Designing Rock & Riprap Structures With Geotextiles
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Transcript of Designing Rock & Riprap Structures With Geotextiles
8/9/2019 Designing Rock & Riprap Structures With Geotextiles
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Designing rock and rip-rapstructures with geotextiles
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Sea Palling, Norfolk: 12-16t armour placed directly on GP99 (HP17) overlying a sandy sub-layer.
a r cs ter separators ave een es gne to prov e susta nepermea ty w st st ma nta n ng structura sta ty. ey prov eexcellent filtering efficiency, a high level of stress absorption and are highlyresistant to abrasion.
QUALITY IN MANUFACTURING
a rics imite is one o t e s ea ing manu acturers o geotexti es. ince its ormation in ,over a mi ion square metres ave een ep oye a ong coast ines an watercourses eneat roc armour
and prefabricated concrete units. Their use is due to the quality of the products, their cost effectiveness
and the comprehensive help provided to design engineers and contractors at every stage of a project.
QUALITY IN SERVICE
e pro ucts ave een esigne an are manu acture to meet t e most eman ing
performance levels. Using a modern computer-controlled plant, all products are manufactured in an
ISO9001 environment and sampled/tested to the appropriate standards.
Designing rock and rip-rapstructures with geotextiles
GEOfabrics Limited is one of the UK’s leading manufacturers of
geotextiles. Since its formation in 1993, over a million squaremetres have been deployed along coastlines and watercourses
beneath rock armour and prefabricated concrete units.
ARTIFICIAL ISLANDS
BEACHES
BRIDGE ABUTMENTS
CLIFFS
DAMS
FLOOD BUNDS
HARBOURS
LAGOONS, LAKES & RESERVOIRS
LAND RECLAMATION
OFFSHORE WIND GENERATORS
OUTFALLS
ROCK GROYNES
SCOUR CONTROL
SUBMERGED BREAKWATERS
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progressively larger grain size, were used to
prevent t is type o erosion.
would exclude them from consideration.
The solutions
HP/HPS needlepunched, non-woven geotextiles provide all
of the required functionality at the levels demanded
for revetment applications.
Graduated-stone filter layer Geotextile filter layer
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PERMEABILITY
FILTRATION
For a cohesive soil, O90 < 10 x d50.
ot t e permea i ity an tration ru es app y
actors o sa ety to a ow or re uctions in t ese
properties by soil particles clogging within the
geotextile. A filter will be regularly flushed if
the system is subject to reversing flows, thus
minimising any re uction in tering e ciency.
PUNCTURE RESISTANCE
The geotextile must be able to withstand
puncture loads imposed during installation and
service. e roc weig t, its angu arity an t e
rop eig t a contri ute to puncture oa .
is can e urt er intensi e i ue care is
not taken during installation. Ideally, it will also
possess isotropic (square) tensile properties in
or er to sprea oa consistent y in a irections.
EXTENSIBILITY
THICKNESS
Selecting the mostappropriate filter/separator
Classic filter rules state that each layer of a filter system must
be more permeable than the layer beneath. Similar rules
developed for geotextiles suggest a coefficient of permeability
10 to 100 times greater than that of the filtered soil.
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Water flow normal to the plane Closely linked to permeability. Very important in
ynamic, ig - ow app ications.
Pore size Defines the opening size of a geotextile and its
a i ity to trap partic es an prevent t eir passage.
Minimum tensile extension Placing rock is potentially the greatest cause
o amage an t e extensi i ity o a geotexti e isimportant to avoi oca ise amage.
Static puncture resistance (CBR) Simulates the in-situ punching effect of rock,
norma to a geotexti e, uring service.
Coefficient of permeability Related to the thickness of a geotextile.
xpresses water ow as a g va ue a owing
comparison wit soi va ues .
ens e strengt imu ates a geotexti es a i ity to e an e
on site using eavy excavators. t is common
or operators to sprea an unro t e geotexti e
using the bucket of an excavator.
us -t roug sp acement imu ates iaxia strain cause y roc p ace
on the geotextile, and the capacity to resist
localised damage.
one rop n icates t e a i ity o a geotexti e to
accommodate dynamic puncture during
roc p acement.
