Section of I-95 collapses after fire burns under overpass... 15

[FacEngrPE]

Leaving the remains of the abutments now, saves some time, as they so not need to be concerned with the dirt behind the abutments being unsupported while the fill is being placed. It may complicate the reconstruction a bit, but as the abutment demo for the reconstruction can now be carefully designed, it can be part of a more normal construction project, where the traffic impact will be better managed.

 

[sgw1009]

It is fascinating to watch the construction process. They appear to be using a weldable mesh material, about 10' by 15' or 20' in size to anchor the entire structure together. First a layer of this mesh was laid down, with the end two feet or so bent upwards vertical, but the rest lying flat. The vertical ends were welded to vertical rods to keep the ends vertical. Then the fill was added, leveled, and tamped, with the weight of the fill anchoring the mesh sheets, including the "ends" (or sides if you will). Once the first layer (approx two feet) was completed, another layer of mesh was laid down, again with the end two feet or so bent vertical, more vertical rods were welded in place, and the process repeated. They are progressing about one two-foot layer every two hours (so about 12 feet so far in about 12 hours). With what appears to be about 16 more feet to go, they should be ready to begin applying the final top layer sometime Sunday evening or so. It is just amazing to watch this process, because it is the weight of all of the fill that will (hopefully) keep the fill in place. Fascinating.

 

[JohnRBaker]

Well, that would avoid have to built cofferdams/retaining walls. In essence, this will result in an all but 'solid' foundation that will have the smallest possible footprint, leaving the most room on either side, allowing them space when it comes time to start to construct the permanent replacement lanes, from the sides, as it were, inward.

Here's a news item with a live video-feed showing the work under way:

https://6abc.com/when-will-i-95-reo...erstate-95-collapse-rebuild-project/13394782/

Also watch the news clip in the item above as it provides a good explanation as to how the reconstruction will proceed.

John R. Baker, P.E. (ret)
Irvine, CA
Siemens PLM:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[hokie66]

Typical reinforced earth process. Highway construction crews do it all the time, both for temporary and permanent works. With permanent works, the facing is concrete panels.

 

[FacEngrPE]

Youtube page linking to the live stream

https://www.youtube.com/@PennsylvaniaDOT/streams

The cross section described i similar to this detail. Continuing the mesh across the entire fill area will minimize the work needed to retain the soil as reconstruction progresses.

 

[human909]

I too am ignorant to this sort of process, but it makes plenty of sense.

A great video from a youtuber here, pitched to be palatable to non engineers but the principle is the same.

https://youtu.be/0olpSN6_TCc?t=339

 

[jerseyshore]

https://www.cbsnews.com/philadelphi...-what-temporary-i-95-repair-will-look-like/#x

This page has a rendering of the temporary bridge and how it's going to look.

 

[Ingenuity]

...mechanically stabilized earth...aka Reinforced Earth...thanks to the French civil engineer, Henri Vidal for his modern-day version from 1960's.

 

[enginesrus]

So what happened? Did the truck and tank roll over and or hit something? How did it end up just sitting there and then a fire ensued?

 

[KevinK2]

This FGA material is a reinforced, aerated foam, as I understand it. It has been used in PA for several projects, as shown in this PP:

https://www.penndot.pa.gov/ProjectA...retate A New and Unique Lightweight Fill.pdf

Even with the material constrained from lateral expansion under load as the temporary overpass support, how could this foam with air content act as a stiff, beam like support to the new roadway? Each of the steel sheet capped building blocks, would seem to act like a vertical spring, with the stacking being like springs in series, loweing the rate, no?

I saw the bulk density was listed as only 8-25 pcf, much less than soil.

 

[davefitz]

A couple of observations:
1. many cities have homeless communities living under these overpasses, and one fire per week per city in the rundown RV's parked under these bridges is pretty typical on the west coast.

2. In addition to the steel failures, there is also the issue of thermal expansion and unseen failures of expansion joints and related fittings. In the hurry to re-open I-95 it is hoped that a complete survey of these expansion features is being addressed.

3.Very fast setiing concrete, called geoploymer concrete , is used by the US military to repair runways that were attacked by munitions, and the runways can be re-opened for air landings/takeoffs within 24 hrs.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

 

[hokie66]

KevinK2,

Density doesn't necessarily determine strength. They have experience in using this material in pavements.

 

[KevinK2]

Hokie66,

Agree. But it's light weight because it contains air, which is compressible based on the primary foam material. They advertise you can buy standard open cell material, or closed cell versions, cells being air pockets.

I'm not concerned about strength so much as stiffness. This stuff has many applications for roadways where the total material height is limited, but I have not seen it stacked this high to offer sole support for an elevated, high traffic interstate. The advertse it for "bridge abutments", that's different. The higher the stack, the lower the spring rate in compression.

