Geotechnical Engineering

DHARM

394 GEOTECHNICAL ENGINEERING

Standard Penetration Test

This test which is popularly used for cohesionless soils is described in detail in chapter

18. The result, which is in the form of the number of blows required for causing a standard
    penetration under specified standard conditions, can be used to evaluate immediate settle-
    ment in a cohesionless soil (De Beer and Martens, 1957). This method has been developed for
    use with the Dutch Cone Penetrometer but can be adapted for the standard penetration test.
    The immediate settlement, Si, is given by:

Si =

H

Cs e

.log

σσ

σ

0

0

F +

HG

I

KJ

∆

...(Eq. 11.1)

where H = thickness of the layer getting compressed,

σ 0 = effective overburden pressure at the centre of the layer before any excavation or

application of load,

∆σ = vertical stress increment at the centre of the layer,

and Cs = compressibility constant, given by:

Cs = 1.5

Cr

σ 0

...(Eq. 11.2)

Cr being the static cone resistance (in kN/m^2 ), and

σ 0 being the effective overburden pressure at the point tested.

The value of Cr obtained from the Dutch Cone penetration test must be correlated to the

recorded number of blows, N, obtained from the standard penetration test. Its variation ap-

pears to be wide. According to Meigh and Nixon (1961), Cr ranged from 430 N (kN/m^2 ) to 1930

N (kN/m^2 ). However, Cr is more commonly taken as 400 N (kN/m^2 ) as proposed by Meyerhof

(1956).

0 200 400 600 800 1000

25

50

Settlement mm

N=50¢

25

(^1330)
10
5
Pressure kN/m^2
Fig. 11.2 Relationship between pressure and settlement of a 305 mm square plate, for differ-
ent values of N′, in cohesionless soils (After Thornburn, 1963)