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Technical Committee 101 - Session II /
Comité technique 101 - Session II
Gas hydrates(GH) are attracting an attention as a next
generation energy source but there are concerns that
dissociation of GH and exsolution of dissolved gas can reduce
the stability of seabed and may induce seafloor landslides. In
paper 2001, Yamashita et al. studied the effects of sample
disturbance due to the exsolution of dissolved gas in gas-
hydrate bearing deep lake bottom sediments in Lake Baikal. The
hand vane shear and cone penetration tests were performed for
core samples. The laboratory simulation of stress relief caused
by bringing samples to the surface was also performed by CO
2
gas. They showed that the effects of the sample disturbance
become larger and the strength is lower with the increase of gas
concentration.
The overburden materials in the coalfields of South East
Queensland are dominated by uncemented rocks, which rapidly
break down on excavation to extract coal and bulk up to a very
loose density. In paper 2782, Williams and Kho performed the
direct shear test and staged creep compression test on scalped
specimens under dry and wet conditions. They found that
wetting-up causes a substantial reduction in shear strength and
they quantifies the settlement and shear strength of uncemented
overburden materials excavated from open pit mining in the
coalfields.
Both the increased production in the copper mining industry and
the decrease of available space for the construction of tailing
deposits led to the design of dam having unprecedented height
above 250m. In paper 2800, Campana et al. performed the
drained and undrained triaxial tests on four different tailing
sands from copper mines located in Chile and Peru by applying
confining pressure up to 3 Mpa. The deformation moduli, static
and cyclic shear strength under drained and undrained
conditions, densities and fine contents have been obtained. It
was found that tailing sands have shear resistance and shear
modulus values greater than expected in natural sands.
2.3.
Soil Fabric and Particle Characteristics
Fabric is a collective term to describe the geometric
arrangement of grains and voids, and the distribution of inter-
particle contacts, and the influence of initial fabric on stress-
strain-strength responses received great attention and the
uniqueness of critical state has been great challenged (Negussey
and Islam, 1994). The particle characteristics such as particle
shape, surface roughness, and angularity can affect inter-particle
behaviors. Soils in nature often become hydrophobic (non-
wettable) due to organic pollutants, wild fire, oil spill, and the
difference in surface properties result in clear difference in flow
and mechanical behaviour even in macro scale (Kim et al.,
2010). Five papers are in this session and two of those are
studied by numerical simulations.
The strength parameters are very important to conduct the
stability analysis of earth structures but test results using
reconstituted specimens change easily depending on the sample
preparation method. In paper 2043, Kotaka et al. studied the
effects of initial water content during sample preparation on
undrained shear behaviour in gravel-mixed sand. They thought
that initial suction in the specimen produce various soil
structure and verified using numerical simulation by the SYS
Cam–clay model.
It was found that numerical simulation can
reproduce the various types of experimental shear behaviours of
the gravel-mixed sand derived from the different soil structures.
The Jacky’s K
o
equation is commonly used for the estimation of
K
o
but uncertain aspect still exists which value of friction angle
be adopted because the friction angle is a state-dependent
variable. In paper 2166, Lee et al. investigated the effects of
particle shape, surface roughness, and angularity on Jacky’s
’-
K
o
relation using normal sand, glass bead, and etched glass bead
in the oedometer type thin-wall K
o
test. They found that the
measured K
o
values for loose sand were close to the calculated
values using inter-particle friction angle whereas for dense sand,
critical state friction angle produced close match to the
measured one, implying that the application of peak friction
angle may underestimate K
o
value. For glass beads, calculated
K
o
values using critical state angle were in good agreement with
measured results in loose and dense states.
In paper 2178, Kim et al. studied the hydraulic and
geomechanical properties of non-wettable sands using
artificially synthesized hydrophobic sands. Sands without any
treatment and with chemical treatment were used. Fig 5 shows
water distribution in hydrophilic and hydrophobic sands
observed by an optical microscope. They found that surface
modification at nano-scale determine the spatial configuration
of water phase in pore space and its impact on fluid flow and
strength with varying degree of saturation prevails.
0.5 mm
0.5 mm
(a) Spatial distribution of water
in the wettable sands
(b) Spatial distribution of water
in the non-wettable sands
(c) Contact angle on the
wettable surface (~13
°
)
(d) Contact angle on the non-
wettable surface (~85
°
)
Fig. 5 Optical observations of water droplet formed on the weattable
and non-wettable samples in the micro scale from Kim et al., paper
2178.
Non-coaxial behavior of saturated sands, which refers to the
non-coincidence of the principal stress directions and the
principal plastic strain rate directions, were studied using
hollow cylinder apparatus in paper 2489. Yang et al. found that
the effective stress ratio has a significant effect on the non-
coaxiality of sand. The volumetric strain of sand induced by
cyclic rotation of principal stress axes was mainly contractive
and it occurs during first few cycles.
Critical state refers to a state where material undergoes
continued distortion at constant volume and constant stresses,
and the advances in modern laboratory tests have initiated the
discussion on the effect of fabric on critical state and thus its
uniqueness. In paper 2960, Yan and Zhang investigated the
fabric evolution of idealized two-dimensional assemblages
having different initial fabrics subject to numerical biaxial
shearing. It was found that a unique fabric of particle orientation
and void space is achieved at very large strains where the
stresses and volume of the assemblages are constant.
3. TREATED SOILS
Soft soils are prominently found in coastal regions and low land
areas where many important infrastructures are located. Various
admixtures are currently used to enhance the mechanical and
flow properties of clay and sand soils. Historically, Portland
cement and lime have been used for this purpose (Tim Newson,
2009). Recently, cement-mixed gravelly soil is used to construct
bridge abutments for high speed trains in Japan and lightweight
