Geotechnical Engineering

DHARM

148 GEOTECHNICAL ENGINEERING

γsat =

Ge

e w

+

+

F

HG

I

1 KJ

.γ

=

(.. )

.

268 072

172

+

× 9.81 kN/m^3 = 19.39 kN/m^3

Total pressure at a depth of 16 m : σ = (3 × 16.51 + 13 × 19.39) = 301.6 kN/m^2.

Neutral pressure at this depth : u = 13 × 9.81 = 127.5 kN/m^2

∴ Effective stress at 16 m below the ground level :

σ = (σ – u) = (301.6 – 127.5)

= 174.1 kN/m^2.

3m 49.53

16 m

264.16264.16 127.5 174.1

37.44

(a) Total stress (b) Neutral pressure (c) Effective stress

All pressures

are in kN/m^2

49.53

Fig. 5.22 Pressure diagrams (Example 5.1)
Example 5.2. A saturated sand layer over a clay stratum is 5 m in depth. The water is 1.5 m
below ground level. If the bulk density of saturated sand is 17.66 kN/m^3 , calculate the effective
and neutral pressure on the top of the clay layer. (S.V.U.—B.E., (R.R.)—Nov., 1969)
The conditions given are shown in Fig. 5.23.

1.5 m Sand-dry (assumed)

WT

3.5 mSand saturated

Clay

1.51.5 mm

3.53.5 mm

63.1063.10

17.64

18.93 18.93

34.34 46.40

All pressuresare in

kN/m^2

(a) Total pressure (b) Neutral pressure

(c) Effective pressure

Fig. 5.23 Soil profile (Example 5.2) Fig. 5.24 Pressure diagrams

Let us, in the absence of data, assume that the sand above the water table is dry. Bulk

density of saturated sand,

γsat = 17.66 kN/m^3.

γsat =

Ge

e w

+

+

F

HG

I

(^1) KJ
γ