USE OF GEOSYNTHTICS IN PAVEMENTS

G L Sivakumar Babu Professor, Department of Civil Engineering

Associate faculty in CiSTUP and CST Indian Institute of Science

Bangalore 560012 Acknowledgments to Mrs. Lekshmi Nair and Sudheer Prabhu

Department of Science and Technology, New Delhi Field studies: CRRI, New Delhi and KRRDA, Bangalore

1

Back ground

Considerable investments being made in the construction of roads and about 35000 km of length will be built as per the five year plan proposals.

Many roads that have already been constructed need rehabilitation and maintenance measures. Pavement construction involves large quantity of aggregates for sub base and base layers.

Though the mechanistic-empirical design of pavements was introduced in the recent years, the evaluation of response of aggregates under repeated/ cyclic loading is desirable to obtain resilient modulus, elastic deformation and plastic deformation which control fatigue and rutting failures.

Geosynthetics are proven to be highly beneficial in constructing roads because they reduce the material costs, facilitate rapid installation, reduced maintenance costs and improve overall traffic performance. 2

Geosynthetics are “geopolymers”mixed with additives into a formulation

Manufactured into a particular type of geosynthetic material and serve different functions such as separation, filtration, drainage, reinforcement and moisture barrier

The development of ‘apparent cohesion’ in geocells

Mean stress

Shear stress

Apparent Cohesion

Failure envelope with geocell

Failure envelope with no geocell

Damages due to lack of drainage and confinement

There is a need for proper design methods in this connection to address the above factors

Pavement failures

Fatigue and Rutting

Use of geosynthetics results in significant savings, improved

performance and very good serviceability in both short term

and long term

Geosynthetics have made it possible to construct roads and

pavements in seemingly difficult situations such as marshy

stretches, soft and organic deposits and in expansive soil

areas

Functions of Geosynthetics in Roadways

1. Acts as a separator to prevent two dissimilar

materials (subgrade soils and aggregates) from

intermixing. Geotextiles and geogrids perform this

function by preventing penetration of the aggregate

into the subgrade (localized bearing failures)

2. Soft subgrade soils are most susceptible to

disturbance during construction activities such as

clearing, grubbing, and initial aggregate placement.

Geosynthetics can help minimize subgrade

disturbance and prevent loss of aggregate during

construction

.

3. The system performance may also be influenced

by secondary functions of filtration, drainage, and

reinforcement. The geotextile acts as a filter to

prevent fines from migrating up into the aggregate

due to high pore water pressures induced by

dynamic wheel loads

4. It also acts as a drain, allowing the excess pore

pressures to dissipate through the geotextile and

the subgrade soils to gain strength through

consolidation and improve with time

Functions of Geosynthetics (contd..)

Concept of Geotextile Separation

1. Lateral restrainment of the base and

subgrade through friction and interlock between the

aggregate, soil and the geosynthetic

2. Increase the system bearing capacity by

forcing the potential bearing capacity failure surface

to develop along alternate, higher shear strength

surfaces

3. Membrane support of the wheel loads

Mechanisms

Reinforcement Functions

Benefits

Reducing the intensity of stress on the subgrade

Preventing subgrade fines from pumping

Preventing contamination of base materials

Reducing the depth of excavation

Reducing the thickness of aggregate required for stabilization of subgrade

(S-Separation, F-Filtration, R- Reinforcement)

S F R

Benefits

Reducing disturbance of subgrade during construction

Allowing an increase in strength over time

Reducing differential settlement in roadway

and in transition areas from cut to fill

Reducing maintenance and extending the life of the pavement

(S-Separation, F-Filtration, R-Reinforcement)

S F R

Subgrade Conditions in which

Geosynthetics are useful • Poor soils

(USCS: SC, CL, CH, ML, MH, OL, OH, and PT)

(AASHTO: A-5, A-6, A-7-5, and A-7-6)

