Developing confidence in critical state soil … confidence in critical state soil mechanics 5....
Transcript of Developing confidence in critical state soil … confidence in critical state soil mechanics 5....
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