Browse Forums General Discussion Re: Slab movement/heaving causing massive cracks 23Feb 23, 2020 10:07 pm Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: Slab movement/heaving causing massive cracks 24Feb 24, 2020 1:52 pm insider Looking at where your cracks are and the inspection hole that has had water flowing in it.You may have had localised heave near the rear of the garage which is lifting the trusses and cracking the plaster internally near the hallway . The stormwater pipe looks way to close to the footing is this correct ?. Even after the leak has been fixed you can still get movement for a long time afterwards. I would get your own geotechnical report done with floor levels so you can monitor the slab movement over time and also get moisture samples taken so you can see if there is an improvement in the abnormally moisture soil conditions. Once it has stabilised then consider a protective concrete path around that area or replacing the existing path if the slope is incorrect. Also you should consider a cut off drain to stop neighbouring seepage getting to your foundations not just an agi drain. The trees in the nature strip are not big enough to cause you issues at this stage. There may be a method to accelerate the clay drying process for a localise heave area I can let you know more if you PM me. If the cause is the plumbing leak then the builder is at fault. Yes, the initial report from the structurcal engineers mentioned exactly what you said. "Heave to the rear of the garage and alfresco area" The stormwater should have never been so close to the slab this is the screwup from the builders original plumber. The builder has offered to get this moved using another plumber worldofmud My understanding is that only the rear wall is underlain by the pier, we were told this is required as the rear wall is too close of the easement. The rear wall is perfectly fine, there are no cracks to that wall. I've asked the builder and their engineers repeatedly if the pier is contributing to this issue in someway but they have confirmed that its not the case. looking at the drwaings (attached ) the piers are just at the back. Am I reading this right? Any recommendation in VIC for a geotechnical engineer that can assist us with getting our independant reports From scouring through the older posts I see Metropolis plumbing come up but looks like they are investigate only plumbing Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Thanks Insider I overlooked the name at the bottom. I've re-uploaded the image in case any else is interested Re: Slab movement/heaving causing massive cracks 26Feb 24, 2020 8:50 pm Seriously, are you going to call out forensic engineers to measure the slab movement every time you see a new crack? What's that going to cost you? I was flabbergasted to read Site traffic control are charging $14K? on this job Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: Slab movement/heaving causing massive cracks 28Feb 24, 2020 10:17 pm donovanjd 'The rear wall is perfectly fine, there are no cracks to that wall.' That would be expected if the cause is related to the pier footing system on that side. If you have the time you might want to try the following methods: 1.Make 2 copies of the layout plan of your house and mark on one plan (with a highlighter) the horizontal defects and the other the vertical defects observable throughout your house 2. Copy these two plans and on each copy rate the defect either 1, 2 or 3, 1 being minor, 3 being major. 3. Go and measure the gap at each end between the slab and the brickwork of the concrete slab which has been displaced on one side of your house. Repost the results along with the P1 footing detail contained in your structural drawings. All free but you should seek some local geotech advice. Can't help there but expect to pay >$200 an hour for an initial site inspection for them to tell you they need to excavate some test pits to learn more. Re: Slab movement/heaving causing massive cracks 29Mar 30, 2020 5:07 pm I wanted to update this thread with latest information about this problem The builder along with their structural engineer came out 4 weeks ago to collect some new readings since some of the plumbing was fixed. We are still waiting these results from the engineer. We pushed the builder to provide us with the older readings and finally have these floor levels. The latest floor levels should tell us if fixing the broken pipe near the slab made any difference. In addition the builder got a plumber to check the sewage and storm water pipes around the property. He has confirmed that there are no broken or leaking sewage or storm water pipes. As the builder was pointing at the neighbours property being higher than ours and the water collecting in the borehole seemed to show it was coming from the neighbours property. We spoke to the neighbour who got his own plumber to check their sewage/stormwater drains, they have also confirmed that they do not have any broken pipes. We had to postpone the DRDBV concilation due to the current COVID-19 situation and to also wait for the engineer to provide us with the latest report. The builder at the stage does not want to get into next steps to resolve this