• Low undrained shear strength

f = Cu < 90ka

CBR<3 {Note: CBR as determined with

ASTMD 4429 Bearing Ratio of Soils in Place}

MR 30MPa

• High water table

• High sensitivity

Summary of Recommendations

Effectiveness of Geosynthetics as a function of subgrade strength

Fatigue Cracking Principles

Crack initiation depends on tensile strain

Crack propagation depends on tensile stress

Interaction of asphalt layer and foundation

Rutting Mechanism for Asphalt Layer

Permanent shear strains near surface

High temperatures

Heavy wheel loads

High traffic volume

Foundation Rutting

Lack of adequate load spreading

Granular layer or soil

Problems of water

Overview of presentation

Background

Materials and Methods

Effect Of Geocell-reinforcement In Granular Bases Under Repeated Loading

Numerical Modeling of Granular Bases Under Repeated Loading

Field studies

Conclusions

23

Objectives

The effectiveness of Geocell reinforcement in the base layer is studied

in terms of permanent deformation, resilient deformation, resilient

modulus at “targeted number of cycles”.

The power term ‘n’ has been calibrated to convert the permanent

deformations at higher loading into permanent deformation due to

standard axle loading

Rut depth reduction studies are carried out in order to compare the

results of geocell reinforced section with unreinforced section

Numerical analysis of geocell reinforced base section was conducted to

calibrate the permanent deformation model

Field studies are conducted to examine the effectiveness

24

Pavement response for different loading conditions (Wermeister et

al.2001)

Effect of Geogrid and Geocell reinforcement on Resilient Modulus (AASTHO T-307) (Elastic and Elastic Shakedown Range)

Geosynthetics increases the resilient modulus of the material.

Geocell provides higher confinement which results in the reduction of resilient deformation and subsequent increase in resilient modulus.

Geogrids employ both membrane effect as well as interlocking effect and reduces the resilient deformations effectively compared to the unreinforced sections.

26

Effect of Geogrid and Geocell reinforcement on Resilient Modulus (Plastic Shakedown and Incremental Collapse Range)

27

Permanent Strains (100 kPa confining pressure)

• The experiments were carried out for confining pressures of 100kPa and 150kPa

• The loading was applied on the sample without rest period

Permanent strain vs no of cycles for reinforced and unreinforced samples at deviaotic stresses of

(a) 125 kPa (b) 250kPa

The permanent strain of the geogrid reinforced and geocell reinforced samples were almost equal.

Permanent Strains (150 kPa confining pressure)

Permanent strain vs no of cycles for reinforced and unreinforced samples at deviaotic

stresses of (a) 125kPa (b) 250kPa

Materials And Methods

Experiments were carried out on unreinforced, Geocell reinforced aggregate systems to evaluate their performance under static and repeated loading conditions.

Static and repeated plate load tests

Two kinds of materials were used in the plate load tests to represent the subgrade and base layer of pavements

• Subgrade Soil - sand

• Base layer - Aggregate

29

Material Properties Sand Subgrade

Parameter Value

D10 0.2mm

D30 0.4mm

D60 0.48mm

Coefficient of Curvature(Cc) 1.67

Coefficient of uniformity(Cu) 2.4

Relative density 55%

CBR (soaked) 7%

CBR (unsoaked) 10% 30

Material Properties Base Aggregate

Properties Values

CBR (soaked) 78.45%

CBR(unsoaked) 115%

Aggregate Impact Value 24%

Aggregate Crushing Value 24%

31

Material Properties – Geocell

The geocell used in the present

study had a material composition of

High Density Polyethylene (HDPE)

with a density of 0.935 – 0.965 g/cc.

Height 100 mm

Thickness 1.3mm

Cell Size 330 × 180mm

Tensile strength 21 kN/m

Tensile strain at break (%) 93.20 %

Properties of Geocell

32

Experimental program

The experimental program was conducted on a iron tank of size 0.9 X 0.9 X 0.6 m

Hydraulic actuator of capacity 50kN was used to load the base material

A circular steel plate of 150 mm diameter was used to simulate the wheel load

The target load for the static test was 30kN

Each repeated plate load test was run for

3000 loading cycles by varying the loading

from 20kN, 25kN to 30kN after every

1000 cycles.

33

Experimental program

Five plate load tests on unreinforced and Geocell reinforced granular base were conducted.

For the construction of the test section, sand was used as sub-grade material and its height was maintained as 200 mm. The thickness of the granular base was varied between 300mm to 150 mm.

The Geocell reinforcement was placed on the top most potion of the base layer with a covering of 20mm.

Haversine loading was applied to the circular plate

at a frequency of 1Hz.

