BEHAVIOR & STABILITY ANALYSIS OF GEOGRID REINFORCED … · 5. PLAXIS 2D PLAXIS 2D version 8.2 is a user friendly geotechnical program intended for two- dimensional analysis of deformation

http://www.iaeme.com/IJCIET/index.asp 1987 [email protected]

International Journal of Civil Engineering and Technology (IJCIET)

Volume 10, Issue 04, April 2019, pp. 1987–2000, Article ID: IJCIET_10_04_198

Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJCIET&VType=10&IType=4

ISSN Print: 0976-6308 and ISSN Online: 0976-6316

© IAEME Publication Scopus Indexed

BEHAVIOR & STABILITY ANALYSIS OF

GEOGRID REINFORCED EARTHWALL:

A CASE STUDY IN VIZIANAGARAM (A.P)

Abdul Asif Baig

PG Student, Department of Civil Engineering,

Chandigarh University, Punjab, India

Aditya Kumar Tiwary

Assistant Professor, Department of Civil Engineering,

Chandigarh University, Punjab, India

ABSTRACT

Reinforced Earth (RE) wall offers a variety of advantages when compared to

conventional retaining walls and embankments for road approaches. This study is

carried out on proposed RE wall design for an approach road on Visakha side using

finite element based computer program “PLAXIS 2D (version 8.6)”. The proposed

Design which is to be executed in the near future is based on limit-equilibrium

approach. The main aim of this study is to find out the Deformation of this RE wall

along with its Stability using finite element approach. The Global factor of safety of

this Geotechnical structure is also determined using PLAXIS 2D. PLAXIS 2D is a

finite element analytical geotechnical Software which gives accurate results compared

to that finite difference and limit equilibrium analytical software’s. Detailed study of

the Design (using limit-equilibrium approach) acquired from the ongoing project site

is

Key words: Finite Element Analysis, Soft Subgrade, Reinforced Earth Wall, Geo-

Grid Reinforcement, Factor of Safety.

Cite this Article: Abdul Asif Baig and Aditya Kumar Tiwary, Behavior & Stability

Analysis of Geogrid Reinforced Earthwall: A Case Study in Vizianagaram (A.P),

International Journal of Civil Engineering and Technology 10(3), 2019, pp. 1987–

2000.

http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=10&IType=3

1. INTRODUCTION

1.1. Reinforced Earth

Reinforced earth is a composite construction material which generally comprises of

cohesionless soil (preferable) and reinforcement. This idea is evolved from the known concept

following in the civil engineering practices, where a composite material of greater strength is

Abdul Asif Baig and Aditya Kumar Tiwary


developed by combining the materials of different strength characteristics. The reinforced

concrete constructions are examples of such composite materials where the tensile strength of

concrete is enhanced by introducing steel in it. Likewise, soils which have little tensile

strength are strengthened by the inclusion of materials having higher tensile strength. In case

of reinforced earth, the tensile strength is developed through bond resistance which is friction

and depends on surface roughness of reinforcement and soil. If the soil is cohesive, the bond

strength is developed through adhesion.

A variety of materials can be used as reinforcing materials .Those that have been used

successfully include steel, concrete, glass fibre, wood, rubber, aluminium and thermoplastics.

Reinforcement may take the form of strips, grids, anchors & sheet material, chains planks,

rope, vegetation and combinations of these or other material forms.

1.1. Reinforced Soil Walls

Reinforced earth walls are the one of the widest applications of reinforced earth and mainly

consists of 3 components. They are cohesionless soil, reinforcement and facing system.The

cohesionless soil should have an angle of internal friction between the compacted fill and the

reinforcing element and not less than 30 degrees. The soil should be predominantly coarse

grained and not more than 10 percent of the particles shall pass 75 micron sieve. The

reinforcement can be of any type and of any form which is already mentioned above in the

reinforced earth.The reinforcing materials generally used in reinforced earth walls are of two

types which are metallic type and synthetic type. Metallic type reinforcement may corrode in

the longer service periods. So, geosynthetics are mostly preferred as reinforcing materials.

