Connection of Reno Mattress to Outfall Headwall 1

[EireChch]

Hi all,
See below image. Is there a standard connection detail for connecting a reno mattress (riprap apron) to a concrete headwall.

The ground downstream of the outlet is sloping and I dont want any movement of the reno mattress.

Have considered fixing U bars into wingwall base and U bars at top of mattress and interlocking but not sure if its the best detail

Also considering posts into the ground and tying mattress into them.

 

[cvg]

instead of (or in addition to) connecting to the structure, anchor using either metal posts or using a gabion anchor trench / cutoff wall.

 

[dik]

I would think that you would want a seal to prevent water from entering under the 'mattress', but I'm not sure.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[EireChch]

cvg - thanks have also considered that. Need to do some excavation work so burying a 1m deep gabion basket and tying into that is not much more work. Although,I feel a U bar connection is the easiest and quickest but doesnt seem to be much on that type of connection online. I will give Maceferri a call on Monday.

Dik - tbh water is going to get under and in and around the mattress as its placed at outlet. Hoever hopefully flows are reduced so it doest cause any erosion!

 

[dik]

watertable may be slightly different than flowing water.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[swazimatt]

The Gabion manufacturer (Maccaferri?) are normally able to assist and review designs
Your sketch looks pretty steep. Have you done a calculation to assess flow velocity vs scour velocity of bed material at the end of the gabion basket
If there is a big drop i would propose the following (alternatively you could concrete the gap at teh top):

 

[BridgeSmith]

Providing an attachment of the wire baskets to the slab/cutoff wall would be difficult, since the wires are fairly small. Possibly, you could embed welded wire reinforcement into the slab and extend it out where it would lay under the gabion mattress.

Another option to consider is using precast articulated block mattresses, instead.

They have cables, which are easier to connect to the CIP concrete.

 

[LittleInch]

That concrete headwall needs to be contoured better and provide some sort of overhang.

Also maybe add some deflectors in the concrete slab to beak up the flow.

Seen this?

https://dcd.kitsapgov.com/ordnances...t/volume2/ConveyanceSystem/OutfallSystems.htm

Some pretty similar things here

http://www.irishtar.ie/wp-content/uploads/2019/06/River-Erosion-Protection.pdf

A lot depends on flows, velocities slopes and ground conditions to anchor the mattresses.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[EireChch]

Thank all, I spoke to someone at Maceferri and they recommended a very simple fixation of hammering in 40mm dia L bars through the mattress, to 1m below the matress. The mattress is 0.5m thick so bar length is 1.5m. One row at top of mattress at 300mm c/c and one row at mindpoint of 4.8m long mattress

I was expecting something more but apparently its a common method to fix them in slopes. (The actual slope isnt as steep as I have shown, its maybe 15 deg. )

 

[LittleInch]

It's often fairly basic engineering from those guys....

Hope you can hammer them in though?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[dik]

'L' bars may be a little tricky to 'hammer'.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[LittleInch]

And that's a pretty thick and heavy bar. a 1.5m bar will weigh nearly 15kg.... you have to keep that upright whist you hammer it through 0.5m of mattrass and 1m of unknown ground. every 300mm. Someone isn't going to like you.

Make sure they machine the end into a point and get a machine ready to hammer them in....
Or someone who works out a lot and give them a sledge hammer.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[EireChch]

Initially they recommended 32mm but I questioned the durability since its in marine environment, so it was use 32mm galvinsed or upsize to allow for corrosion and go with 40mm.

But very fair points re hammering them in, I did think of the issue of hammering the L shape. I suppose you could tack weld a small straight portion on top of the L and then use a pneumatic hammer to install. Then grind off the temporary straight bit.

 

[cvg]

in the past - i hammered in regular steel fence posts and then tied the mattress to those posts. i believe it was a grid at 1 meter spacing

we were unable to drive some of the posts all the way, so they had to be cut off flush with the top of gabions

 

[gbam]

Interesting topic, I know i am a bit late but FYI:
We like to pin to the outlet of the culvert so if there is erosion or settlement it stays connected to the outlet. We have used stainless or galvanized eyes anchored into the concrete at the top of cut-off wall or bottom of wingwall, etc... We also spec out high survivability Filter Fabric under the gabions. Note, I have seen the aftermath of the failure of soil anchoring pins and the outlet of the culvert was almost lost.

 

[EireChch]

It actually looks like we are going back to connection to head wall as the riverbed is a lot softer than anticipated.

The proposal is the include a rectangular plate with some holes within the mattress. The holes are to receive bolts chemically fixed to headwall