Browse Forums General Discussion 1 Feb 04, 2020 8:51 am Hi, We are looking on a vacant land which going to developed into lots in coming months and register in mid June. The civil works are starting in couple of weeks time. We managed to do a soil test on the natural land.Based on approved plans the top fill on the lot is not much <500mm. Soil classification is H1 on natural land. We are in our finance period currently. We are sorting the finance which includes the land and house build. Does anyone care share some feedback in whether having builders to provide fixed price contract based soil test done on natural land lot? Re: Fixed price building contract on undeveloped vacant land 2Feb 04, 2020 8:06 pm Hi spin7, I can offer a little feedback which may be of use: Getting a site classification on natural soil is the norm in my experience and generally preferable in most circumstances. When fill is placed and compacted over natural soil it can either decrease or increase the estimated movements-sometimes significantly and depends on type fill and method of compaction. If clay soils are placed and compacted the estimated movements will increase. Even if the fill is site won, excavation then re-compaction to the same level will result in higher surface movements than natural soil. Alternatively, if granular soils are placed as fill the estimated movements will decrease. The end result can be an increase or decrease in class so most geotech reports will advise against use as clay as structural fill. If you find out what soil type is being placed the geotech should be able to run the numbers (or however they have arrived at the H1class) and revise the estimated surface movement accordingly. Problems can arise as the structural design will be based on the site classification and inappropriate slab design is not uncommon if the effect of fill placement is not considered. On a side note, one borehole is not normally conducive to controlling costs. Re: Fixed price building contract on undeveloped vacant land 3Feb 04, 2020 8:24 pm worldofmud Hi spin7, I can offer a little feedback which may be of use: Getting a site classification on natural soil is the norm in my experience and generally preferable in most circumstances. When fill is placed and compacted over natural soil it can either decrease or increase the estimated movements-sometimes significantly and depends on type fill and method of compaction. If clay soils are placed and compacted the estimated movements will increase. Even if the fill is site won, excavation then re-compaction to the same level will result in higher surface movements than natural soil. Alternatively, if granular soils are placed as fill the estimated movements will decrease. The end result can be an increase or decrease in class so most geotech reports will advise against use as clay as structural fill. If you find out what soil type is being placed the geotech should be able to run the numbers (or however they have arrived at the H1class) and revise the estimated surface movement accordingly. Problems can arise as the structural design will be based on the site classification and inappropriate slab design is not uncommon if the effect of fill placement is not considered. On a side note, one borehole is not normally conducive to controlling costs. Thanks for info. We did about three bites on our lot. Based on the report it mentioned Predicted surface movement Ys of 50mm and class P. The existing soil encountered was silty clay underlain by natural silty clay. The developer has mentioned about certified clean fill, not sure about it’s composition. Re: Fixed price building contract on undeveloped vacant land 4Feb 04, 2020 8:37 pm spin7plus worldofmud Hi spin7, I can offer a little feedback which may be of use: Getting a site classification on natural soil is the norm in my experience and generally preferable in most circumstances. When fill is placed and compacted over natural soil it can either decrease or increase the estimated movements-sometimes significantly and depends on type fill and method of compaction. If clay soils are placed and compacted the estimated movements will increase. Even if the fill is site won, excavation then re-compaction to the same level will result in higher surface movements than natural soil. Alternatively, if granular soils are placed as fill the estimated movements will decrease. The end result can be an increase or decrease in class so most geotech reports will advise against use as clay as structural fill. If you find out what soil type is being placed the geotech should be able to run the numbers (or however they have arrived at the H1class) and revise the estimated surface movement accordingly. Problems can arise as the structural design will be based on the site classification and inappropriate slab design is not uncommon if the effect of fill placement is not considered. On a side note, one borehole is not normally conducive to controlling costs. Thanks for info. We did about three bites on our lot. Based on the report it mentioned Predicted surface movement Ys of 50mm and class P. The existing soil encountered was silty clay underlain by natural