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I-55 Bridge in Memphis

Started by Charles2, October 09, 2014, 08:34:58 PM

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The Ghostbuster

The Supreme Court put the kibosh on Interstate 40 through Overton Park. Even if the Supreme Court hadn't intervened, I highly doubt the original alignment of Interstate 40 through Memphis would have been constructed. The exits east of the eastern Interstate 40/240 interchange should have been renumbered to reflect Interstate 40's relocation on former Interstate 240's northern alignment.


Plutonic Panda

BUILD A FUCKING TUNNEL LIKE EVERY OTHER COUNTRY!!!! lol but yes I would support a tunnel believe it or not. Connect it with Sam Cooper. Toll it. I'd pay a toll.

lordsutch

Quote from: MikeTheActuary on December 19, 2023, 09:26:35 AM
I don't see such pressures as driving the states and the feds to be willing to spend an extra billion dollars for an entirely new alignment, but I do think that there would have to be a significant change in political and judicial climate before any plan that would impact the former veterans' hospital, erode access to the neighborhood, impact the Chickasaw Heritage (formerly Desoto, formerly Jackson) Park, or require residences to be removed.

Since the new bridge location just south of the existing bridge would have none of those impacts, I think it would not be an issue. Compared to the interchange modification work, the impact on the French Fort neighborhood would be minimal (as you note).

Quote from: bwana39 on December 19, 2023, 04:44:55 PM
If you say so. This was supposed to be I-40.....

https://maps.app.goo.gl/AXptQ2z8yfyzcQP3A

I-40 through Overton Park was not in the same league as building a new bridge 200 feet south of an existing bridge and tying into the existing infrastructure.

That said a more creative TDOT would have cut and covered I-40 under North Parkway, but that's not the TDOT we had or have.

triplemultiplex

Since it was referenced recently, a more updated version of my thoughts on I-55 in Memphis:
[url]https://www.aaroads.com/forum/index.php?topic=3618.msg2855492#msg2855492[/i]
"That's just like... your opinion, man."

civilengineeringnerd

Quote from: Wayward Memphian on January 06, 2015, 03:56:04 PM
Quote from: Grzrd on January 06, 2015, 03:26:25 PM
Quote from: Charles2 on October 09, 2014, 08:34:58 PM
Oy vey!!
http://www.wmcactionnews5.com/story/26740818/tdot-leaders-consider-shutting-down-old-i-55-bridge-for-two-years
Quote from: Brandon on October 09, 2014, 09:53:36 PM
More like...
OH SHIT!That narrows it down to just the I-40 bridge there.

Apologies if this story has already been linked in another thread, but this December 22, 2014 article reports that the FBI recently warned local authorities that ISIS might beat TDOT to the punch and try to close the I-55 bridge in a sudden and unannounced manner:

Quote
The Federal Bureau of Investigation's Memphis Division is warning police officers about a threat to blow up the Memphis-Arkansas Bridge sometime in December.  FOX13 News obtained the FBI bulletin sent to Mid-South Law Enforcement agencies warning about a possible Islamic State terror plot targeting the I-55 Bridge.
"According to an anonymous complainant, as of December 2014, ISIS instructed an ISIS member, a presumed USPER in Memphis, with a direct order to blow up the Memphis-Arkansas bridge on an unknown date, activating ISIS terror cells in the United States," the warning reads.
USPER is a law enforcement acronym for U.S. person
  ....
A Memphis Police spokesperson told FOX13 the department is aware of the threat and officers are patrolling the area around the bridge looking for suspicious activity.  Surveillance cameras linked the  MPD's Real Time Crime Center are focused on the bridge 24 hours a day.
I drove across it multiple times this past weekend, the bridge itself is narrow and dangroup and quite frankly needs replaced period, end of story, for the I 55 aspect of it.
i don't mean to turn this into a geopolitical point, but there is a danger to having only one bridge open. the current hamas/israel war, and the current conflict with us naval ships in yemen, there was reports of global terror being on the rise for the next few years because of it. with the I-55 bridge closed to traffic, that I-40 bridge becomes a prime target for any terrorist groups both foreign and domestic, i don't think TDOT is thinking straight, they are thinking with their head in a engineering book instead of a more broader brush. and considering how I-40 is a truck corridor for mostly the entire state and a lot of points due east, it shouldn't come as a surprise if NC and maybe even Georgia start chiming in on such a bottleneck.
i imagine even mississippi would raise some hell with tennessee legislatures over it as well, all that traffic going to 1 bridge, and that one bridge not only becomes a much more critical corridor than what it was designed to be, but it becomes a target for any would be terrorist organizations. lets hope TDOT understands how silly that is and impliments a through traffic for I-40 and local traffic uses the I-55 bridge, which would help keep the peace locally, and give some options. hell i imagine the move might even make arkansas start on a mississippi river crossing for I-69 much sooner and it might push both arkansas and tennessee to build a 4th bridge across the mississippi to complete a bypass around the memphis metro area, that way I-269 becomes a full loop around memphis metro area.
Every once in awhile declare peace! it confuses the hell outta your enemies!