The aggregate offers excellent shear stability for retaing walls, etc.

The latest video shows what looks like massive concrete slabs, stacked on ends, likely to cap off the current stack.

I hope it works as planned,
Debbie Downer

 

[hokie66]

Yes, stiffness is a legitimate concern. But all pavement materials contain air, and are compressible to a certain extent. I also hope it works.

 

[KevinK2]

True about pavement materials. But typical crushed rock/stone, imho, will be a stiffer bed in compression than even a compacted layer of this material:

https://images.squarespace-cdn.com/...0DYLOCCY3XDGHSQAGK/IMG_3561Lo.jpg?format=500w

From the literature:
1.1 Production of foamed glass
Foamed glass is produced industrially by treating cleaned glass particles. These glass particles are
ground into a powder of under 0.1 mm and mixed with a foaming agent. The powdered glass is then
spread onto a conveyor belt and then slowly passed through a furnace. The furnace heats the
powdered glass to a temperature of 900 °C. This causes the glass mass to expand to five times its
original size and it subsequently hardens into foamed glass. 92 % of foamed glass´s composition is
air bubbles. As the foamed glass cools, it breaks up into pieces and forms foamed glass aggregate.

I assume 92% by volume.

Applications:
• Many uses for lightweight aggregates
• Embankment fill over soft soils
• Retaining walls
• Bridge abutments
• Reduced lateral load of backfill
• Lightweight fill over culverts and utilities
• Under foundation slab insulation and drainage
• Insulation layer
• Horizontal or vertical
• Greenroofs

The primary advatages of this material is light weight, and shear stability as was the original heavy product. Perfect for retaining walls.

I have not yet found another application like this one on I95. Classic beam with pinned ends on an elastic foundation.

 

[Retiredat46]

How are they going to remove the aggregate and reinforcement materials when they are no longer needed? I can't see how they could lift it over the active roadways or load it onto trucks between the active roadways. That leaves "mining" it by tearing into the sides of the pile from below the newly constructed bridges, and letting the pile collapse as it's carried away.

 

[KevinK2]

This image may help understand the project:

https://assets3.cbsnewsstatic.com/h...066ced.jpg?v=23da2bed74e9783333cf303fba619e89

Originally it was at least 4 lanes each way. The temporary support is under the central 2 or 3 lanes each way. Once completed, construction will begin on permanent repairs to those outer lanes on each side. When completed, the central temorary lanes will be rebult with permanent support:

"When eventually constructing the (temporary) bridge, there will be six lanes — three for northbound and three for south in the center area of the “void”, according to Pa. Transportation Secretary Mike Carroll.

The outer 35 feet will be under construction and not impact traffic. Once completed, the reconstruction will then move toward the center of the bridge."

 

[KevinK2]

SGW1009,

While observingthe creation of the large "bricks" of the light fill, fully encased in a welded on wire mesh, did you observe a step to compact the material to a denser condition? Or mabe it was precompacted?

The PP I linked on 19 Jun 23 14:41, suggests compaction is necessary for minamal rigidity, going from a loose 15 pcf to 18 pcf.

 

[KevinK2]

The rapid response to get traffic moving again is admirable. From this daily update link:

https://www.penndot.pa.gov/RegionalOffices/district-6/Pages/AlertDetails.aspx

"7:40 p.m. on June 18, Today marks one week since a vehicle fire led to the collapse of a section of Interstate 95 in Philadelphia .... the Shapiro Administration expects the roadway will reopen within the next two weeks."

"Crews continue to make headway on the interim roadway, which will open temporary travel lanes on I-95, three in each direction, while work proceeds to rebuild the outer sections of the permanent bridge. The process to fill in the roadway in the area of the collapse with a specially designed, Pennsylvania-made recycled glass aggregate is expected to conclude within the next day or two. Once fill is complete, eight inches of modified sub-base will be installed, edge and median barrier will be installed, and the transition between the new roadway and existing lanes will be prepped. Paving operations will begin soon after. Equipment is being staged and mobilized for next steps and work continues."

A lot of progress in 1 week, but was enough engineering put into this unique application of this super light fill ? Politics has interfered with engineering before, with a space shuttle launch when engineers said it was too cold for the critical o-ring seals.

 

[Retiredat46]

I saw men pushing around what looked like small compactors with handles, and some rubber-tracked Bobcat sized loaders going back and forth. I never saw anything larger being used, and none of what I watched looked like they were compacting the entire area, just the sides, ends, and spots here and there. It didn't appear that the layers were very flat. The track loader would pitch noticeably as it moved around over uneven places.

It looked to me like they were only using large pieces of black fabric rather then wire mesh for most of the areas. It was really flexible, easily folded, and appeared to be pretty light by the way it was being handled and spread out.