Sawcutting foundation 2

[Gus14]

Two columns in two separate buildings share the same footing. Service load on each column is 1000 kn. Building number one will be demolished and a new basement below the footing depth of embedment will be built, while building number two will remain untouched. The contractor wants to saw cut the footing but the resulting eccentricity will be huge and not safe for overturning. What do you think is the solution ?

 

[r13]

Is this a temporary condition until new building is erected? Will the new building column share the same footing? How many columns are affected? Can you use sheetpile instead of soldier pile? Can you post structural framing above? Thanks.

 

[Gus14]

Is this a temporary condition until the new building is erected?
No, the second building remains as it is.

Will the new building column share the same footing?
No, the new building has a basement while the old one did not.

How many columns are affected?
Three columns lay on the property line and have the same problem.

Can you use a sheetpile instead of a soldierpile?
Would that make a difference and why?

Can you post structural framing above?
Do you mean the new building foundation lay out. I am worried about the old building footing stability after saw cutting.

 

[Gus14]

I'm thinking about cutting only a portion of the footing so that the load remains within the kern distance and shore around it
but the owner is determined to cut the whole part that rests on his property.

 

[HTURKAK]

If you saw cut the footing, the remaining footing will experience eccentric loading and the rebars will be cut and will not work.

I will suggest two options;

1- Suspend the columns with shoring for the bldg number two and construct new combined footing with strap beam , similar to the following picture;

2- Extent the new footing for bldg no. one under the columns of bldg no. two with pillars connected to the basement wall of bldg one.

Both options require the shoring of bldg no. two.

 

[Gus14]

Option 1 would not work because the owner of the second building won't allow it.

Option 2; Do you mean to temporarily saw cut the footing then shore the second column with the piles? ( if not then how to construct a footing below the col no 2 ?) Then extend two columns from building number 1 basement wall and connect them to col number 2. (How?)

 

[HTURKAK]

If the owner of the 2nd bldg does not corporate , the cost will be a different animal.. In this case i will suggest underpinning of the wall and footings at property limit .

The service load 1000 kN is a big number..

I will suggest the following steps,

i = demolish the 1st bldg including the column , keep the ftg.. excavate a pit and drive steel pile with jacking against the wt of 2nd bld. The piles shall be in segments ..

ii= Underpin the wall with staggered concrete wall or jet grouting

iii = Excavate the full pit and saw cut the ftg.

Below find some descriptive pictures and doc. below

 

[hokie66]

The owner of the new building, Building No 1 with the new basement, must bear the cost of adequately supporting Building No 2. This is analogous to a party wall where two adjacent buildings share a common bearing wall. One owner cannot simply remove half the thickness of the wall. There are risks involved, which the Building No 1 owner must accept responsibility for. The owner of Building No 2 should insist on a preconstruction condition assessment by an independent engineer.

 

[Gus14]

Thank you HTURKAK and hokie66 for your responses.
The contractor engineer suggested the following (feel free to tell me what you think);
He suggested to :
1) Extend the steel soldier piles above the footing.
2) weld steel beams with soldier piles on top of the footing to prevent it from rotating around the potential point of overturning when the soil below the footing fails.
3) keep 40 cm of the footing within the first building and cut the rest of it.
4) Dig below the footing and shore while digging using steel beams welded between the soldier piles spaced 3 meters apart. (the footing length is 3 m)

The attached plans explain his idea.

 

[HTURKAK]

1) Extend the steel soldier piles above the footing.
A 1 = Soldier piles together with timber boards are used for soil retention. The ftg load for bld no 2 is 1000 kN. In this case the two soldier piles near ftg shall be driven to a depth to resist the mentioned load.

2) weld steel beams with soldier piles on top of the footing to prevent it from rotating around the potential point of overturning when the soil below the footing fails.

A 2 = How the steel beam will be connected to the top of ftg ? is there a grade beam to support the wall ? I proposed Underpinning with steel-pipe piles jacked in short sections under the column axis.

Pls provide more info. and clues.. soil type, size of the ftgs and columns, excavation depth.. a scaled sketch will be helpful..



Good luck..

 

[r13]

You are facing 2 scenarios:

1. The neighbor agree to work with you, and there is a solution reached, that allows tie your footing into the new construction. This is a temporary condition, the column can be stabilized by proper shoring, until the capacity of the footing is restored.
2. There is no intention/possibility to tie your footing to the new construction, one of the option to consider is relocating your column, if the framing and space permit.

For the contractor's suggestion, you need to ensure the soldier piles and leggings are designed for the additional soil pressure from your column, and the horizontal beam is properly tied to both the soldier piles and the footing to prevent potential movement. I would be wary on such supporting scheme.