MikieTimT

#105
Quote from: civilengineeringnerd on January 01, 2024, 12:30:46 AM
Quote from: Wayward Memphian on January 06, 2015, 03:56:04 PM
Quote from: Grzrd on January 06, 2015, 03:26:25 PM
Quote from: Charles2 on October 09, 2014, 08:34:58 PM
Oy vey!!
http://www.wmcactionnews5.com/story/26740818/tdot-leaders-consider-shutting-down-old-i-55-bridge-for-two-years
Quote from: Brandon on October 09, 2014, 09:53:36 PM
More like...
OH SHIT!That narrows it down to just the I-40 bridge there.

Apologies if this story has already been linked in another thread, but this December 22, 2014 article reports that the FBI recently warned local authorities that ISIS might beat TDOT to the punch and try to close the I-55 bridge in a sudden and unannounced manner:

Quote
The Federal Bureau of Investigation's Memphis Division is warning police officers about a threat to blow up the Memphis-Arkansas Bridge sometime in December.  FOX13 News obtained the FBI bulletin sent to Mid-South Law Enforcement agencies warning about a possible Islamic State terror plot targeting the I-55 Bridge.
"According to an anonymous complainant, as of December 2014, ISIS instructed an ISIS member, a presumed USPER in Memphis, with a direct order to blow up the Memphis-Arkansas bridge on an unknown date, activating ISIS terror cells in the United States," the warning reads.
USPER is a law enforcement acronym for U.S. person
  ....
A Memphis Police spokesperson told FOX13 the department is aware of the threat and officers are patrolling the area around the bridge looking for suspicious activity.  Surveillance cameras linked the  MPD's Real Time Crime Center are focused on the bridge 24 hours a day.
I drove across it multiple times this past weekend, the bridge itself is narrow and dangroup and quite frankly needs replaced period, end of story, for the I 55 aspect of it.
i don't mean to turn this into a geopolitical point, but there is a danger to having only one bridge open. the current hamas/israel war, and the current conflict with us naval ships in yemen, there was reports of global terror being on the rise for the next few years because of it. with the I-55 bridge closed to traffic, that I-40 bridge becomes a prime target for any terrorist groups both foreign and domestic, i don't think TDOT is thinking straight, they are thinking with their head in a engineering book instead of a more broader brush. and considering how I-40 is a truck corridor for mostly the entire state and a lot of points due east, it shouldn't come as a surprise if NC and maybe even Georgia start chiming in on such a bottleneck.
i imagine even mississippi would raise some hell with tennessee legislatures over it as well, all that traffic going to 1 bridge, and that one bridge not only becomes a much more critical corridor than what it was designed to be, but it becomes a target for any would be terrorist organizations. lets hope TDOT understands how silly that is and impliments a through traffic for I-40 and local traffic uses the I-55 bridge, which would help keep the peace locally, and give some options. hell i imagine the move might even make arkansas start on a mississippi river crossing for I-69 much sooner and it might push both arkansas and tennessee to build a 4th bridge across the mississippi to complete a bypass around the memphis metro area, that way I-269 becomes a full loop around memphis metro area.

It's not just terrorists that see this as a weak point in our nation's road system.  The idiot Hamas protestors picked the I-55 bridge closure last weekend to shut down the I-40 bridge with their protest, so tell me how we have sufficient resiliency in the Memphis area even in peacetime?  Don't think for a second that this didn't get noticed and won't be repeated.

