Formula to compensate TPZ
- Thread starter Glennak
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Boa07
ArboristSite Operative
Stick to the standard or better (and provide compelling evidence that it is better - good luck) and you won't go far wrong.
Corymbia
ArboristSite Operative
Who wrote the SRZ formula
I actually said that it was from the Standard but where did they get the formula from? Is it published or did some mathematician at SA just work out a formula that produced a curve close to Mattheck's or what?
Here we are producing a figure based on a formula that may not be at all related to any published SRZ formula. The author or source of the formula does not appear to be cited in the Standard or did I miss it?
Does anyone know?
I actually said that it was from the Standard but where did they get the formula from? Is it published or did some mathematician at SA just work out a formula that produced a curve close to Mattheck's or what?
Here we are producing a figure based on a formula that may not be at all related to any published SRZ formula. The author or source of the formula does not appear to be cited in the Standard or did I miss it?
Does anyone know?
Glennak
ArboristSite Member
Why should a formula be published any where for them to use it? They have published it now. When I asked my son what formula would follow this graph he looked and said Y = (X * A) ^B*C and showed me on his calculator, he was doing year 12 at the time. I tried changing the constants to make it fit but it never fitted properly like Standards Australias formula. I'm sure who ever made up their formula and I were not the only ones who got pissed off trying to read off a tiny graph and wanted a formula. The software Math Mechanixs (which is free) will make a formula to fit any data thats what I used.
Corymbia
ArboristSite Operative
The formula is based on the graph?
OK! That makes more sense. So if I understand correctly what we have is a formula that replicates the upper curve for the data for failed trees from page 187 of the Body language of trees. That is fine but it would seem reasonable that the source of the information relating to SRZ's be made known since the size of the SRZ is NOT generally accepted.
Yes, it does make a huge difference from where industry best practice comes. If it comes from a small committee at SA (many of whom lack even graduate studies in arboriculture) then it may not be industry best practice at all ... Surely our profession should determine best practice and the standard then reflect that and not the other way around?
In fact it only takes a few seconds to look at the graph and the data to realise that the size of the SRZ that leads to failure can vary enormously and in fact there were failures that occurred above the curve. With the exception of smaller trees the data largely refers to trees that failed ... that is trees that had defective root plates ... What this data set looks at is the point of failure and not the SRZ
If we look at a tree with a 200mm trunk it needs a TPZ of 2.4 metres a SRZ of 1.26 metres using the formula and yet the data set says that the SRZ could be as large as 2 metres and as small as 0.5 m. If we accept that volume is cubic then there is a potential variation in the mass and volume of a failed root plate of 6400%. It is a good thing that this approach is not used to determine housing interest rates
Lastly, none of the research that I have found considers how partial encroachments into the SRZ affect stability if at all. Ignoring the obvious dilemmas with the data set mentioned above it has to make you wonder what the function of calculating the SRZ is then in terms of Protection of Trees on Construction sites. Perhaps on the odd rare occasion it may be useful to calculate but in most instances it appears to be little more than irrelevant.
Please let me know what I have misunderstood
OK! That makes more sense. So if I understand correctly what we have is a formula that replicates the upper curve for the data for failed trees from page 187 of the Body language of trees. That is fine but it would seem reasonable that the source of the information relating to SRZ's be made known since the size of the SRZ is NOT generally accepted.
Yes, it does make a huge difference from where industry best practice comes. If it comes from a small committee at SA (many of whom lack even graduate studies in arboriculture) then it may not be industry best practice at all ... Surely our profession should determine best practice and the standard then reflect that and not the other way around?
In fact it only takes a few seconds to look at the graph and the data to realise that the size of the SRZ that leads to failure can vary enormously and in fact there were failures that occurred above the curve. With the exception of smaller trees the data largely refers to trees that failed ... that is trees that had defective root plates ... What this data set looks at is the point of failure and not the SRZ
If we look at a tree with a 200mm trunk it needs a TPZ of 2.4 metres a SRZ of 1.26 metres using the formula and yet the data set says that the SRZ could be as large as 2 metres and as small as 0.5 m. If we accept that volume is cubic then there is a potential variation in the mass and volume of a failed root plate of 6400%. It is a good thing that this approach is not used to determine housing interest rates
Lastly, none of the research that I have found considers how partial encroachments into the SRZ affect stability if at all. Ignoring the obvious dilemmas with the data set mentioned above it has to make you wonder what the function of calculating the SRZ is then in terms of Protection of Trees on Construction sites. Perhaps on the odd rare occasion it may be useful to calculate but in most instances it appears to be little more than irrelevant.
