Browse Forums Building A New House Re: Site Costs - Please advise 21May 04, 2020 11:41 pm Hi, Doesn't look too bad-the first quote made the builder sound like there a pit of unknowns-may have been standard clauses. Footings should come back as piers into the clay which should be no dramas. The fill looks okay to put the piers through. Uniform clayey silt soil will usually stay open during auger drilling for the piers so no collapsing problems look obvious. There is no mention of boulders or obstructions so pier installation shouldn't need to worry about breaking cobbles/hard bits to advance auger. Check the groundwater comments at the bottom of the log-providing no groundwater was encountered that is another win-can cause problems with piers. The piers will likely be designed to found in the clay under the natural clayey silt soils. The clay looks like a residual soil so less chance of any surprises so that a bonus. Things that could result in additional costs: The main one is the bedrock-if that gets any shallower and is found in the base of the piers (say to the right of BH1 and along the boundary to the right if I'm picturing it correctly) all footings might need to extend to bedrock to fulfil the structural design and prevent differential movement. It would be a good idea if you can to either determine where the hard bedrock (bottom of BH1) is elsewhere or get something written into the contract if you can. Things that could safe money: The geotech looks pretty limited-no worries there really, it justs means the design will be conservative. That 40-60mm (H1) seems high for that soil it could be an estimate (no worries there) but it might be a lower class than that which you could show with a little bit of lab testing. Ask the builder to provide cost for M classification-if significantly less it would be worth looking into. Strength of the founding soils looks like it has been estimated (i.e. no testing) so the design will probably say piers in stiff clay will allowable bearing pressure of 100-150kPa which is pretty low. In reality, the strength of the clay is probably more than that (300-400kPa) so ask the structural engineer to estimate if the soil offered 300-400kPa bearing capacity would the number of piers reduce and by how much. Then annoy the builder off again by asking for another estimate based on stronger clay. Then do the sums to see if it is worth determining the strength of pier founding soils. Shame the boreholes didn't go a bit deeper and there was one more. You could have bedrock not far below 3.0m and 750-1000kPa bearing pressures so as above you may be able to reduce the number of piers by drilling a bit deeper and get a more robust design. And...3 boreholes on a rectangular block for a rectangular house. Just no. How did the boundary wall retention issue go in the end? Do you need retaining walls? That's enough to ponder I think. Re: Site Costs - Please advise 22May 08, 2020 7:31 am worldofmud Hi, Doesn't look too bad-the first quote made the builder sound like there a pit of unknowns-may have been standard clauses. Footings should come back as piers into the clay which should be no dramas. The fill looks okay to put the piers through. Uniform clayey silt soil will usually stay open during auger drilling for the piers so no collapsing problems look obvious. There is no mention of boulders or obstructions so pier installation shouldn't need to worry about breaking cobbles/hard bits to advance auger. Check the groundwater comments at the bottom of the log-providing no groundwater was encountered that is another win-can cause problems with piers. The piers will likely be designed to found in the clay under the natural clayey silt soils. The clay looks like a residual soil so less chance of any surprises so that a bonus. Things that could result in additional costs: The main one is the bedrock-if that gets any shallower and is found in the base of the piers (say to the right of BH1 and along the boundary to the right if I'm picturing it correctly) all footings might need to extend to bedrock to fulfil the structural design and prevent differential movement. It would be a good idea if you can to either determine where the hard bedrock (bottom of BH1) is elsewhere or get something written into the contract if you can. Things that could safe money: The geotech looks pretty limited-no worries there really, it justs means the design will be conservative. That 40-60mm (H1) seems high for that soil it could be an estimate (no worries there) but it might be a lower class than that which you could show with a little bit of lab testing. Ask the builder to provide cost for M classification-if significantly less it would be worth looking into. Strength of the founding soils looks like it has been estimated (i.e. no testing) so the design will probably say piers in stiff clay will allowable bearing pressure of 100-150kPa which is pretty low. In reality, the strength of the clay is probably more than that (300-400kPa) so ask the structural engineer to estimate if the soil offered 300-400kPa bearing capacity would the number of piers reduce and by how much. Then annoy the builder off again by asking for another estimate based on stronger clay. Then do the sums to see if it is worth determining the strength of pier founding soils. Shame the boreholes didn't go a bit deeper and there was one more. You could have bedrock not far below 3.0m and 750-1000kPa bearing pressures so as above you may be able to reduce the number of piers by drilling a bit deeper and get a more robust design. And...3 boreholes on a rectangular block for a rectangular house. Just no. How did the boundary wall retention issue go in the end? Do you need retaining walls? That's enough to ponder I think. With regards to the retaining wall, the first builder mentioned there will be a retaining wall next to the garage but not that big given that the land developer has installed retaining wall on the north and west side of the lot. I will keep you posted Re: Site Costs - Please advise 23May 08, 2020 10:40 am I live in BV home on strip footings and stumps built 40 years ago (not my build) and is perfectly functional. It was built probably without soil test, definitely without engineering. Now we have soil tests, engineering, slab costs, slab upgrades and huge site costs. Who is conned? 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: Site Costs - Please advise 24May 09, 2020 2:23 pm Its always the customer who is a loser and conned hehehehe I am not sure whether Perth has its own way of doing things in regards to this. Most of Perth has class A (sandy soil), except for some areas near rivers or hills. 2 13098 Is anyone building with Mojo and have a recent site cost tender 0 15952 Henley should give you some indication of site costs. Too many variable to give you any reasonable accuracy 1 1882 |