There are much smaller cities north and east of Memphis with roads less choked that have many more river crossing lanes serving their areas.  It just boggles the mind why we have the infrastructure we do at such a critical point of the IHS.

edwaleni

Quote from: MikieTimT on February 06, 2024, 09:03:54 AM
  It just boggles the mind why we have the infrastructure we do at such a critical point of the IHS.

Because in the first 30 years of the IHS we intentionally built net excess capacity anticipating growth, but since then we have been consuming net capacity and yet still absorbing the growth.

So instead of build in anticipation, we wait and build until its way past needed.

abqtraveler

Quote from: MikieTimT on February 06, 2024, 09:03:54 AM
Quote from: civilengineeringnerd on January 01, 2024, 12:30:46 AM
Quote from: Wayward Memphian on January 06, 2015, 03:56:04 PM
Quote from: Grzrd on January 06, 2015, 03:26:25 PM
Quote from: Charles2 on October 09, 2014, 08:34:58 PM
Oy vey!!
http://www.wmcactionnews5.com/story/26740818/tdot-leaders-consider-shutting-down-old-i-55-bridge-for-two-years
Quote from: Brandon on October 09, 2014, 09:53:36 PM
More like...
OH SHIT!That narrows it down to just the I-40 bridge there.

Apologies if this story has already been linked in another thread, but this December 22, 2014 article reports that the FBI recently warned local authorities that ISIS might beat TDOT to the punch and try to close the I-55 bridge in a sudden and unannounced manner:

Quote
The Federal Bureau of Investigation's Memphis Division is warning police officers about a threat to blow up the Memphis-Arkansas Bridge sometime in December.  FOX13 News obtained the FBI bulletin sent to Mid-South Law Enforcement agencies warning about a possible Islamic State terror plot targeting the I-55 Bridge.
"According to an anonymous complainant, as of December 2014, ISIS instructed an ISIS member, a presumed USPER in Memphis, with a direct order to blow up the Memphis-Arkansas bridge on an unknown date, activating ISIS terror cells in the United States," the warning reads.
USPER is a law enforcement acronym for U.S. person
  ....
A Memphis Police spokesperson told FOX13 the department is aware of the threat and officers are patrolling the area around the bridge looking for suspicious activity.  Surveillance cameras linked the  MPD's Real Time Crime Center are focused on the bridge 24 hours a day.
I drove across it multiple times this past weekend, the bridge itself is narrow and dangroup and quite frankly needs replaced period, end of story, for the I 55 aspect of it.
i don't mean to turn this into a geopolitical point, but there is a danger to having only one bridge open. the current hamas/israel war, and the current conflict with us naval ships in yemen, there was reports of global terror being on the rise for the next few years because of it. with the I-55 bridge closed to traffic, that I-40 bridge becomes a prime target for any terrorist groups both foreign and domestic, i don't think TDOT is thinking straight, they are thinking with their head in a engineering book instead of a more broader brush. and considering how I-40 is a truck corridor for mostly the entire state and a lot of points due east, it shouldn't come as a surprise if NC and maybe even Georgia start chiming in on such a bottleneck.
i imagine even mississippi would raise some hell with tennessee legislatures over it as well, all that traffic going to 1 bridge, and that one bridge not only becomes a much more critical corridor than what it was designed to be, but it becomes a target for any would be terrorist organizations. lets hope TDOT understands how silly that is and impliments a through traffic for I-40 and local traffic uses the I-55 bridge, which would help keep the peace locally, and give some options. hell i imagine the move might even make arkansas start on a mississippi river crossing for I-69 much sooner and it might push both arkansas and tennessee to build a 4th bridge across the mississippi to complete a bypass around the memphis metro area, that way I-269 becomes a full loop around memphis metro area.

It's not just terrorists that see this as a weak point in our nation's road system.  The idiot Hamas protestors picked the I-55 bridge closure last weekend to shut down the I-40 bridge with their protest, so tell me how we have sufficient resiliency in the Memphis area even in peacetime?  Don't think for a second that this didn't get noticed and won't be repeated.

