Designing Rock & Riprap Structures With Geotextiles

8/9/2019 Designing Rock & Riprap Structures With Geotextiles

http://slidepdf.com/reader/full/designing-rock-riprap-structures-with-geotextiles 1/12

Designing rock and rip-rapstructures with geotextiles



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



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



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.



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



■

■

■

■

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.



The design mechanism

Note: Individual product data sheets are available on request or they can be downloaded

rom www.geofabrics.com



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.



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



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.



JOINTS

Detailing



Skelton Grange Roadtourtonee s

United Kingdom

e :ax:

Email: [email protected] : www.geo a rics.com

Date post:	01-Jun-2018
Category:	Documents
Upload:	ghulam-rasool
View:	217 times
Download:	0 times

Designing Rock & Riprap Structures With Geotextiles

Documents