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[205.201.135.142]) by mx.google.com with ESMTPS id e2si999520ywc.571.2017.08.24.04.46.56 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 24 Aug 2017 04:46:56 -0700 (PDT) Received-SPF: pass (google.com: domain of bounce-mc.us1_1820657.2563001-cmollekopf=gmail.com@mail142.atl61.mcsv.net designates 205.201.135.142 as permitted sender) client-ip=205.201.135.142; Authentication-Results: mx.google.com; dkim=pass header.i=@nowiknow.com header.s=k1 header.b=PhDhbCtl; dkim=pass header.i=@gmail.mcsv.net header.s=k1 header.b=RCXi0ciN; spf=pass (google.com: domain of bounce-mc.us1_1820657.2563001-cmollekopf=gmail.com@mail142.atl61.mcsv.net designates 205.201.135.142 as permitted sender) smtp.mailfrom=bounce-mc.us1_1820657.2563001-cmollekopf=gmail.com@mail142.atl61.mcsv.net DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; s=k1; d=nowiknow.com; h=Subject:From:Reply-To:To:Date:Message-ID:List-ID:List-Unsubscribe: Content-Type:MIME-Version; i=dan@nowiknow.com; bh=0j/vBe5PYyLtNIrTeg7ECKupBfn4J4reSBQ13Fmj1Ww=; b=PhDhbCtlZ0sTf/uiePM3Y3Zile2xSiBfMLEpBeRI037MIT0Wd+3EjXb6mWocbkZTj8uXslIHeTFb S6+VtwbwnCZfLXnB43tDWpWhTVYK5EQpgwfE/3LbSm7hc7SgG5gGw8j6ybkh6RluUXox+uwFQ4P1 USYaWqIo5H3ZH12dJ+M= DKIM-Signature: v=1; a=rsa-sha1; c=relaxed/relaxed; s=k1; d=gmail.mcsv.net; h=Subject:From:Reply-To:To:Date:Message-ID:Feedback-ID:List-ID: List-Unsubscribe:Content-Type:MIME-Version; bh=VvDgaXeZiQZDe15cLybJQr285RQ=; b=RCXi0ciNwW82Ta0gJ6lw549iAT4DjwqJRZ2TZqWtIymAkhBGiSW7LikSHPofApky3mq1F3wGVOJp VVJoZQQhEfaMhPMOMEibhnsdIwP5LYwUx4r5SoWd3xIP/2dZIlwngOEeW23oAAVx+T9iKkuZLCnQ s81PkHcv0+Gm6H6H80A= Subject: =?utf-8?Q?Now=20I=20Know=3A=C2=A0Why=20Pisa=E2=80=99s=20Tower=20Leans?= From: =?utf-8?Q?Dan=20Lewis?= Reply-To: =?utf-8?Q?Dan=20Lewis?= To: Date: Thu, 24 Aug 2017 11:36:21 +0000 Message-ID: <2889002ad89d45ca21f50ba46.cd30a9a755.20170824113521.1b9800e15a.bf27651e@mail142.atl61.mcsv.net> X-Mailer: MailChimp Mailer - **CID1b9800e15acd30a9a755** X-Campaign: mailchimp2889002ad89d45ca21f50ba46.1b9800e15a X-campaignid: mailchimp2889002ad89d45ca21f50ba46.1b9800e15a X-Report-Abuse: Please report abuse for this campaign here: http://www.mailchimp.com/abuse/abuse.phtml?u=2889002ad89d45ca21f50ba46&id=1b9800e15a&e=cd30a9a755 X-MC-User: 2889002ad89d45ca21f50ba46 Feedback-ID: 1820657:1820657.2563001:us1:mc List-ID: 2889002ad89d45ca21f50ba46mc list <2889002ad89d45ca21f50ba46.580325.list-id.mcsv.net> X-Accounttype: pd List-Unsubscribe: , List-Unsubscribe-Post: List-Unsubscribe=One-Click x-mcda: FALSE Content-Type: multipart/alternative; boundary="_----------=_MCPart_2013239186" MIME-Version: 1.0 This is a multi-part message in MIME format --_----------=_MCPart_2013239186 Content-Type: text/plain; charset="utf-8"; format="fixed" Content-Transfer-Encoding: quoted-printable And: is it just part of an old European dance craze? (Well=2C no.) View this email in your browser (http://nowiknow.com/why-pisas-tower-leans= /) =C2=B7 Missed one? Visit the Archives (http://nowiknow.com/archives/) http://MIR.INSIRE.COM/click?s=3D188055&layout=3Dmarquee&li=3D689d00e31c&e= =3Dcmollekopf@gmail.com&p=3D1b9800e15a