Thrust Block Passive soil strength

[jake_1]

I am working on a pipeline project which includes the use of thrust blocks for lateral resistance and am providing capacities per unit depth. Eg. 160 psf per foot of embedment at midpoint height of the thrust block. My question is we limit the lateral resistance of the soil at a certain depth. 10 feet or so. For example at 10 feet depth or greater we would limit the resistance to a maximum allowable capacity of 1,600 psf. Should we have a limit on the resistance and if so why? The pipeline on this project is up to 30 feet deep.

Thank you for any replies.

 

[PEinc]

Maybe when the thrust block gets very deep, it is more appropriate to consider horizontal bearing capacity rather than passive resistance. Use the lesser of the two?

http://www.PeirceEngineering.com

 

[jayrod12]

I agree with PEinc (which is a common theme for this kind of stuff). There's a point at which the failure mode changes.

 

[geomane]

What is the equation for lateral bearing capacity? Point to to a reference if that would be easier?

 

[Guest090822]

I’ve only seen thrust blocks designed to an at-rest condition. You don’t want the pipe to move!

 

[Ron]

In my opinion, 0nce passive resistance is mobilized the failure mode would then become shear failure along a horizontal plane at the bottom of the thrust block.
The resistance will be horizontal bearing capacity (soil mass resistance) and sliding friction along the shear plane.

 

[PEinc]

jmcc3265, AASHTO LRFD Bridge Design Specifications, 2014, Sec. 10.6.3.2a gives formulas for i_c, the footing inclination factor. I don't know how steep of an inclination can be used with the formulas. For a thrust block 30' deep, I would be surprised if an inclination factor would be needed.

http://www.PeirceEngineering.com