What is the aim?
Mobilisable Strength Design (MSD)
Example 1: circular (square) footing on clay
Plastic deformation mechanism
Stresses and strains for circular footing
Design procedure
Relation to a triaxial test
Validation by non-linear FEA
Soil profile around the representative element
Soil displacements by FEA
MSD versus FEA
More FE validation: BRICK model Many soil profiles and realistic stress-strain curves have been checked, all with the same high quality of fit.
Why does it work so well?
Field validation: Kinnegar test Lehane (2003) Stiff square pad footing treated here as a circle of diameter 2. 26 m
Kinnegar soil profile
Normalised stress-strain behaviour
MSD predictions for Kinnegar Also predicts Jardine’s Bothkennar test rather well, and matches Arup’s observations of large rafts on London Clay. But most field tests are not accompanied by the necessary stress-strain data from a shallow sample. This is a lesson well taught by MSD methodology.
Example 2: ground movements around braced excavations
Stability calculations
Incremental displacements
Plastic deformation mechanism
Wavelength L: free-end condition
Wavelength L: fixed-end condition
Wavelength L: intermediate end condition
Estimation of the mobilised shear strength
Assumption of a mobilisation ratio
Calculation procedure for bulging movements
Surface settlement
Effect of cantilever movement
Plastic deformation mechanism for cantilever retaining walls
Permissible stress field
Mobilised strength versus excavation depth for cantilever retaining walls
Calculation procedure for cantilever retaining walls
Whittle’s data of Boston Blue Clay
FE validation comparing with Hashash and Whittle (1996)
Case history: Boston Post Office Square Garage (Whittle et al. 1993)
Measured and predicted displacements
Measured and predicted settlements
Braced excavation in Singapore soft clay
Soil profile at Moe Building
Stress-strain response of Singapore Soft Marine Clay (after Wong and Broms 1989)
Measured and predicted displacements
Measured and predicted displacements
Conclusions
The future
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