1588
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
modulus (G
0
) as well as damping ratio (D
min
) at small strains.
Moreover, the factors influence small-strain shear modulus,
shear modulus reduction curve and damping curve were
examined, with the particular attention paid to the mean
effective stress (p’). In addition to this, the impact of low and
very low shear strain (
) on soil behaviour was also included.
To achieve specified objects resonant column (RC) tests were
conducted.
2.
TEST MATERIAL AND EXPERIMENTAL
PROCEDURE
The material investigated belongs to a natural cohesive soil
formation in the Warsaw area, precisely from the region of the
express way S2. It is a clayey sand, clSa, (see Figure 1) with
index properties listed in the Table 1.
0
10
20
30
40
50
60
70
80
90
100
0,001
0,01
0,1
1
10
100
Clayey Sand
Particle size [mm]
Percentage passing [%]
100
0
10
20
30
40
50
60
70
80
90
Figure 1. Grain size distribution of test material.
The samples were taken from the depth of around 2.0m
selected carefully considering the uniformity of the soils
structure, its physical properties and its double-phase.
Table 1. Index parameters of specimens.
Parameter
Value
w
L
(%)
31.20
w
P
(%)
12.62
I
P
(%)
18.58
G
S
(-)
2.68
w (%)
12.82
(kg/m
3
)
2230
where
w
L
is the liquid limit,
w
P
is the plastic limit,
I
P
is the
plastic index,
G
S
is the specific gravity,
w
is the water content,
is the mass density.
The details of the experimental program can be found in
another article of the authors (Sas et al. 2012), which relates to
the similar topic. Nevertheless, some important phases of the
experiments should be outlined here as well. Before the proper
dynamic measurements were performed, test material required
correct preparation. The initial stages of the study, consisting in
modelling of the natural conditions of the samples in field,
included: flushing of the equipment, saturation, control of
Skempton’s B parameter and consolidation. Undisturbed sample
was set up in the cell, then saturated by back pressure methods,
which was increased accordingly to ensure the saturation of the
sample until the Skemption’s B value was higher than 0,90.
When full saturation was achieved, consolidation process
started. The soil was consolidated to predetermined isotropic
stress. In every test, an isotropic effective confining pressure
was applied in steps, namely 45, 90, 135, 180, 225, 270 and
315kPa. The experiments were stopped with the mean effective
stress equal to 315kPa, due to the equipment’s limitations.
During the consolidation phase, the volume change and the
axial deformation of the specimen were measured. Moreover,
the void ratio of the specimens was updated during
consolidation at each loading stage. In order to excite the
electromagnetic field and induce a wave propagating through
the examined material, the corresponding coil voltage values
were placed, from the value 0.1V up to 1.0V, with a step of
0.1V. Then finally, RC tests were performed.
3.
EXPERIMENTAL TECHNIQUE
The testing procedure applied by the authors is the resonant
column technique. This method allow to determine shear
modulus, shear damping, rod modulus (usually referred to as
Young’s modulus) and rod damping for solid cylindrical
specimens of soil in the undisturbed and remolded conditions by
vibrations. The vibration of the material may be superposed on
a controlled ambient state of stress in the specimen. The
apparatus and sample are commonly enclosed in a triaxial
chamber and subjected to an all-around pressure, sometimes as
well as an axial load. Additionally, the specimen can be
subjected to another controlled conditions, such as pore-water
pressure, temperature or degree of saturation. The resonant
column technique is considered nondestructive if the strain
amplitude of excitation is less than 10
-4
rad. At that time many
measurements may be done on the same sample but with
various states of ambient stress (ASTM 2000).
Figure 2. Schematic illustration of the resonant column implemented in
the authors researches (GDS 2010).
The resonant column device successfully used in this work
were manufactured by British company GDS Instruments Ltd.
The apparatus is presented in details in the papers (Sas and
Gabryś 2012, Gabryś et al. 2013). The scheme of the equipment
is shown in Figure 2.