http://MIR.INSIRE.COM/click?s=3D188058&sz=3D116x15&li=3D689d00e31c&e=3D= cmollekopf@gmail.com&p=3D1b9800e15a http://MIR.INSIRE.COM/click?s=3D188059&sz=3D6= 9x15&li=3D689d00e31c&e=3Dcmollekopf@gmail.com&p=3D1b9800e15a http://nowiknow.com/ Just likes yesterday: I'm on vacation this week=2C so today's Now I Know i= s a re-run=2C originally from 2010. (The Weekender is still TBD.) -- Dan (= http://s.nowiknow.com/DLewisNet) ** Why Pisa=E2=80=99s Tower Leans ------------------------------------------------------------ The Leaning Tower of Pisa is over 800 years old. Construction started on= it in 1173 and=2C almost two centuries later (and after two work stoppage= s)=2C completed in the 1370s. For history=E2=80=99s sake=2C it is a good= thing that there were two work stoppages =E2=80=94 otherwise=2C the struc= ture probably would have collapsed long ago. The Tower is built on=2C bas= ically=2C a marsh =E2=80=94 a thin layer of alluvial silt (http://s.nowikn= ow.com/2voNXQl) atop soft marine clay. The work stoppages gave time for= the existing incomplete infrastructure to settle in the soft soil=2C comp= acting the ground beneath it and=2C effectively=2C letting Mother Earth ad= apt before construction resumed. A minor miracle=2C in and of itself. It therefore makes sense that the Tower is unstable=2C likely to shift its= position any which way as time passes. But the mystery runs deeper. The= Leaning Tower of Pisa only leans to the south. Assuming the unstable gro= und beneath is uniformly so=2C that did not make a lot of sense. In 1989=2C the Tower was leaning roughly 15 feet off its center=2C when di= saster struck =E2=80=94 in Milan. Another tower=2C the Civic Tower of Pav= ia (http://s.nowiknow.com/2vo26xt) =2C crumbled=2C killing four passersby.= Fearing a similar fate for Pisa=2C the Italian government closed the tow= er and made a $40 million grant to researchers=2C hoping to stave off the= Tower=E2=80=99s tilt into destruction. The task was daunting=2C as rese= archers were split =E2=80=94 some believed the problem was with the underl= ying land; others believed the problem was with the structure itself. Red= oubling these problems were the art historians=2C who insisted on preservi= ng the artistic value of the Tower; in short=2C propping the Tower up was= a non-starter. Finding a solution took four different tries and almost a decade. In the= end=2C the team used something called =E2=80=9Csoil extraction=E2=80=9D= =E2=80=94 as described (http://s.nowiknow.com/2vorzXl) by the Telegraph= (UK)=2C this meant =E2=80=9Cdrilling out slivers of soil from beneath the= northern side of the tower =E2=80=93 away from the lean =E2=80=93 and all= owing gravity to coax the structure back upright.=E2=80=9D It was a nuanc= ed task in and of itself. Professor John Burland=2C a soil engineer at t= he Imperial College London=2C lead the efforts with the help of 120 sensor= s placed in=2C around=2C and outside the Tower=2C and an army of fax machi= nes. For two years=2C twice a day=2C the sensor readings were faxed to hi= s attention; he=E2=80=99d run some calculations and inform the drillers ho= w to continue. The Tower re-opened in late 2001. In capturing all these data points =E2=80=94 two a day for two years =E2= =80=94 Burland had in front of him the answer to the previously unanswerab= le question of the Tower=E2=80=99s southward tilt. In 2003=2C he figured= it out. The water table (http://s.nowiknow.com/2vovXWF) on the north si= de of the Tower rose up to a foot higher at times during Pisa=E2=80=99s ra= iny season. In effect=2C the water tower slowly=2C slightly=2C and tempor= arily boosted the land on the north side=2C pushing the Tower to lean sout= h. Using a custom drainage system to normalize the water table=2C Burlan= d has stemmed the Tower=E2=80=99s further tilt entirely =E2=80=94 since th= e solution was put in place seven [now 14!] years ago=2C the Tower=E2=80= =99s tilt has remained the same. http://s.nowiknow.com/NIKPatreon Now I Know is supported by readers like you. Please consider becoming a pa= tron by supporting the project on Patreon. Click here to pledge your suppo= rt (http://s.nowiknow.com/NIKPatreon) . Bonus fact: Groundwater flows can prevent problems=2C too. In 1958=2C the= town of Concord=2C Massachusetts opened a landfill adjacent to Walden Pon= d=2C the eponymous site of Henry David Thoreau=E2=80=99s On Walden Pond. = Because the groundwater table ran from the pond to the landfill (and not= vice versa)=2C the pond remained relatively unpolluted by the nearby refu= se.=E2=80=8B From the Archives: Patent Leather Shoes (http://dlewis.net/nik-archives/pa= tent-leather-shoes/) : How Michael Jackson managed to pull off an incredib= le=2C gravity-defying lean of his own. Related: A 3-d=2C Leaning Tower of Pisa puzzle (http://s.nowiknow.com/2v5D= xKs) . http://MIR.INSIRE.COM/click?s=3D97521&sz=3D300x250&li=3D689d00e31c&e=3D= cmollekopf@gmail.com&p=3D1b9800e15a http://MIR.INSIRE.COM/click?s=3D2054&sz=3D116x15&li=3D689d00e31c&e=3D= cmollekopf@gmail.com&p=3D1b9800e15a http://MIR.INSIRE.COM/click?s=3D96003&sz=3D69x1= 5&li=3D689d00e31c&e=3Dcmollekopf@gmail.com&p=3D1b9800e15a http://www.facebook.com/sharer/sharer.php?u=3Dhttp%3A%2F%2Fnowiknow.com%2F= why-pisas-tower-leans%2F Share (http://www.facebook.com/sharer/sharer.php?= u=3Dhttp%3A%2F%2Fnowiknow.com%2Fwhy-pisas-tower-leans%2F) http://twitter.com/intent/tweet?text=3DWhy%20does%20the%20Leaning%20Tower%= 20of%20Pisa%20lean%3F%20: http%3A%2F%2Fnowiknow.com%2Fwhy-pisas-tower-lean= s%2F Tweet (http://twitter.com/intent/tweet?text=3DWhy%20does%20the%20Lean= ing%20Tower%20of%20Pisa%20lean%3F%20: http%3A%2F%2Fnowiknow.com%2Fwhy-pisa= s-tower-leans%2F) http://us1.forward-to-friend.com/forward?u=3D2889002ad89d45ca21f50ba46&id= =3D1b9800e15a&e=3Dcd30a9a755 Forward (http://us1.forward-to-friend.com/forwa= rd?u=3D2889002ad89d45ca21f50ba46&id=3D1b9800e15a&e=3Dcd30a9a755) =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D ** Learn more about RevenueStripe... 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(Well=2C no.) =09=09
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<= td style=3D"mso-line-height-rule: exactly;-ms-text-size-adjust: 100%;-webk= it-text-size-adjust: 100%;">
3D""
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Just likes yesterday: I'm on vacation= this week=2C so today's Now I Know is a re-run=2C originally from 20= 10. (The Weekender is still TBD.) -- Dan

