Geotechnical Design Help

1. Sep 23, 2014

Dhillon123

I am looking for some insight with a problem I have. I am trying to design a foundation that is partially under the current water table.

It is a hollow rectangle that is 30 m long, 11 m wide and 9 m high with a wall thickness of 0.5 m, it is attached to a triangular shape foundation that is 35 m long, 11 m wide and 9 m high with a wall thickness of 0.5 m. The structure sticks out 0.5 m above the current ground level.

I was able to calculate the volume of the concrete structure which is 890.27 m^3
Using the water table information we found that the volume of water displaced is 4076.325 m^3

From this I know I need to calculate the buoyancy force and try to get neutral buoyancy so it does not move. I am just wondering how to go about this. Should we increase the dimensions of the structure (thickness is the only thing that we can think or altering) or consider using anchors or bracing to equal out the forces.

2. Sep 24, 2014

256bits

I guess you want to avoid having a concrete boat type of situation.
Density of heavy concrete is around 2500 kg/cubic meter, and that of water 1000 kg/ cubic meter.

From what you have stated about the volumes, it looks like your boat would float!!

Depending upon soil conditions, anchoring, and all that, a consultation with cival engineer may be the best route to pursue.
Someone other here at PF though may have experience and knowledge to help you out.

3. Sep 28, 2014

Baluncore

You must consider the buoyancy in the soil rather than in pure water. Soil has greater density so the hydrostatic pressure at depth is often sufficient to force water above the surface.

Maybe you could actively drain the area immediately outside the wall so as to reduce the soil movement and buoyancy effect.

Another solution might be to drive piles deep into the ground, they can then anchor the structure.

What is the soil type and depths?
What is the rock type and depth?