Browse Forums General Discussion Re: Site too wet to cut 24Aug 14, 2020 11:05 am insider Legendary Thanks insider - appreciate the info. By cut off drain, do you mean a deep trench through the site with something non-permeable to carry water away? The builder has suggested the ag drains sit in trenches that are not back-filled (ie. left exposed) - will this work or do you think a different design is necessary? No it's basically an agi drain but with builders plastic on one side of the trench(the side you are trying to protect). One thing about agi drains and cut off drains is most of the time they are not deep enough.If the agi/cut off trench doesn't go into the clay it won't work. The builder says 500mm deep but you have said 700-900 so that would have to be the depth of the trench must be into the clay. Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Thanks insider - builder is speaking with the drainage plumber but it looks like we will go with this approach. The property slopes gently right to left (200mm fall across 17m) and front to back (400mm fall across 42m) so we are looking at putting one drain all the way down the low side on the left and one drain all the way across the back Re: Site too wet to cut 25Aug 14, 2020 11:06 am sunny05 Legendary Hi sunny05 - what did you end up doing to address this issue? I am having a similar problem at a KDR site in Melbourne's east, there is waterlogged clay soil down to 700-900mm that is preventing the site cut from occurring. Seems to be due to the record rainfall we had in April - it was the wettest April since 1960. Given the cool temperatures and rainfall since, the soil is has not dried out beneath the surface. Current options are (1) wait 3-4 months for the soil to dry out; (2) suspend the entire slab on dozens of screwpiles so that it sits above the surface and minimal scrape is required ($30k); (3) trench and install a couple of agi drains about 500mm deep through the site and connect into stormwater to help drain away the moisture; (4) dig through some gypsum and lime to break up the clay and improve drainage. Currently looking at (4) and (5) in the hope that improved drainage will help the site dry out enough in 2-3 weeks to allow site cut to proceed. Hi Legendary, We ended up getting rid of the wet soil and proceed with the build process. At this stage the slab has been completed and they are working on the frame. We were only given 2 options by the builder either wait until spring and hope the site dries out or pay extra and get rid of the top wet soil. The wet weather was not helping and if the site didn’t dry out until spring, we would end up paying anyways. So, we decided to get rid of the wet soil. Also, the builder advised that once they reach clay, they can get the slab underway and the site under the slab would be less exposed to rain (i.e. less wet). The builder has installed a waffle pod slab on footings. Hope this helps Thanks sunny05 - good luck with your build. Taking a different approach so will see if we have any luck - the time/cost delay for us is not worth the cost of soil removal at this point, even if we had to wait for a summer site scrape Re: Site too wet to cut 26Aug 14, 2020 4:02 pm Legendary insider Legendary Thanks insider - appreciate the info. By cut off drain, do you mean a deep trench through the site with something non-permeable to carry water away? The builder has suggested the ag drains sit in trenches that are not back-filled (ie. left exposed) - will this work or do you think a different design is necessary? No it's basically an agi drain but with builders plastic on one side of the trench(the side you are trying to protect). One thing about agi drains and cut off drains is most of the time they are not deep enough.If the agi/cut off trench doesn't go into the clay it won't work. The builder says 500mm deep but you have said 700-900 so that would have to be the depth of the trench must be into the clay. Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Thanks insider - builder is speaking with the drainage plumber but it looks like we will go with this approach. The property slopes gently right to left (200mm fall across 17m) and front to back (400mm fall across 42m) so we are looking at putting one drain all the way down the low side on the left and one drain all the way across the back Depending on the natural slope of the land the drain should be on the high side to cut off the natural flow onto the block. Maybe you should get the soil testing company to investigate first so the drain is constructed properly. Re: Site too wet to cut 27Aug 14, 2020 6:02 pm The water-logged soil is much more prominent on the lower (left) side and particularly so at the back of the site - there is no overland flow from neighbouring properties due to house walls and other infrastructure. So the flow is contained within the site and the water is settling at the low points on the block. Re: Site too wet to cut 28Aug 14, 2020 6:11 pm Legendary The water-logged soil is much more prominent on the lower (left) side and particularly so at the back of the site - there is no overland flow from neighbouring properties due to house walls and other infrastructure. So the flow is contained within the site and the water is settling at the low points on the block. Then a cut off drain is probably not going to be as effective as a standard agi drain and even then may not work if there is no flow onto the block. Is there any obvious sources of water eg. neighbouring overflowing cutters, disconnected downpipes, roof areas with no gutters, watering systems etc next door ? Re: Site too wet to cut 29Aug 14, 2020 6:18 pm There was zero drainage on the block - not even stormwater connection - and significant tree coverage. The block was cleared and then it rained heavily for 6 weeks afterwards and the water had nowhere to go, it has just sat there in the first 800mm of soil above the heavy clay. It doesn't even flow into the downhill neighbouring property due to a large retaining wall Re: Site too wet to cut 30Aug 14, 2020 6:26 pm Legendary There was zero drainage on the block - not even stormwater connection - and significant tree coverage. The block was cleared and then it rained heavily for 6 weeks afterwards and the water had nowhere to go, it has just sat there in the first 800mm of soil above the heavy clay. It doesn't even flow into the downhill neighbouring property due to a large retaining wall Ok sounds very difficult, water is probably ponding against the retaining wall as you say. Good luck PM me your email. I have a build excavation calculator you can use based on your plans to double check what your builder is telling you. Cheers Simeon 1 10206 All sorted guys. Just needed to buy a blade with the correct bush. Dunno how to delete this post, can't find any help file. Cheers. 1 3657 Fine with me... just let 'em step in with some affordable (but good) gear... 12 5479 |