Fix Large Cracks in Concrete Drainage Swales (V-Ditches) 5

[dynamics5]

I am part of a homeowner association with 20+ acres of land with hillsides graded roughly 2:1, separated by 2 to 3 levels of horizontal concrete drainage swales that collect slope runoff to vertical swales. Each side of the swale measures about 4 feet wide. Some work has started to fix LARGE cracks in the concrete (up to 1/2 inches wide) by cutting 1 foot wide sections of the swale, up to 10 feet wide. The thinness of the swales, only 2 inches thick in some places, makes it difficult to drill holes into both sides of the swales to insert rebar that would help hold the 2 pieces together. As such, some of the rebar is just hanging loose. In other instances, the rebar was cut too short and so is only anchored on one side. PVC irrigation pipes will be buried in the dirt in open space before concrete is poured to seal the opening. Questions: is this a viable way to fix the cracks? Swales must be stable, not leak water or soil underneath will be undermined, leading to potential slope failure!! Questions/concerns include: Is a soil test advisable? Should rebar or mesh, or some other material be used? If rebar, what should be rebar spacing and density? How deep should the holes be drilled for insertion of rebar? Should the rebar/concrete interface be coated with epoxy? Is it ok if rebars are only attached on one side? What minimum thickness should the concrete be over the rebar? Should concrete glue be used to help new and old concrete bond on both sides of the swale? Should the opening be filled with any other material besides concrete? DO YOU BELIEVE THIS WORK REQUIRES PERMITS (CA)? Is this approach ok? If not, would appreciate recommendations on how best to fix LARGE cracks in the swales. Thank you!!

 

[zebco]

dynamics5, my first thoughts for 1/2" cracks is to use some concrete patch materials that are available, and just fill them in and trowel finish. Undermining is always a potential problem with paved ditches, most in NC have switched to rip-rap with a geo-fabric underneath. I would not avise a soil test for this project. I'm sure others with more direct experience will weigh in.

 

[Ron]

The approach they are using is reasonable, but doesn't go far enough. The repair section should be thicker than the existing and soil should be excavated under the existing concrete for about 4 inches to provide a support ledge and tie-in the the existing. Further, a good quality bonding agent should be used on the existing concrete to bond the old concrete to new concrete. The rebar should be set in epoxy on both sides, with a penetration into the existing concrete of at least 4 inches.

Check your state laws. Depending on the age, you might have a latent defect construction claim. Homeowner's associations have certain rights in various states.

 

[hokie66]

With the thickness of the existing concrete only 2" in places, don't expect too much in the way of durability with the repairs. I doubt that reinforcing, dowels, bonding agents, etc. will do much to improve the performance of these ditches.

 

[oldestguy]

Rigid concrete, which will crack, is not a good application for this,but you are stuck with it.

The advice of Ron is good assuming you continue with this this method.

If appearance is not problem, I'd opt to take out failing sections and install a well graded rip-rap as a replacement. It would hove to be thicker than what you have, and should be dimensioned by an engineer experienced in its use.

The beauty of rip-rap is that it is flexible and petty much will follow uneven support.

Some here might suggest placing a rock layer on a geotech fabric. That also has to be designed based somewhat on your soils, while a well graded rip rap (from coarse to fines) would work in most soils and costs much less than what you are doing.

Grass can grow there also and that tends to act like a thatched roof in preventing erosion.

I'd ask your local DOT maintenance guys for examples where they have lined channels with rip-rap to see how it works. Although I have found many an experienced DOT guy lacks the know how for the best ways to fix these things.

 

[cvg]

2 inch thick is substandard IMO, I always use 4 inch minimum shotcrete with reinforcement at 12" max spacing. Rebar is OK, but wire works too if you can keep it off the ground and in the middle of the slab. Drilling and epoxy and bonding agent at each end might help a little, but don't expect much. Were there any expansion / contraction joints? Sounds like there should have been some and they should have been filled with joint filler. I am assuming the original concrete was not reinforced at all? Shrinkage cracks were then able to form and widen? If so, that was not done correctly and I would expect further problems down the line with the remaining concrete.

 

[beej67]

What about a cold mix asphalt patch?

I mention it because it's flexible, will fill in cracks and whatnot, doesn't need rebar, and it's cheap. Not the prettiest solution, nor the most permanent, but might work better than trying to use concrete given the poor initial job, and if the asphalt fails in a decade you could just patch it again with more asphalt.



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