Civil Engineering Reference
In-Depth Information
Figure 17.4
Probing tests (schematic).
continuously. Most static cone penetrometers have a sleeve behind the cone which
measures a frictional or shearing resistance. Some modern cones, known as piezocones,
also measure pore pressures generated at the tip or shoulder of the cone. Methods for
interpretation of static cone tests were given by Meigh (1987). Many of these depend
on empirical correlations between test observations and soil characteristics.
(b) Loading tests
In these tests an instrument loads the soil in a controlled manner and stresses and
deformations are observed. The ultimate load, when the deformations are large, is
related to the strength of the soil and the load-deformation behaviour is related to
soil stiffness. Plate loading tests illustrated in Fig. 17.5(a) may be carried out near the
ground surface or at the bottom of a borehole and measurements are made of the load
on the plate
F
and its settlement
. Simple analysis of plate tests are rather like the
methods used for design of foundations, discussed in Chapter 22.
The shear vane test, illustrated in Fig. 17.5(b), is used to measure the undrained
strength
s
u
. A vane with four blades is pushed into the ground from the surface or
from the bottom of a borehole. The vane is rotated and the torque
T
measured. At the
ultimate state the shear stress on the cylinder of soil containing the vane is given by
ρ
D
2
H
1
s
u
1
2
π
1
3
D
H
T
=
+
(17.1)