There are much smaller cities north and east of Memphis with roads less choked that have many more river crossing lanes serving their areas.  It just boggles the mind why we have the infrastructure we do at such a critical point of the IHS.
All the more reason why TN and AR need to prioritize building a third bridge across the Mississippi River in the Memphis area.
2-d Interstates traveled:  4, 5, 8, 10, 15, 20, 24, 25, 27, 29, 35, 39, 40, 41, 43, 45, 49, 55, 57, 64, 65, 66, 69, 70, 71, 72, 74, 75, 76(E), 77, 78, 81, 83, 84(W), 85, 87(N), 89, 90, 91, 93, 94, 95

2-d Interstates Clinched:  12, 22, 30, 37, 44, 59, 80, 84(E), 86(E), 238, H1, H2, H3, H201

The Ghostbuster

The trick is finding a good place for a third bridge to be constructed. It also depends on whether the bridge will be a freeway bridge or a local street bridge. If there weren't barriers in the way, bridges connecting the TN 300/future Interstate 69 stub and the TN 385/future Interstate 269 stub would be no brainers, though both would have to connect with Interstate 55 in Arkansas to likely be well-utilized.

bwana39

Quote from: The Ghostbuster on February 07, 2024, 11:45:21 AM
The trick is finding a good place for a third bridge to be constructed. It also depends on whether the bridge will be a freeway bridge or a local street bridge. If there weren't barriers in the way, bridges connecting the TN 300/future Interstate 69 stub and the TN 385/future Interstate 269 stub would be no brainers, though both would have to connect with Interstate 55 in Arkansas to likely be well-utilized.

I know that Mississippi is broke, but the right place for the bridge is in Desoto County MS. The growth in Metro Memphis is there and along I-22. Perhaps to connect to I-40 around Forrest City

https://wreg.com/video/pro-palestinian-demonstrators-shut-down-lanes-on-i-40-bridge/9399726/
Let's build what we need as economically as possible.

MikeTheActuary

Quote from: Plutonic Panda on December 19, 2023, 08:10:01 PM
BUILD A FUCKING TUNNEL LIKE EVERY OTHER COUNTRY!!!! lol but yes I would support a tunnel believe it or not. Connect it with Sam Cooper. Toll it. I'd pay a toll.
Quote from: lordsutch on December 20, 2023, 06:11:32 PM
That said a more creative TDOT would have cut and covered I-40 under North Parkway, but that's not the TDOT we had or have.

Three problems with that:

1.  Local geology.  I'm not an engineer or a geologist, but I suspect that the loess that Memphis sits upon, plus seismic concerns would make construction of any big tunnel difficult.

2.  Depending on the specific alignment of the tunnel, a portion of North Parkway abuts a hoity-toity neighborhood that is home to several locally-influential people.

3.  Also depending on the specific alignment, the need to not further disrupt the remnants of old growth in Overton Park would be a consideration.

I lived through the arguments and the alternative plans explored, since I grew up within walking distance of Overton Park, and my father worked in the Shelby County planning office, while my mother worked at the zoo.   I think I remember tunneling being considered and quickly rejected due to expense, geology, and inability to avoid the concerns that caused the preferred plan to be blocked.

Now that the two I-40/I-240 interchanges have been redesigned, the current alignment is good enough, and is probably quite a bit less congested than the original alignment would have been (especially with the shift of the de facto CBD away from downtown to around Poplar and I-240).

rlb2024

Quote from: MikeTheActuary on February 08, 2024, 09:38:30 AM
I lived through the arguments and the alternative plans explored, since I grew up within walking distance of Overton Park, and my father worked in the Shelby County planning office, while my mother worked at the zoo.   I think I remember tunneling being considered and quickly rejected due to expense, geology, and inability to avoid the concerns that caused the preferred plan to be blocked.

Now that the two I-40/I-240 interchanges have been redesigned, the current alignment is good enough, and is probably quite a bit less congested than the original alignment would have been (especially with the shift of the de facto CBD away from downtown to around Poplar and I-240).
I also grew up in Memphis, although out by Memphis State (as it was called at the time).  I remember a lot of discussion about a cut-and-cover tunnel through Overton Park and it being rejected for several reasons (exhaust fumes in the zoo and park, flooding concerns during heavy rains, cost and maintenance, etc.).  And this was before there were a lot of seismic concerns about Memphis' proximity to the New Madrid fault.

