Pile Design and Construction Practice, Fifth edition

Ground investigations, contracts and testing 505

the increase in diameter of the cylinder over an increasing range of cell pressures. Apparatus
developed for this purpose includes the Ménard pressuremeter(6.22), the Camkometer(11.5), or
Cambridge Self-boring pressuremeter (SBP), and the High Pressure Dilatometer (HPD)(11.6).
The Ménard pressuremeter is operated in boreholes ranging in diameter from 34 to 80 mm.
Three independent rubber cells are mounted, one above the other, in the probe to apply a
uniform pressure to the soil. The central cell is filled with water pressurized pneumatically,
and the upper and lower cells are expanded by air. The measured co-ordinates of pressure
and displacement can be inserted directly into design equations using empirical correlations
based on a large data bank from standard tests. The Cambridge Insitu SBP, developed from
the simpler Camkometer, is a self-boring pressuremeter with a rotating drilling bit mounted
at the base of the probe so that a plug of soil is removed and replaced with the instrument
in order to preserve the state of stress in the soil. The cell is expanded by compressed air and
the radial deformation is measured by electrical gauges attached to feelers within the probe.
The device is particularly useful in a very soft or loose soil where disturbance of the soil
around a pre-drilled hole could be detrimental to accurate measurements. The Cambridge
Insitu HPD, 73/75 or 93/95 mm diameter, for use in stiff soils or weak rocks is placed in a
good quality pre-drilled cored borehole and inflated using either hydraulic oil or compressed
gas to a maximum pressure of 300 bar. Displacement is measured on three axes by six full

Figure 11.4Relationship between Dynamic Cone Penetration Tests nand Standard Penetration

Test N(after Cearns and McKenzie(11.4)) (a) in sands and gravels (b) in chalk.

40

35

30

25

20

15

10

5 0 6 5 4 3 2 1 0

036912

SPT N (blows/300 mm)

15 18 20

0 5 10 15 20 25 30 35 40

SPT N (blows/300 mm)

45 50 55 60 65 70 75

DCP

n (blows/100 mm)

DCP

n (blows/100 mm)

n^5

0.31

N

n 5 0.25N

(a)

(b)