[Strawbale] Re: SB Earthen Render Test fo Plasticity

Huff & Puff Construction huffnpuff at shoal....au
Fri Feb 21 03:32:57 CET 2003

G 'day Earthlings

I copy here a response to the tests conducted on the soil that Mike Faine
from the University of Western Sydney used in the load bearing tests on
earthen rendered straw bales.  As usual if any of you can adsvise me as to
what it means in layman's/builders terms I would be for ever grateful.

Colin Newtion is the other half of the Newtons of Queensland owners,
engineers and builders of the Newton House, Chris is the Queensland
Represenative of AUSBALE check them out, good stuff:


Kind regards
The Straw Wolf
61 2 6927 6027

"Good morning John,

A brief history of the what the Atterburg test for soil measures .

The liquid limit (L.L) - is the moisture content at which the soil stops
acting as a liquid,
and starts acting as a plastic solid. A soil with a very high moisture
content behaves as a liquid.
So when a shear stress is applied to the soil, it will continue to deform as
long as the load is applied
to it without failing. As the soil dries out, there will be a point when the
soil begins to resist the applied load.
At this point, if the load is removed, it is found that the soil has
experienced a permanent deformation: it
is acting as a plastic solid and not as a liquid.

The plastic limit (P.L) is the limit between plastic and brittle failure.
That is, as more moisture is driven out of
the soil, the soils resistance to large shearing stresses become possible.
Eventually the soil exhibits no
permanent deformation and simply fractures with no plastic deformation, i.e.
it acts a brittle solid.

The plasticity index (P.I) is the range of moisture content in which soil is
plastic: the finer the soil the
greater its plasticity index.

                                            P.I = L.L - P.L

Liquid Limit (for three samples) = 29.03%

Plastic limit = 21.76%

Plasticity Index (PI) = LL- PL is 7.29.

Based on the laboratory soil test results given above, the soils that you
gave to Mike are probably a
low plasticity organic clay (fine grained) or a low plasticity silt.

Any feed back on my interpretation of the results would be greatly
appreciated. Trust this information
proves helpful to you.

Colin Newton
Associate, Senior Engineer"

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