Browse Forums Eco Living 1 Mar 09, 2015 6:27 pm Just noticed an issue with my water tank at my new home. It appears that over the last couple of days the tank has started to rise out of the ground Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ I noticed it when I was brushcutting, that the sleepers I had put up uphill from it were no longer level, as I had originally put them in place. Got around closer to inspect things and found this. :- Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ The gap is around 300mm from where it should be !! A closer look you can see the remaining intact pipe has pulled up much higher than where it was supposed to be. Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Another picture shows how much it has rising by the water marks on the side of the tank :- Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Your opinions are most welcome. I haven't been in touch with the tank builder (Taylex), as I wanted some feedback first. They were the ones that installed the tank, I just had the hole dug for them. The tank is around 75-80% full of water. Edit: The only change to our situation was the compulsory first flush system put on the tank, which drains out immediately on the other side of the tank by the plumber. Rainfall here has been fairly light, with the only large amount of rain back a few weeks ago from the tropical low depression of the remains of cyclone Marcia. There has however been some rain, which has activated the first flush system on several occasions. Owner Building at Jimboomba Woods in Logan City Qld. Blog : http://bandlnewhomebuild.blogspot.com H1 thread : viewtopic.php?f=38&t=68283 . Re: Floating water tank ! 2Mar 17, 2015 10:57 am After further investigation, with Taylex and my plumber, the common train of thought is that they earth has slipped down the side of the hill, rather than the tank floating. Taylex said tanks don't float evenly to the surface as mine has appeared to do. The plumber has said that the first flush system and the leaking mains supply would not have put sufficient water to cause it to float. They both state that it would be impossible to push a tank out of the ground that weighs around 45 tonne, as the tank is nearly full (I took the manhole cover off, and the water level was just below the overflows), with tank alone being around 15 tonnes according to Taylex, and 31500 litres of water being 31.5 tonnes of water. I've since brushcut the tall grass around the tank, and see in different spots large cracks in the ground, so that makes sense that the ground has slipped down the hill a bit. From memory, the tank's location was never properly compacted. Owner Building at Jimboomba Woods in Logan City Qld. Blog : http://bandlnewhomebuild.blogspot.com H1 thread : viewtopic.php?f=38&t=68283 . Re: Floating water tank ! 3Mar 17, 2015 7:37 pm Brendan, Would the weight of the tank (31.5 tonnes) had anything to do with causing the land to slip? Next weekend I am installing a 40,000 litre fire tank (40 tonnes) over 1.5 metres of fill. Should I be worried? P.S. How is your build going. Have you moved in yet? Re: Floating water tank ! 4Mar 17, 2015 8:26 pm Effective weight of around 45 tonnes including the tank. The tank base actually sits below natural ground level on a 100mm thick gravel base of 5-7mm gravel. I would assume the 1.5m of fill is clean fill and at least partially compacted ? One of the warranty void issues with this tank is no large rocks (chunks of concrete) up against the side or bottom of the tank. We've moved in a couple of weeks ago, but I didn't want to tell anyone until I updated my neglected blog ! Owner Building at Jimboomba Woods in Logan City Qld. Blog : http://bandlnewhomebuild.blogspot.com H1 thread : viewtopic.php?f=38&t=68283 . Re: Floating water tank ! 5Mar 18, 2015 12:03 pm Interesting. What is being proposed to stop any further land slip? Also look forward to the neglected blog Build thread: viewtopic.php?f=38&t=75302 Re: Floating water tank ! 6Mar 18, 2015 2:18 pm Quote: Next weekend I am installing a 40,000 litre fire tank (40 tonnes) over 1.5 metres of fill. Should I be worried? You're on clay aren't you ? What is retaining the soil at the bottom of the slope ? If nothing I'd suggest a decent kind of retaining wall. Clay once it is wet becomes pretty viscous and can move around a bit particularly under load from some of the weights you guys are talking about. Stewie Re: Floating water tank ! 7Mar 18, 2015 3:08 pm It's the tricky part, how do you build a retaining wall to stop wet clay from slipping down the hill when it gets particulary wet ? I'm sort of thinking tiered retaining walls, starting at the point where the filled ground meets the natural sloped ground, and putting some agi pipe at each tier to take the water away. I'll have to get in touch with the earthmoving guy who did the work here, and see if has any recommendations. Owner Building at Jimboomba Woods in Logan City Qld. Blog : http://bandlnewhomebuild.blogspot.com H1 thread : viewtopic.php?f=38&t=68283 . Re: Floating water tank ! 8Mar 19, 2015 9:26 pm You really need a land slip assessment by a qualified geotechnical engineer.Not all geotechs are able to do them it is very specialised. It could be the start of a larger movement.You should fix the broken pipe immediately with a flexible connection because excess water will accelerate the slip.Look for any sources of water further up the slope.Check with your local council to see if you are in a high risk land slip area. Re: Floating water tank ! 9Mar 20, 2015 10:11 pm Thanks for the info insider. Soon as I found the broken pipe I took action to fix and replace it.... initially I cut off both to the tank, and replaced the T pipe and routed water coming through to the drain pipes that run out downhill side of the tank. Closed the other side of the T's to ensure nothing came out that end in a downpour, and gave it a chance to properly dry out... okay, it was only a week and a bit, and Sunday I'll join the tank back up to the pipes. Before the geotech engineer, I want to bring in the earthmoving guy to get his opinion as to if he thinks I should get a geotech engineer in, and subject to how he answers that, I might be able to skip out on the added expense... not saying I won't get one in though. Water further up the slope should be draining in to agi pipes around the house, and I will divert more water away from the side to further away. Owner Building at Jimboomba Woods in Logan City Qld. Blog : http://bandlnewhomebuild.blogspot.com H1 thread : viewtopic.php?f=38&t=68283 . Re: Floating water tank ! 11Mar 22, 2015 10:09 am The soil test indicated H1 soil for the slab, so there's clay there. I had a retaining wall on the garage side of house, but that ground like near the water tank was not compacted either. As well as the sleeper holding the 800mm high wall only went around 600 - 700 in to the ground (was only going to be 600 high initially). So basically I'm strongly leaning towards the idea that lack of compaction in those two areas is my problem, that will settle down more as I take care of general drainage/run off around the block. Owner Building at Jimboomba Woods in Logan City Qld. Blog : http://bandlnewhomebuild.blogspot.com H1 thread : viewtopic.php?f=38&t=68283 . 18 90421 From what I know about water tanks (I've been working with a client on them for a few years now) is this - The concrete can last a lifetime if they don't crack for some… 2 10619 If you can calculate the reasonable charged head from let's say 100mm below the gutter to the top of where the vertical riser's horizontal discharge pipe will be, that… 11 17524 |