Soil arching effect on pipe endcap? [X-POST: Earth Retention Engineering]

[ajmar]

Hello all,

Hopefully simple question with simple answer:

I'm considering capping a 60" pipe with a CMU wall. The pipe inv is approx 20ft below grade. Now, what should I assume are the pressures acting on the CMU wall? Will there be a soil arching effect against the wall, in that, only a relatively small conical section of soil will effect the wall? Similar to the arching effect of soldier piles.

Your input is appreciated.

Thank you

 

[PEinc]

At 20' deep, there could be great hydrostatic pressure acting on the CMU bulkhead, probably a lot more pressure than the earth pressure.

http://www.PeirceEngineering.com

 

[cvg]

typically the cap would be a plug, that is inside the pipe and would be several feet thick to handle water and soil pressure. placing inside the pipe will greatly reduce the soil pressure and increase the lateral support. it will also reduce seepage into the pipe.

 

[BigH]

Why don't you just weld on a steel end plate?

 

[rconner]

While some pipes have long been e.g. temporarily plugged in a workmanlike manner with brick or masonry block walls, this is may or may not be a simple question -- what kind of pipe is involved (service, pressure or gravity, and if the latter how much head) and what kind of joints?

 

[nwong]

My thoughts are that there is a soil arching effect.

Arching occurs when there is a difference of the stiffness between the installed structure and the surrounding soil. If the structure is stiffer than the soil then load arches onto the structure. Otherwise, if the structure is less stiff than the soil then load arches away from the structure. Vincent T. H. CHU

Contractors routinely cap deep pipes and underground storm structure openings with unreinforced brick and CMU which would readily fail if full depth earth pressure is used.

CVG's detail (source and complete document unknown...CVG can you provide?) shows the plug as a function of only pipe size regardless of depth and unreinforced...though it's unknown whether the plug is sized for max depth burial but likely not as it's not a function of pipe class either (higher class pipes can be buried deeper).

Can anyone else weigh in?

 

[cvg]

its not totally regardless of depth, per the notes on the detail it is to be used for depths between 5 - 10 feet which covers most typical cases. for depths less than 5 or greater than 10, the plug thickness is to be increased. the detail is a typical agency standard, in use for years and I have not heard of any plug failures in at least the last 20 years.