Again, there are wide variety of geoynthetics available like geogrids, geotextiles, geonets,

geomebranes, geosynthetic clay liners, geofoam, geocells and geocomposites. Each type of

the geosynthetics is employed in soil for different purposes.These above mentioned types of

reinforcement may take the form of strips, grids, sheets, planks, ropes, combinations of these

or other material forms.

Figure 1 Different types of Geosynthetic reinforcement

Behavior & Stability Analysis of Geogrid Reinforced Earthwall: A Case Study in Vizianagaram (A.P)


The third component of RE Wall is facing system which can be hard or soft. The main

purpose of facing system is to prevent falling over of the fill and also to provide firm

anchorage to the reinforcement. The facing shall comprises of following:

Precast reinforced concrete panels

Precast concrete blocks and precast concrete hollow blocks

Gabion facing

Wrap around facing using geosynthetics

Other proprietary and proven systems

Figure 2 Panel facing in Jaipur… Figure 3 Modular block facing in Velachery

Figure 4 Rock filled Gabion facing in Pune



Figure 5 The Components of Reinforced Earth wall.

2. PROBLEM STATEMENT

The performance of an RE wall depends on both deformations and stability. But,

deformations are not explicitly considered in the conventional design where the design is

verified for external stability and internal stability only. Also, the design is time independent.

So, Finite element method based PLAXIS software provides a means for analysing both

stability and deformations accurately. This project focuses on modelling the conventionally



designed “ RE wall of Visakhapatnam side ” in connection with construction of road over

bridge with 54 m clear span bowstring girder along approaches with RE walls at entrance of

vizianagaram town in PLAXIS 2D which is a finite element program. This construction is

currently ongoing in Vizianagaram, AP which is a Railway Project. So, the response of the

designed RE Wall which is yet to be constructed is found out in this study using PLAXIS 2D.

3. METHODOLOGY

In this study, 4 phases are implemented to achieve all the targeted objectives. This project is

started with literature review on the topic of RE Wall. Secondly, a detailed study is done

about the conventional design involved in RE Wall by following 2 codes of practice which are

BS 8006:1995 and Federal Highway Administration (FHWA) guidelines of USA. Thirdly, we

have collected both the input parameters and Design output from the site, which is an

essential data to model this geotechnical structure in PLAXIS 2D (version 8.6). Finally we

have modelled the proposed RE wall Design in PLAXIS 2D (version 8.6) and analysed

deformations and global factor of safety of the RE Wall.

Figure 6 Top view of the Project site in Google maps

Figure 7 Site of Visakha Side RE Wall



4. DATA COLLECTION FOR SOIL PARAMETERS

The data (input data and design output) for the study was acquired from ongoing construction

project loacted at vizianagarm.

Table 1 Input soil parameters

c’(kN/m

2)

φ’(degree) γ(kN/m

3

)

Reinforced Infill Soil 0 32 22.1

Retained Soil 0 32 22.1

Foundation Soil 0 30 20

Depth of water table below the initial ground level Dw = 5 m

Depth of foundation, Df = 1.2 m Depth of embedment, Dm = 1 m

Input wall geometry:

Design height = 7.23 m Vertical batter = 0 degrees

Input external loads:

Dead load surcharge = 12 kN/m2

Live load surcharge = 24 kN/m2

Input facing panel details:

Depth of facing block = 0.18 m

Unit weight of facing block = 24 kN/m3

5. PLAXIS 2D PLAXIS 2D version 8.2 is a user friendly geotechnical program intended for two-

dimensional analysis of deformation and stability. It provides operable geometry, simulation

of staged construction and a reliable calculation package, making a complete solution for

geotechnical design and analysis. Applications ranges from excavations, embankment and

foundations to tunnelling, mining and reservoir geomechanics.

