TRIAXIAL STRESS AND STRAIN - Introduction to Soft Soil Geotechnique: Content, Context and Application - page 97

TABLE 7.2 PRACTICAL VALUES FOR K 0
type of soil K 0 type of soil K 0

loose sand 0.4 - 0.6 normal clay 0.5 - 0.7

dense sand 0.3 - 0.5 over-consolidated clay 1.0 - 4.0

peat 0.1 - 0.6 compacted clay 0.7 - 2.0

In case of saturated soil, the local pore pressure u plays a role. It can be
incorporated by adding it to all effective stresses. In this respect, the coefficient of
earth pressure in terms of total stress becomes, by elaboration of equation (7.5a) for
c = 0 and an apparent total-stress earth pressure coefficient K p,total .

h = h '+u = K p v '+u = K p ( v ) + u (1 K p )

K p,total = h / v = K p + (1 K p ) u/ v (7.5c)

which reveals how the pore pressure is involved. For the active state a similar
analysis can be made.

A

total stress circle

B

c

1

2 ' 1 '

2

s ' s

u

c

pore pressure

B'

effective stress circle

A'

Figure 7.5 Effect of pore pressure for the Mohr-Coulomb model

D TRIAXIAL CELL
In a triaxial cell the stress and strain state have a cylindrical symmetry 35 , i.e. in
the horizontal direction they are invariant: 3 . The vertical and

horizontal directions are principal directions (no shear stress and deformation).
The total stress state may be expressed in terms of the deviator stress q and the
mean normal stress p , according to

2 = 3 and 2 =

q = 1 - 2 and p = ( 1 + 2 3 )/3 (7.8)

35 In the triaxial compression test the vertical direction is assigned to suffix 1, and
horizontal to suffix 2 or 3.