Post Tensioned Slab Failure. test recomendations??

[tweedledee]

I'm working on a building that was built in 1970. It has a basement post tensioned slab. The building is near the sea, so in high tides the water table is higher than the slab. The slab was designed for upward pressure, but apparently not enough because the slab has been leaking since the 1990's after some severe weather caused the water table to rise above what the slab was designed for. We think the slab has failed in punching shear.

What I need to know is this:
Is there any tests I can do to measure what the hydrostatic pressure is during high tides. I was thinking of some kind of tube placed through the slab into the soil. With this I can measure the head of water.

I'm also interested in any suggestions of how to increase the punching shear capacity of the existing slab at the columns.

Any ideas/suggestions would be greatly appreciated.

 

[Slowzuki]

My suggestion would be to figure out what is currently in the slab design, figure out the soil pressure and find out how far off the slab is.

I don't know what is done in industry but a simple manometer epoxied to a tap drilled into below the slab can tell you what happens at high tide.

From there you can look at what is done to design slabs for punching shear in the first place. You could use a steel bearing plate to increase the perimeter and therefore the shear capacity.

You could epoxy some rebar or similar in diagonally drilled holes which cross the shear plane perpendicular.

Really all sorts of repair or redesign options exist.

 

[eric1037]

Slope Indicator

http://www.slopeindicator.com/

, RST Instruments

http://www.rstinstruments.com/,

and Roctest

http://www.roctest.com/

all manufacture a variety of piezometers and pressure indicators. Contact a good, local geotechnical engineer and they should be able to help you out.