Excavation Support

[moe333]

I'm trying to come up with some options to support an excavation in an urban environment. A 1960s building with a basement is to be demolished including the basement walls and slab, and the footprint of the building is to be backfilled up to street grade.

The basement walls support sidewalks/city streets on two sides with various underground utilities, locations unknown at this point. The basement walls are within about 6 feet of a historic building built in the 1930s. The assumption is the 1930s building does not have a basement.

Soil conditions are not yet known but groundwater will probably not be an issue. My first thought was to underpin the adjacent building, and install tiebacks through cutouts in the basement wall, then excavate, shoot shotcrete, and tension the tiebacks sequentially by cutting horizontal panels out of the basement wall. After the excavation reaches the basement slab, backfill could begin.

This seems like a lot of work and very expensive so I am looking for other options. It would be a lot easier if the basement walls and slab could be left in place, but they can't.

Appreciate any suggestions.

 

[PEinc]

Are you a consulting engineer or a contractor? This sounds like a design best left to a specialty contractor. I agree that the historic building most likely needs to be underpinned. However, you lose me after that when you talk about installing tiebacks through a basement wall, using shotcrete, and sequencially removing the basement wall. Usually, existing basement walls are left in place when the abandoned basement is backfilled.

How deep is the basement? How deep are the historic building's foundations? If the buildings are only 6 feet apart, it is possible that the historic building was underpinned when the 1960's building was built.

http://www.PeirceEngineering.com

 

[jdonville]

moe,

It seems like you have alot of unknowns at this point. Suggest that you check into the historic buildings foundations, do a preliminary utility survey and then come up with an exotic and expensive work plan

Jeff

 

[jheidt2543]

If the existing basement wall of the building to be demolished is only 6' away from the historic building, why not make use of that wall in supporting the historic building? Why disturb the existing conditions with the added costs and potential for disaster? Even if you want any new building to be closer, there are ways to still make that work.

Just my two cents!

 

[moe333]

Thanks for the replies,

I am a consulting engineer and I agree that a specialty contractor is better qualified to tackle this but I am providing some concepts to the owner as a starting point. Yes there are a lot of unknowns which I hope to have answered soon but wanted to see what other ideas people may have given my assumptions.


I have told the owner that leaving the basement walls in place is the best solution but they want them gone. I was also thinking that the historic building may be underpinned if it doesn't have a basement but that is yet to be determined.

 

[BigHarvey]

You can underpin the ajacent buildings with jet grouting and then remove the basement wall.

 

[fattdad]

Can you just leave the basement wall in place and backfill the basement (well maybe remove the top few feet of the basement wall to facilitiate new construction (i.e., footings and utilities)?

f-d

¡papá gordo ain’t no madre flaca!

 

[PEinc]

Jet grouting is usually more expensive than conventional underpinning unless there are other conditions, such as groundwater, that would increase the underpinning cost.

http://www.PeirceEngineering.com

 

[moe333]

Any other ideas for supporting the excavation (on street and building side) and removing basement walls other than my idea below:

"install tiebacks through cutouts in the basement wall, then excavate, shoot shotcrete, and tension the tiebacks sequentially by cutting horizontal panels out of the basement wall"

 

[Ron]

What about filling the existing basement with flowable fill or compacted fill...that way you leave the walls in place, provide support for all surrounding structures, then you can remove the existing structure with little or no detriment.

 

[BigH]

Why not try ground freezing techniques??? Assuming the soil between the basement wall and the historic building are not frost susceptible (but if you don't have groundwater - then that may not even be a problem). After you start backfilling, you could start incremental defreezing from the bottom up. Just a thought - but then again I am in Bangkok enjoying myself!!!

 

[BigHarvey]

Ground freezing is definitely the most expensive technique. To be used only if there is no other solution.
I am afraid tiebacks will require permission from the neighbours ( very often far from being granted ).

Jet grouting presents the advantage of being both an underpinning solution and also an earth retention system in replacement of the basement walls.

 

[Mccoy]

Why not try ground freezing techniques??? Assuming the soil between the basement wall and the historic building are not frost susceptible (but if you don't have groundwater - then that may not even be a problem). After you start backfilling, you could start incremental defreezing from the bottom up. Just a thought - but then again I am in Bangkok enjoying myself!!!

BigH, from what you're saying I assume you are pretending to enjoy yourself while actually suffering from excessive heat and humidity, it's all too obvious the freezing technique has been conjured by your mind to relieve the utter discomfort caused by the bangkok heat wave