A monopole with foundation above gr 1

[A.F]

A monopole with foundation above groun. foundation tilted on one edge.
A geotecnical consultant recommended dismantling tower ,doing necessary soil reinforcement then erecting the tower again.
Is there another method to reinforce soil and removing the signifucant foundation tilt
Without tower dismantling

 

[r13]

What kind of tower, lattice steel, steel pipe, size and weight? Just to see if it can be lifted off the foundation without completely take it apart. Can it be dismantled into manageable segments?

 

[A.F]

25m monopole
Weight around 18t
2 pieces
We need to put the site down for telecomm dismantling

 

[A.F]

R13
Footing is precast around 6*6

 

[A.F]

R13
The footing precast aroun 6*6
The challenge is to resolve the problems of weak backfill and tilting while the site is on air

 

[r13]

Okay, two segments is much better than one, as 18t is pushing the envelope of crane lifting capacity. Here is a typical spec for the tower crane FYI. Good luck.

 

[A.F]

Is soil injection a doable option here

 

[r13]

It depends the type of onsite soil and other factors, which I have no clue. You should ask your geotechnical consultant for the feasibility then.

 

[r13]

May I ask more questions to be more clear on your situation, so even if I couldn't help, someone else may chime in.

What is the retrofit procedure your geotechnical consultant has proposed, will it involves demolishing the foundation (pile cap)? And you told me "Footing is precast around 6*6", does it mean you have a total of 36 precast piles in a square layout? If so, the plie spacing will be at least equal to 5m c/c (for 25m Ø monopole), is that correct? What is the minimum pile spacing your code/standard allows, can adding more piles be an option, which might solve the problem without the headache of soil reinforcing? Sorry for the series of questions, just curios and speaking loud.

 

[A.F]

Precast just on groynd without piles

 

[HTURKAK]

IMO, shoring and jacking to vertical the monopole and the PC ftg and jetgrouting should work..

Another option, drive 4 piles and pour new ftg with increased dim's. similar to the following sketch..

 

[A.F]

r13
Please note
Georeport shows first 2m silty sand to be removed
Spt not mentioned fir this layer

 

[A.F]

Hturkak
Can injection under pressure do the dual job of soil reinfircement and removing the tilt
Soil is silty san first 2m no spt fir it mentioned in report

 

[A.F]

Just thinking loud for jacking or pressurused grouting may be doing some pad checking capacity is necessary,actually first time I encounter such an issue

 

[HTURKAK]

Nope !!..

You can not control and fix the plumbness. Just write helical pile and search to see the concept. You are expected to lift the tilted ftg with jacking against the helical piles or similar arrangement then apply jet grouting..

The set should be similar to the picture below ; (a snap from the book Helical Piles A Practical Guide to Design and
Installation by Howard A. Perko, Ph.D., P.E. )

 

[A.F]

Hturkak
Thanks. So as I understood: 3 elements
Jacking
Groutibg
Shoring.
For shoring
how to shore the monopole given
site only 7*7 and
on 3 sides private buildings
On fourth site there is public road

 

[HTURKAK]

If you decided to use helical piles you will need 2 steps.. installing helical piles and jacking the footing to level and jet grouting. The shoring of ftg and monopole is necessary if you decide only jet grouting.. If you post some pictures , you may get better responds ..

 

[A.F]

r13
Please note the precast foundatio has lifting hooks to remove and reinstall again
Thanks

 

[A.F]

Hturkak
Thanks for the info. Provided

 

[r13]

r13
Please note the precast foundatio has lifting hooks to remove and reinstall again

So glad to hear that. A clever foresight. HTURKAK has provided excellent retrofit plan, if there is adequate space for operation. With buildings so close to the site, IMO, you should consider adding auger-cast piles instead only relying on concrete pad foundation. Good luck.