You would need piers through the fill and they have to be distributed evenly, yes.
You would need piers for H1 too and sometimes even for M.
Send us your engineering report or drawing here when you get it.
Site costs
Page 2 of 2
So it is a class "P" site that has been re classified as H1 because the fill is certified level 1 compaction. In these situation
there will be expected approximate uniform settlement but will be within the tolerance of a H2 slab. The problem is when you support one section like your garage on piers down to the natural soil and let the rest of the slab settling in the fill, this could cause differential movement. Most engineers will pier the whole slab in these situations especially in it is a double storey house which will have a greater load on the fill.
there will be expected approximate uniform settlement but will be within the tolerance of a H2 slab. The problem is when you support one section like your garage on piers down to the natural soil and let the rest of the slab settling in the fill, this could cause differential movement. Most engineers will pier the whole slab in these situations especially in it is a double storey house which will have a greater load on the fill.
where have you read regarding re-classification?
There is 2.3m of fill which is a class "P" site unless re classified.
There is 2.3m of fill which is a class "P" site unless re classified.
I understand with regard to the fill, but I am not seeing anything re H1. From what I see, they took soil samples from the fill and classified them as H2.
Yes sorry your right but still has to have been class"P" and reclassified to H2 off the compaction report.
If he has L1 compaction report, most probably the soil has been replaced/added, as otherwise what was the whole purpose of compaction?
But I agree with insider, you can't have piers just on one side.
Another important aspect is that on the reactive soil piers are to be connected to the rest of the slab with the steel reinforcement, I am struggling to understand why no one is actually doing this! When/if water gets under the slab, it will lift the slab up and the dirt will get in between piers and slab, so eventually you can still end up in a slab heave as the amount of dirt may not be proportional. I guess the whole idea of the piers was to make sure that due to their friction with the soil they will be limiting slab movements both up and down, not just down.
But I agree with insider, you can't have piers just on one side.
Another important aspect is that on the reactive soil piers are to be connected to the rest of the slab with the steel reinforcement, I am struggling to understand why no one is actually doing this! When/if water gets under the slab, it will lift the slab up and the dirt will get in between piers and slab, so eventually you can still end up in a slab heave as the amount of dirt may not be proportional. I guess the whole idea of the piers was to make sure that due to their friction with the soil they will be limiting slab movements both up and down, not just down.
If you're struggling with the concept of not connecting a slab to a pier, then you're going to hate this product: https://www.bladepilevic.com.au/products/pile-cap/
Matt it is interesting.
They have had issues in USA where they do connect the piers to slabs but the soil still heaves in-between the piers and creates damage. I think the only reliable way to prevent upwards and downward movement is a slab on piers with void formers but this would add a lot to the costs of construction. It could be used in certain situations where there is a high probability of slab heave like very dry initial soil conditions or recent tree removal before construction (clay rebound).
Matt it is interesting.
They have had issues in USA where they do connect the piers to slabs but the soil still heaves in-between the piers and creates damage. I think the only reliable way to prevent upwards and downward movement is a slab on piers with void formers but this would add a lot to the costs of construction. It could be used in certain situations where there is a high probability of slab heave like very dry initial soil conditions or recent tree removal before construction (clay rebound).
They have had issues in USA where they do connect the piers to slabs but the soil still heaves in-between the piers and creates damage. I think the only reliable way to prevent upwards and downward movement is a slab on piers with void formers but this would add a lot to the costs of construction. It could be used in certain situations where there is a high probability of slab heave like very dry initial soil conditions or recent tree removal before construction (clay rebound).
what about simply pouring slab and piers in one go? why no one is doing this?
Matt it is interesting.
They have had issues in USA where they do connect the piers to slabs but the soil still heaves in-between the piers and creates damage. I think the only reliable way to prevent upwards and downward movement is a slab on piers with void formers but this would add a lot to the costs of construction. It could be used in certain situations where there is a high probability of slab heave like very dry initial soil conditions or recent tree removal before construction (clay rebound).
They have had issues in USA where they do connect the piers to slabs but the soil still heaves in-between the piers and creates damage. I think the only reliable way to prevent upwards and downward movement is a slab on piers with void formers but this would add a lot to the costs of construction. It could be used in certain situations where there is a high probability of slab heave like very dry initial soil conditions or recent tree removal before construction (clay rebound).
what about simply pouring slab and piers in one go? why no one is doing this?
