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8/2/2019 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).
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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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Page 3 of8
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 .
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Mitchell, P. W "Collapsing Soils". Presentation to Geomechanics Chapter / Footings
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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Page 4 of8
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).
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Mitchell, P. W "Collapsing Soils". Presentation to Geomechanics Chapter / Footings
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.
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Mitchell, P. W "Collapsing Soils". Presentation to Geomechanics Chapter / Footings
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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Page 6 of8
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).
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Mitchell, P. W "Collapsing Soils". Presentation to Geomechanics Chapter / Footings
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.
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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.