The deformation results procured from the LVDT’s

were later resolved to permanent and

resilient deformations.

34

Effect of Number of pockets of Geocell Static Loading

The number of pockets

affected the

performance of the

reinforced base layer

tremendously as it

increased the load

carrying capacity of

the base section.

The load is getting

distributed beyond the

width of the 4 cells of

Geocell thus resulting

in performance similar

to that of unreinforced

section.

35

Experimental Results on Repeated loading

36

Total deformation generated with number of cycles

Permanent Deformation Studies

With the increase in the pressure sudden increase in deformations were observed for unreinforced section.

As the loading cycles progressed, the rate of deformation decreased and almost becomes constant in the case of reinforced sections compared to the unreinforced section.

37

Permanent Deformation Studies

The reinforced sections reduce the

deformations by more than 70%

compared to the unreinforced section

having same thickness.

The rate of deformation did not attain a

constant value in the case of unreinforced

section and is much higher than the

reinforced section.

The shake down behavior was clearly

visible in case of Geocell reinforced

section

38

The geocell reinforced sections had

lower resilient deformations

compared to the unreinforced

section.

Even the geocell reinforced section

with lowest thickness of base

section, i.e. 150mm provided high

resistance to the deformations

compared to unreinforced section

of much higher thickness.

As the thickness of the base layer

increases, the resilient deformation

decreased.

As the applied pressure is increased

after each 1000 cycles, the resilient

deformation also increased

Resilient Deformation Studies

Resilient Deformation Studies

The resilient deformation of both reinforced and unreinforced section shows a fluctuating behavior throughout the cycles creating an uncertainty to the data.

All experimental data is correlated up to a certain limit known as correlation distance or scale of fluctuation, beyond which they will be treated as uncorrelated

Coefficient of variation and Correlation distance

40

2

e

1.96

hrN

Section Mean

(mm)

Standard

of deviation

COV

(%)

Scale of

fluctuation

(cycles)

300mm

unreinforced 1.0154 0.0899 11.48 3

300 mm

reinforced 0.7156 0.0822 8.521 17

150mm

reinforced 0.8792 0.0835 9.104 9

Resilient Modulus

The resilient modulus of the base section was back calculated from the resilient

deformations of the plate load studies.

𝛿 : Resilient deformation of a particular cycle

B: Diameter of the loading plate

q: pressure applied on the top

𝛿 =𝐵𝐼𝑞(1−𝜈2)

𝐸

• The geocell reinforced section of least

base layer thickness, 150mm has resilient

modulus higher compared to the

unreinforced section of base layer

thickness 300mm.

• As the number of cycles increases, the

resilient modulus values also increases

which is in accordance with the shake

down theory of pavements.

41

Equivalent Axle Load Factor

The loading used on the base material was much higher compared to the

standard tyre pressure of 550kPa.

To convert the permanent deformations due to higher loading cycles into

equivalent number of standard axle loading by using the concept of

Equivalent Axle Load Factor (EALF).

The value of n can be found out from the regression analysis by plotting

EALF vs P’/550 as EALF would be known from the experiment for each

loading of P’/550.

Sun et al. (2015) concluded that the value of power term n as 1.9 for

unreinforced section.

'

550

' 550

n

N PEALF

N

42

Equivalent Axle Load Factor

• Repeated plate load tests were carried out on 200mm thick base course to

investigate the load equivalency for Geocell reinforced unpaved road and to

find the value of power term n.

• The intensities of cyclic loading applied were 0.6t, 0.8t, 1t, 1.2t and 1.4t

which correspond to a pressure of 330kPa, 440kPa, 550kPa, 660kPa and

770kPa respectively.

• Each loading was maintained for 250 cycles and the number of cycles

required to reach a certain permanent deformation was noted. Since the

material was strong the deformations were fixed to be 1mm and 2mm.

• By gradually increasing the loading and restricting the number of cycles to

250, the shake down behavior of the aggregate was not allowed to occur.

• This study helps to model the response of an unpaved section under long

term loading stresses in relation to the stress corresponding to the standard

stress (550kPa).