You need the plastic moisture barrier under the slab between the slab and the soil. You would also have material falling down the pier excavations as you construct the formwork etc for the slab. Piers are normally inspected just before they are poured this would be almost impossible if you have the pre slab preparation above it, Plastic, reo, formwork etc.
Moisture barrier is needed if concrete is not waterproofed, but I see the point here.
In US slab heaved in between piers and slab or in the ribs between piers (on a horizontal scale)?
In US slab heaved in between piers and slab or in the ribs between piers (on a horizontal scale)?
Not 100% sure what you are asking but in the US as far as I know they tie the piers to the slab a lot more than here. So if the soil heaves then the edge beam is lifted in between piers but is held down where the piers are connected to the slab. So you get an arching effect between piers. Here we get the slabs lifting off the piers as there is nothing to hold them down. Soil heaves laterally first if there are cracks in the soil they are closed then the soil swells vertically.
Not 100% sure what you are asking but in the US as far as I know they tie the piers to the slab a lot more than here. So if the soil heaves then the edge beam is lifted in between piers but is held down where the piers are connected to the slab. So you get an arching effect between piers. Here we get the slabs lifting off the piers as there is nothing to hold them down. Soil heaves laterally first if there are cracks in the soil they are closed then the soil swells vertically.
Isn't it supposed to be addressed with the increased rigidity of the edge beam?
Can also just a floating rafted slab on top of foam foundation with only 30-40 cm without piers be a decent alternative? I know they use them actively in Europe (e.g. Sweden) and it works pretty well on almost all soil types.
https://www.treehugger.com/green-architecture/floating-foam-foundation-insulation-system-legalett-wraps-house-bottom.html
Not 100% sure what you are asking but in the US as far as I know they tie the piers to the slab a lot more than here. So if the soil heaves then the edge beam is lifted in between piers but is held down where the piers are connected to the slab. So you get an arching effect between piers. Here we get the slabs lifting off the piers as there is nothing to hold them down. Soil heaves laterally first if there are cracks in the soil they are closed then the soil swells vertically.
Isn't it supposed to be addressed with the increased rigidity of the edge beam?
Can also just a floating rafted slab on top of foam foundation with only 30-40 cm without piers be a decent alternative? I know they use them actively in Europe (e.g. Sweden) and it works pretty well on almost all soil types.
https://www.treehugger.com/green-architecture/floating-foam-foundation-insulation-system-legalett-wraps-house-bottom.html
Yes you can increase the rigidity of the beam and have the slab connected to piers increase reo etc but the costs are going up and up. The swell pressure of a highly or extremely reactive clay can be surprising.
A slab on piers with void formers is probably going to end up cheaper or even pre watering a dry site back to reasonable moisture which could be a bit more hit and miss. An engineer could design a slab that will most likely never move in any scenario but the cost would be very high. The Aus standards acknowledge there must be a balance between the economic costs and engineering design. I know that sounds reasonable................... until it is your house that has problems.
If you rest the slab on foam and the ground under it dries out due to a tree or has fill that is not properly compacted and settles a large amount the foam is going to nothing to stop your slab from moving.
They generally put the slab on foam on top fo 30-40 cm compacted fill of sand and gravel.
How expensive are void formers, by the way?
If they only add $2-3K to $20-30K slab, then it is a decent option and very small add-on to the cost of the overall house.
How expensive are void formers, by the way?
If they only add $2-3K to $20-30K slab, then it is a decent option and very small add-on to the cost of the overall house.
Hi. I have received the engineering report.
[i:31ycrpwu]The site at the time of testing was found to be filled to form a level pad.[/i:31ycrpwu]
[i:31ycrpwu]Information relating to the above site was collected and studied. This included ___ Testing Level One Certification.
We recommend that the site be cut and filled to form a level pad after being scraped free of significant vegetation.
Any new fill should be clean (i.e. free from material which is subject to decay) and mechanically compacted in 150mm layers.
[/i:31ycrpwu][i:31ycrpwu]This fill is not to exceed 250mm depth beneath the floor slab.
A footing system as detailed herewith may be constructed for this site.
[/i:31ycrpwu][i:31ycrpwu]SITEWORK (continued)
Prior to construction, to achieve floor levels required architecturally, the site requires filling. This filling should be mechanically compacted to 97% Standard Density. Throughout the fill profile, this density is to be verified by compaction testing. The following recommendations are given based on this requirement.
NOTE: If compaction is not achieved, a system of footing and slab piers will be required. Vegetation on this site consisted of sparse grasses. Site drainage was assessed as fair.
