Geotechnical Engineering

DHARM

294 GEOTECHNICAL ENGINEERING

t

Shearing strength

Normal pressure

Effective stress envelopeTotal stress envelope

Total stress circles

Effective stress circles

f¢cu

O fcu s

Fig. 8.39 Consolidated undrained tests in triaxial compression on remoulded,
saturated, and normally consolidated clay (consolidated under different
cell pressures and sheared undrained under the same cell pressures)
The corresponding equation for a normally consolidated clay is:
s = σ tan φcu ...(Eq. 8.55)
Here, σc is the consolidation pressure and σ is the applied normal pressure.
The envelope is generally curved up to the preconsolidation pressure and shows a cohe-
sion intercept. The corresponding equations for shear strength in terms of effective stresses
are written with primes.

cC cu1

u1

O s

t

c cu2

Cu2

O s

t

cCu3cu3

O s

t

O

Envelope for normally

consolidated clay

Envelope for

overconsolidated clay

sp sc 1 sc

cCu 3

cCu 2

cCu 1

cCu 0

Apparent cohesion sc 2 sc 3

(a) Failure envelope for the first series

with consolidation pressure

(b) Failure envelope for the second series

with consolidation pressuresc 2

(c) Failure envelope for the third series with

consolidation pressuresc 3

(d) Variation of apparent cohesion

with consolidation pressure

Consolidation pressure

cCu

Fig. 8.40 Consolidated undrained tests in triaxial compression on remoulded, saturated,

and normally consolidated clay consolidated under a particular cell pressure

and sheared undrained under cell pressures different from consolidated pressures