MyFirst
.....he put large wood chips all around the slab area except for areas with agi. drain and garage driveway area.
I am sure that the fill should be compacted, wood chips, mulch etc just doesn't cut it.
Browse Forums General Discussion Re: Slab Heave Cause? 81Aug 27, 2018 8:13 pm MyFirst .....he put large wood chips all around the slab area except for areas with agi. drain and garage driveway area. I am sure that the fill should be compacted, wood chips, mulch etc just doesn't cut it. 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Re: Slab Heave Cause? 82Aug 28, 2018 7:33 am Yes agreed, fill should be clay, compacted and sloped away from dwelling to an outfall. Wood chips and mulch placed on top is to provide non slip working surface for OH&S. If done well it is satisfactory. Foremost Building Expert in Australia,assisting with building problems/disputes, building stage inspections,pre-contract review advice for peace of mind 200 blogs http://www.buildingexpert.net.au/blog Re: Slab Heave Cause? 83Aug 28, 2018 9:17 am building-expert Yes agreed, fill should be clay, compacted and sloped away from dwelling to an outfall. Wood chips and mulch placed on top is to provide non slip working surface for OH&S. If done well it is satisfactory. During site prep. Yes it was done nicely. However when the electrician , drainer and concrete contractors came in together with rainy days. The site end up like a mud pool. So after concrete was laid i guess wood chips around perimeter of slab make sense to prevent the slopes from been trampled further into new mud pools. I doubt the contactor added new clay to build up the slopes. Eventhough he came in with a bobcat. Re: Slab Heave Cause? 84Aug 28, 2018 8:11 pm How do you retain or increase the moisture in our gardens? you mulch.So putting mulch (wood chips,gravels,rubble.pebbles)around the outside of a house under construction we increase the moisture content of the soil increasing the chances of slab heave.This is true for poorly compacted fill batters sloping away from the slab as well, it too increases the soil moisture.Grading the soil away from the slab is the only way to drain the site correctly and is required by AS2870. Re: Slab Heave Cause? 85Aug 29, 2018 7:29 am Good point from insider but for the builder there are opposing requirements. Firstly there is requirement to protect foundation material and this is best done with a compacted layer of clay sloping away from dwelling Ito outfall. Compacted clay layer is impermeable and will create runoff before water gets through the layer. However this leaves wet and slippery clay surface on top that is OH&S risk. How do you deal with that? Many builders do nothing and the site is mud bog, other provide a layer of wood chips and or bark. Anyone got a better idea? Foremost Building Expert in Australia,assisting with building problems/disputes, building stage inspections,pre-contract review advice for peace of mind 200 blogs http://www.buildingexpert.net.au/blog Re: Slab Heave Cause? 86Aug 29, 2018 9:24 am Yes there is a solution. First the builder need to grade the soil away and then puts OH&S material down.An alternative is to put builders plastic down first and then OH&S Material down or a combination of all three.There are other solutions but protecting the slab from changes in soil moisture which haven't been considered by the builders. An overal method for protecting the slab and the workers can be worked out but there seems to be no push for it. I recently have done a presentation to builders and engineers on the current problems with construction methods and the impact on changes to soil moisture. Re: Slab Heave Cause? 87Aug 29, 2018 2:21 pm My slab was poured on Friday (The removed the formwork in the afternoon) . On Monday evening I saw that they had added plastic and fill all the way around sloping away, and then covered with woodchips. I was pleasantly surprised to see this as other slab around me have just been left with big craters and puddles all around them. Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Re: Slab Heave Cause? 88Aug 29, 2018 4:20 pm brokenstick My slab was poured on Friday (The removed the formwork in the afternoon) . On Monday evening I saw that they had added plastic and fill all the way around sloping away, and then covered with woodchips. I was pleasantly surprised to see this as other slab around me have just been left with big craters and puddles all around them. Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Oh yeah, I didn't pay attention if mine they put plastic first before the wood chips... Is your slab waffle slab or raft slab? Re: Slab Heave Cause? 89Aug 29, 2018 4:42 pm MyFirst brokenstick My slab was poured on Friday (The removed the formwork in the afternoon) . On Monday evening I saw that they had added plastic and fill all the way around sloping away, and then covered with woodchips. I was pleasantly surprised to see this as other slab around me have just been left with big craters and puddles all around them. Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Oh yeah, I didn't pay attention if mine they put plastic first before the wood chips... Is your slab waffle slab or raft slab? Waffle, on 36 piers and 16 screw piles Re: Slab Heave Cause? 