brosur tensar ground stabilisation with geogrid biaxial

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Tensar International Limited

New Wellington Street

Blackburn BB2 4PJ

United Kingdom

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Contact Tensar International or your local distributor to receive further

literature covering Tensar products and applications.

Also available on request are product specifications, installation guides

and specification notes.

The complete range of Tensar literature consists of:

• Tensar Geosynthetics in Civil Engineering A guide to the products

and their applications

• Ground Stabilisation Reinforcing unbound layers

in roads and trafficked areas

• Steep Slopes Constructing embankments

with steep slopes

• Retaining Walls Constructing retaining walls in reinforced soil

• Foundations over Piles Constructing over weak ground

without settlement

• Basal Reinforcement Constructing embankments over

weak ground

• Railways Reinforcing ballast under railway track

• Asphalt Pavements Reinforcing asphalt layers

in roads and trafficked areas

• Erosion Controlling erosion on soil and rock slopes

Tensar is a registered trade mark.

©Copyright Tensar International Limited

Printed February 2003 Issue 4, 79010035

The information provided verbally, or in this document or as a Free Application

Suggestion is of an illustrative nature and is supplied without charge. It does not

form any contract or intended contract with the user. No liability in negligence will

arise from the construction of any project based on such information or material.

Final determination of the suitability of any information or material for the use

contemplated and the manner of use is the sole responsibility of the user and the

user must assume all risk and liability in connection therewith.

Tensar geogrids are manufactured under tightly controlled

conditions. The quality assurance procedures covering design and

application and the manufacturing process have been certified by

the British Standards Institution as a Registered Firm in

accordance with BS EN ISO 9001:2000

Q05288

GroundStabilisation

Reinforcing unbound layers in

roads and trafficked areas

Soft sensitive subgrades.

The interlocking between the geogrid and the aggregates particles limits lateral movement when dynamic loading is applied.

Tensar geogrids reduce cost and save timein road construction

Using Tensar biaxial geogrids in road

construction can solve or reduce the

problems described above. Designers

can optimise their pavement design,

especially when conditions are

challenging. Contractors can reduce

cost and save time. Including Tensar

biaxial geogrids in a pavement:

• Reduces granular thickness by up to

40%, thereby conserving valuable

aggregate resources and the

environment

• Reduces excavation, disturbance

and subsequent disposal of

subgrade soils

• Improves fill compaction

• Increases design life and improves

life-cycle management

• Helps control differential settlement

over variable soils and spans voids

or soft spots

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Tensar biaxial geogrids work by interlockingwith aggregates

Tensar biaxial geogrids can solve

pavement problems because they

interlock very efficiently with

granular materials. When granular

particles are compacted over these

grids, they partially penetrate and

project through the apertures to

create a strong and positive interlock.

The Tensar manufacturing process

produces a unique grid structure,

consisting of full strength junctions

and stiff ribs, which present a thick

square leading edge to the

aggregate. This allows the aggregate

particles to get a good “grip” on the

geogrid, and results in effective

mechanical interlock. Interlock helps

prevent lateral movement and

dilation of aggregate particles, so

that a very high effective angle of

Road construction problemsConstruction of road pavements is

expensive and time consuming.

Difficult access conditions can become

impossible, especially in wet weather.

Soft sensitive subgrades frequently

require large thicknesses of aggregate,

much of which is lost due to deep

rutting. Aggregates are expensive and

scarce, and their extraction damages

the environment. They must be

transported, placed and compacted.

shearing resistance is mobilised.

Vertical load applied through

aggregate particles above the grid

can generate tensile resistance in the

ribs with very small deflection. The

combination of these features

ensures that, in Tensar geogrid

reinforced granular layers:

• Tensile load in the grid is generated

at very small deflections of an

applied vertical load

• Reinforcement benefit is localised

and can be generated within the

loaded area

This mechanism is also referred to as

“confinement”, because interlock

effectively immobilises and confines

the aggregate particles.

Very difficult access.

Wet weather conditions.

Building a pavement over Tensar geogrids (UK).

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The interlock mechanism.