RECOMMENDATIONS
Abnormal Moisture Conditions
Any quoted “normal” Ys does not take into account ground movements generated by abnormal moisture. The following must be considered.
• How the proposed development will change the existing equilibrium of the soil moistures.
• The long-term impact on the soil moisture equilibrium of existing and future vegetation and structures. • Appendix H and/or CH of AS2870-2011.
The companion book to AS2870-2011 (SAA HB28-2011) on page 153 advises:
Capacity of Designs – “It should be appreciated that the standard designs can cope with significant one sided mounds resulting from quite large tree movements without failure”.
This is also the case when other sources of abnormal conditions exist. Since 1997, it has been our experience that by creating normal site conditions at the time of site preparation and using a normal slab design of sufficient stiffness to cope with an increased Ys (ie. Abnormal Ys) then providing the owner/occupiers of both this site and adjoining sites maintains these sites in accordance with the CSIRO guidelines, performance with the AS2870-2011 criteria is not an unrealistic expectation.
This involves either removing or negating the effects of any tree(s) within the zone of influence of the proposed footing.
When this is done, in our judgement and experience, the following design criteria should give a performance level with the AS2870-2011 performance criteria for the proposed footing system.
Normal Ys Abnormal Equivalent Design Class
55-65mm -- H2
Note: The engineer may also decide to support the footing system on piers taken down to competent strata to negate any future planting of trees.
Floor Slab:
We recommend reinforcing the waffle raft floor slab with SL92 slab mesh with the slab thickenings founded in compacted fill and/or natural ground. (Refer to footing/slab cross section).
[/i:31ycrpwu][i:31ycrpwu]Brickwork – Control Joints:
All brickwork must be articulated for its full height at a maximum spacing of 6m. To assist you, we refer you to the Building Code of Australia - Housing Provisions, Sections 3.3.1.8 and 3.3.3.2 for construction details and brick wall ties data. These control joints may be incorporated into window and door openings and may be concealed by stormwater downpipes where possible.
Note: This is a general building requirement (not a special soil requirement). As such, the builder can offer alternative building systems to alleviate movements from moisture or ambient temperature changes.[/i:31ycrpwu]
Any thoughts? the builder will fix the site cost as per this report. Do I need to ask them to put more piers? Can someone explain this to me in more layman's terms.. Is this enough or I require more? Do I need to put concrete apron, is that mandatory in this case? Also if I want to put pool later at the back, will this cause me problem as I have H2 soil? Thank you
[i:31ycrpwu]The site at the time of testing was found to be filled to form a level pad.[/i:31ycrpwu]
[i:31ycrpwu]Information relating to the above site was collected and studied. This included ___ Testing Level One Certification.
We recommend that the site be cut and filled to form a level pad after being scraped free of significant vegetation.
Any new fill should be clean (i.e. free from material which is subject to decay) and mechanically compacted in 150mm layers.
[/i:31ycrpwu][i:31ycrpwu]This fill is not to exceed 250mm depth beneath the floor slab.
A footing system as detailed herewith may be constructed for this site.
[/i:31ycrpwu][i:31ycrpwu]SITEWORK (continued)
Prior to construction, to achieve floor levels required architecturally, the site requires filling. This filling should be mechanically compacted to 97% Standard Density. Throughout the fill profile, this density is to be verified by compaction testing. The following recommendations are given based on this requirement.
NOTE: If compaction is not achieved, a system of footing and slab piers will be required. Vegetation on this site consisted of sparse grasses. Site drainage was assessed as fair.
RECOMMENDATIONS
Abnormal Moisture Conditions
Any quoted “normal” Ys does not take into account ground movements generated by abnormal moisture. The following must be considered.
• How the proposed development will change the existing equilibrium of the soil moistures.
• The long-term impact on the soil moisture equilibrium of existing and future vegetation and structures. • Appendix H and/or CH of AS2870-2011.
The companion book to AS2870-2011 (SAA HB28-2011) on page 153 advises:
Capacity of Designs – “It should be appreciated that the standard designs can cope with significant one sided mounds resulting from quite large tree movements without failure”.
This is also the case when other sources of abnormal conditions exist. Since 1997, it has been our experience that by creating normal site conditions at the time of site preparation and using a normal slab design of sufficient stiffness to cope with an increased Ys (ie. Abnormal Ys) then providing the owner/occupiers of both this site and adjoining sites maintains these sites in accordance with the CSIRO guidelines, performance with the AS2870-2011 criteria is not an unrealistic expectation.
This involves either removing or negating the effects of any tree(s) within the zone of influence of the proposed footing.
