60" HDPE storm to 60" RCP embedded in an existing headwall

[hornchase]

I am replacing an existing ditch with two 60" HDPE Dual Wall pipes to match the (2) two 60" RCP culverts on each end of the ditch. Advance Drainage Systems (ADS) does not seem to have a typical connection detail for RCP to HDPE besides wrap couplers. This will not work due to the 60" RCP's are embedded/flush with a headwall. I have found some smooth wall inserts to use but it is not suggest to use downstream. I am connecting to the headwalls both upstream and downstream. I thought this would be a problem ADS ran into alot but they could not give me a solution last time we spoke. Let me know if anyone has done this before I am open to suggestions.

 

[oldestguy]

Build a temporary liner, expandable, at the joint, say of sections of steel plate or large diam pipe, or plywood, combined with some hydraulic jacks or wedges and struts. Then, on the outside, surround the joint with with an encasement with stiff 6 bag mix concrete. Immediately before concreting dob onto roughened headwall concrete with a thick "cream" of Portland cement and water. That concrete surface should be bone dry to encourage the paste to enter voids by capillary action. At the head walls insert dowels to help hold the encasement "patch". Possibly include some circular steel re-bar lengths within the "patch". Later for backfilling use a mix of sand-gravel with bentonite at about 20 percent powdered bentonite covering the patch maybe one foot minimum thickness. Also look to using clay backfill beyond that all the way around at each headwall. Of course remove the interior "liner" later. My experience with the cement paste at the contact of new and old concrete is that it is stronger than either (old or new) concrete. To avoid forming on the outside, follow the patch work with the specialized backfilling as it goes from the invert to the crown. Of course if you are not too worried about some leakage, you can skip the concrete and use the sand-gravel-bentonite mix assuming leaks are no problem. Or only use the concrete.