Please let me know what I have misunderstood
Glennak
ArboristSite Member
Corymbia what do you mean the SRZ is not generaly accepted? Yes it would have been good if they gave the source I just assumed it was from Mattheck as their formula is close to the graph.
Why do fallen trees need to have defective root plates? Strong winds push over trees with any sort of root system unless the trunk snaps first.
What else is a Structural root zone but the area needed to hold the tree up ie the point of failure.
Your example of a tree with a 200mm trunk I assume that is diameter. I get SRZ 1.68 and CRZ of 1.56 which is about 8% more than the CRZ. Where does your 1.26 come from?
As for your data set shows from 2m to 0.5m??????????? I assume this is Matthecks data to which you are referring. It is plotted radius not diameter. So your 20cm radius shows trees that failed with root balls of 2.35m to about 0.5m. The SRZ has to be based on the larger the 0.5 could have been caused by anything but it is data and should be shown even if it is not used.
Where do you get "it comes from a small committee at SA" if you look at the standard it states who they consulted. I have been on committees to discuss the prunning standard and training levels in the aboricultural industry it is a lot of unpaid work so don't knock'em. They don't even get a free copy when it is finished. The ISA sent me an email to say the draft standard was out and to read and send comments. I did so and was ignored did you send any suggestions?
Yes the SRZ is usuallly well inside the TPZ and is often not needed but it can be relevent as the standard states that encroachments into the TPZ should not enter the SRZ or something similar.
Why do fallen trees need to have defective root plates? Strong winds push over trees with any sort of root system unless the trunk snaps first.
What else is a Structural root zone but the area needed to hold the tree up ie the point of failure.
Your example of a tree with a 200mm trunk I assume that is diameter. I get SRZ 1.68 and CRZ of 1.56 which is about 8% more than the CRZ. Where does your 1.26 come from?
As for your data set shows from 2m to 0.5m??????????? I assume this is Matthecks data to which you are referring. It is plotted radius not diameter. So your 20cm radius shows trees that failed with root balls of 2.35m to about 0.5m. The SRZ has to be based on the larger the 0.5 could have been caused by anything but it is data and should be shown even if it is not used.
Where do you get "it comes from a small committee at SA" if you look at the standard it states who they consulted. I have been on committees to discuss the prunning standard and training levels in the aboricultural industry it is a lot of unpaid work so don't knock'em. They don't even get a free copy when it is finished. The ISA sent me an email to say the draft standard was out and to read and send comments. I did so and was ignored did you send any suggestions?
Yes the SRZ is usuallly well inside the TPZ and is often not needed but it can be relevent as the standard states that encroachments into the TPZ should not enter the SRZ or something similar.
Ekka
Addicted to ArboristSite
The minimum SRZ will be 1.5m
The minimum TPZ will be 2.0m
That's in the standards, Corymbia if you used the online calculator you would have got the right answers.
Why calculate the SRZ's? What about activities inside the TPZ like putting in posts or piers? What about other stumps? If for example a tree has a 10m radius TPZ and 3m Radius SRZ and was a wooded site I could grind stumps right out when I'm say 7m away from the tree however within the SRZ I would only lick them off to the soil surface.
The minimum TPZ will be 2.0m
That's in the standards, Corymbia if you used the online calculator you would have got the right answers.
Why calculate the SRZ's? What about activities inside the TPZ like putting in posts or piers? What about other stumps? If for example a tree has a 10m radius TPZ and 3m Radius SRZ and was a wooded site I could grind stumps right out when I'm say 7m away from the tree however within the SRZ I would only lick them off to the soil surface.
Corymbia
ArboristSite Operative
The minimum SRZ will be 1.5m
The minimum TPZ will be 2.0m
That's in the standards, Corymbia if you used the online calculator you would have got the right answers.