43

Load cycles to reach same surface deformation under different pressure intensities

Type Permanent Deformation

(mm)

Pressure Applied on the Base Material

Geocell

Reinforced

330kPa 440kPa 550kPa 660kPa 770kPa

1 NA 120 85 46 28

2 NA 245 150 92 60

2.55'

550

' 550

N P

N

44

Permanent deformation vs number of cycles for Standard axle load

Permanent deformation vs number of cycles for Standard axle load

(550kPa).

• The number of cycles required

to experience a particular

deformation will be

encountered with more number

of cycles for standard axle

stresses

• These experimental studies are

highly helpful as it is tedious

to monitor very high number

of cycles in the field while the

same can be studied in the

laboratory setups by

conducting lesser number of

cycles.

45

Rut Depth Reduction

• The rut depth reduction is used as to quantify the performance improvement of

geocell reinforcement over unreinforced section under repeated loading.

• The rut depth reduction is defined as the ratio of difference between

cumulative permanent deformations of the unreinforced layer and Geocell

reinforced layer to that of the unreinforced layer for a particular number of

loading cycle

( ) (1 ) *100reinN n N n

unrein

CPDRDR

CPD

46

Rut Depth Reduction

As the thickness of the reinforced section reduced, RDR values also reduced considerably.

The negative value of RDR in the reinforced section of 150mm shows that, during the initial cycles, rate of reduction in permanent deformation or rut depth reduction is not as much as that of unreinforced section having 300mm thickness. But as the number of cycle increases, 150mm thick reinforced layer is found to be more effective in reducing the permanent deformation compared to the unreinforced section.

In all the cases the RDR rate decreased as the number of cycles increased. This was due to the reduction in rate of permanent deformation due to the densification of the reinforced layer.

47

Modeling permanent deformation of Geocell reinforced Base layer

In Mechanistic Empirical Pavement Design Guide (MEPDG), the behavior of

granular soil under repeated load is analyzed using a mechanistic empirical model,

based on the observation that when the applied load is lower than a threshold level,

granular soil will eventually become purely resilient after a large number of load

passes and accumulate permanent strain with the increase in number of load cycles

The model developed for granular base materials by Tseng and Lytton (1989)

The vertical resilient strains along the center line of the load at the mid depth of the

base layer can be acquired by two methods.

Extract the strains from software packages

The strains from strain gauges fixed on the walls of geocell.

0( ) N

p cal v

r

N h e

48

Modeling permanent deformation of Geocell reinforced Base layer

Finite Element modeling (Plaxis 2D) was

used in order to obtain the strain at the

middle of the layer

Standard boundary condition was applied

on the section i.e. the bottom of the model

was fixed in the horizontal and vertical

directions while only horizontal

movement was restrained at the sides of

the model.

The Geocell reinforced base layer was

modeled as a soil layer with improved

properties.

A linear elastic model was used to model

the soil properties of subgrade sand while

the unreinforced and Geocell reinforced

base layers were modeled using Hardening

Soil (HS) model.

49

Modeling permanent deformation of Geocell reinforced Base layer

The parameters like 𝜀0

𝜀𝑟 , ρ and β

along with βcal were calibrated

and validated for unreinforced

and geocell reinforced section

from these two models.

Section Calibrated parameters

Unreinforced

βcal = 1 ; ρ = 700

β = 0.2 ; (𝜀0

𝜀𝑟) = 270

Reinforced

βcal = 1.5 ; ρ = 1800

β = 0.2 ; (𝜀0

𝜀𝑟) = 75

50

Field Studies

• Field studies were carried out to study how geocell reinforced

pavements preformed in the real traffic conditions.

• The performances of the geocell reinforced pavements were

further analyzed by comparing its performance with other

reinforcing methods like geogrid, bamboo and road mesh.

• In Chamarajnagar district, Kestur Village a rural road of

4.285km stretch is selected for the construction and analysis.

• The sections used in the field correspond to a thickness of

20mm for bituminous surface and 175mm thickness for the

granular subbase layer.