problem but wants to get to DBDRV and see what they have to say. From what we can tell the cracks around the house are still faintly getting bigger I will update how we get on once the latest report comes through and what the builder is sugegsting as next steps. Thank you everyone for your valuable advice and suggestions. Much appreciated. Re: Slab movement/heaving causing massive cracks 30Mar 19, 2021 1:22 pm Latest update on this issue. Due to the COVID and the multiple lockdowns, things progressed slowly. Also, due to the investigation moving to slow with the builder and advice from others on this forum, we engaged our own independent inspector to investigate the slab heave. Summarizing some of his findings: According to the inspector's report and analysis from the soil samples, the cause of the heave is moisture. The soil samples collected from a couple of boreholes revealed the clay from the boreholes to be wetter than usual. The relatively elevated, moisture content in the clay from one of the boreholes was consistent with an artificial moisture source such as a plumbing leak, and/or poor site drainage rather than normal seasonal variations. In addition to moisture, there were few other issues identified with the slab, The 2.5 meters piers at the rear of the property is founded well into the natural, high bearing strength silty clay, while the remaining sections of the slab are founded on filling. Due to the likelihood of differential movements between the filling and the natural silty clay. Also, from NearMap review of the property, reactive clay filling was placed across this site during October 2016. Placement of reactive controlled clay filling over a site less than 5 years prior to construction can significantly increase the characteristic surface movement After submitting our report to the builder, the builder then came back saying they want to engage their own independent inspector/forensic investigator to investigate further. This was further prolonged due to the lockdowns and the inspector's availability. Just before the Christmas holidays, the builder was able to get the independent inspector to the property and investigate the issue. Summary of their findings Soil samples that their geo-tech engineer took confirmed abnormal moisture conditions This time they wanted soil samples from the rear of the property near the easement, and while collecting soil samples, they identified a gap of up to 35mm between the top of the piers and the underneath side of the slab. The theory is that the slab is lifting off the piers with the moisture levels, also verifying this. The original soil report correctly classified the site as a P, solely for the reasons of the filling. But as they did not take into consideration the moisture variations and the effects of the trees that had been taken down between January 2014 and October 2015, they should have treated the soil as having no cracks in it as it was well under the five year timeframe required by Australian Standard 2870 in assessing fill; Their advice that it was a H1 site and this could be utilised for design purposes is in error. Without determining moisture regimes, without making allowance for the potential for over compaction of filling, i.e. the elimination of cracks within the same and having no moisture levels to make guidance, the correct decision should have been an E slab or a stiffer H2. New floor levels were taken that also confirmed the heave isolated to the dining/alfresco area (nothing new so far) A 3rd new plumber came out with the inspector, and from their CCTV investigation, they found more leaks in the stormwater pipes and previous pipes repairs not fixed correctly. The builder sent out another plumber to fix the leaks that were identified during the investigation. The inspector also had a theory that there is water collecting in the easement trench at the back and potentially flowing along the trench under the house. To isolate this, they installed a camera with a sensor that monitors a stick with gradings on it, acting as a flotation device. The stick enclosed in a pipe was placed in a hole dug to the depth of about ~2 meters. Preliminary footage showed no water at this depth, concluding that the abnormal moisture is surface-level moisture. We are currently waiting on further remediations steps from the inspector/builder. Also, we have our conciliation meeting at the DBDRV next week to move this forward. Re: Slab movement/heaving causing massive cracks 31Mar 19, 2021 1:58 pm "According to the inspector's report and analysis from the soil samples, the cause of the heave is moisture. The soil samples collected from a couple of boreholes revealed the clay from the boreholes to be wetter than usual. The relatively elevated, moisture content in the clay from one of the boreholes was consistent with an artificial moisture source such as a plumbing leak, and/or poor site drainage rather than normal seasonal variations." Sometimes I love how reports are written. Dark matter scientist, can breathe underwater, mind reader and can freeze matter just by willing it. Trust me, its in my sig. Re: Slab movement/heaving causing massive cracks 32Mar 21, 2021 1:39 pm “ they identified a gap of up to 