Soldier Pile Wall w/ Surcharge 2

[DSKENGR]

I'm designing a soldier pile and lagging retaining wall. There is an existing building (2 story house) that will be near the wall (1 to 2ft from the back). I plan to design the wall with an appropriate surcharge from the house foundation and limit the deflection of the top of the wall to reduce potential settlement. What should the maximum settlement be? And also, is there any need for underpinning in addition to the wall and/or should I sequence the drilling operation to alternate piles (i.e., every other pile installed first) to reduce the settlement potential?

 

[PEinc]

In my opinion, the building should be underpinned and you should not be supporting it with a soldier beam/lagging wall.
What type of lagging were you thinking of using and how do you think it will be installed?

http://www.PeirceEngineering.com

 

[DSKENGR]

One thought I've had is to install a welded bracket to the back of the soldier pile support the foundation. Any thoughts?

Alternately, if I underpin, how deep do I need to go below the new excavation? The underpinning concrete column is designed for lateral loading in addition to vertical, so I would still need to go deep enough to get enough passive pressure, right? Also, are underpinning pits typically reinforced? An underpinning pit is essentially a cantilevered, reinforced retaining wall with a vertical load at the top, correct?

I've been looking for a good design example of underpinning, but they seem sparse.

Thanks for your input.

 

[GeoPaveTraffic]

What kind of soil(s) is present?

How deep is the excavation going to be?

Does the same person/company own the house as is performing the excavation?

What kind of construction is the existing house?

There will be damage to the house. Underpinning and/or shoring can reduce that damage, but some damage will occur.

Mike Lambert

 

[PEinc]

Depending on the ground conditions, the house could be underpinned with concrete piers, helical piers, or bracket piles. After underpinning the house, the wall could be built in front of the underpinning or be attached to the pier underpinning or bracket piles. Considering your original question and your previous posts about soldier beam walls, I suggest you contact an engineer who specializes in underpinning and retaining walls or find a specialty contractor who is very experienced in major underpinning jobs. I say very experienced in major underpinning jobs because almost all engineers and contractors think they know everything about underpinning, but most do it incorrectly.

http://www.PeirceEngineering.com

 

[DSKENGR]

I suggested helical piers to underpin in combination with the soldier pile/wood lagging wall in front, like you mention, but the geotechnical engineer said he is worried the helical piers have no lateral resistance and may move over time if there is any gap behind the lagging from over digging during installation. I'm not so sure about this but have to consider it.

The soil is sandy silt/silty sand with SPT blow counts between 49 and 96 blows per foot, between zero and ten feet below grade. The excavation will be about 10-11 feet. Another issue the geotech brought up regarding helical piers is that we may get refusal before getting to 10 or 11 feet because of density of material. I'm not sure this would actually be a problem either.

In answer to other questions from GeoPave, the house is a two story wood framed building. Home owners have hired a contractor to do this and other work.

 

[msquared48]

I would consider both vertical pin pile (2" to 3" at 4 foot intervals under the foundation of the house, and intermittent pin batter pile to take the lateral load in tension, if it can be developed. I would also extend the pin pile around the side of the house at least the depth of the excavation in horizontal distance.

As for any interior footings, pin pile would probably not work, meaning re-shimming the footings as settlement occurred.

Mike McCann, PE, SE (WA)

 

[PEinc]

The geotech is correct. If the soil is that dense, the helical piers may not advance as far as needed. The house could be underpinned with similar underpinning brackets attached to auger-cast piles with a steel threaded bar inside.
If the excavation is 10 to 11 feet, cantilevered soldier beams will deflect unless they are very stiff and the soil is very dense. Helical piers will add little or nothing for lateral support.
If you are worried about the condition of the soil behind the lagging, you may have the wrong contractor.

http://www.PeirceEngineering.com

 

[BUGGAR]

I like Mike's idea of pin piles. I suggest a "Top down" constructed pin pile wall using mesh and shotcrete. And you can get CALTRANS details for this.

As a bonus, you can have the shotcrete sculpted like they do at Disneyland.

Bob

 

[RFreund]

Mike,

Pin piles can take horizontal lateral loads? I was thinking only helical could be used in such case. Do you know where design values would be located?

You touched on this briefly and that is the idea of the building now having differential settlement if only underpinning the adjacent side.
Does anyone know if this is typically a problem? Is there a certain age of the structure where this is generally not a problem? Or do you typically underpin a certain extent (depth of the excavation) as mentioned. Should/does the geotech generally address this?

In this case there could be an issue with crossing the property line with the 'tiebacks'. But I suppose if you're going to underpin it then there probably is not an issue. I wonder how many cases there are where underpinning is the better solution but there is a property line issue so other type of bracing is used instead...

Thanks


EIT

http://www.HowToEngineer.com

 

[dcarr82775]

Different people use different words, what is a pin pile?

 

[Ingenuity]

Different people use different words, what is a pin pile?

Pin Piles are small diameter high capacity drilled and grouted piles also called minipiles or micropiles.

 

[RFreund]

I was actually thinking they were "push piles" basically the same as Ingenuity describes but they are not drilled. They are pushed using the weight of the existing structure to provide resistance. I supposed if they are drilled and grouted then their lateral load capacity is similar to a grouted tieback?

EIT

http://www.HowToEngineer.com

 

[Ingenuity]

The attachments maybe of assistance re Pin Piles:

http://files.engineering.com/getfil...4&file=Pin_Piles_for_Building_Foundations.pdf

http://files.engineering.com/getfil...7caef2bac&file=Pin_Piles_for_Underpinning.pdf

 

[Ingenuity]

...sometimes referred to as "root piles" which was once a worldwide tradename.

 

[mudman54]

if you replace the soldier piles with jet-grouted pipe piles you can underpin the structure as part of the retaining wall.
it is important to do alternating piles as mentioned above so the jet grouted soil can harden.