PROJECT SITE

Longitudinal cross section

Table- Cross section details of different experimental sections

Type of Experimental Section Cross section details

Conventional 20mm PMC, 150 mm Granular base, 125mm

GSB, compacted subgrade

Geocell-150mm 20mm PMC, 150mm geocell infilled GSB,

compacted subgrade

Geocell-100mm 20mm PMC, 100mm Geocell in filled GSB,

compacted subgrade

Bamboo 20mm PMC, 250 mm Granular base infilled in

bamboo grid, 125mm GSB, compacted

subgrade

Road Mesh 20mm PMC, 200 mm Granular base infilled in

road mesh, 125mm GSB, compacted subgrade

Geogrid 20mm PMC, 100 mm Granular base above

geogrid, 125mm GSB, compacted subgrade

Fig. Laying of geocell and placing of infill

Fig. Spreading and anchoring geogrid

Fig. Laying of bamboo and placing of infill

Prepared Test Pit

GEOCELL

GEOGRID BAMBOO

Characteristic Rebound Deflections on Experimental Road Sections by Benkelman Beam Method

Type of

experimental

section

Chainage Measurement

interval (m)

Characteristics

deflection (mm)

From

(km)

To

(km)

Conventional-1 0.9 1.414 50 2.29

Bamboo 1.414 1.917 50 2.60

Conventional-2 1.917 2.659 50 2.65

Road mesh 2.659 2.847 20 2.28

Geocell-150mm 2.847 3.095 20 5.89

Geocell-100mm 3.095 3.347 20 3.27

Geogrid 3.449 3.652 20 2.60

Conventional-3

3.652 4.285 50 2.28

Resilient modulus values of Different Component Layers Based on FWD Data (I Year)

Type of

experiment

al section

Chainage Length

of

section

(m)

E-value s of different component Layers

From

(km)

To

(km) Pre-

mix

carpet

Water

bound

macadam

Bamboo

with soil

aggregat

e

Road

mesh +

soil

aggregate

150mm

geocell

with

GSB

100mm

geocell

with

GSB

Geogrid

with

soil

aggrega

te

GSB Subgrade

Conventiona

l-1

0.9 1.414 514 566 757 - - - - - 377 127

Bamboo 1.414 1.917 503 667 - 498 - - - - 305 86

Conventiona

l-2

1.917 2.659 742 405 563 - - - - - 199 91

Road mesh 2.659 2.847 188 444 - - 451 - - - 304 75

Geocell-

150mm

2.847 3.095 248 520 - - - 248 - - - 54

Geocell-

100mm

3.095 3.347 252 533 - - - - 432 - - 81

Geogrid 3.449 3.652 203 428 - - - - - 561 388 79

Conventiona

l-3

3.652 4.285 633 536 707 - - - - - 241 114

Resilient modulus values of Different Component Layers Based on FWD Data (III Year)

Type of

experiment

al section

Chainage Length

of

section

(m)

E-value s of different component Layers

From

(km)

To

(km) Pre-

mix

carpet

Water

bound

macadam

Bamboo

with soil

aggregat

e

Road

mesh +

soil

aggregate

150mm

geocell

with

GSB

100mm

geocell

with

GSB

Geogrid

with

soil

aggrega

te

GSB Subgrade

Conventiona

l-1

0.9 1.414 514 533 656 - - - - - 256 114

Bamboo 1.414 1.917 503 565 - 310 - - - - 148 73

Conventiona

l-2

1.917 2.659 742 514 358 - - - - - 125 67

Road mesh 2.659 2.847 188 539 - - 338 - - - 157 68

Geocell-

150mm

2.847 3.095 248 519 - - - 207 - - - 57

Geocell-

100mm

3.095 3.347 252 523 - - - - 244 - - 78

Geogrid 3.449 3.652 203 525 - - - - - 410 291 79

Conventiona

l-3

3.652 4.285 633 520 707 - - - - - 265 112

Materials

Cost of

materials in

rupees

Total cost in

rupees

Geogrid in m2 139 193.47

Bamboo in m2 167 316

Geocell in m2

(Height-100mm) 270 387.8

Geocell in m2

(Height-150mm) 415 592

Conventional

method in m3 - 728.12

(Rural road specifications are adopted for the construction of road from Kestur to

Mellahallimala in Kollegal Taluk, Chamarajanagar and cost data provided by

KRRDA).