35mm between the top of the piers and the underneath side of the slab. The theory is that the slab is lifting off the piers with the moisture levels, also verifying this.” I’m no structural engineer, but I would have thought they would make sure the slab rebar was tied to the piers to stop this happening. Re: Slab movement/heaving causing massive cracks 33Mar 21, 2021 1:49 pm donovanjd Latest update on this issue. Due to the COVID and the multiple lockdowns, things progressed slowly. Also, due to the investigation moving to slow with the builder and advice from others on this forum, we engaged our own independent inspector to investigate the slab heave. Summarizing some of his findings: According to the inspector's report and analysis from the soil samples, the cause of the heave is moisture. The soil samples collected from a couple of boreholes revealed the clay from the boreholes to be wetter than usual. The relatively elevated, moisture content in the clay from one of the boreholes was consistent with an artificial moisture source such as a plumbing leak, and/or poor site drainage rather than normal seasonal variations. In addition to moisture, there were few other issues identified with the slab, The 2.5 meters piers at the rear of the property is founded well into the natural, high bearing strength silty clay, while the remaining sections of the slab are founded on filling. Due to the likelihood of differential movements between the filling and the natural silty clay. Also, from NearMap review of the property, reactive clay filling was placed across this site during October 2016. Placement of reactive controlled clay filling over a site less than 5 years prior to construction can significantly increase the characteristic surface movement After submitting our report to the builder, the builder then came back saying they want to engage their own independent inspector/forensic investigator to investigate further. This was further prolonged due to the lockdowns and the inspector's availability. Just before the Christmas holidays, the builder was able to get the independent inspector to the property and investigate the issue. Summary of their findings Soil samples that their geo-tech engineer took confirmed abnormal moisture conditions This time they wanted soil samples from the rear of the property near the easement, and while collecting soil samples, they identified a gap of up to 35mm between the top of the piers and the underneath side of the slab. The theory is that the slab is lifting off the piers with the moisture levels, also verifying this. The original soil report correctly classified the site as a P, solely for the reasons of the filling. But as they did not take into consideration the moisture variations and the effects of the trees that had been taken down between January 2014 and October 2015, they should have treated the soil as having no cracks in it as it was well under the five year timeframe required by Australian Standard 2870 in assessing fill; Their advice that it was a H1 site and this could be utilised for design purposes is in error. Without determining moisture regimes, without making allowance for the potential for over compaction of filling, i.e. the elimination of cracks within the same and having no moisture levels to make guidance, the correct decision should have been an E slab or a stiffer H2. New floor levels were taken that also confirmed the heave isolated to the dining/alfresco area (nothing new so far) A 3rd new plumber came out with the inspector, and from their CCTV investigation, they found more leaks in the stormwater pipes and previous pipes repairs not fixed correctly. The builder sent out another plumber to fix the leaks that were identified during the investigation. The inspector also had a theory that there is water collecting in the easement trench at the back and potentially flowing along the trench under the house. To isolate this, they installed a camera with a sensor that monitors a stick with gradings on it, acting as a flotation device. The stick enclosed in a pipe was placed in a hole dug to the depth of about ~2 meters. Preliminary footage showed no water at this depth, concluding that the abnormal moisture is surface-level moisture. We are currently waiting on further remediations steps from the inspector/builder. Also, we have our conciliation meeting at the DBDRV next week to move this forward. Thanks Donovanjd for the update. At least the builder is investigating further and will be interesting what the rectification works will be. I'm sure you will get a second opinion. Re: Slab movement/heaving causing massive cracks 34Mar 21, 2021 1:51 pm Unfortunately there is no holding down on waffle slabs they are free to move up and down on the piers. Unlike a slab and grid beam (Rebar for sagging and hogging) which is far superior Cheers Chris Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: Slab movement/heaving causing massive cracks 35Mar 21, 2021 7:38 pm When I asked them about the slab moving up, they said the waffle pod slab just sits on the piers, nothing to hold them down We are still waiting on the rectification steps from the builder and their inspector. Regarding the slab, they said to us