PLAXIS uses predefined structural elements and loading types in a CAD-like

environment. This empowers the user with fast and efficient model creation, allowing more

time to interpret the results. This finite element computer program used to perform

deformation and stability analysis for various types of geotechnical application. Therefore,

lateral and vertical movement of wall can be predicted.

With Staged Construction, users can accurately model the construction process, by

activating and deactivating soil clusters and structural elements in each calculation phase.

With plastic, consolidation and safety analysis calculation type, a broad range of geotechnical

problems can be analyzed. Constitutive models range from simple linear to advanced highly

non-linear models wide range of soil and rock behaviour can be simulated. Well proven and

robust calculation procedures ensure converging calculations and accurate results. With multi-

core calculations and 64-bit architecture, PLAXIS can deal with the largest and most complex

models.

5.1. Finite Element Analysis

The proposed RE Wall design is modelled in PLAXIS 2D and the deformations and stress

distribution and also global factor of safety of this geotechnical structure is found out through

finite element analysis.



Input Data for PLAXIS 2D

Table 2 Characteristics of soil materials

Property Reinforced Retained fill Hard Clay Hard Clay

fill soil soil with SDR

Mohr Mohr Mohr Mohr

Constitutive Coulomb Coulomb Coulomb Coulomb

model

Material type Drained Drained Drained Drained

Youngs 1.500E+05 1.500E+05 7.500E+04 7.500E+04

modulus(Mpa)

Poisson‟s ratio 0.35 0.35 0.200 0.2

Unit 22.1 22.1 20.3 19.6

weight(kN/m3

)

Friction angle (º) 32 32 27 25

Dilatancy angle 0 0 0 0

(º)

Cohesion(kPa) 0.0001 0.0001 26 23

RINTER 1 1 1 1

Table 3 Specifications of facing panel

Property RCC Panel.48 RCC Panel.75 RCC Panel1.5

0.18 0.18 0.18

Depth

0.48 0.75 1.5

Width

22360679 22360679 22360679

Youngs

modulus(Mpa)

1.932E+06 3.019E+06 6.037E+06

EA 5210.040 8161.650 1.630E+04

EI

Table 4 Specifications of Geogrids

Geogrid No. Tensile Strength( KN) EA Value(KN/m/m)

1. 40 1449

2. 60 2173

3. 80 2898

4. 100 3623

5. 120 4347

6. 150 5434

Table 5 Specifications of Levelling Pad

S.no. Property Levelling Pad

1. Constitutive model Mohr -coulomb

2. Material type Non-porous

3. Youngs modulus (Mpa) 2.236E+07

4. Poisson‟s ratio 0.15

5. Unit weight(kN/m

3)

24

6. Friction angle (º) 0

7. Dilatancy angle (º) 0

8. Cohesion (kPa) 0

9. Rinter 0.8



6. ANALYSIS AND DISCUSSIONS

6.1. Modelling Procedure in PLAXIS 2D

The modelling sequence consists of the following stages:

Step 1: In the project properties, dimensions in the x and y direction are to be entered, in this

case those are entered as -3.5 m to 18 m in x-direction and -6 m to 8 m in y-diretion

respectively.

Step 2: In the model generation, we have 8 elements to be modelled in which 2 elements are

clusters consisting of foundation soil, 2 elements which are clusters of fill materials,

remaining 4 elements are levelling pad, geogrids, RCC panels and load on the top of the wall.

Step 3: Initially, 2clusters of foundation soil and a levelling pad are to be modelled.The 2

soils namely are hard clay and hard clay with lime & soft disintegrated clay.

Step 4: So as to assign the soil, select “Soil and interfaces”, “New” tab isselected and

properties of the soil such as material model, modulus of elasticity, poisson‟sratio, cohesion,

angle of internal friction, angle of dilation and the interface value are enteredas per this

generation of model is considered.

