Collapsing Soils 15Aug05

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Mitchell, P. W "Collapsing Soils". Presentation to Geomechanics Chapter / Footings

Australia Division), 15A 2005--~~~~== ---=--------------------------

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Definition of collapsing soils.

Collapse settlement when soil under footing is

wetted. Sources of water include rainfall,

garden watering and leaking services.

Example of house on collapsing soil in upper

Yorke Peninsula, damaged by leaking

underground water service. Note the

magnitude of comer settlement (photo courtesy

of J. Goldfinch).

Example of house on collapsing soil in upper

Yorke Peninsula, damaged by leaking

underground water service. Note the

magnitude of comer settlement (photo courtesy

of J. Goldfinch).



Mitchell, P. W . "Collapsing Soils", Presentation to Geomechanics Chapter / Footings

Group, Engineers Australia (SA Division), 15August 2005

Slide 11 Bulk:·1 Fo.dors Earthworks bulking factors for varying soil

Volu~< M ~"e. /",' ~ %% s .... " " r e I types (after C. Fitzhardinge). Note high values

for collapsing soils.

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Geological background.

Dune sand development. An aeolian soil type.

Note sand grains in a saltatorial condition on

leeward side, leading to a loose soil structure.

Cross section of dune sand deposit at Port

Augusta.

Measurement of collapse settlement of a Port

Augusta soil in the oedometer (after

D. Cameron). Note magnitude of collapse

settlement even at low pressures .




Group, Engineers Australia (SA Division), 15A 2005--~---------------------------

Slide 16 Construction of a large institutional building at

Port Augusta. Single storey brick veneer

construction. Stiffened raft footing with main

sub-beams 650 mm deep gridded

longitudinally and transversely.

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Slide 20 After J. Selby 1982

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Broken underground internal waste services

noted after construction caused settlement of

the order of 70 mm, as shown by the gap

between base of floor slab and soil. Leak is

located under the re-entrant corner of the slab

on the right-hand side of the photo (Photo

courtesy P. Gunson).

The person's foot is on the edge of the footing

beam on the other side of the room from the

leak. (Photo courtesy P. Gunson).

Despite high collapse settlement, footings

performed well with structural distortion

confined to ceiling and wall cracking as shown.

However, this example illustrates the need to

incorporate flexible service connections for

structures on collapsing soils (Photo courtesy

P. Gunson).

Wind blown dune sand on Adelaide's coast

line and calcareous silt deposited adjacent to

Para Fault block (after J. Selby).




Group, Engineers Australia (SA Div 15A 2005--~---------------------------

Slide 21 A typical soil profile containing the potentially

collapsing aeolian calcareous silt.

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Train derailment due to collapsing nature of

calcareous silt, causing a railway cutting to

slump onto rails.

Slumping of the calcareous silt cutting onto

railway lines. Note presence of stormwater

discharge at top of slope.

Waikerie Water Treatment Plant. Piles were

required to overcome effect of a Riverland

collapsing soil.

Broken service connection at Waikerie Water

Treatment Plant caused by the collapsing

Riverland soil. Illustrates the need for flexible

service connections.




Group, E Australia (SA Divisi 15 2005--~--------------------------

Slide 26 "APPVLP p,£~u", Example of oedometer results of a Riverland

~ f I ' S " " ~ ' D collapsing soil from Loxton (after

i D. Stapledon).

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Example of problem buildings on Riverland

soils (provided by M.S. Humphris and

P. Gunson).

Distribution of Poor aka Formation in Adelaide

area (after Sheard & Bowman). An example of

an outwash stream deposit that may have a

loose structure that is potentially collapsing.

Damage to a school building on Pooraka

Formation (photo provided by S.Wawryk).

Settlement of about 100 mm due to a broken

waste service.

Roadway in the SA Mid-North taken in April,

located on the Pooraka Formation (photo

provided by K. Lee).




Engineers Australia Division), 15A 2005

Slide 31 Roadway in the SA Mid-North taken in April,

located on the Pooraka Formation (photo

provided by K. Lee).

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Roadway in the SA Mid-North taken in

August, located on the Pooraka Formation

(photo provided by K. Lee).

Example of potentially collapsing biotic soil

caused by animal activity.

Example of potentially collapsing biotic soil

caused by decay of gum tree roots.

Example of collapsing soil caused by human

activity. Note the shadowing effect of coarse

particles leading to extensive voids, and hence

a potentially collapsing soil profile.



M itc hell, P . W

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Example of collapsing soil caused by human

activity. Poorly compacted backfill of a pit of

a former underground storage tank.

Engineering solutions.

Conclusions.

Collapsing Soils 15Aug05

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