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RE: Footing Retrofit/Replacement Ideas

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Micropiles can indeed have large capacities. In fact, there are now being
used for new construction more often and are a good option versus drilled
shafts (caissons) depending on the soil or rock conditions. They are also
extensively used for footing retrofit and upgrade. 

A micropile with a capacity of 5-20 kip would not be a micropile, it would
likely be more the type of underpinning that is either screwed in the ground
(Helical Piers), pushed (Atlas piers), or expanded inside a predrilled hole
("Manta Ray" piers). These may have limited application, although they may
very well be a suitable solution for the underpinning problem as originally
described. 

A micropile is a grouted element inside a predrilled hole that may provide
very large capacities, certainly far greater than 20 kip even in soft
ground. Its main advantage in the context of the original question is that
it can be installed through or beside the existing footing from grade, it
can be easily connected via a steel frame to the superstructure, and that it
is strong. Therefore, the whole footing support can be accomplished without
significant excavation.



-----Original Message-----
From: Eli Grassley [mailto:elig(--nospam--at)psm-engineers.com] 
Sent: Monday, February 13, 2006 2:49 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Footing Retrofit/Replacement Ideas

>J. Gomez wrote:
> Can have capacities in excess of 300 kip each depending on the  
>subsurface conditions.


I don't think quoting a capacity of 300kips for micropiles is doing anybody
any favors here.  A more realistic capacity to expect is on the range of
5-20 kips.  If your soil is so dense that you can get 300kips out of a
micropile, the you probably wouldn't be having any problems with your
foundation in the first place.

~~ Eli ~~


-----Original Message-----
From: Jesus Gomez [mailto:jgomez(--nospam--at)schnabel-eng.com]
Sent: Friday, February 10, 2006 6:25 PM
To: 'seaint(--nospam--at)seaint.org'
Subject: Re: Footing Retrofit/Replacement Ideas

Micropiles are extensively used for this application. They can be drilled
from the ground surface, either through or beside the existing footing. Can
have capacities in excess of 300 kip each depending on the subsurface
conditions. 

If drilled through the footing, they can be bonded directly to the footing
(they are grouted with neat cement grout). Bond stress would be about 100
psi allowable in your case ( difficult to clean corehole through footing).

If installed beside the footing, can just tie to pier through steel beams.
In this case, they can be preloaded.
 

-----Original Message-----
From: Daryl Richardson
To: seaint(--nospam--at)seaint.org
Sent: Thu Feb 09 21:08:14 2006
Subject: Re: Footing Retrofit/Replacement Ideas

Sir,
 
        I have two possible ideas for brainstorming consideration only.  I
would only use these with the advice of a geotechnical engineer.
 
        First: if the soil upon which the footing is permeable an
application of pressure grouting may consolidate the soil sufficiently to
increase the allowable bearing capacity and make any other repair
unnecessary.
 
        Second: I once provided a second opinion for a scheme to remove
contaminated soil from underneath a number of row houses.  Under this scheme
small diameter "mini piles" about 2.5" to 3" in diameter were jacked into
the ground at about 4' centers around the houses and bolted to the
foundation walls allowing petroleum contaminated soil to be removed from
under the houses (including basement slabs on grade) and replaced with clean
material.  This was a large budget project; you'd need all of your fingers
(plus some toes too) to count the cost in millions of dollars.  This project
was completed successfully.
 
        In your case four such piles, either placed through holes cored in
the footing near the column or installed at the edges of the footing might
give you a combined pile/spread footing foundation suitable to carry the
load.
 
        Just a couple of thoughts that may or may not be helpful.
 
Regards,
 
H. Daryl Richardson

	----- Original Message ----- 
	From: Eknrinc(--nospam--at)aol.com 
	To: seaint(--nospam--at)seaint.org 
	Sent: Thursday, February 09, 2006 7:50 AM
	Subject: Footing Retrofit/Replacement Ideas

		I have a project which limits me to having to upgrade a
concrete pad footing bearing area. The existing footing is 4' square x 12"
deep. Here are my initial ideas:
	 
	1. Underpin (this requires shoring supported beams)
	2. Demolish and replace (this requires shoring supported beams)
	3. Pad extension on two sides (may run into existing reinforcement
for continuous flexural reinforcement installation/coring)  
	 
	Any other ideas?
	 
	Thanks in advance.

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immediately notify postmaster(--nospam--at)schnabel-eng.com

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