Foundation on small site

[SteelPE]

I have a site that has undesirable soil with a proposed 4 story building. These soils are fairly shallow and were recommended to be removed by the geotechnical engineer and replaced with structural fill. Depth to ledge is around 10’-0” +/-. The site is very small requiring the building to be place close to the property line. An existing building (on the other property) is already located tight to the property line. Foundations for the existing building are located 4’-0” below grade. This makes removal of the unsuitable soil very difficult as this method would require shoring the existing building during removal of the unsuitable soil (I don't know how this could be done with ledge 10 feet below grade).

Hopefully I explained this situation properly.

Are there any other types of methods I can use to construct this foundation? Or are we going to be forced to underpin the existing foundation?

We would like to avoid any situation that involves remediation to the existing structure as the two owners do not get along.

 

[fattdad]

Not sure of the need for a structural slab for the ground floor. I understand the potential need to convey the structural loads of a 4-story building through the soil (i.e., to the ledge), but for the slab on grade, I'd just proofroll, fix any problem areas and build the slab on the subgrade.

It seems alot of money is potentially going to be thrown around and I'm not sure it's needed.

f-d

¡papá gordo ain’t no madre flaca!

 

[worldofmud]

Unsure if you have considered it but, if a understand the above correctly, removal and replacement of the soils on site will require some degree of dewatering during the works-i would be careful to ensure that temporarily lowering the water table does not create a groundwater 'cone of depression' and subsequently induce off site settlement of the next door neighbours footings.

 

[apsix]

If possible, I would advise taking a back seat during the ground improvement phase of the project, let the geotechnical engineer design and supervise that.

You can design the structure, advising that you give no guarantee of foundation performance.

 

[hokie66]

apsix,

That approach will not keep him out of the firing line if damaging settlement does occur. He may not be found liable, but by that time he will have spent a lot of money defending.

 

[darthsoilsguy2]

a concrete slurry wall should be added to the list of possibilities to explore

 

[jnimens]

Continuous helical piles such as those available from HSD Foundation Technologies are the perfect solutions to each the vertical load of the building, the shoring requirements, and the underpinning.