Step 5: After entering the properties of soil, now to assign this soil to the clusture, the

generated clusture is selected and right click is given in which soil option is available and in

that option the soil added formerly is shown and with a click on it soil is assigned to the

generated clusture.In this manner, soil properties are added and the soil assigned to the cluster

respectively.

Step 6: It is a staged construction where initially a panel is placed. Then, the reinforced fill

and retaining fill are placed and compacted. Finally, a geogrid layer is placed. This process is

repeated until required wall height is attained. So, RCC panel for 1st

stage is modelled and the

properties of the RCC panel is inputed using “plates” set in material sets.

Step 7: Reinforced fill and retained fill clusters for the 1st

ge are modelled and the

properties are assigned to the respective clusters.

Step 8: A geogrid layer is modelled in the geometry. Using “Geogrids” set in “material sets”

tab “New” option is selected and EA value of geogrid is entered and geogrid iscreated in the

geogrids tab.By right clicking on the modelled geogrid, the appropriate material is selected

and assigned to imported structure.

Step 9: Step 7 to step 9 is repeated until the required wall height of 7.23m is reached.

Step 10: Using “Interface” option, an interface is created for geogrids and RCC panel wall.

Step 11: Now, two loads are created on the top of themodel. So for creation of the loads, load

symbol isselected and the co-ordinates of the udl are entered and the appropriate load is

applied inthe negative Y-direction. After application of these loads, the whole RE wall model

is generated andit is proceeded to next step for mesh generation.

Step 12: In the “Mesh” mode, “Generate Mesh” option is selected and fine mesh is generated.

To further refine the mesh at critical areas, “Refine” option is selected in “Mesh” mode. Area

near the RCC panel wall from top of the wall to its bottom is selected and mesh is generated.

After generation of the mesh to view mesh, “View mesh” option is selected and using “Select

point for curves” a point is selected where the analysis of the retaining wall is to be done.

Step 13: Now select “initial conditions” to assign water table. Now, assign the position of

ground water table and calculate the pore water pressures. Also calculate the initial stresses.

Step 14: Now select “calculate” to go to calculations. Now define all the phases and set the

number of steps to 250 and select “plastic analysis” in “calculation type” and mark “staged



construction”. Now, define all the phases and activate soil clusters, geogrids and panels stage

by stage.

Step 15: In last stage, external loads are activated and select “Phi/c reduction” in “calculation

type” to find factor of safety.

Step 16: Completion of the calculation phase gives out result obtained from “View

Calculation results” tab which opens the output of the project in which results regarding the

retaining wall can be known such as displacements, stresses, strains, factor of safety, etc.

6.2. Model generated in PLAXIS 2D

Figure 8 Generated Model

Figure 9 Generated Finite Element Mesh



7. RESULTS AND DISCUSSION

Presentation of results on subgrade and embankment fill soil The results are presented from

table

Figure 10 Graphs shows the soil phenomenon

Figure 11 Grain size distribution curve for embankment fill soil



Table 6: Test results of subgrade soil

Parameters Results

Liquid limit 56.5%

Plastic limit 28.63%

Plasticity index 27.87%

USCS Soil classification CH

Optimum moisture content 24.25%

Maximum dry density 14.95KN/m^2

Cohesion (c) 19.6kpa

Angle of internal friction (ᶲ) 6.6 degrees

CBR unsoaked 4.83%

CBR soaked 2.18%

Figure 12 Graphs shows the compaction test and shear test

Table 7 Test results of embankment filling soil

parameters Results

Soil classification SW

Optimum moisture content 10.73%

Maximum dry density 20.9KN/m^3

Cohesion(c) 9.1kpa

Angle of internal 24.20 degrees

7.1. Results obtained from PLAXIS 2D after analysing RE Model

Figure 13 Deformed Mesh



The extreme total displacement is 0.774 m

Figure 14 Total Displacement

The extreme horizontal displacement is -0.643 m

Figure 15 Total Horizontal Displacements

The extreme vertical displacement is -0.572 m

Figure 16 Total vertical displacement



Figure 17 Slip circle

Factor of safety at geogrid layer 9 near to the panel is 1.65

Figure 18 Factor of safety vs Total displacements at point A (Georgid layer 9 near to the panel)

