30
Coastal Engineering: Theory and Practice
Most wildly used formula for permeability after Fair and Hatch [1933]
,
K3
k — ---y
(2.20)
where,
K =
1
(2.21)
where K = spécifie permeability, k = coefficient of permeability, n — porosity, A = packing factor (taking a value of about 5), b = sand shape factor
ranging between 6.0 to 7.7 for spherical grains to angular grains respectively, P = percentage of sand held between two adjacent sieves, and Dgm
is the géométrie mean of the mesh sizes of the two sieves.
n - Porosity =
volume of voids in a sample of sédiment
Total volume of the sample
2.12 Bulk Creep
Continuous yielding of soit particles in un-drained stress conditions is
termed as creep or plastic flow. Attributable to the repeated loading effect,
creep exhibits a long term depreciation/weakening in the shear strength
of the sédiments. Recurring load reversais are susceptible to occur during
earthquakes and with much lesser impact during its exposure to continuous
wave action. Cyclic stress level, periodicity, frequency and duration, and
sédiment types are the factors on which the effect of repeated loading will
dépend.
The pore water pressure will tend to increase along with the stress, when
a recurring load is applied on soils with poor drainage and fine sands in a
confined space. This leads to réduction in shear strength of the residue over
time and catastrophic events like earthquake and stormy wave increases the
fluid pressure which in turn results in further réduction of shear strength.
For huge land mass, this réduction in shear strength influenced by pore
water pressure may lead to liquéfaction.
2.13 Sédiment Motion
2.13.1 General
The motion of sédiment such as érosion or déposition on the seabed is
normally termed as fluvial process. Erosion can happen either when the flow
Coastal Engineering: Theory and Practice
Most wildly used formula for permeability after Fair and Hatch [1933]
,
K3
k — ---y
(2.20)
where,
K =
1
(2.21)
where K = spécifie permeability, k = coefficient of permeability, n — porosity, A = packing factor (taking a value of about 5), b = sand shape factor
ranging between 6.0 to 7.7 for spherical grains to angular grains respectively, P = percentage of sand held between two adjacent sieves, and Dgm
is the géométrie mean of the mesh sizes of the two sieves.
n - Porosity =
volume of voids in a sample of sédiment
Total volume of the sample
2.12 Bulk Creep
Continuous yielding of soit particles in un-drained stress conditions is
termed as creep or plastic flow. Attributable to the repeated loading effect,
creep exhibits a long term depreciation/weakening in the shear strength
of the sédiments. Recurring load reversais are susceptible to occur during
earthquakes and with much lesser impact during its exposure to continuous
wave action. Cyclic stress level, periodicity, frequency and duration, and
sédiment types are the factors on which the effect of repeated loading will
dépend.
The pore water pressure will tend to increase along with the stress, when
a recurring load is applied on soils with poor drainage and fine sands in a
confined space. This leads to réduction in shear strength of the residue over
time and catastrophic events like earthquake and stormy wave increases the
fluid pressure which in turn results in further réduction of shear strength.
For huge land mass, this réduction in shear strength influenced by pore
water pressure may lead to liquéfaction.
2.13 Sédiment Motion
2.13.1 General
The motion of sédiment such as érosion or déposition on the seabed is
normally termed as fluvial process. Erosion can happen either when the flow