The unique cross-sectional shape of Tensar ribs provides bearing points for aggregate particles and works like the triangular rack supporting a pyramid of snooker balls.

applied force

Road building aggregates are becoming scarce

and expensive - they must be transported,

placed and compacted.

Tensar. The valueengineeredsolution

In Tensar you’ll find a partner

with the experience and

flexibility to respond to your

project requirements. From

design to completion, we’ll

make sure you always benefit

from a practical, cost-

effective solution to your

specific need.

Tensar SS-G composite.

Installing Tensar biaxial geogrids using an overlap between

adjacent rolls.

4

5

This is a common question when

considering using a geogrid in a road

pavement. The answer is: NO.

Geotextiles cannot interlock with

aggregate particles, so they cannot

generate the same very efficient

interaction and confinement of the

aggregate. Geotextiles are normally

used as separators only, but if they

are designed to reinforce a pavement

by developing tension, then they

must form a “tensioned membrane”

which requires large deformations,

and fixed wheel paths. It is not

suitable for use in the design of

normal surfaced or permanent

pavements. The difference is

illustrated on the diagrams below.

Do geotexiles work in the same way? Designing pavements with Tensar geogrid

Installation of Tensar biaxial grids

This difference in performance is

emphasised by the rut profiles shown

above, measured as part of a detailed

pavement trial carried out by TRL

(Transport Research Laboratory, UK).

These are cross-sections of the trial

pavement, showing both the top of

the sub-base (320 mm thick) and the

top of the subgrade (CBR = 1.5%),

before and after completion of

trafficking. After 5000 passes a deep

rut has formed in the geotextile

reinforced sub-base with a

considerable amount of heave, and

a similar rut has developed at the top

of the subgrade. This results in

remoulding and softening of the

subgrade. For the Tensar SS30 section,

after 10,000 passes the rut in the sub-

base is much smaller with little heave,

and the rut in the subgrade is

negligible with no heave (mainly

consolidation settlement of the clay

subsoil). The strength of the woven

geotextile is slightly higher than that

of Tensar SS30, yet performance is

quite different.

TENSAR GEOGRID REINFORCED

PAVEMENT

• Interlock stiffens the aggregate layer

• Load spread is increased

• Aggregate transfers the load

• Performance is improved

TENSIONED MEMBRANE REINFORCED

PAVEMENT

• Geotextile is anchored at edges

• Load is transferred to geotextile

• Geotextile and subgrade deform

• Negligible performance gain

Designing with Tensar geogrids results in reduced layer thickness.

Designs are carried out using sophisticated software.

Adjacent rolls may be joined together using HDPE braid.

Correct method of placement and spreading of granular

material is important.

Design of road pavements depends on:

• Subgrade strength (CBR)

• The properties of the fill/aggregates

• The number and loading of the axles

• The maximum rut depth or bearing capacity

Tensar International provides a full

design service and has developed

sophisticated computer software based

on a number of different national

pavement design guidelines.

The reinforcing benefit of Tensar

geogrids is incorporated in the design

methods, using data from independent

pavement tests and trafficking trials.

These methods of designing reinforced

pavements are reliable and have been in

use for many years. Detailed test and

trial data are given in “Properties and

Performance of Tensar Biaxial Geogrids”,

available from Tensar International.

Tensar SS biaxial geogrids are

manufactured in three grades (SS20,

SS30 and SS40) with apertures suited to

typical sub-base gradings (75mm

maximum particle size). Tensar SSLA

biaxial geogrids have larger apertures

making them suitable for aggregates of

larger particle size. Two grades are

available SSLA20 and SSLA30. Choice of

grade depends principally on subgrade

condition and strength, but axle load

and service life are also taken into

account. In addition, Tensar SS-G and

SSLA-G are geocomposite products

comprising a Tensar biaxial geogrid

laminated to a non-woven geotextile.

The products are particularly suited for

use with uniformly sized aggregates.

Documents giving detailed

recommendations for choice of grid type

are available from Tensar International.

