1393]

I recently learned about the towers of Bologna, Italy, and in particular Garisenda Tower of the "Two Towers", which also has an extreme lean and was closed earlier this month (December 2023) for fears of a collapse. Fascinating stuff!

[@gregknipe8772]

thank you for this long running series of interesting and thought provoking moments of learning. awesome!!

[@gregknipe8772]

recreational geology and heavy construction, anyone?

[@ninosanjaya]

Dr. Ratio be like:

[@yankeexpress]

I climbed the Pisa tower around 1988. Was officer on a US flag merchant ship delayed in Livorno port due to a longshoreman holiday. It was a spectacular day weatherwise as a cold front had passed, clearing out all the smog. Pisa was packed with tourists from all over the world on the inside stairway, very orderly up/down. I photographed from every level going up (film Canon AE-1). The top story to the roof was a mere metal rung ladder only wide enough for one person. Followed two young French women in mini skirts going up. The whole day is A wonderful memory.

[@edcew8236]

Love your animation of the wars! And your whole series, for that matter.

[@filoudadidou]

@integza being mentioned in your video must be a life achievement completed ! Love you both !

[@sayemhossainemon98]

Pls add language audio track like bangla, hindi etc

[@robythebesthacker95]

I'm from Pisa, fun fact, the entire height of the tower is under the sea level

[@cmdOptEscape]

One of your finest videos this, Grady. Bravo ♥️

[@user-qc3mg3pp2s]

Outstanding presentation. Very informative!!!

[@solmarin_]

Dr ratio reference😫🫣😱

[@fuzzix]

I remember news reports in the early 90s about closure of the tower and the addition of lead ingots. Great to know the rest of the story!

[@christophertesta8097]

As a young geotechnical engineer, this detailed and creative thinking is just inspiring. Thank you for the great explanation Grady.

[@dcterr1]

I'm glad they were able to prevent the tower from collapsing! This is truly a triumph of modern engineering! Bravo!

[@Gremlack13]

I went to the tower in 2017 and it was an amazing experience and view of the surrounding areas.

[@niklashumberg69]

The Company which did this is from the Ruhr Valley. I love how the Know-How from Decades of Mining can still be very usefull in some cases, although everything Mining related has already shut down in Germany. It shows how a transition for a industry reliant Region to a Tech Region is possible. I am proud to be a part of this process :)

[@obuudeozo8978]

Brilliant presentation and analysis 👏

[@remsmith3233]

Great discussion on trying, and apparently, coming up with a workable engineering “save” for the Tower of Pisa. Thanks.

[@josephtrahan8045]

I never realized it was fixed so recently I thought that was corrected along time ago. Thanks for the info. Very informative.

[@TamarLitvot]

Just found this channel -- loved this video and will be watching a lot more of them

[@paulhaynes8045]

Really enjoyed that - one of your best episodes.

[@Valtrach]

Interesting and well made. Thank you for your work.

[@bga6262]

Thank you so much for providing this high-quality video for free. I'm a Korean interested in engineering. Recently, I've been watching many English videos without subtitles to improve my English skills. Your kind narrator is very helpful to me as an English beginner.🥰

[@TwoToneShoes]

"It still does, but it did back then, too!" Never thought I'd hear Practical Engineering pull out the Mitch Hedburg joke! Made my day.