Why raise the ground level and THEN dig trenches for pipes when you can just bury them? 1

[Sharkbiteattack]

My company is reclaiming an old quarry for real estate development and a storm water bypass sewer system consisting of 84" RCP needs to be installed. I don't understand why they are going to fill the quarry up with soil first to the proposed ground elevation and then go back to dig trenches up to 25ft deep for the pipes to rest in. Whats wrong with laying out the sewer system first at the correct elevation and then burying the whole thing in soil?

 

[cvg]

read up on positive and negative projecting trenches. compaction and load on the pipe will vary depending on how you construct the trench

 

[cvg]

http://www.concrete-pipe.org/pdf/DM_Chp_4.pdf

 

[fel3]

However, it may not be necessary to go all the way up before going all the way back down with the trenching. I have never had to deal with this myself, but I know of several similar situations around here where maybe half of the fill was placed and compacted, then the trenches dug and pipes installed and backfilled, then finally the rest of the fill was placed. I would expect that the project civil requested this be covered in the geotechnical report.

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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[GeoPaveTraffic]

The bigger problem is settlement of the fill placed in the quarry. Has this not been discussed/considered?

If you placed the pipes and then placed the fill, unless the pipes are founded on the floor of the quarry; the pipes will settle. Depending on the depth of the quarry/thickness of fill to be placed the amount of settlement could be measured in feet. Also, unless granular material is being used to fill the quarry, the settlement will continue for years.

I've see very few filled in quarries that can be used for future developement.

Mike Lambert

 

[cvg]

to mitigate settlement, it may be recommended to fill and wait for most of the short term settlement to occur first, then install the storm drain in trenches. minimum slope should include generous allowances for differential long term settlement

 

[chicopee]

Aside from the excellent comments made by the above responders, have you any idea about the nightmare that equipment operators would have by backfilling the quarry once the sewer system is installed. The trunk line and all lateral connections would be susceptible to damage from heavy equipment and ultimately result in unnecessary delays and cost.

 

[jgailla]

+1 for chicopee's statement. A contractor on one of my projects laid the storm pipe before the fill was placed and they ended up digging up the pipe and replacing once it got destroyed by the fill placement operations.