Why Pisa=E2=80=99s Tower Leans
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The Leaning Tower of Pisa is over 800 years old.&nb= sp; Construction started on it in 1173 and=2C almost two centuries later (= and after two work stoppages)=2C completed in the 1370s.   For h= istory=E2=80=99s sake=2C it is a good thing that there were two work stopp= ages =E2=80=94 otherwise=2C the structure probably would have collapsed lo= ng ago.  The Tower is built on=2C basically=2C a marsh =E2=80=94 a th= in layer of alluvial silt atop soft marine clay. &= nbsp; The work stoppages gave time for the existing incomplete infrastruct= ure to settle in the soft soil=2C compacting the ground beneath it and=2C= effectively=2C letting Mother Earth adapt before construction resumed.&nb= sp; A minor miracle=2C in and of itself.

It th= erefore makes sense that the Tower is unstable=2C likely to shift its posi= tion any which way as time passes.  But the mystery runs deeper. = ; The Leaning Tower of Pisa only leans to the south.  Assuming the un= stable ground beneath is uniformly so=2C that did not make a lot of sense.=

In 19= 89=2C the Tower was leaning roughly 15 feet off its center=2C when disaste= r struck =E2=80=94 in Milan.  Another tower=2C the Civic To= wer of Pavia=2C crumbled=2C killing four passersby.  Fearing a si= milar fate for Pisa=2C the Italian government closed the tower and made a= $40 million grant to researchers=2C hoping to stave off the Tower=E2=80= =99s tilt into destruction.   The task was daunting=2C as researchers= were split =E2=80=94 some believed the problem was with the underlying la= nd; others believed the problem was with the structure itself.  Redou= bling these problems were the art historians=2C who insisted on preserving= the artistic value of the Tower; in short=2C propping the Tower up was a= non-starter.

Findi= ng a solution took four different tries and almost a decade.  In the= end=2C the team used something called =E2=80=9Csoil extraction=E2=80=9D= =E2=80=94 as described by the Telegraph (UK)=2C this= meant =E2=80=9Cdrilling out slivers of soil from beneath the northern sid= e of the tower =E2=80=93 away from the lean =E2=80=93 and allowing gravity= to coax the structure back upright.=E2=80=9D  It was a nuanced task= in and of itself.   Professor John Burland=2C a soil engineer at the= Imperial College London=2C lead the efforts with the help of 120 sensors= placed in=2C around=2C and outside the Tower=2C and an army of fax machin= es.  For two years=2C twice a day=2C the sensor readings were faxed t= o his attention; he=E2=80=99d run some calculations and inform the driller= s how to continue.  The Tower re-opened in late 2001.

In ca= pturing all these data points =E2=80=94 two a day for two years =E2=80=94= Burland had in front of him the answer to the previously unanswerable que= stion of the Tower=E2=80=99s southward tilt.  In 2003=2C he figured i= t out.  The water table on the north side of the= Tower rose up to a foot higher at times during Pisa=E2=80=99s rainy seaso= n.  In effect=2C the water tower slowly=2C slightly=2C and temporaril= y boosted the land on the north side=2C pushing the Tower to lean south. &= nbsp; Using a custom drainage system to normalize the water table=2C Burla= nd has stemmed the Tower=E2=80=99s further tilt entirely =E2=80=94 since t= he solution was put in place seven [now 14!] years ago=2C the Tower=E2=80= =99s tilt has remained the same.
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3D""
=09 =09=09=09 =09=09=09=09
Now I K= now is supported by readers like you. Please consider becoming a patron by= supporting the project on Patreon. Click here to pledge your s= upport.
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Bonus fact: Groundw= ater flows can prevent problems=2C too.  In 1958=2C the town of Conco= rd=2C Massachusetts opened a landfill adjacent to Walden Pond=2C the= eponymous site of Henry David Thoreau=E2=80=99s On Walden Pond.  Because the groundwater table ran from the pond to the landfill= (and not vice versa)=2C the pond remained relatively unpolluted by the ne= arby refuse.=E2=80=8B

From the Archives:= Patent Leath= er Shoes: How Michael Jackson managed to pull off an incredible=2C gra= vity-defying lean of his own.
 
Related: A 3-d= =2C Leaning Tower of Pisa puzzle.
 
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