View Full Version : raising ground level, installing channel drains, etc
24th Jan 2012, 08:50 PM
hi all, we are currently awaiting the ark in deagon. we believe it might be early this time around given the amount of water falling from the heavens and the amount not running off our block. kids love it and certainly saves money on putting in a pool but does present certain other problems. now, deagon, similar to most north brisbane suburbs has a clay base about 30cm to 60cm beneath the surface so water just sits there making planting a nightmare for us novices. thats another question entirely, methinks.
so, we want to get some sleepers and border the block on three sides. then get some cleanfill in to lift and level the ground around the house. down one side i want to lay some channel drains or maybe even some sort of agg pipe to get water out to the street. what sort of fill should i be using and what else should i be considering?
27th Jan 2012, 01:53 PM
27th Jan 2012, 02:26 PM
Hello, I'm on southside Brisbane, live on a sloping block and have silty clay soil with maybe 20cm of topsoil and plants grow very well in it. I thought I would have problems with the clay as well but have planted a native garden and it has really taken off. I keep it healthy with good applications of mulch (I buy 'forest mulch' at $25 per cubic metre) which improves the condition of the soil as well as makes the garden look nice and prevents weeds. I grow fruit trees and vegetables too, and on these sites I have dug in gypsum, manure, compost etc and mulch with sugarcane to provide a few more nutrients to the plants. So my point here is that you will do very well with 30-60cm of topsoil!
If you put in sleepers, you will need to put in agg drain behind all of them and drain them to your stormwater. If you don't put in agg drain the pressure of expanding soil/water behind the retaining wall can cause it to shift or bow. I would also advise against using treated pine- I have just removed some treated pine sleepers from a soggy dirt area under my house that were put in some time in the last 5 years. They had already started to rot and were H4 grade! Not at all impressed. You can drain the back of your retaining walls with drainage gravel (5-10mm) encased in geofabric (bidim) with agg pipe enclosed in a sock to take the water away. You will of course need to ensure that it all flows downhill. It is quite a large job.
I would be very cautious about building up the ground around your house so that it is higher than your house (I have seen some people who have their patio which is retaining walled around the edge with the ground built up above the patio). I think this is just asking for flooding. Runoff should always flow away from your house! If you are determined to use clean fill, then try to find some locally so you can have the same soil type across your block.
Finally, a diagram of your block showing the elevations of each corner (you can make one with Google Earth and paint if you don't have a council one) and your house in relation to your proposed plans will help people to provide you with more assistance. Good luck!
27th Jan 2012, 05:47 PM
will attempt to do something on google earth. never really had much success with it before but now that i have a mission, it might turn out better. i had read that treated pine had to be a certain grade for in ground work so was planning to use hardwood to be safe. also thought that by using channel drains, i might find the slope easier to manage. they will also give a nice edge whereas gravel/rocks of any sort will get weeds growing through making it hard to mow. as to your last point of caution re building up around the house: we are not going anywhere near the floor height itself - our house is off the ground on 80cm stumps. the idea for going around the house is to push the fill in underneath the house to ensure the ground is slightly higher than around the house so that rain drains away from the house and we don't get pooling underneath.
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