Cement Bag Retaining Wall

[WoodChuckDad]

The stone is supposed to lock together easier, and require very little compacting. It also worked out for me because I am not just filling the hole back in, I am trying to create a bridge that rises up and changes the contour of the land right there. Basically a large ramp.

 

[EddieWalker]

Not to beat this to death, but could you provide a link to where it says to use gravel on a spillway pipe?

 

[WoodChuckDad]

Not to beat this to death, but could you provide a link to where it says to use gravel on a spillway pipe?

No problem. I used ADS pipe so their documentation was one that I followed, as well as reading several state's highway standards.
ADS drainage handbook
Drainage Handbook- ADS Pipe

table 5-2 in the installation section lists different materials to use for fill
http://www.ads-pipe.com/pdf/en/ADH5-Installation_March_21_2016.pdf

page 5-16 specifically talks about compaction
COMPACTION
The level of compaction will vary depending on the material and installation requirements, see product specific guidelines in Appendix A-5, Table A-5-2 for minimum compaction requirements based on soil type and application. Crushed stone or similar materials are usually not compacted, but do require care during installation to eliminate large voids in the backfill envelope. Using a shovel to 'slice' or 遡nife the material under and around the pipe is many times sufficient.
For other materials, compaction methods will depend primarily on the amount of compaction, or modulus of soil reaction, required and the moisture level of the material. At optimum moisture levels, some Class II and III soils can be compacted to minimum recommended levels simply by walking on each backfill lift. While this technique may not be acceptable for all installations, the point is that compaction need not always require a great deal of extra effort or mechanical equipment. If, however, mechanical compaction equipment is needed in the backfill envelope or elsewhere on the site, the subsequent paragraphs provide guidance on compaction equipment and the soils for which they are most appropriate."

 

[WoodChuckDad]

Not to beat this to death, but could you provide a link to where it says to use gravel on a spillway pipe?

I also found several videos from ADP that show installation techniques.
This one specifically uses gravel as backfill. I used crushed stone, which is considered a class I fill.
HDPE Pipe Installation Video - HDPE Pipe Backfill Procedure - YouTube

I spent significant time knifing the material in, and really trying to pack it into the ribs with the bad of the shovel. I did the same with the clay on the front end of the pipe. On the outlet end, I still need to add fill. Also, I "walked the fill in" in layers. Meaning I would spread small layers of the gravel, then get down and knife it into the sides, then stomp back and forth thru the trench to try to work it together and lock it in place. You can feel it being a little loose wen you first put it in, but after working it for a bit it becomes very solid under your feet. I even got down on all fours, and basically did a bear, mountain climber sort of push with my feet to try to grind the stones into the edges of the trench and against the pipe. I have at least one more weekend worth of work to do before I will be done, but it will be worth it because I will not feel like I have to worry too much about the bridge. Continued maintenance and observation, of course, but I will have a lot more faith in it's stability.

 

[Ford850]

I can see how they are using gravel backfill for near level trenches with the HDPE pipe since it has little or no water pressure to seep around the pipe and wash out. A spillway is much different though, isn't it? I think you said you are only using the gravel in the center area of the long trench, with clay on the upper and lower ends. Hopefully that clay will seal the upper end.

 

[EddieWalker]

Good links. I enjoyed reading them and seeing the video on how to join the pipe. From everything you've posted, compared to the links you provided, in my opinion, you are doing everything right for a culvert installation on a road. Easily going above what is needed and not cutting any corners.

My concern is that you are also using the pipes as a pond overflow. Crushed rock is one of the best materials in the world to allow water to flow through it. If any water gets past your cement bag retaining wall, it will eventually undermine the integrity of the foundation under your pipes. Will you even notice it? How long will it take until there is a problem? With everything you've done, and how often the pond overflows, you may very well never have an issue. If it was me, I would just do all I could to ensure water did not get under your pipes and into the gravel.

 

[WoodChuckDad]

That is why the first 8 feet at the inlet is clay that I have tamped in by hand. Once I get the cement retaining wall built I will decide if I need to make a more advanced inlet. The concerns you listed have definitely been on my mind. I think that by having the inlet side be clay and having 3-5 feet of compacted clay over the rock I should have a pretty good set up to prevent erosion under the pipe. I may also dig down in front of the pip band do a cast in place inlet ramp with concrete. That remains to be seen.

 

[Ford850]

Bentonite is an option to seal the upper portion of the pipe too. I'm looking forward to more pictures, especially when you get to the wall. :thumbsup:

 

[WoodChuckDad]

I wasn't familiar with bentonite. Interesting stuff.

 

[jcummins]

The county recently replaced a culvert.....which I found going out right after a storm...It was quite old......right near the end of my drive. They dug the old out, laid the new one in, and encased it in road pack type gravel...not a smidgen of dirt. Seems to do the job, and when it rains really hard water will go up and over the road at that culvert point.