90Oct 28, 2018 11:09 pm insider FirstHome builder25 I hope this helps you. This is just my opinion from the limited info you have posted and photos you have provided with my knowledge of your estate and the soil conditions there around the time of your house construction. Your soil profile is probably the worst scenario for slab heave.Higly reactive dry fill over highly reactive clay.The problem with this is that moisture gets trapped in the fill layer by the relatively less permeable undrlying natural highly reactive clay layer.This causes the fill layer to get saturated and swell fairly quickly even during construction.The natural layer below will get wet and swell also but at a slower rate. The loads put on the slab by materials used being light weight cladding and metal roof mean there is vitually no weight resistance to slab heave.The builder by overpouring the footings shown in the photos also has decrease the load on each perimeter beam footing. The builder has not complied with the standards by grading the ground away from the slab.The engineers drawings will include drainage recommendations and design because it is a highly reactive site.Going by the photos, the drainage design and recommendations are unlikley to have been followed.You should check the drawings. The builder by not having the downpipes attached i(seen in your photos) or temporary downpipes installed during construction again has not complied with AS2870 by allowing water to pond against the footing. The slab will not return to it’s original level as heaving up to 62mm bends the reo and cracks the slab on the underside.Once the reo is bend and stretched it will be permanetly be in a dish shape. I have seen slabs with less than 20-30mm return to close to their original level but not exactly.The soil will never return to the pre construction drought levels again there will always be some soil volume increase compared to the original pre construction drought dry moisture condtions. The good news is by putting a correctly constructed concrete path around the perimeter of your house you may have stopped the continued saturation of the highly reactive fill layer. Your limited test holes indicate that it maybe working as the soil is no longer saturated.If that is the case then you should monitor the slab floor levels for at least the next 12 months or so to see if the slab has stabilised.This should be your main aim if you want to stay there or not persue the builder. Will slab heave come back to you in the future?It is unlikely as now the swelling clay fill is in a drying phase if your borehole moisture description is correct.The first swelling phase of highly reactive fill is the largest so subsquent swelling (even if it does get that wet again)of this fill will be less. I have seen lots of slabs with gaps formed under the slab as the soil dries and shrinks down with the slab is permanetly bent up on the perimeter. The vast majority of your heave probably has come from the original dry conditons combined with the builders non compliance with the standards.There always many other factors but these two will be the most inportant. As SaveH20 has suggested you need a good Geotech to investigate.At the very least continue to do floor level surveys. Thank you Insider, I have setup talks with the builder as I have now also discovered the slab has not been built as per the engineering drawings. The notes stipulate that the slab must be founded 100mm into natural clay/virgin dirt however it is sitting about 200 mm above the virgin dirt. Re: Slab Heave Cause? 91Oct 29, 2018 8:26 pm Was wondering,as ive never seen it ,with clay been regulation around slabs to stop water soaking through,where does this clay come from and how pure does it have to be,as this reg seems to be treated as caspars reg by most builders Re: Slab Heave Cause? 92Oct 29, 2018 8:39 pm Joker Was wondering,as ive never seen it ,with clay been regulation around slabs to stop water soaking through,where does this clay come from and how pure does it have to be,as this reg seems to be treated as caspars reg by most builders Well compacted clay will be sufficiently impermeable to shed water away from the dwelling however clay that has dried out too much will shrink and crack. This may allow volume of water to get through before clay swells and closes up cracks Foremost Building Expert in Australia,assisting with building problems/disputes, building stage inspections,pre-contract review advice for peace of mind 200 blogs http://www.buildingexpert.net.au/blog Re: Slab Heave Cause? 93Oct 29, 2018 8:40 pm Joker Was wondering,as ive never seen it ,with clay been regulation around slabs to stop water soaking through,where does this clay come from and how pure does it have to be,as this reg seems to be treated as caspars reg by most builders joker Clay and silt from the site excavations or trench excavations and the important thing is it isn't compacted so water easily penetrates through and then the fill restricts evaporating so it is worse than doing nothing.Add a layer of tanbark or gravels for OH&S on top and then you have created a moisture accumulator and trap. Firstly the ableflex that has been installed needs (manufactures specification) a sealant cap over the top, preventing water draining down between the slab and the… 3 5398 1 5020 |