When this is done, in our judgement and experience, the following design criteria should give a performance level with the AS2870-2011 performance criteria for the proposed footing system.
Normal Ys Abnormal Equivalent Design Class
55-65mm -- H2
Note: The engineer may also decide to support the footing system on piers taken down to competent strata to negate any future planting of trees.
Floor Slab:
We recommend reinforcing the waffle raft floor slab with SL92 slab mesh with the slab thickenings founded in compacted fill and/or natural ground. (Refer to footing/slab cross section).
[/i:31ycrpwu][i:31ycrpwu]Brickwork – Control Joints:
All brickwork must be articulated for its full height at a maximum spacing of 6m. To assist you, we refer you to the Building Code of Australia - Housing Provisions, Sections 3.3.1.8 and 3.3.3.2 for construction details and brick wall ties data. These control joints may be incorporated into window and door openings and may be concealed by stormwater downpipes where possible.
Note: This is a general building requirement (not a special soil requirement). As such, the builder can offer alternative building systems to alleviate movements from moisture or ambient temperature changes.[/i:31ycrpwu]
Any thoughts? the builder will fix the site cost as per this report. Do I need to ask them to put more piers? Can someone explain this to me in more layman's terms.. Is this enough or I require more? Do I need to put concrete apron, is that mandatory in this case? Also if I want to put pool later at the back, will this cause me problem as I have H2 soil? Thank you
Hi again. Just bumping the thread..I have been searching all over about this but found limited info. If anyone know of similar scenario please share. Thanks..
I read on the general building recommendation to ensure site drainage, soil surface should be sloped away at 1:20 for a minimum of 1.2m width apron. How do I ensure this to happen? Is this something that is supposed to be written on the plan or contract? I am planning to get the concrete apron later around build completion, due to funds limitation..
I ask the builder last time about if I need piering at the back for future pool I was told no.
Before I sign the contract, I want to know given that it's mentioned here that having piers distributed evenly is the way to go to avoid differential settlement..I'm confused why then the engineering report piers are only on one side.I have asked this question to the builder last week but haven't gotten proper response. I will ask again tom. Can this design work? Any suggestion?
Has anyone had a piering done only on one side? if my lot has level 1 compacted fill, does it automatically need piering or not? In this instance, the bored piers are needed on one side being close to the retaining wall. So in general they don't recommend piering only one side? is this absolute?
I read on the general building recommendation to ensure site drainage, soil surface should be sloped away at 1:20 for a minimum of 1.2m width apron. How do I ensure this to happen? Is this something that is supposed to be written on the plan or contract? I am planning to get the concrete apron later around build completion, due to funds limitation..
I ask the builder last time about if I need piering at the back for future pool I was told no.
Before I sign the contract, I want to know given that it's mentioned here that having piers distributed evenly is the way to go to avoid differential settlement..I'm confused why then the engineering report piers are only on one side.I have asked this question to the builder last week but haven't gotten proper response. I will ask again tom. Can this design work? Any suggestion?
Has anyone had a piering done only on one side? if my lot has level 1 compacted fill, does it automatically need piering or not? In this instance, the bored piers are needed on one side being close to the retaining wall. So in general they don't recommend piering only one side? is this absolute?
They claim that piers won't be needed if soil is compacted to at least 97, so you would need to see a report from soil compaction testing lab to confirm that.
Generally, it is hard to move water away from waffle pods at highly reactive sites, so you must do what you can.
I would start with a perimeter aggregate drainage and will make sure that when you cut for the site, there is a minimum slope at the bottom of excavation, so even if water gets under your slab and passes through sand, it is poured away with the gravity right into the drainage, otherwise, you will be just having a swamp under your slab after every rain, this will be disaster and no compaction will help you to go around.
The easiest option will be to pier along the full contour, but I would still prefer to have drainage in place and slope under your sand.
Concrete apron would help, but you would need to make sure that under the apron you have a clay and not sand or gravel as well as perimeter drainage, as otherwise the water routed away by the apron will still have a good chance to get under the apron and under your slab.
Just my 2 cents.
Generally, it is hard to move water away from waffle pods at highly reactive sites, so you must do what you can.
I would start with a perimeter aggregate drainage and will make sure that when you cut for the site, there is a minimum slope at the bottom of excavation, so even if water gets under your slab and passes through sand, it is poured away with the gravity right into the drainage, otherwise, you will be just having a swamp under your slab after every rain, this will be disaster and no compaction will help you to go around.
