artificial surf reefs construction

[Prepakt1]

We are investigating building an artificial reef to create surf . The proposed method from the client is to use sand which has already been stockpiled and fill fabriform bags by pumping. There is a method of using bags dropped from hoppers but this is not acceptable. I propose using ballistic nylon fabric bags and the client wants to fill them with pumped sand. I have my reservations both on filling with sand and on bag stability in the ocean.I would like comments.
Dave Ritchie
Intrusion Prepakt

 

[dirtsqueezer]

Just as an informal disclaimer, I don't have any credentials to speak for here. It sounds like you're looking for an inexpensive method of creating some surf- definitely a worthy cause.
I don't know that sand bags will provide resistance to surf as there would seem to be a size limitation; also potential long-term wear on the fabric. I can offer a cheap solution that our local geologists use to resist fluid motion in rivers. The term does not come to mind. The process amounts to filling a rectangular cage with cobble-sized rocks. If that is too realistic in the way of potential harm to your surfers (clipped wire ends poking out, ect.), you may just want to import boulder-sized rocks to construct a surf-break similiar to a jetty, only underwater. I don't know the magnitude of your surf. You may want to have a geophysicist on hand for consulting as to minimum boulder size and design for maximum force and longevity.

Anyway, there are a few ideas.

 

[Prepakt1]

Thanks for yr comments.We do need to use sand. The best method is to use large rocks and grout them to-gether but for this purpose we dont want bodies hitting large rocks.
I have suggested to the client that the reef could be constructed from a grid of helical piles screwed into the sea floor then 12" layers of mat built up to form the reef shape with holes in the mat to fit over the piles and nylon cabling running through the mat and the holes. Then grouting these holes to form concrete columns tying the structure to-gether.
How well it would stand up to sea forces is always a question even with rock and concrete the sea will eat away
at the structure.

 

[proletariat]

When I worked for NCDOT, we used a system like the one you're describing to stabilize oceanfront roadway after hurricane Isabel destroyed it. We weren't allowed to use hardened structures (against NC law), so we used sandbags. The contractor would hang a water pump from the bucket of an excavator and dip it into the surf zone. the liquified sand and water would travel through fire hose to a piece of about 20', 4" diameter pipe. The contractor had ordered the bags with a hole in them so the pipe nozzle would fit. The water/sand mixture would run into the bag, deposit the sand, and the water would leak through the fabric. Extremely slick. The contractor was based out of Edenton, NC. I can't remember their name, but if you look them up, they might tell you who their bag vendor was if they realize you not competition.

 

[Prepakt1]

Thanks for your reply ,we do make bags ouselves. The key to this is the fabric weave.Different weaves let different
fines pass .Bags have to be manufactured in a basketweave pattern for strength and to ensure that they do not rip if punctured.