Trench Compaction with obstacles 1

[DirtDelight]

Hello All.

Any help would be appreciated. We are backfilling a 8" sewer line. The cuts are approximately 12'deep.The trench width is three feet. The existing trench wall material is a silty sand. Max of 125.0 at 10 % H20. The next section we will do has a few existing utility crossing thru trench at about 3-5 feet below the finish grade, spanning about 4 foot linear. I am doing the compaction testing on the fill and am a little concerned about the access for compaction equipment in and around these crossings. They are dry utilities as well a small pvc irrigation line. Wouldn't be to concerned about it, but is in a proposed street area. The engineer does not want any water jetting performed. My suggestion was to fill the trench in this area with sand around these crossings and water-jet. The engineer is concerned about water not being able to go anywhere due to the existing bottom of trench as well as side facing material.

Any ideas would help to achieve proper compaction around these obstacles. Have to deal with this Monday morning?
Thanks,
Bill

 

[msucog]

if it were me, i'd tell the contractor to be careful and that he might want to have his hands on small machanical tamp (aka wacky packers or jumping jacks) or even manual hand tamps and possibly even a 16lb sledge hammer (works great in tight spaces). it may be a matter of putting the backfill in 2" lifts and using the manual hand tamps. for the wacky packer, you can usually be careful enough not to damage small lines as long as you don't do something silly like run it right on top of the conduit. if the contractor happens to break a small irrigation line, that's easy enough to fix but it might make things too wet to work for a day or so if they don't know where the shutoff is prior to breaking the thing. either way, my advice to you would be not to get too wrapped up in doing the contractor's job (ie. means and methods). if you tell them how to do it and it busts a line or doesn't work, you might be held liable for "directing the work". but i do understand wanting to help resolve the situation since that is in essence what we do in our profession...solve problems. so offer up "suggestions" and let them decide which way works and then run your tests.

perhaps this might be a good place to use lean concrete in the hardest to reach spots as long as the contractor provides some cushion/protection immediately around the pipes. good luck

 

[Dirtguy4587]

I agree with msucog. Whenever I have a tight space to compact, I usually use fillcrete. It doesn't cost that much, and will avoid alot of problems if you can't get acceptable compaction. Of course you do need to protect the existing infrastructure, but I find that some 1" or 2" rigid insulation works well for that.

 

[oldestguy]

Another reason for no jetting. It does not do the job equal to compaction. I've seen too many of these jetted jobs settle later.

 

[DirtDelight]

Thanks for the help. We used hand compaction equipment around the tight areas. A jumping jack around the base and sides of the 24 " crossing as well as a powder puff. We used the jumping jack in between the conduits. Seemed to tighten up fine.


Thanks Again

Bill

 

[dgillette]

I know about Wackers, jumping jacks, and big sledge hammers, but what's a powder puff in this context?

 

[Dirtguy4587]

I was going to ask the same question...

 

[civilperson]

Powder puff is field name of compressed air powered striker with a 3" diameter plate at the end of cylinder/shaft,(hand held and can compact horizontally as well as vertically). Cycles approximately 150/minute.

 

[dgillette]

Oh, OK. Thanks. I would have called that a 'pogo stick,' which could be a regional or archaic term used only in Erie County in the 1970s.

A thesis topic for an English major finding himself working construction because of a shortage of English-major jobs: "Regional Linguistics and Informal Terminology in North American Construction-Site Usage."