An existing telecom tower footing. 3

[A.F]

An existing telecom tower footing.
Due to heavy water flow aroun half of the footing is exposed due to collapse of backfilling above the pad.
If backfilling to he restored any suggestion anout the procedure given the sxisting unaffected soil

Any proposal to protect the soil from heavy water flow is welcomed

 

[1503-44]

A picture, or description of how much soil washed away would help. What was the existing soil cover? Sandy, clay, gravel? Was it compacted? Is the area adjacent to a stream or river that is subject to frequent flooding. Was the area slopped? Was the area subject to severe currents?

Assuming that the soil cover needs to be provided to prevent tower overturning, for now I might suggest that you replace the soil that has washed away with a crushed limestone and clay mix, or similar material and cover that and enough of the surrounding area with geotextile followed by laying gabion mattresses on top.

I might change my mind, depending on further information.

 

[A.F]

There are few hills nearby causing the veavy flow
Original backfill material specified selected fill or engineering fill above footing
Photo attached
For example if we specify to restore backfillng is should a procedure be specifief to interlock the new backfilling with the soil which did not collapse

Some ditches were proposed around the site
Is it enough

Proposals from geotech. Engineers arecappreviated on howcro restore the backfill/ and ptotect

 

[PEinc]

That has to be one of the worst photos I ever saw.

http://www.PeirceEngineering.com

 

[A.F]

On left exposed chimney with protective material.
On right soil which withstood

 

[1503-44]

Let's go with a sketch.

Holding topsoil in place by "interlocking with subsoil" doesn't sound like it would be effective. Topsoil would be gone by the time the interface was exposed. You need to protect all surfaces exposed to the water flow. Gabion mattresses usually work well in that application.

 

[A.F]

Attached anothet photo
My espcialty not geotech what is gabion matrsses

Is there specific procedure to backfill beside existing slope
As a civil is it enough to specify " backfill material and procedure to be under the geotech. Consultant

 

[1503-44]

OK, looks like you damn near lost the entire tower. I guess the high winds went elsewhere at the time.

Gabions basically are "chicken wire", or chain-link fencing type material formed into cages or mats of various forms and dimensions, and filled with rocks. Wire is usually coated with polyethylene. They are very commonly used along drainage paths and channels, sides of bridge abuttments and anywhere else you need to protect against erosion from flowing water, or small wave actions and/or to provide slope stability, and for retaining wall structures built alongside a road cut, etc. The mattress form is perfect for providing a blanketing coverage alongside a stream bank, around comm towers, or even placed on a river or stream bed, for example to protect a crossing pipeline buried below from being exposed by excessive erosion by the river's flood currents.

You can see various forms and applications as shown in these typical images,

https://duckduckgo.com/?q=gabion+matresses&t=brave&iax=images&ia=images

 

[r13]

I still couldn't figure out what is happening, but see a lot of soil collapsed into a pit. Is that the tower located to close to an open excavation, and on the open side, the bank has collapsed due to heavy surface runoff? Please confirm.

If it is the case:

1) Stabilize the tower through mechanical means.
2) Shore the foundation, and dewatering the pit, if necessary.
3) Clean up the loose soil, both the bottom and the vertical surface, to the sound soil layer.
4) Coordinate with the geotechnical engineer to determine slope protection and backfill measures.

 

[oldestguy]

1503-44 has shown the correct way to fix this and prevent another loss of the backfill. Pay attention to the rules of stone sizes if that stone material is not enclosed in the wire baskets. Stone size is set by the velocity of the flow.

 

[A.F]

Ok
prelimibary plan, based on discussions
To have the geoconsultant supervise backfilling restoration
To propos Gabions
To provide some ditches around the site

 

[chicopee]

Oldestguy, River banks are lined with rip rap what's wrong with that method?

 

[fel3]

chiopee...

I don't see where oldestguy said there was anything wrong with the proposed method. He just cautions that if gabion baskets are not used, the unenclosed riprap must be sized.

For riprap sizing methods, see, for example, FHWA HEC 11 "Design of Riprap Revetment," HEC 23 "Bridge Scour and Stream Instability Countermeasures," HEC 25 "Highways in the Coastal Environment," Caltrans Highway Design Manual, Chapter 880 "Shore Protection," and other publications.

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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[1503-44]

Nothing wrong with riprap, however a larger rock size and a greater volume as well as more depth of riprap fill is needed. It also lacks the structural integrity of the wire bonds between the riprap particles that gabions provide making localized failures less common. Extreme events may remove riprap during high flow velocities and the river may not drop rocks of similar size and placement as velocities slow, leaving inadequately protected stream banks for the next event. Localized washouts in riprap along drainage courses, that can lead to widespread failures, are prevented with the gabion mattresses' wire bonds and overall performance is vastly improved. Some sizing specifications of the rocks used in various configurations of gabions is also required. I've been using gabions for erosion protection of pipelines for over 30yrs and, if designed properly, I can assure you that you will not be disappointed with their performance.