PDA

View Full Version : any experience pouring concrete boat ramp?


bcd
08-13-2012, 12:58 PM
With the lack of rain, the Mississippi is pretty low right now. Our club boat ramp is about 4 feet out of the water right now. When the water gets low, we usually have a load of rock dumped in and then leveled out to get us by. Every spring, the ice goes out and water comes up, and we lose our rock. Since the water is near record low, we're talking about extending the ramp down into the water.

The plan is to build up a coffer dam, pump the water out, excavate, form, pour, let set up, and then remove the dam. We were thinking 6" thick concrete with rebar should work. We would drill into the existing ramp and tie in with the rebar. We weren't going to go too far into the water, maybe 2-3' deep, and our plan now is to use plywood for the dam walls. I'm a little concerned about shoring that up enough to prevent a blow out.

Does anyone have any experience? Is 6" thick enough? My X-2 is the biggest boat to use the ramp, the rest are ski boats. How long do we need to let the concrete set up before we can stop pumping the water? I'm sure there are different cement blends, so do we just rely on the company to recommend the best for our application?

I think there's concrete that you can pour underwater, but not sure if that works for boat ramps or not. Also, not sure if the river current would be bad on that as well.

Any other recommendations, suggestions, or tips to help the project run smooth?

thatsmrmastercraft
08-13-2012, 01:51 PM
I have no experience with this but I know of a number of places using precast slabs. Don't know if that could work for your application, but it could remove a lot of the variables.

zsqure
08-13-2012, 02:32 PM
In a previous life the addition of "eucon" or super plasticizer allowed us to pour caissons under water. Hopefully someone on here is a civil engineer, or foundation inspector/ concrete contractor that will chime in. I have been involved with the addition/renovation of the old Portage Lakes state park boat ramps. That was driven sheeting but ODNR was footing the bill.

Jim@BAWS
08-13-2012, 02:35 PM
Preform a slab with visqueen (sp) then tie it into existing ramp somehow at 3-4 attachment areas
You will need something to lift or push it in

Concrete does harden in water...pain in the but and the finish is not very good afterwords

Jim@BAWS

76S&S
08-13-2012, 03:03 PM
You could pour on land and then push it into the water (after it sets) with a dozer if you have access to one.

bjames
08-13-2012, 06:20 PM
Yeah, I would guess that most launches (like ours here) use precast panel slabs (saw tooth top profile) that are laid in place. some are connected together by chains. You would need a loader/small crane to position them. Each slab may weight 1/2 a ton.

zsqure
08-13-2012, 06:26 PM
Check out a place that makes pre-cast concrete catch basins. They may have a top to a grease trap or septic that can be used. They aren't that expensive. They can make almost anything. And they will deliver and place it if there is access.

petermegan
08-13-2012, 07:12 PM
We did exactly as you stated for our local boat ramp when our lake was getting low, we just pushed the soil out with our backhoe loader into a dam wall. It leaked a fair bit and we had to have a pump going every few hours to keep it dry. 6" is plenty thick enough for concrete with mesh for reo. Plan B, assuming your current slab is smooth and level, could be to lay down some plastic and pour a slab on top of the one you have then use a bobcat or loader to push it in after a week. You will need to drill into the old slab and chain to the new one. You could also pour this slab elsewhere and bring on site but depending on the size this may be difficult. Plan C is to use or if not available pour concrete sleepers with reo and chain links put in them so you can join them together. Just add as needed. I would recommend this as being the simplest, but depending on how level your soil is at the end of your existing ramp you may need to level it first, but you will have to do that regardless. Have fun

bjames
08-14-2012, 12:07 PM
We did exactly as you stated for our local boat ramp when our lake was getting low, we just pushed the soil out with our backhoe loader into a dam wall. It leaked a fair bit and we had to have a pump going every few hours to keep it dry. 6" is plenty thick enough for concrete with mesh for reo. Plan B, assuming your current slab is smooth and level, could be to lay down some plastic and pour a slab on top of the one you have then use a bobcat or loader to push it in after a week. You will need to drill into the old slab and chain to the new one. You could also pour this slab elsewhere and bring on site but depending on the size this may be difficult. Plan C is to use or if not available pour concrete sleepers with reo and chain links put in them so you can join them together. Just add as needed. I would recommend this as being the simplest, but depending on how level your soil is at the end of your existing ramp you may need to level it first, but you will have to do that regardless. Have fun

Good info... The only other detail I would investigate is what to do with the subgrade. You should check to see if the subgrade is stable enough to lay the slabs on top - or will they slowly disapear under the lake bed. The shore line is dynamic, so Im not sure what kind of subgrade prep would be required... lots of granular? compaction?? to maintain a flat slope that will not undermine the concrete.

milkmania
08-14-2012, 01:55 PM
bcd,
whatever you do...... video tape it and throw it up on youtube
there's not a lot out there:(

Ski-me
08-14-2012, 02:24 PM
I agree on the sub-base. I would suspect you need at least 12" or maybe more of some crushed rock as a base. Compaction would be good and at least use a plate compactor. If you can do it in a few layers that would make it better.....aka 6" layer, compact, 6" layer.

I've only seen big bridge construction in waterways so the method is probably over the top. We used big, steel plates that had ribs that locked together. You could basically drive them into the ground out in the middle of the water area and then put a pump in there to drain the water. As the water was dispersed out of the center, the outside water created more pressure against the steel plates....thus locking them together better. This was for large bridge foundation footings though so pretty "over the top".

I do remember using some special concrete that would cure underwater.....but you can't really put a finish on it. Pretty much big clumps that filled voids in the footings.

Anyways, just a little more info from my "early days" of civil construction in Seattle..... :)

Strictly going by his title....wouldn't this question be for "Tideengineer"?!? :o (I have no idea what he does)!

madcityskier
08-15-2012, 01:36 AM
Helped make one by framing it out with 2x6's in the late 80's. Poured it right in without displacing the water. Dragged a long 4x4 over to level it. As has been said, a bit rough, but was there about 5 years ago and it was still in use.

cpr05xtr
08-15-2012, 01:56 PM
How is this "off topic"?

tideengineer
08-15-2012, 08:22 PM
I'm a civil engineer. We built our slab on land and pushed it in place with a back hoe.