Excavation inside an existing industrial facility

[GalileoG]

I am designing reinforcement for existing footings and the top of existing footings have to be excavated and exposed. The top of the deepest footings is about 2m below top of slab-on-grade. This is inside an industrial facility, so the less slab-on-grade I have to demolish the better (i.e. no open cut).

How would one go about excavating inside an existing building and retaining the soil without going for open cut but also minimizing settlement of the existing slab? There is equipment on the existing slab which would be sensitive to settlement.

What could be some of my options? There is about 5m of headroom. Geotech on the job is recommending micropiles secant wall, but this seems overkill? Surely there are other systems that could be appropriate for this case?

Thanks for your help!

 

[PEinc]

Can you provide more information? Size of each hole to be excavated? Quantity of holes to be excavated? Ground conditions? Type and thickness of existing paving to be removed? Ground water condition? Depth of existing foundations adjacent to the excavations? Loads on existing adjacent foundations? Clearance from edge of existing foundations to edge of excavation? Excavation contractor's expertise? Depending on your answers, you might need both underpinning and temporary sheeting.

http://www.PeirceEngineering.com

 

[geotechguy1]

You need to:

[ol 1]
[li]Establish what the ground conditions are (strength, stiffness, soil types)[/li]
[li]Establish where groundwater is (excavating above or below the groundwater table will make a huge difference[/li]
[li]Establish what the settlement criteria are. How much total and differential settlement can the slab and any supported equipment tolerate[/li]
[li]Assess the options for retaining the excavation in terms of displacements[/li]
[/ol]

One useful international reference is CIRIA 760 (or the previous versions - CIRA 580 and I think one or two before that).

There are lots of options but you need to know what the ground conditions and criteria are...a soldier pile wall with timber lagging probably isn't going to work if you have to go below groundwater.