S.No Work Executed GHG emissions in /1000 tonne

1 Earthwork-procurement and execution 4.38 tonne

2 Excavation in rock & disposal 1.88 tonne

3 Crushing of rock for aggregate production 2.74 tonne

4 Granular sub-base course (GSB) construction 11.40 tonne

5 Wet mix macadam construction 13.59 tonne

6 Preparation & Construction of bituminous mixes

90.12 tonne

7 Preparation & Construction of dry lean concrete

128.45 tonne

8 Preparation & Construction of cement concrete pavement

223.83 tonne

Influence of road construction activities in terms of GHG emissions in India (Nanda et al. 2011)

Implications

•For a rural road 5.5m wide, there is a thickness reduction of GSB to the extent of 0.15m leading to savings of 1898.5 t of GSB material per km. •This leads to reduction in carbon foot print of 21.6 t per km which is significant.

DEVELOPMENT OF DESIGN CHARTS

Analytical Model by Yang and Han (2013):

The additional confining pressure induced by the geocell reinforcement was calculated using the following equation:

𝛥𝜎3 =𝑀

𝐷−

𝛥𝜎3

𝑀𝑟,1+

𝜎1 − (𝜎3 + 𝛥𝜎3)

𝑀𝑟,2

휀0

휀𝑟

𝑒𝜌

𝑁𝑙𝑖𝑚𝛽

1 + 𝑠𝑖𝑛𝜓

1 − 𝑠𝑖𝑛𝜓

Where: M=tensile stiffness of the sample (kN/m); D= diameter of the sample (m); Nlim= number of cycles; εo, εr, ,ρ, β,=resilient model parameters; and ψ=dilation angle

k1 k2 k3 ε0/εr ρ β ψ

450 0.56 0 150 2000 0.3 0o

Input parameters for reinforced UGM properties of geosynthetics

Resilient modulus versus number of cycles

(through Yang et. al (2013) method)

SUMMARY AND CONCLUSIONS

From the studies it was observed that the geosynthetic reinforcement in the unbound granular layers effectively reduces the permanent deformation compared to the unreinforced section.

For the same thickness, it was noted that the permanent deformation per cycle was much higher for unreinforced section compared to the reinforced section

It was noted from the study that the geosynthetic reinforcement could reduce more than 70% of the permanent deformation when compared to that of unreinforced section.

The resilient deformation for the reinforced section was much lower when compared to the resilient deformation of the unreinforced section

Field studies clearly showed the effectiveness of geosynthetics in pavements

70

Thank you for your attention

Dr. G L Sivakumar Babu

Professor

Department of Civil Engineering

Indian Institute of Science

Bangalore 560012

Email: gls@civil.iisc.ernet.in

M 9448480671

72

Geotechnical failures

due to natural

hazards, manmade

hazards

…. Welcome to Paris!

Final Meeting, Brussels, 26 January 2009

Natural causes such as earthquakes, rainfall etc

Manmade causes

Site investigations

Insufficient investigations (laboratory and field)

Selection of design parameters

Design deficiencies

Construction errors

Material defects

Maintenance deficiencies

73

December 8-10, 2016

Satish Dhawan Auditoriam Bengaluru

Evidence/data collection

Distress characterization

Design review/Analysis of conditions of failure

Specifications/standards review

Use of diagnostic tests (laboratory and field tests)

Role of instrumentation and sensor based technologies

Failure hypothesis formulation

Back analysis

Technical short comings

Risk analysis

Liability assessment

75

Prof. David Frost, USA Prof. Bob Gilbert, USA

Prof. Krishna Reddy, USA

Prof. Anand Puppala, USA

Prof. Binod Tiwari, USA

Prof. Miguel Pando, USA

Dr. Maureen K. Corcoran, USA

Mr. Mike Drerup, USA

Prof. Ikuo Towhata, Japan

Prof. Masayuki Hyodo, Japan

Prof. Yoshinori Iwasaki, Japan

Prof. Malek Bouazza, Australia

Prof. Gopal Madabhushi, UK

Prof. Limin Zhang, Hong Kong

Prof. Vikas Thakur, Norway

Prof. W F Lee, Taiwan

Prof. Sai Vanapalli, Canada Prof. Manoj Datta, India Prof. . G V Rao, India

Analysis of failures and learning from failures need to form an important of geotechnical engineering analysis and design.

This leads to better design and analysis procedures

Better codal procedures can be developed.

It ultimately saves lives and infrastructure losses and ensures proper accountability.