No responsibility is accepted by

Tensar International for any project

which does not involve the use of

Tensar biaxial geogrids installed

pursuant to Tensar International’s

full design service.

No special plant, equipment or

techniques are required to install

Tensar biaxial geogrids. Site formation

should be prepared in the normal way,

and any large obstructions, tree stumps

and other protrusions should be

removed. On very soft wet subgrades,

biaxial geogrid is often used as a

method of getting access onto the site,

to allow initial layers of fill to be placed.

Rolls of Tensar biaxial geogrid are light

and stiff, and do not require a core.

They can easily be lifted and rolled out

by two workers. Special lifting frames

and cranes are not required. They are

normally held in position by small piles

of fill.

Adjacent rolls are usually overlapped

to give continuity of the reinforcing

function. The required overlap is

between 300 and 600mm depending on

the condition of the underlying material.

The larger overlaps are required over

softer subgrades, whereas minimum

overlap may be used over competent

subgrades or for second layers.

An alternative to a full overlap is to use a

smaller overlap of two to three apertures,

then join the rolls together using

HDPE braid.

It is important that fill is placed correctly

for maximum benefit. It should be tipped

onto stockpiles on top of the existing

placed material, then a mechanical

excavator or bulldozer should lift and

cascade the material onto the grid.

If the material is pushed forwards from a

stockpile, then it can create a bow wave,

and over soft soils it will tend to push the

grid into the subgrade soils. This will

diminish the interlocking effect.

If the fill grading requires a geotextile

separator as well as geogrid

reinforcement, both functions can be

served by a single Tensar SS-G composite.

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Tensar SS geogrid properties

Versatility of Tensar biaxial geogrids

Road widening, Auckland (New Zealand).

Temporary access road across peat swamp,

Machap (Malaysia).

Construction of major highway (Oman).

New taxiway at Adelaide Airport (Australia).

Wharf area (Latvia).

6

Heavy duty pavements may require two or three geogrid layers.

AIRPORT PAVEMENTS

Loadings on airport pavements are

very high, and frequently lead to

multi-layer reinforced construction.

The US Army Corps of Engineers

carried out some special pavement

trials in the early 1990’s to examine

the benefit of geogrid reinforcement

in aircraft pavements. These well

documented comparative trials

showed that Tensar biaxial geogrids

were the only materials used which

gave a significant improvement in

performance.

HEAVY DUTY HANDLING AREAS

Container yards, logging areas and

fabrication sites frequently require

vehicles with very high track or axle

loads, and the pavements are often

unsurfaced. Tensar biaxial geogrids

have been used in many such

applications, frequently with multiple

layer construction. Performance of

these types of pavement in service has

shown that reinforcement improves

traffickability and reduces

maintenance and regrading.

WHARF AND PORT AREAS

Wharf and port areas are subject to

heavy loads from cranes and transport

vehicles, as well as from the goods

being handled. The subgrades are

frequently poor marginal soils or fills.

Tensar biaxial geogrids improve

bearing capacity and help to create

high quality pavements. Since the early 1980’s several hundred

million square metres of Tensar biaxial

geogrids have been used in tens of

thousands of projects. They have been

used in most countries in the world,

under a wide variety of climates and

soil conditions, and frequently they

have been used to solve difficult

design or construction problems.

ACCESS OVER VERY SOFT SUBGRADE

Some subgrades are so soft or

waterlogged that the main problem is

to get access to place fill or sub-base

material. These include very soft mud,

peat and tailings deposits. Tensar

biaxial geogrids act like a “snow-

shoe”, providing immediate support

to workers and the initial fill layers.

In addition, the interlocking effect

allows some compaction to be

achieved, even in the fill directly

above the soft subgrade.

TEMPORARY ACCESS ROADS

Tensar biaxial geogrids are excellent for

helping to build temporary access

roads, especially when the subgrade is

soft, trucks are heavy and good fill is

scarce. The wide rolls are ideal for a

single track road to carry typical

construction vehicles, and they are

easily transported and deployed.

MAJOR HIGHWAYS

Major highways require large

investment, and the cost of pavement

building materials is normally a

significant proportion. Also, costing of

this type of pavement must take into

account future maintenance, in terms

of overlays and possible reconstruction.