The easiest option will be to pier along the full contour, but I would still prefer to have drainage in place and slope under your sand.
Concrete apron would help, but you would need to make sure that under the apron you have a clay and not sand or gravel as well as perimeter drainage, as otherwise the water routed away by the apron will still have a good chance to get under the apron and under your slab.
Just my 2 cents.
They claim that piers won't be needed if soil is compacted to at least 97, so you would need to see a report from soil compaction testing lab to confirm that.
Generally, it is hard to move water away from waffle pods at highly reactive sites, so you must do what you can.
I would start with a perimeter aggregate drainage and will make sure that when you cut for the site, there is a minimum slope at the bottom of excavation, so even if water gets under your slab and passes through sand, it is poured away with the gravity right into the drainage, otherwise, you will be just having a swamp under your slab after every rain, this will be disaster and no compaction will help you to go around.
The easiest option will be to pier along the full contour, but I would still prefer to have drainage in place and slope under your sand.
Concrete apron would help, but you would need to make sure that under the apron you have a clay and not sand or gravel as well as perimeter drainage, as otherwise the water routed away by the apron will still have a good chance to get under the apron and under your slab.
Just my 2 cents.
Generally, it is hard to move water away from waffle pods at highly reactive sites, so you must do what you can.
I would start with a perimeter aggregate drainage and will make sure that when you cut for the site, there is a minimum slope at the bottom of excavation, so even if water gets under your slab and passes through sand, it is poured away with the gravity right into the drainage, otherwise, you will be just having a swamp under your slab after every rain, this will be disaster and no compaction will help you to go around.
The easiest option will be to pier along the full contour, but I would still prefer to have drainage in place and slope under your sand.
Concrete apron would help, but you would need to make sure that under the apron you have a clay and not sand or gravel as well as perimeter drainage, as otherwise the water routed away by the apron will still have a good chance to get under the apron and under your slab.
Just my 2 cents.
Thanks for the reply Alex.
Here is the compaction report. It looks like it's above 97% if I am reading it right?
*edited
I am not sure where to look for drainage plan but this is what I found in terms of roof water drainage, downpipes and field gullies
I will ask more about the drainage..
Do you know the estimate cost for an engineer to supervise this stage? It says they don't do full supervision unless asked in writing, otherwise they will come for inspection only as per requirement.
When you say pier along the full contour, you mean all of the sides?
No, they say that they will be replacing up to 250 mm of soil under the slab with new fill and compacting it in layers in certain areas. This will be a pre-requisite for your slab preparation:
We recommend that the site be cut and filled to form a level pad after being scraped free of significant vegetation.
Any new fill should be clean (i.e. free from material which is subject to decay) and mechanically compacted in 150mm layers.
This fill is not to exceed 250mm depth beneath the floor slab.
Not sure about engineer to supervise the stage, I guess it will be better to discuss with the current engineer to make sure he specifies drainage and soil slope post excavation (confirm if "slope to front" label on the drawing is actually specifying it?). Also, he should specify that new fill under the slab to be porous and act as a drainage (e.g. sand, roadbase, sandstone, gravel, etc.). If it is a sand, then generally it is a good idea to install geo-textile to prevent compacted sand from mixing with clay.
The drainage around the slab is not really related to your roof drainage and downpipes.
Piers along all the sides, yes.
We recommend that the site be cut and filled to form a level pad after being scraped free of significant vegetation.
Any new fill should be clean (i.e. free from material which is subject to decay) and mechanically compacted in 150mm layers.
This fill is not to exceed 250mm depth beneath the floor slab.
Not sure about engineer to supervise the stage, I guess it will be better to discuss with the current engineer to make sure he specifies drainage and soil slope post excavation (confirm if "slope to front" label on the drawing is actually specifying it?). Also, he should specify that new fill under the slab to be porous and act as a drainage (e.g. sand, roadbase, sandstone, gravel, etc.). If it is a sand, then generally it is a good idea to install geo-textile to prevent compacted sand from mixing with clay.
The drainage around the slab is not really related to your roof drainage and downpipes.
Piers along all the sides, yes.
I have asked and builder wants to with as per engineer's design so no additional piers. I was told they will slope the earth away from the slab..
Thank you for your advice
Thank you for your advice
Related
17/04/2024
1
Henley should give you some indication of site costs. Too many variable to give you any reasonable accuracy
18/06/2023
0
Looking to tile the facade pillars rather than rendering. Builder is quoting 2500$ laying cost for upto 10msq. The 2 pillars come to be 16msq. So laying costs are 5000$…