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