Using Tensar biaxial geogrids can

reduce the cost of capital investment

and future maintenance.

ROAD WIDENING

Widening existing roads is common

due to increasing traffic and

requirements for higher standards.

Generally the existing road must be

kept open, and there are frequently

services already in place. Using Tensar

geogrids can reduce the thickness of

the new pavement, thereby

minimising disruption. This can also

help avoid relocation of existing

services if they are shallow. Linking

the geogrid into the existing

pavement can help minimise

differential settlement between the

old and new sections.

Heavy DutyPavementsWhen axle or vehicle loads become

very heavy, number of axle passes

becomes very great or the subgrade is

very soft, granular layer thickness

increases to an extent where more

than one layer of biaxial geogrid is

required to maintain continuity of the

reinforcing function. In such cases

two or possibly three layers of

geogrid are required.

Getting access over very soft subgrade.

Property Units Tensar geogrid

SS20* SS30* SS40* SS2 SSLA20* SSLA30*

Polymer (1) PP PP PP PP PP PP

Minimum carbon black (2) % 2 2 2 2 2 2

Roll width m 4.0 & 3.8 4.0 & 3.8 4.0 & 3.8 4.0 3.8 3.8

Roll length m 50 50 30 50 50 50

Unit weight kg/m2 0.22 0.33 0.53 0.29 0.22 0.32

Roll weight kg 46 & 44 67 & 64 65 & 62 60 43 65

Dimensions

AL mm 39 39 33 28 65 65

AT mm 39 39 33 40 65 65

WLR mm 2.2 2.3 2.2 3.0 4.0 4.0

WTR mm 2.4 2.8 2.5 3.0 4.0 4.0

tJ mm 4.1 5.0 5.8 3.8 4.4 7.0

tLR mm 1.1 2.2 2.2 1.2 0.8 1.7

tTR mm 0.8 1.3 1.4 0.9 0.8 1.5

Rib shape Rectangular with square edges

Quality Control Strength (longitudinal)

Tult(3) kN/m 20.0 30.0 40.0 17.5 20.0 30.0

Load at 2% strain (3) kN/m 7.0 10.5 14.0 7.0 7.0 11.0


Approx strain at Tult % 11.0 11.0 11.0 12.0 10.0 9.0

Quality Control Strength (transverse)

Tult (3) kN/m 20.0 30.0 40.0 31.5 20.0 30.0



Approx strain at Tult % 10.0 10.0 10.0 10.0 10.0 9.0

Junction strength as % of QC strength (4)

Minimum junction strength % 95 95 95 90 95 95

*SS-G & SSLA-G

Geocomposite properties

All of the geogrids marked * are also available as

a geocomposite. The geocomposite comprises

the geogrid heat bonded to a geotextile

separator. The properties of the geotextile are

given in the following table.

Geotextile component

Puncture resistance (CBR) (5) N >1500

Effective opening size (6) µm 125

Permeability (7) m/s 0.135

Unit weight (8) kg/m2 0.16

(1) PP denotes polypropylene.

(2) Carbon black inhibits attack by UV light. Determined in accordance with BS 2782:Part 4: Method 452B:1993.

(3) Determined in accordance with BS EN ISO 10319:1996 and as a lower 95% confidence limit in accordance

with ISO 2602:1980 (BS 2846:Part 2:1981).

(4) Determined in accordance with GRI GG2-87 and expressed as a percentage of the quality control strength.

(5) Determined in accordance with BS EN ISO 12236:1996.

(6) Mean value of O90 determined in accordance with wet sieving test to BS EN ISO 12596:1999.

(7) Mean value expressed as velocity index VIH50 determined in accordance with BS EN ISO 11058:1999.

(8) Mean value determined in accordance with BS EN 965:1995.

(9) All quoted dimensions and values are typical unless stated otherwise.

Roll Length(Longitudinal)

Roll Width(Transverse)

Ribs

AL

tLR

tJ tTR

Junctions ATWLR

WTR