Trench compaction

[Jumbo]

CDF (Controlled density fill) 35% cement 65% sand is one mix we use, I also think there are several variations of the sand/cement combinations, but that seems to be the standard I get when ordering CDF.

I have been told by inspectors and in the specifications that pea gravel is the only material besides CDF that does not require compaction. I use that in special applications like a vault that I will need to access to 6 months down the road, since it comes out easy with a vactor truck. It is more pricy than CDF counting placement.

I like CDF because I can back fill a ditch quicker, with less labor and less question by inspectors. One person can backfill the ditch while the digging equipment is still digging and moving ahead. Thus, progress keeps moving on and a second machine is not tied up back filling in small increments. Back filling with compactable material seems to be a minimum of three people one placing material in the ditch however you do it, two people in the ditch one with a compactor and one with a shovel flattening out the high spots. Moreover, I repeat, in the ditch with all the BS that trying to work in a ditch entails.

Having one person walk down the ditch line steering a chute on a barrel truck is so much faster. The CDF is cheaper that the total cost of labor. Around here, even non-union work gets charged out at $90+ an hour to the customer. The cost of an operator and machine is way past that.

:my2c

 

[crusier_32]

I am late getting here, but my question is. How deep can one safely work a jumping jack in a trench. From what I understand anything deeper then 4' needs to be cut back.

If I am compacting a 5'x16" trench in 12"-16" lifts that puts me around 4' feet for the first lift? Is this still considered safe? I have done it before, and it always feels a but marginal to me. I am just wondering what others feel is safe?

Will

 

[old-iron-habit]

I am late getting here, but my question is. How deep can one safely work a jumping jack in a trench. From what I understand anything deeper then 4' needs to be cut back.

If I am compacting a 5'x16" trench in 12"-16" lifts that puts me around 4' feet for the first lift? Is this still considered safe? I have done it before, and it always feels a but marginal to me. I am just wondering what others feel is safe?

Will

OSHA says 5'. At 5' and above it has to be sloped 2 to 1 or shored. To slope steeper than 2 to 1 it has to be approved in writing by a registered engineer. At 5 ft and deeper you need to have access within 25 ft of travel, translates to a ladder every 50 ft. While most 5 ft trenches are OK I would never be down on my knees in one. Trench cave ins are the second most construction site killer in the US next to falls.

 

[CM1995]

I agree old-iron. Trenches are dangerous and should be treated with respect for the damage/killing they can do.

This is a means and methods procedure but this is how we do it and of course varies considerably as this method can't be used all the time. Since we are always on a new construction site, we have the room and leeway to do this way.

The most common sized storm pipe we lay is 18" to 36", depths range from 3' to 7-8', average would be 5' deep or less. Most of the time the storm line is in a parking lot or other paved area and compaction is very important. I like to excavate the trench to depth and cut back the sides, stair stepping them as needed to keep the main or bottom trench no deeper than 4' from the first bench, usually it's 3' or so. Running a 42" bucket usually gives enough room to lay the pipe in the bottom or main trench and a 4' wide bench on either side as depth requires (a 42" bucket with side cutters will cut a 4' swath). The bench gives you a place to carry the pipe laying tools forward as you go and is easier to get in and out of the trench and lay the pipe.

This solves two purposes, the most important being safety and the other achieving adequate compaction over the pipe. If the line is in a paved area, backfill to the top of the pipe with #57 stone as it flows easily and fills the voids around the pipe. When we go to backfill, place 12 to 18" of dirt over the pipe and run the 533E over to compact it. The is where the previously cut bench allows the roller to get a full width in the trench and thus a more homogenous fill layer over the top of the pipe, tying it into the surrounding soil.