Thickness under load Ensures that there is a water path beneath the
stone allowing dissipation of pore water pressure.
Thickness reduction ratio for 2kPa The ability of a geotextile to resist compression
and 200kPa under varying loads.
t ansea, ast ng o or s re: t roc roppe onto over y ng san y c ay.
Selecting the mostappropriate filter/separator
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The design mechanism
Soil type Filtration d50 (mm) Permeability k s (m/s)
ayey si t . x -9
andy silt 0.02 1 x 10-7
Fine sand 0.30 1 x10 5
oarse san . x 4
ixe san s ing e . x 3
a e
rovisiona y se ect an gra e ase upon its permea i ity e.g. i soi permea i ity is 5m s
then the grade must have a permeability >10-4m/s.
ec t at t e gra e s 0< 50 o t e su soi . is requirement is satis e y most o t e
pro ucts.
5 Check that the selected grade can withstand installation loading without puncture.
For armour <100kg: HPS3 can be selected.
or armour < g: , w t a e ng ayer o stone, may e cons ere at t e
scret on o t e eng neer.
Brean, Somerset: GP60 (HPS6), bedding layer,
500mm thick 40-200mm stone, two layers
- . t armour, : s ope.
Chyandour, Cornwall: GP60 (HPS6), 500mm
hick, 150mm bedding stone & 8-12t armour
stoney su - ayer.
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The design mechanism
Note: Individual product data sheets are available on request or they can be downloaded
rom www.geofabrics.com
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PERMEABILITY:
FILTRATION:
DAMAGE RESISTANCE:
EXTENSIBILITY:
Worked example
orngum a anage etreat, ast ng o or s re: eneat precast concrete
units to protect a high-pressure gas main from the effects of scour & also beneath armour to
protect a g t ouse.
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Specification considerations
British Standard (BS) and European (EN) index tests are
available to enable engineers to compare one geotextile
with another
PERFORMANCE SPECIFICATION
e geotexti e to e use as a ter separator eneat t e roc armour s a e a non-woven a ric
manu acture y nee epunc ing virgin, stap e res o po ypropy ene incorporating a minimum o
1% by weight active carbon black. Geotextiles manufactured from fibres of more than one polymer
will not be permitted.
e geotexti e s a ave t e o owing properties:
Test description Approved Units Typical
test method value
tatic puncture strengt
us -t roug ispacement mm
Tensile strength EN ISO 10319 kN/m 74
Tensile extension EN ISO 10319 % 88
one rop per oration o e iameter mm .
Thickness @2kPa EN ISO 964-1 mm 6.8
Thickness reduction for pressure increase BS EN 964 % 25
rom a to a
Apparent pore size - 90% finer [O90] EN ISO 12956 μm <69
Water flow normal to the plane of the EN ISO 11058 l/s/m 28
geotextile @50mm head
Coefficient of permeability EN ISO 11058 m/s 3.8 x 10-3
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e o owing e nitions s a appy w en consi ering test resu ts:
A set of test results shall be those results derived from specimens cut from one sample.
e ean va ue or any set o test resu ts s a e t e arit metic mean o t at set o resu ts.
The haracteristic value is the value below which not more than 5% of the test results may be
expected to fall. This represents the value at 1.64 standard deviations below the mean value.
mo e spec cat on n or ormat s ava a e on request or t can e own oa e
rom www.geo a r cs.com
Specification considerations
Felixstowe Ferry, Suffolk: 2m x 1m pre-fabricated bags (HPS7) filled with sand & gravel & installed
e ow t e water ne at t e toe o a r prap revetment. e so t ags were use to com at scour
to prevent damage to boats at low tide.
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JOINTS
Detailing
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Skelton Grange Roadtourtonee s
United Kingdom
e :ax:
Email: [email protected] : www.geo a rics.com