Deep Interceptor Sewer Project - Construction, Inspection, etc. 3

[MarshfieldTimC]

Our project includes an extension of an interceptor sanitary sewer. Pipe sizes range from 21-inch to 8-inch ID. The depth will vary between 10-feet and 34-feet, with a majority of the project over 20-feet. I assume much of this will be open cut excavation (with double stacked trench boxes), however there will also be borings (bore & jack, steel casing pipe) at a few road crossings. I am considering the use of PVC pipe for the entire project. Backfiling and compaction will be a major task (clay soils). Pipe and manholes will be televised, however only the pipe will be pressure tested.
If anyone has experienced a similar project I would appreciate any comments or suggestions, including:
Inspection of construction - how does the inspector see anything at the bottom of the deep excavation (such as placement and thickness of select bedding/cover material)?
Any problems with large diameter, deep, PVC pipe?
Should manholes be tested? Pressure or vaccuum tested?
Anything else to watch-out for?
All comments appreciated!

 

[nackra]

Depending on depth of bury, you might consider Hobas and HDPE lined RCP for larger diameters

 

[cvg]

If the trench is properly shored and OSHA requirements are met, the inspector should be able to safely go down in the trench and inspect the trench and bedding and pipe isntallation.

21 inch is not that large of diameter, not sure why RCP would be necessary. there are other types of PE pipe that might be worth looking at besides lined RCP.

 

[bimr]

Solid wall PVC and closed profile PVC pipe are also consider to be quality pipe.

 

[NPSEngineer]

I did a lift station, which was over 20 feet deep, in Washington State ,and they wouldn't let us use a trench box. The shoring had to be designed by a structural engineer and stamped.

 

[bpattengale]

Make sure the specs include a mandrel or deflection testing for the pipe. The pressure test will tell if there are any leaks but not if the pipe is exceding allowable deflection. If those

 

[dicksewerrat]

All excavation at 20 feet need a P.E. to design the support system. If you used stacked trench shields without the P.E. stamp, you could get a fine from OSHA. Read the OSHA manual. Watch the pipe installation from the top and bottom. Watch the surveyors. Get all the daily logs from the contractor. If the trench is wet, watch closer. Get compaction reports from a THIRD party testing lab. Watch the compaction tests.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[rconner]

While other materials might indeed work, I have seen some organizations insist on ductile iron pipe for some very deep sewers/tough conditions [there could thus be some at least local experience-based reasons for why folks over many years have gravitated, so to speak, to this predilection] see e.g.

http://www.chattanooga.gov/Sanitary...nd_Construction_Manual_Section_IV_11_pgs.pdf,

http://www.ci.maryville.tn.us/wendy/Standard Drawing - sewer- 1of2.pdf,

and

http://www.troyalabama.com/Utilities/Sewer Department/Sewer Specs. Rev 1.doc

etc.