Hydraulic Structures: Fourth Edition

Equation (2.4) may be divided by ∆ 1 and rearranged as

B ̄B 1 (1 A) (^1) . (2.5)
ParameterB ̄is an overall coefficient of particular relevance in the predic-
tion of porewater pressures generated in the course of embankment dam
construction. It is obtained from tests in which the sample is subjected to
stress changes corresponding to those anticipated within the prototype
embankment.
2.3.2 Shear strength
Theshear strengthof a soil is defined as the maximum resistance to shear-
ing stresses which can be mobilized. When this is exceeded failure occurs,
usually along identifiable failure surfaces. Shear strength is usually quanti-
fied through two component parameters:

1. apparent cohesion, c, essentially arising from the complex electrical
   forces binding clay-size particles together;


2. angle of shearing resistance, , developed by interparticle frictional
   resistance and particle interlocking.

The shear strength of a soil at a point on a particular plane can be
expressed as a linear function of the normal stress, n, at that same point
using the Mohr–Coulomb failure criterion:

fcntan (2.6a)

wherefis the shear strength at failure.

∆ 3



∆ 1

∆uw



∆ 1

ENGINEERING CHARACTERISTICS OF SOILS 49

Fig. 2.4 Principal stress increments and porewater pressures