Developing confidence in critical state soil mechanics
5. Modified Cam Clay (MCC)
Mike Jefferies, PEng
Dr. Dawn Shuttle, PEng
January, 2015
Why Modified Cam Clay (MCC) ?
February 11, 2016 2
∆εvp
∆ε q
p
Modified vs Original Cam Clay
OCC MCC
Flowrule
Yield Surface
Hardening
February 11, 2016 3
η
M=
2 pc
p−1
η
M=1 − ln
p
pc
η−= MDp
&pc
pc
=1+ e
λ −κ&εv
p
Dp =
M2 − η2
η2
&pc
pc
=1+ e
λ −κ&εv
p
Stress dilatancy (= flowrule)
February 11, 2016 4
Mod Cam ClayOriginal Cam Clay
Nova
Rowe
M
5
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
-1 -0.5 0 0.5 1 1.5
Dp
ηη ηη
D662D667
jjjjqjq
jjjjvjvp
jGqq
KppD
3/)()(
/)()(
111,1,
111,1,
−+−+
−+−+
−−−
−−−=
εε
εε
Stress dilatancy of Erksak sand
Implementing MCC
� Make copy of the OCC worksheet
� Rename it MCC
� Change
� Spacing ratio to 2
� Dp equation to MCC dilation
� η equation to MCC yield surface
� MCC is “pathological” on dilation
� Must kludge the spreadsheet
� Switch to incrementing volumetric strain for first ~0.5% strain
� Thereafter revert to incrementing shear strain
February 11, 2016 6
7
Implementing MCC by modifying MCC sheet
8
Implementing MCC by modifying MCC sheet
Over to you…
February 11, 2016 9
Computed soil response
February 11, 2016 10
Original Cam ClayModified Cam Clay
Mod Cam Clay
� “Improved theory” simply shows lack of understanding
� Work dissipation is unclear / unreasonable
� Mathematically “pathological” to implement
� Does not fit any known soil data
February 11, 2016 11
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