Why calculate the SRZ's? What about activities inside the TPZ like putting in posts or piers? What about other stumps? If for example a tree has a 10m radius TPZ and 3m Radius SRZ and was a wooded site I could grind stumps right out when I'm say 7m away from the tree however within the SRZ I would only lick them off to the soil surface.
TPZ radius according to 3.2 will be 2.4 metres (12 times).
You are right SRZ radius will be 1.68 metres I inputted radius rather than diameter
That makes the situation worse! Most guys in the US would move this size tree with a John 90 or a radius of 1.1 metres ... something seems odd here unless of course the standard says somewhere that this is the maximum SRZ size but it may be smaller and to seek suitably qualified and experienced advice ... I just couldn't find that clause. So if the SRZ is not accurate then why calculate it.
You suggest to limit the location of piers ... but why should an inaccurate figure be used to restrict construction?
You suggest stump grinding and I would agree ... there are grinder operators out there who just don't think but any smart arborist, such as yourself, looking at the image you show should know to operate the grinder that close to another tree with care. If they are not smart enough to figure that out they certainly wont be using the formula or the on line calculator.
If you did need a formula to know how to handle that stump then you shouldn't be using machinery. I have a great sticker on my grinder it says ... "This machine does not have a brain so use yours"
Ekka
Addicted to ArboristSite
With the numbers I posted it wasn't specific to your 200mm DBH tree but just saying that's the minimum in the standard for all trees.
Corymbia
ArboristSite Operative
Got it ... again I don't pretend to understand that one either ... small or young trees are given additional protection? In fact a 1 inch caliper tree is given 120 square feet of protection yet you can buy a nice one 12 inch B&B ... or less than 1 square foot? I just wonder who pays ... the developer or all the young trees that get removed because of crazy stuff like that!
Glennak
ArboristSite Member
Yes the standard is hopeless when it comes to small trees but who would report on a tree with a 1" caliper? Anything small can be replaced or moved.
Corymbia
ArboristSite Operative
I guess that same argument could be raised about most trees up to somewhere between 8-12 inches. Unfortunately it is this sized tree that is frequently valued lowest in the design process but the size that adapts to development most readily.
Instead we seem to value the bigger older trees more highly and then try and squeeze and manipulate the design and the tree protection to retain trees that are often less than 50 years older than the smaller trees that are simply trashed.
By comparison if a boat sinks it is the young and the women that get first dibs on the life rafts. We understand the value of youth at that point but not when we design.
Instead we seem to value the bigger older trees more highly and then try and squeeze and manipulate the design and the tree protection to retain trees that are often less than 50 years older than the smaller trees that are simply trashed.
By comparison if a boat sinks it is the young and the women that get first dibs on the life rafts. We understand the value of youth at that point but not when we design.
Ekka
Addicted to ArboristSite
Here's a paragraph I recently wrote regarding this issue. Often I see large old half dead trees being saved whilst the vigorous good formed smaller ones get dozed.
Corymbia
ArboristSite Operative
Space for growth
I guess providing for the future needs depends on a lot of factors but we regularly see street trees growing in very confined space with roads on one side and condos on the other. Or worse still planted in the median strips in the middle of the road yet often seem to do very well and there are many youngish trees with 3 foot trunks.
The bigger problem is damage to the surrounding infrastructure and that is probably more due to poor workmanship, inadequate engineering and a lack of forethought.
I guess providing for the future needs depends on a lot of factors but we regularly see street trees growing in very confined space with roads on one side and condos on the other. Or worse still planted in the median strips in the middle of the road yet often seem to do very well and there are many youngish trees with 3 foot trunks.
The bigger problem is damage to the surrounding infrastructure and that is probably more due to poor workmanship, inadequate engineering and a lack of forethought.
