Geotechnical Engineering

DHARM

SHEARING STRENGTH OF SOILS 285

Figure 8.26 shows that stress paths for a consolidated undrained test on a normally
consolidated clay.

t

o

Failure envelope

F

AB

TSP

ss,

TSSP

ESP

Fig. 8.26 Stress paths for consolidated undrained test
on a normally consolidated clay
Figure 8.27 shows the stress paths for a consolidated undrained test on an over consoli-
dated clay.

t

o

Failure envelope

F

AB

TSP

ss,

TSSP

Fig. 8.27 Stress paths for consolidated undrained test
on an overconsolidated clay
[Note : TSSP to the right of ESP indicates of positive excess pore pressure; TSSP to the left of
ESP indicates negative excess pore pressure. Both coincide for zero excess pore pressure].

Stress-path approach enables the engineer to predict and monitor the shear strength
mobilized at any stage of loading/unloading in order to ensure the stability of foundation soil.

8.11 SHEARING CHARACTERISTICS OF SANDS

The shearing strength in sand may be said to consists of two parts, the internal frictional
resistance between grains, which is a combination of rolling and sliding friction and another
part known as ‘interlocking’. Interlocking,which means locking of one particle by the adjacent
ones, resisting movements, contributes a large portion of the shearing strength in dense sands,
while it does not occur in loose sands. The Mohr strength theory is not invalidated by the
occurrence of interlocking. The Mohr envelopes merely show large ordinates and steeper slopes
for dense soils than for loose ones.

The angle of internal friction is a measure of the resistance of the soil to sliding along a
plane. This varies with the density of packing, characterised by density index, particle shape