Stress on concrete slab due to HDD.

[nthmrb1]

I am trying to figure out how to calculate if a concrete slab will be safe if I perform a horizontal directional drill beneath it. What calculations can I do to prove that it is safe? I was thinking of proving that the slab is strong enough to span over the 12" bore hole I will do 10' below the slab by using a one way slab calculation but not sure if I am thinking about this correctly.

 

[Ron]

Unless your slab has incredibly high loading, this should not be an issue. No void should develop in proximity to the slab bottom so there is nothing to span. At worst you might have a slight reduction in soil density at the slab bottom but even that will be minimal.

A separation of 10' is sufficient to protect the slab for a 12" diameter void. Even if your soil is clean sand, you'll get a bridging effect from the soil.


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[robyengIT]

in sewer pipe laying (any diameter, even 144") when the depth is 10 ft or bigger the traffic load is negligible. I agree with Ron

 

[nthmrb1]

Thank you for the information. The loading is H-20 loading so did not think it would be a big issue. Do you guys know of any equations to show this not effecting the concrete? Only thing we have done in the past is to monitor the slab during operations to check any movememnt.

 

[robyengIT]

For load calculation see attached literature.
For structural calculation of the slab I have two book (digitized) but in Italian. In any case two types of calculations are listed : Westergaard and Meyrerhof simplified. Let me know