Excavation for 3 Basements 6

[BUILDKENYA]

I am planning on excavating an area of 25m X 40m X 12m Deep
There is a 8 storey building located approximately 3m away from the 25m side
What precautations can / should be taken to prevent the pit from collapsing and the tall building from falling!
Any assistance on this will be much appreciated

 

[dik]

You likely have a serious shoring issue and you need to discuss this with a competent geotechnical consultant...

dik

 

[MiketheEngineer]

Especially since you are going down 12M or almost 40'

 

[dik]

Mike...
It was the 3m away from an 8 storey building that ran up the red flag... Reminds me of the condo in China a year or so back...

Dik

 

[MiketheEngineer]

Totally agree - but if it was 1' deep - I wouldn't be too concerned but 3' away and 40' deep ---- OOPS

 

[msquared48]

dik:

Red flag because it was in China?

I agree - get a geotech. Should be one or two in Nairobi.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[FixedEarth]

As a starting point- talk to the owner of the building that is 3 m away. See if you can talk to the soils engineer and the shoring engineer involved with that project. If you don not find local firm to do shoring design, you may go to south Africa or Asia and hire a firm from there.

If your firm has not done anything close to this complex project, it maybe wiser to pass it on to more specialized structural firm. Sometimes, saying "no" is necessary. Good luck.

 

[JAE]

Well, one thing you absolutely should do is fully understand what sort of foundations the adjacent building has (deep or shallow) and go from there.

Do you have insurance? It probably won't do any good

 

[dik]

You should do a damage assessment of the adjacent structure(s) before you commence construction, too...

Dik

 

[PEinc]

You need to know what type of foundation the adjacent building has. Does it have a deep basement? If the adjacent building is on deep foundations (piles or drilled shafts), you may be able to design sheeting to support the soil under the building. If the building is on spread footings, you may need to underpin the building. If the adjacent building is as deep as the proposed building, you may need to do nothing except install sheeting along the remaining sides of the excavation.

If you had to ask the question, you probably are not qualified to design the support system and this isn't the job to learn on.

http://www.PeirceEngineering.com

 

[fattdad]

In the U.S. temporary construction excavation bracing is the onus of the contractor as it doesn't contribute to the betterment of construction. If you are the designer, your concern is to make sure that the finished engineering improvements are stable for the forces of the completed construction (including transient live loads and such).

In order to "wish" the new construction into place, a contractor will need to do all sorts of stuff that's fundamentally temporary. This may include shoring of existing utilities, shoring of excavations, use of temporary excavation bracing, etc. It's best that you let the contractor do what the contractor is obligated to do and focus on the engineering that's required for the owner's interests.

Yeah, I'm aware that there is a great geotechnical effort to design temporary excavation bracing for the contractor. I think it's very interesting. I just want to reference that there is a division of responsibility to consider in these sorts of questions.

f-d

¡papá gordo ain’t no madre flaca!

 

[BUILDKENYA]

Thank you for the very useful information - I am an Architect here in Nairobi
Building with Deep basements are now becoming the norm here as space is expensive

 

[molerat2210]

I generally agree with the comments of fattdad that it will be the contractor's responsibility to design and implement the excavation support system. However, the architect and his design team has a responsibility to provide some information for the contractor and provide general requirements for an excvation support system. Information supplied by the design team prior to bidding should include soil borings and any available information of the adjacent foundations. The specifications should include a section for excavation support systems. For this project, the contractor should be required to perform pre and post condition surveys of the adjacent building, provide instrumentation (crack gages, inclinometers, optical survey points, etc), submit engineered shop drawings of the support system. The design should include any additional pressure from adjacent foundations and address any impact of dewatering (if relevant). There may be other unique issues to Kenya soils that require you to have a local geotech to identify.

If you do not have experience with design of below grade walls then you should consult with another architect. A mistake in the design of the drainage system can be difficult to repair.