On my infrequent trips back to Memphis now, I'm really glad they didn't build I-40 through that area.

abqtraveler

Quote from: The Ghostbuster on February 07, 2024, 11:45:21 AM
The trick is finding a good place for a third bridge to be constructed. It also depends on whether the bridge will be a freeway bridge or a local street bridge. If there weren't barriers in the way, bridges connecting the TN 300/future Interstate 69 stub and the TN 385/future Interstate 269 stub would be no brainers, though both would have to connect with Interstate 55 in Arkansas to likely be well-utilized.
That's a big part of the problem about building a third bridge to the north of the existing ones. A bridge at TN-300 would be difficult because DeWitt Spain Airport sits directly between the end of TN-300 and the river. A bridge at the north end of TN-385 has to deal with the Meeman-Shelby Forest State Park. Technically both could be built, but to avoid the airport and the state forest would mean building the bridge and its approaches in a manner that is so far out of the way that it ends up being underutilized, with no substantial relief for the two bridges in Memphis.
2-d Interstates traveled:  4, 5, 8, 10, 15, 20, 24, 25, 27, 29, 35, 39, 40, 41, 43, 45, 49, 55, 57, 64, 65, 66, 69, 70, 71, 72, 74, 75, 76(E), 77, 78, 81, 83, 84(W), 85, 87(N), 89, 90, 91, 93, 94, 95

2-d Interstates Clinched:  12, 22, 30, 37, 44, 59, 80, 84(E), 86(E), 238, H1, H2, H3, H201

triplemultiplex

There's always the option to get rid of that tiny airport.  How many planes are even using it?  If Chicago can ditch Meigs Field (albeit thru a bit of chicanery) then Memphis can certainly consign their tiny airport to the dustbin in favor of a much more valuable piece of transportation infrastructure.  Lot more small planes fly to Chicago than Memphis.
"That's just like... your opinion, man."

wriddle082

Quote from: triplemultiplex on February 09, 2024, 11:50:29 AM
There's always the option to get rid of that tiny airport.  How many planes are even using it?  If Chicago can ditch Meigs Field (albeit thru a bit of chicanery) then Memphis can certainly consign their tiny airport to the dustbin in favor of a much more valuable piece of transportation infrastructure.  Lot more small planes fly to Chicago than Memphis.

No doubt, if they still need a small general aviation airport in the area, there's a lot of land in Arkansas where one can be built.  Or better yet, Fayette County, since that's where all of the big economic development in the area is going these days.

abqtraveler

Quote from: triplemultiplex on February 09, 2024, 11:50:29 AM
There's always the option to get rid of that tiny airport.  How many planes are even using it?  If Chicago can ditch Meigs Field (albeit thru a bit of chicanery) then Memphis can certainly consign their tiny airport to the dustbin in favor of a much more valuable piece of transportation infrastructure.  Lot more small planes fly to Chicago than Memphis.
The could close DeWitt-Spain Airport, since you have the Millington-Memphis Airport near the US-51/TN-385 interchange, and Charles W. Baker Airport even closer than that. Doing so would open up an option for a future bridge, which also just so happens to be right on the proposed alignment of I-69 through that area. If that were done, then you have a high-speed interchange roughly where the airport sits today, where I-69 turns northeast and TN-300 continues west to the new bridge.
2-d Interstates traveled:  4, 5, 8, 10, 15, 20, 24, 25, 27, 29, 35, 39, 40, 41, 43, 45, 49, 55, 57, 64, 65, 66, 69, 70, 71, 72, 74, 75, 76(E), 77, 78, 81, 83, 84(W), 85, 87(N), 89, 90, 91, 93, 94, 95

2-d Interstates Clinched:  12, 22, 30, 37, 44, 59, 80, 84(E), 86(E), 238, H1, H2, H3, H201

MikeTheActuary

Quote from: triplemultiplex on February 09, 2024, 11:50:29 AM
There's always the option to get rid of that tiny airport.  How many planes are even using it?

