centre island drainage?

[swazimatt]

I am busy doing a junction safety improvement and will be adding some mini-roundabouts and a central pedestrian refuge island between roundabouts.

all the islands will be raised about 200mm above the existing road surface with kerbed edges, some granular fill and then a concrete slab on top. The road will then be resurfaced with 30mm asphalt.

My question is we will need to cut into the existing road surface and base to lay the kerbing (bedded in concrete); will i need to make some provision to drain any moisture that could seep through the concrete construction joints and eventually end up in the base layer? see attached sketch and please ignore spelling mistakes

 

[Debaser]

If you are laying a concrete slab next to your PCC kerbs will you be using some form of joint between the two? This material should prevent most wmoisture getting into the pavement.
If you excavate beyond the actual extents of the island and down to subbase, to allow the surface, binder, base and subbase layers to be properly keyed in and compacted underneath and next to the new kerbs then I think you should be able to maintain the shape of the structure, i.e. keep the crown line and drain to the edges of the carriageway as you've shown on your sketch.
If the subbase material is compacted properly (making sure the material is properly profiled at 2.5% or so) I shouldn't think you'll have any more problem with moisture than you would normally get between kerb and blacktop.

One of my favourite sites for practical highways information;

http://www.highwaysmaintenance.com/drainage.htm

 

[swazimatt]

thanks, have bookmarked the site for future reference.

I was not planning on using any jointing (polysulphide) in the concrete, and i have a feeling that the client may insist on interlocking paving bricks. If they do there will def be some water flowing into the island, but would it be if any gereat significance or should i place some sort of weep holes between the PCC kerbs? say every 4m?

 

[Debaser]

My other favourite site for practical highway matters;

http://www.pavingexpert.com/rigidbpv.htm

As an engineer I've no problem listening to those 'operatives' who do this sort of work everyday.