Glennak
ArboristSite Member
Yes with structural soils this is not a problem. We had medium strip street trees in Williamstown (300-400mm diameter spotted gums) a few years ago that were dug all the way around 1m deep some with less than 1m root balls. (the engineer was told this would kill them but he thought he new better than the arborist). These trees got 100km/hr winds on this day and didn't move only one died. The soil they were planted in was structual soil formed accidentally when the road was made in the distant past. Very few roots were cut as they all went down 45deg or steeper. The whole lot were removed as no one would say they were safe and the company that planted new ones dug this structural soil up and put in some top soil to a depth of 1.5 m or so. I thought this would have caused the roots to run along the surface and destroy the road but all seems OK maybe they found the structural soil out side the top soil and have the best of both worlds? The residents lost an avenue of trees and had to pay for replacements at great expence and the idiot kept his job
Corymbia
ArboristSite Operative
Using grey matter
Another option is to engineer things so that they are not damaged by roots. My favourite house was built on screw piers. I used the concept to design a footpath that could not be lifted or broken by roots of a fig tree.
This picture shows the underneath of a brick house with concrete floors.
Now basements ... that is another set of problems altogether
Another option is to engineer things so that they are not damaged by roots. My favourite house was built on screw piers. I used the concept to design a footpath that could not be lifted or broken by roots of a fig tree.
This picture shows the underneath of a brick house with concrete floors.
Now basements ... that is another set of problems altogether
Ekka
Addicted to ArboristSite
Screw piers are very good. Also an engineering option for a clay soil with ground water, screw to spec torque and slab on top
Corymbia
ArboristSite Operative
Another strange standard
I agree. New AS draft standard (DR AS 2870) for residential slabs and footings is out for comment and they suggest getting rid of trees (or planting no trees and shrubs on most residential lots) rather than figuring out that at some stage they may get planted ... I say screw piers for all reactive soils ... screw the cost ... screw the footings rather than screwing with the trees.
Unfortunately the draft standard it is too big to attach as a pdf file. I'll see if I can split it into two
Here are some salient points ... no arboricultural representation on the committee.
References as follows
That's right ... not a single relevant arboricultural text. Perhaps engineers should go about and do their job properly (screw piers) and let us go about doing ours
I agree. New AS draft standard (DR AS 2870) for residential slabs and footings is out for comment and they suggest getting rid of trees (or planting no trees and shrubs on most residential lots) rather than figuring out that at some stage they may get planted ... I say screw piers for all reactive soils ... screw the cost ... screw the footings rather than screwing with the trees.
Unfortunately the draft standard it is too big to attach as a pdf file. I'll see if I can split it into two
Here are some salient points ... no arboricultural representation on the committee.
References as follows
That's right ... not a single relevant arboricultural text. Perhaps engineers should go about and do their job properly (screw piers) and let us go about doing ours
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Corymbia
ArboristSite Operative
A delightful little quote
From DR_AS_2870
To think all the time I thought roots were attracted by mini skirts. So to use some Australian vernacular "the tree root humps its swag and billy and goes looking for water"? For anyone who believes that I own the Sydney Harbour Bridge and have shares for sale
From DR_AS_2870
To think all the time I thought roots were attracted by mini skirts. So to use some Australian vernacular "the tree root humps its swag and billy and goes looking for water"? For anyone who believes that I own the Sydney Harbour Bridge and have shares for sale
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Glennak
ArboristSite Member
Yes Corymbia those engineers want a document so they can blame trees for even more problems. Many years ago I was told of a court case where a house in Carlton was cracked while digging to repair they discovered the house had no footings, The sewer was cracked under the house behind the crack, and there were a few tree roots there. It was a crack caused by lifting and the tree was trying its hardest to shrink the soil back and repair the problem but it got the blame.
It was a Melaleuca stypheloides which is high on the SA list of trees causing damage so council should have known better. And of cause no tree should be planted within 1.5 times its eventual height from any structure (ie no trees in suburban areas).
The SA list was compiled of a list of trees that caused damage in Adelaide no thought of how many of which type of trees are planted. So this list is a list of the most common trees planted in Adelaide and is used all over Australia as a list of trees that causes damages. Now a reference for this new standard.
It was a Melaleuca stypheloides which is high on the SA list of trees causing damage so council should have known better. And of cause no tree should be planted within 1.5 times its eventual height from any structure (ie no trees in suburban areas).
The SA list was compiled of a list of trees that caused damage in Adelaide no thought of how many of which type of trees are planted. So this list is a list of the most common trees planted in Adelaide and is used all over Australia as a list of trees that causes damages. Now a reference for this new standard.
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