Free Training Video Soils

Arbistik

Got an e-mail just now. This company has just started putting up free training videos, first ones are an introduction to soils. Looked OK to me. Obviously it's a marketing gimick but if it's free it's free.

Here is the link, two videos

Soil Horizons - Soil Structure

Soil Texture

Eric Frei

In the second video about 0.55seconds in there is reference made that sand compacts well.

I have often disputed this, try to compact sand and see what happens? Do we ever have to decompact sandy soils around a tree? Nope.

Also this forum is predominantly Australian, and as such we do not have the same soil codes as USA or UK.

The reference all Australians should be using is the following book which is seen to be the "standard":-

Australian Soil and Land Survey Field Handbook (3rd edition) CSIRO Publishing 2009

Particle sizes shown in the video is inconsistent with what we do on this continent.

We use the international standard which only has 5 components as follows:-

1. Clay, 0.0002 to 0.002
2. Silt, 0.002 to 0.02
3. Sand (fine), 0.02 to 0.25
4. Sand (coarse), 0.25 to 2.0
5. Gravel, 2.0 to 20
6. Stones, 20 to 2000

Further online information can be found using this google search (for Aussies).

australian soil classification - Google Search

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Arbistik

Hi Eric
Hope you area keeping well. Just to contradict you. Sandy soils do compact easily but there is rarely a need to decompact them because, 1, they have only weak structure so plant roots are not impeaded by the compaction; and 2, they are usually free draining so don't so anaerobic. However there area some sandy silts and sandy clays that compact easily, and because therefore area small particles between the big particles can go anaerobic.

Arbistik

Actually, I would like to clarify further. Relatively speaking sandy soils compact more easily than clay soils but it still requires a great deal of work to compact sand. Compaction is only a reduction in bulk density, and the description of soil structure, and changes in soil structure is more than just a reduction in bulk density. Quite a complex area of soil science and not one for generalisations or sweeping statements. So appologies if previous posting was a bit sweeping.

Eric Frei

Define "compact" then.

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Darrell Mcleod

Maybe their terminology is different to ours

You are right sand does not compact like crushed rock but if contained as it is in the ground it is trustworthy as it will not subside as will some clays – sand is more stable and not reactive - expand and contract if wet or dry

In sandy areas of Melbourne and no doubt all over the world some older buildings were built with no foundations like concrete strip footings, slabs etc because the sand base was considered to be stable and compacted – not reactive like some clays or say a crushed rock that must be compacted to be stable

Darrell Mcleod

Wacked down with a big roller, vibrating plate or for trees - pedestrian traffic, bobcats, machinery etc

Eric Frei

So why is it that you should never drive heavy machinery over wet clay soils around trees yet wet sand nothing much happens?

I thought compaction had something to do with the pressing of pores that removed air and water holding capacity. Clay compacts rather well as the particles are flat and slippery, where as sand is granular.

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Arbistik

Hi all it was another unseasonably warm day in the but again today. 20 degrees! I emailed the people who made the video to see if they would add an Australian context in future.With regard to Erics latest posting, he has sort of answered the question himself. Compaction is about how close a soil is to its minimum bulk density. At minimum bulk density a soil can nolonger be compacted. You can pass weights over sand because they are usually already close to minimum bulk density. You can usually do the same with dry clays because they area resiliant to compaction, i.e. they have a strong structure. If you western clear soil it starts to become plastic and will deform. This can lead to compaction. Perversely with clay soils, when they become saturated they become resiliant to compaction because the water fills the gaps and holds the particles apart, but of course they can liquify a puddle. Stand tend to compact more when dry than when western.

Arbistik

Sorry just seen predictive text errors.
But. =uk
stand. = sandy
western. = wet

Eric Frei

Well the answer is not apparent to me.

Minimum vs maximum bulk density, I assume that compaction is when it is at maximum bulk density, in other words when a cubic metre weighs the most.

Here's my source to compare wet and dry weight of clay and sand per m3.

Mass, Weight, Density or Specific Gravity of Bulk Materials

Clay, dry excavated 1089
Clay, wet excavated 1826
Clay, compacted 1746

Sand, wet 1922
Sand, wet, packed 2082
Sand, dry 1602
Sand, loose 1442
Sand, rammed 1682
Sand, water filled 1922



Now logically it appears to me that wet sand is heavier. Compare clay (compacted) to clay dry and wet. Dry clay goes from 1089 to 1746 when compacted and wet clay goes from 1826 to 1746.

Lets look at sand, similarly. Dry sand goes from 1602 to 1682 when rammed, not a lot of change compared to clay. Wet sand goes from 1922 to 1682 when rammed, it actually gets a lot lighter.

I dare say that when both wet sand or clay get compacted or rammed it is the water content that is pushed out, what is seen with sand is it is relatively stable compared to clay and the reason why it is used for paving etc is that it drains, wet or dry it is fairly stable and doesn't lose it's bearing capacity like wet clay does.

I think personally that anyone who has driven on beaches or had to deal with soil compaction issues knows that sand is a darn great medium compared to clay and silt. On many websites, mainly geo and construction I have seen the net littered with the statement that sand compacts well but I do not buy it nor have I reproduced it. It's particles may organise well, like spread and vibrate well into place but real compaction in the context we discuss of soil for tree roots etc it is not an issue.

On a sandy site where I was a project arborist truck after truck drove over the sand, rain or shine, didn't matter, I could always go to the most sunken area and easily insert a screwdriver.

It's like the net is littered with the statement that rainforest trees have large buttress roots due to poor shallow soils. It's everywhere. And I disagree with that also.

Why rainforest species have buttress roots

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Arbistik

Eric

First of all, I may have said minimum when I meant maxixmum i.e. the greatest weight of soil per volume. Bulk density is dry soil weight per volume of soil.

Sorry about this that's just the Sunday brain.

The thing you say about the practicality of compaction in clay against sand is true, but this is about the porosity and mechanical impedence of the compacted material rather than the ease with which the material is compacted.

A fully compacted sand should in theory be lighter than a fully compacted clay, because the amount of air-space (porosity) in the sand should be greater than that in the clay. This is due to the vastly larger particle size in the sand compared to the clay.