Most recent 12 month operation totals for Memphis-area public airports, per the FAA (as-of dates vary):

MEM: 213,418
OLV (Olive Branch): 100,605
M01 (DeWitt-Spain): 57,194
AWM (West Memphis): 50,200
NQA (Millington): 32,226
2MB (Charles Baker): 28,250
54M (Wolf River): 8,000

It's perhaps worth observing that DeWitt-Spain is the replacement airport for the old Mud Island airport that was closed due to the construction of the I-40 bridge.  It's a convenient airport for flight training and business travel for those folks who don't want to have to schlep out to airports further out, or deal with all the FedEx traffic at MEM.

Rothman

Reminds me of that Chicago mayor that just had bulldozers dig big Xs on the Meigs airport runway to get rid of it.  Got away with it because of the Chicago Machine...
Please note: All comments here represent my own personal opinion and do not reflect the official position(s) of NYSDOT.

edwaleni

Quote from: abqtraveler on February 09, 2024, 09:14:30 AM
Quote from: The Ghostbuster on February 07, 2024, 11:45:21 AM
The trick is finding a good place for a third bridge to be constructed. It also depends on whether the bridge will be a freeway bridge or a local street bridge. If there weren't barriers in the way, bridges connecting the TN 300/future Interstate 69 stub and the TN 385/future Interstate 269 stub would be no brainers, though both would have to connect with Interstate 55 in Arkansas to likely be well-utilized.
That's a big part of the problem about building a third bridge to the north of the existing ones. A bridge at TN-300 would be difficult because DeWitt Spain Airport sits directly between the end of TN-300 and the river. A bridge at the north end of TN-385 has to deal with the Meeman-Shelby Forest State Park. Technically both could be built, but to avoid the airport and the state forest would mean building the bridge and its approaches in a manner that is so far out of the way that it ends up being underutilized, with no substantial relief for the two bridges in Memphis.

Technically you could get a 6 lane urban style highway south of the runway, you would just have to be careful on the elevation rise leading to the bridge and over the sewer plant. Elevate too soon and it would interfere with flight operations, too low and the rise for the bridge would be too abrupt.  And I think we all know that there are many, many major highways within yards of the end of a commerical airport runway. This is a general aviation airport (DeWitt-Spain).

triplemultiplex

Quote from: Rothman on February 09, 2024, 04:00:11 PM
Reminds me of that Chicago mayor that just had bulldozers dig big Xs on the Meigs airport runway to get rid of it.  Got away with it because of the Chicago Machine...
And honestly, this is a case where breaking the 'rules' ending up being the right decision.  Such a better use of that land now rather than an elitist convenience for rich assholes and their private jets.  A large, lakefront park right next to The Loop with a concert venue, beach, and marina. What a great asset.
"That's just like... your opinion, man."

Rothman

Quote from: triplemultiplex on February 15, 2024, 09:40:23 AM
Quote from: Rothman on February 09, 2024, 04:00:11 PM
Reminds me of that Chicago mayor that just had bulldozers dig big Xs on the Meigs airport runway to get rid of it.  Got away with it because of the Chicago Machine...
And honestly, this is a case where breaking the 'rules' ending up being the right decision.  Such a better use of that land now rather than an elitist convenience for rich assholes and their private jets.  A large, lakefront park right next to The Loop with a concert venue, beach, and marina. What a great asset.
Meh.
Please note: All comments here represent my own personal opinion and do not reflect the official position(s) of NYSDOT.

MikeTheActuary

Quote from: triplemultiplex on February 15, 2024, 09:40:23 AM
Such a better use of that land now rather than an elitist convenience for rich assholes and their private jets.

So, you weren't a fan of Flight Simulator back in its classic days?  :)

Keep in mind that Meigs did have commercial air service, albeit limited to helicopters and small turboprops.

I flew through CGX a couple of times.   It was a helluva lot less miserable than O'Hare, and more convenient than Midway if your destination was in/near the Loop.

edwaleni

I would like to agree with a prior poster who promoted the tunnel effort with a colorful metaphor.

Don't have numbers to support it, but I would suspect the largest user of *any* new north/south driven river crossing would be freight/truck based.  Bridges look nice and are used as monuments to political and financial prowess and many cases civic pride, but I do think Memphis already has enough of those today and don't need yet another.

