Environmental Engineering Reference
In-Depth Information
Camkometer
Description:
The Camkometer is a self-boring pressuremeter developed in the early 1970s
by Cambridge University (Clough and Denby, 1980). The 80-mm-diameter device is cov-
ered by a rubber membrane that incorporates two very small cells for pore-pressure meas-
urements. It is drilled into position and the membranes expanded; transducers permit the
pressure response to be converted into electrical impulses. An effective stress-strain curve
is plotted from the data.
Applicability:
It is used primarily in soft clays and sands for
in situ
measurements of
shear modulus, shear strength, pore-water pressure, and lateral stress
K
o
. Formerly, values
for
K
o
were obtained only by empirical methods or laboratory tests.
Advantages over conventional pressuremeter:
Lateral stress is measured directly because
the instrument is self-boring and stress relief is not permitted. Records are obtained from
precise electrical impulses, whereas conventional pressuremeters record total volume
changes of hydraulic fluid within the flexible membrane and furnish only average values.
Disadvantages:
As with all pressuremeters, soil anisotropy is not accounted for. Smear
caused by drilling in soft clays reduces the true permeability and affects the pore-pressure
measurements. To reduce drainage effects, undrained tests are performed at high strain rates.
Penetration Tests (SPT, CPT, and DMT)
General
SPT, CPT and FDT are discussed in
section 3.4.5.
Intercorrelations between SPT and CPT
have been correlated with various soil properties.
CPT Test Correlations
Estimating E
s
:
Values for the elastic modulus can be obtained from correlations with the
cone resistance
q
c
and the normalized cone resistance
g
t
, and the shear wave velocity meas-
ured in the CPT containing an accelerometer (
Section 2.3.4)
(Robertson, 2000).
Consolidation parameters:
c
h
and
c
v
, and OCR can be estimated from CPTU tests (Section
2.3.4) (Robertson, 2000).
Flat Dilatometer Test (DMT)
Consolidation parameters
c
h
and OCR can be estimated from DMT tests (Section 3.4.5).
Plate-Load Test (ASTM D1196)
Purposes
Vertical modulus of subgrade reaction
k
sv
is obtained from plate-load tests. Results are used
occasionally for estimating settlements in sands. In direct application, however, it must be
considered that the depth of the stressed zone is usually much smaller than the zone that
will be stressed by a larger footing, and the results will not necessarily be representative.
This constraint is overcome by performing tests at various depths to stress the entire zone to
be stressed by the footing or by performing full-scale load tests. Plate-load tests are not per-
formed on clay soils for settlement measurement because of long-term consolidation effects.
Procedure
A 12- or 30-in.-diameter plate is jack-loaded against a reaction to twice the design load,
and the plate deflection measured under each load increment. The test setup is shown in