silty clay. The developer has mentioned about certified clean fill, not sure about it’s composition. Certified clean fill just means it is not contaminated-its illegal to import non-clean fill to a greenfield site for building purposes. The P classification may mean they have not undertaken the required tests to qualify the fill as controlled-therefore the default is uncontrolled fill. Re: Fixed price building contract on undeveloped vacant land 6Feb 05, 2020 7:49 pm Hi, I'm curious: What was the reason provided for the P classification? Future fill? Seems a shame. I don't really know about the contract side of things but are their other options apart from fixed price? Cheers Re: Fixed price building contract on undeveloped vacant land 7Feb 05, 2020 8:32 pm worldofmud Hi, I'm curious: What was the reason provided for the P classification? Future fill? Seems a shame. I don't really know about the contract side of things but are their other options apart from fixed price? Cheers From the report it was mentioned Class “P” due to a poor bearing capacity, the depth of uncontrolled fill and abnormal moisture conditions. As per AS 2870-2011 Clause 2.1.3 (a), (c) & (e). I haven’t gone back to the builder yet before doing up more research on this. What other options are there from contract side? Re: Fixed price building contract on undeveloped vacant land 8Feb 05, 2020 10:27 pm spin7plus worldofmud Hi, I'm curious: What was the reason provided for the P classification? Future fill? Seems a shame. I don't really know about the contract side of things but are their other options apart from fixed price? Cheers From the report it was mentioned Class “P” due to a poor bearing capacity, the depth of uncontrolled fill and abnormal moisture conditions. As per AS 2870-2011 Clause 2.1.3 (a), (c) & (e). I haven’t gone back to the builder yet before doing up more research on this. What other options are there from contract side? Ah-I misunderstood you. Your plot already has a layer of fill placed on the top. I thought you meant the site comprises natural soil and the earthworks in a few weeks were to raise the levels by 500mm to enable construction. I was thinking splitting earthworks and lowering class to M (If possible) might be cheaper overall where if the fill was still to be placed. Re: Fixed price building contract on undeveloped vacant land 9Feb 06, 2020 3:51 am Hi, There is a small layer 300mm of uncontrolled fill, the developer is going fill this area up to 500mmn. What you assume is still correct. At the moment it is H1 , H1/H2 is fine by us when it comes on the final compacted soil. More concern the possibility of E classification. Re: Fixed price building contract on undeveloped vacant land 10Feb 06, 2020 8:27 pm I'm with you-poosibly... I think the classification has to be P because of the unknowns involved not necessarily because they currently exist. At the moment your site has a thin bit of fill (probably topsoil-makes no real difference) but is classed H1 in its current condition. If future fill is to be placed it can't be classified as per AS2870 because the site classification will be determined by the fill quality/type and compaction. If clay fill is used, movements will likely increase but there is no simple way of accurately determining how much and even then could be loose/variable and unsuitable to build on. So unless the existing fill is being removed and granular fill placed the fixed price should allow for: Footings will need to be designed as per the geotech report but will likely need to extend through the fill and found at a minimum of 0.8m depth. Slab probably can't be ground bearing and will need to incorporate a void former/compressible layer or be fully suspended (i.e. the builder will need to allow for the potential for 'E type' soil movement, loose zones, dry areas etc.) Economies of scale being what they are the developer might be giving you a good deal but it should be checked to make sure it's included in the cost. If it was an isolated plot, importing non-clay fill and removing the existing fill may be the better option as the site can be reclassified as per AS2870 and fill used to support structure. Course I am reading between the lines a bit. An easier explanation might be that there is a tree and a duck pond in the middle of your site.... Re: Fixed price building contract on undeveloped vacant land 11Feb 07, 2020 6:00 am Thanks heaps for your info sharing . It’s top soil at the moment. I did check with the developer where he is getting the clean fill from and it’s composition. I noticed some builders are hesitant in proving fixed price when the land is not yet developed. (Also understand from their point of view) Thanks once again. Thank you so much everyone. This all makes a lot of sense. I guess when you talk to a builder who butters up everything to look very polished, you get to start believing… 7 17615 So AFAIk the outcomes of the BAL ratings form part of a clause that allows them to pass these costs on to you. However the more relevant detail is how did it go from 19… 1 9165 You talk about deletions, are they variations or PS and PC adjustments? pleas list them 1 16568 |