Geotechnical Engineering

DHARM

870 GEOTECHNICAL ENGINEERING

Unit weight of soil = 16 kN/m^3

Safe bearing capacity under static loading conditions = 200 kN/m^2

Coefficient of elastic uniform compression of soil = 5 × 10^4 kN/m^3

Velocity of Tup before Impact

v = α

2 gW pah

W

t

t

(.)+

Take α = 0.65

Substituting Wt = 50 kN, p = 900 kN/m^2 , a = 0.2 m^2 , and h = 1 m

v = 065

2 9 81 50 900 0 2 1

50

.

×+××.( .)

m/s

= 6.2 m/s

Preliminary Calculation of Weight of Foundation and Base Area

na = W

W

a

t

=^1000

50

= 20

W

W

f

t

= nf = 8(1 + e)v – na

= 8(1 + 0.5) × 6.2 – 20

= 54.4

∴ Wf = 54.4 × 50 = 2720 kN

This is the minimum weight of foundation required (including that of backfill).

A

W

a

ev

t f qa

==

+

=

20 1 20 1 0 5+×6 2

200

() (.).

= 0.93

∴ Minimum base area, A = 0.93 × 50 = 46.5 m^2

Size of Foundation

The outline of the foundation block proposed, based on the preliminary values of weight and
base area, is shown in Fig. 20.35.

Volume of concrete adopted

= 7.5 × 6.5 × 1.5 + 4.5 × 2 × 0.5 × 1.0 + 2 × 4 × 0.5 × 10 = 91.50 m^3

Volume of backfill used

2 × 1.0 × 6.5 × 2.0 + 5.5 × 1.25 × 2.0 × 2.0 = 53.5 m^3

Total weight of foundation and backfill = 91.5 × 24 + 53.5 × 16 = 3,052 kN

Actual base area provided = 7.5 × 6.5 = 48.75 m^2

Amplitudes of Motion

spring constant of soil

k 1 = Cu′A 1 = 3 CuA 1 , taking the correction factor as 3.

∴ k 1 = 3 × 15 × 10^4 × 48.75 = 73.2 × 10^5 kN/m

spring constant of pad