that once the moisture source is blocked the clay should dry out and the slab would move back down on to the pier Re: Slab movement/heaving causing massive cracks 36Mar 23, 2021 10:15 pm I was cross-referencing some of the original structural engineering documents with the recent reports from the builder's inspector. The original reports have a section for "Tree Influence" and it's marked N/A The inspector's report calls out that the pre-existing conditions on the site prior to subdivision commencing involved a great stand of trees running across the front and their rooting system has been detected all the way to the kitchen zone at depth i.e. natural soil level. In addition, we have subdivisional filling having been put on to a depth of approximately 800mm or more in some locations, noted as level I controlled fill but it was less than five years when a soil report was initiated. Further, depending upon when the controlled filling went in, it may have infilled all the cracks within the soil below, noting the natural soil profile would have had cracks as the tree roots would have been drying it out and thus cracks would have been normal, even late into autumn. Thus, we get an amplification of any movement caused by wetting up the soil. Does this mean the original structural engineers completely overlooked this fact? This paragraph in the engineer's report is very distressing "I further note here that irrespective of all actions taken, it may be many years before the ground underneath this property dries out or equalises up in moisture level throughout and creates a more uniform level throughout the whole house. When and if that occurs, further plumbing failures will happen, and they will need to be fixed urgently. This will require a block flood monitoring of the property on a three-month basis for the foreseeable future. We at our wit's end dealing with all this Re: Slab movement/heaving causing massive cracks 37Mar 24, 2021 9:47 am What do you expect the builders engineer to say? As an engineer I can honestly say the Builder isn't off Scot free with another report. OT, The first and second engineer were all hired by the Builder you may need to hire your own independent engineer The person doing the site works and supervising has a duty of care to remove roots and prepare the site properly. my2c, If some builders stopped r!pping into clients with piering, stormwater, etc costs, then clients would be reluctant to opt for minimum engineering. As you have come to realise engineering is a critical factor in the Build You will need to monitor your slab for differential movement over a period of time to determine what further action is required You can get someone to do that at great expense or you can set up a monitoring system using a Line Laser GLL 3-80 CG Professional Here Checking Room Dimensions (XYZ Coordinates) with Bosch Lasers Collect the data, simulations will be used to determine liability hth Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: Slab movement/heaving causing massive cracks 39Mar 25, 2021 9:12 am First thing you'll need to do is cut back the apron concrete path sufficiently to get agri pipe and stormwater disposal system in ASAP as we move into the wetter months. Your geotech engineer will calculate the size system based on the rate of fill/discharge. Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: Slab movement/heaving causing massive cracks 40Apr 18, 2021 12:07 pm donovanjd Sorry to hear seems not much progress on any definitive answers on determining original source of water or even if there was one. The previous moisture conditions, trees, fill etc. may be playing a secondary role but from what you've posted it just 'feels' like something has been missed somewhere and that is what needs to be found. Reading over the past posts, the attention has been on leaking pipes, water coming into site, poor drainage etc. which is understandable. Just curious, has the house wall cavity drainage (if present) been discounted yet? Weep holes functioning, no irregularities with relative heights of slab checked out? This would have required holes drilled through the external walls and a look around with pinhole camera. If slab construction possibly dubious someone should also check that concrete hasn't been lost externally into the rolled fill around deepened detail at front-will anchor slab if lost 'unseen'. Checking the above may not reveal the answer but are cheap and simple to do and will provide more information which seems a bit short at moment. Currently you have gained enough information for each party to deny liability and are awaiting a fix without being able to clearly define the cause. Understandable that you are over it. Have look at your house plans and you will probably find that brick articulation joint has been missed. Maximum allowable spacing is 6M or 5.5M for a wall with window… 17 20661 Are they stumps or screw piles ? How much fill is there, is the site a class "P" ? A "H2" site is not supposed to have stumps it is supposed to have grid beams according… 1 7135 House movement is always a potential problem and there is a cause. Yes you should have it inspected by a competent and experienced building consultant 2 7922 |