While Memphis and the general area does have some geological issues, tunnel technology has come a long way in the past 30-40 years.

What makes this area an easy, yet tough tunneling environment is caused by the same thing.

It sits in the middle of the Mississippi Embayment, an alluvial plain that dates back millions of years when a super continent of Rodinia tried to split in two. The split failed and the ground sunk into the rift that was formed between the Appalachian and Ouachita Mountains. That rift has filled with ocean and river sediments over the centuries and so the layers of compressed sand and other byproducts go down hundreds of feet below ground level.

Compressed sand make for somewhat easy tunneling compared to trying to work though solid rock or the basalts encountered when going through tall mountain ranges.

But it is this compressed sand that causes other issues. The faults created underneath the failed continental split are still active and move regularly (about a tenth of the movement of the very active San Andreas fault) and when they slip, quakes occur.  A tunnel built at about 60-100 feet below ground level is going to have to face a significant amount of vertical pressures as they move up through the weak sand (this is what caused the "sand blows" people saw in 1811).

So any tunnel design is going to have to be able to flex at periodic points to able to absorb the seismic activity. It's the same energy that causes buildings to sway.


bwana39

Quote from: edwaleni on February 19, 2024, 12:46:24 AM
I would like to agree with a prior poster who promoted the tunnel effort with a colorful metaphor.

Don't have numbers to support it, but I would suspect the largest user of *any* new north/south driven river crossing would be freight/truck based.  Bridges look nice and are used as monuments to political and financial prowess and many cases civic pride, but I do think Memphis already has enough of those today and don't need yet another.

While Memphis and the general area does have some geological issues, tunnel technology has come a long way in the past 30-40 years.

What makes this area an easy, yet tough tunneling environment is caused by the same thing.

It sits in the middle of the Mississippi Embayment, an alluvial plain that dates back millions of years when a super continent of Rodinia tried to split in two. The split failed and the ground sunk into the rift that was formed between the Appalachian and Ouachita Mountains. That rift has filled with ocean and river sediments over the centuries and so the layers of compressed sand and other byproducts go down hundreds of feet below ground level.

Compressed sand make for somewhat easy tunneling compared to trying to work though solid rock or the basalts encountered when going through tall mountain ranges.

But it is this compressed sand that causes other issues. The faults created underneath the failed continental split are still active and move regularly (about a tenth of the movement of the very active San Andreas fault) and when they slip, quakes occur.  A tunnel built at about 60-100 feet below ground level is going to have to face a significant amount of vertical pressures as they move up through the weak sand (this is what caused the "sand blows" people saw in 1811).

So any tunnel design is going to have to be able to flex at periodic points to able to absorb the seismic activity. It's the same energy that causes buildings to sway.

There are tunnels under SF Bay. Ventilation is a larger issue than seismic activity.
Let's build what we need as economically as possible.

MikeTheActuary

Quote from: bwana39 on February 19, 2024, 01:03:56 PMThere are tunnels under SF Bay.

The Transbay Tube was constructed in sections on land which were then floated out to the right location, submerged into a prepared trench, and then cushioned/fastened to the bottom with sand and gravel.

Constructing this way, and by avoiding bedrock, is thought to cushion the tunnel in such a way as to reduce the chance of failure in an earthquake.

I suppose that something equivalent could be done in Memphis, by cutting a trench, building the highway in the trench, and then covering/cushioning structure, but such a construction tactic would have many of the same park-disruption problems that killed the original I-40 ROW, plus the added disruption to all the houses that have since been constructed in the former right of way.   (I haven't paid attention to where things stand with the last un-redeveloped plot of the ROW.  Last I heard, neighborhood folks were trying to fix a problem of having no nearby parks, while developers were chomping at the bit at the prospect of being able to build in a part of town seen as up-and-coming.)

The only way you'd get I-40 tunneled under Memphis is by boring through the loess.   It'd be easy to bore the tunnels; it'd be far more difficult to bore the tunnels in such a way as to survive various potential causes of collapse.  (Although, in fairness, Google tells me that the Chinese have had some success...and a few failures...in this regard.)

I still don't see that happening to save 3 miles in a city that has been pursuing road diets, in a state that tends to be miserly when it comes to transportation projects in that part of the state.



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