Basement Floor Slab on Piled Foundation

[MPHenry]

I am currently designing a 3 storey reinforced concrete structure over basement on a very loose sand/silt sub-grade. The Geotechnical Investigation Report recommends bored piles for the foundations.
The basement of this building will be subjected to ground water ingress so I wish to tank the external walls and floor structure below grade. My main concerns are as follows:

If I design the basement floor slab as an overall pile cap for the concrete bored piles, how can I effectively tank the underside of the basement slab where it adjoins the bored piles?

Should I design independent pile caps for the pile groups and pour an independent floor slab over the top. This method would allow me to fully tank the underside of the basement slab.

In the above approaches I am assuming that the basement slab acts as a raft foundation for the reinforced concrete support columns of the building.

I would appreciate your feedback.

Regards

Mike

 

[Ginger]

Mike

I would go for the second proposal of using independant pile caps with the floor slab sitting over. Trying to seal the connection between the pile and the slab will be frought with problems because you do not cast the pile and the floor slab in the same pour. Also, you cannot cast the waterbar into the pile concrete to form a good seal because of the nature of pile construction and the need to break off the top metre of concrete of the pile where the contaminated concrete is located.

Servicised and other similar sealant manufacturers do produce pile cap waterbar but this is designed to seal between individual pile caps and the overlying slab (so you are back to option 2 again!!).

Regards

Andy

 

[suqlainUK]

Have you considered "watertight" concrete as an option. The cost of concrete increase by the addition of the admixture but there is construction programme saving as well as saving on the water proofing membranes. "Caltite" is one product that is used in the UK. Pudlo Concrete is another option.

 

[MPHenry]

Thanks SuqlainUK and Andy for your comments. I think I will be going with Option 2. I have considered "watertight" concrete but because of the occupancy of the proposed basement area I will go with the fully tanked option to ensure no water leaks.

Regards

Mike