Factor of safety at geogrid layer 2 near to the panel is 1.65

Figure 18 Factor of safety vs Total displacements at point B (Geogrid layer 2 near to the panel)



8. CONCLUSIONS

The modeled RE wall and analysis will help in understanding failures before construction is

taken up. The contribution of reinforcement in improving stability is significant. There is an

improvement of 1.2 to 1.5 in Fs with reinforcement. Higher tensile capacities are

recommended for Higher Fs requirement.

Using PLAXIS, the final settlements of the structure after application of loading

(pavement load and vehicular load) are found out. The settlements after each stage of

construction can also be found out.

The global factor of safety of the RE Wall found out using PLAXIS is 1.65 and generally

the required factor of safety ranges between 1.3 – 1.5.

The slip circle for this geotechnical structure is also found out in this analysis using

PLAXIS.

REFERENCES

[1] Hatami, K., Bathurst. R.J. and Di Pietro. (2001) „Static response of reinforced soil

retaining walls with nonuniform reinforcement‟. The International Journal of

Geomechanics, 1(4), pp.477–506.

[2] Roy, D. and Singh, R. (2008) „Mechanically Stabilized Earth Wall Failure at Two Soft

and Sensitive Soil Sites‟. J. Perform. Constr. Facil., 22(6), pp.373-380.

[3] Stuedlein, A.W., Bailey, M., Lindquist, D., Sankey, J. and Neely, W.J. (2010) „Design and

Performance of a 46-m-High MSE Wall’. J. Geotech. Geoenviron. Eng., 136(6), pp.786-

796.

[4] Abdelouhab, A., Dias, D. and Freitag, N. (2011) „Numerical analysis of the behaviour of

mechanically stabilized earth walls reinforced with different types of strips‟. Geotextiles

and Geomembranes, 29(2), pp.116-129.

[5] Robert M. K. and George R. K. (2011) „The importance of drainage control for

mecahnically stabilized geosynthetic reinforced mechanically stabilized earth walls‟.

Journal of GeoEngineering, 6(1), pp.3-13.

[6] Hossain, M.S., Kibria, G., Khan, M.S., Hossain, J. and Taufiq, T. (2012) „Effects of

Backfill Soil on Excessive Movement of MSE Wall‟. J. Perform. Constr. Facil., 26(6),

pp.793- 802.

[7] Kibria, G., Hossain, S. and Khan, M.S. (2014) „Influence of Soil Reinforcement on

Horizontal Displacement of MSE Wall‟. Int. J. Geomech., 14(1), pp.130-141.

[8] Bilgin, O. and Mansour, E. (2014) „Effect of reinforcement type on the design

reinforcement length of mechanically stabilized earth walls‟. Engineering Structures, 59,

pp.663–673.

[9] Jewell, R.A, Reinforced soil walls analysis and behaviour. In: Jarret, P.M., McGown, A.

(Eds.), The Application of Polymeric Reinforcement in Soil Retaining Structures. Kluwer

Academic Publishers, 1987, pp. 365–408.

[10] Kaniraj, S . R . & Abdullah, H., Rotational stability of unreinforced and reinforced

embankments on soft soils. Geotextiles and Geomembranes, 13, (1994)707-726.

[11] Kaniraj, S.R. & Abdullah, H., Rotational stability of narrow crested reinforced

embankments on soft soils Geotextiles and Geomembranes, 12, (1993),599-614.

[12] Low, B.K., Stability analysis of embankments on soft ground. 1. Geotech. Engng.

Div.ASCE, 115 (2), (1989). 211-27.

Documents

BEHAVIOR & STABILITY ANALYSIS OF GEOGRID REINFORCED … · 5. PLAXIS 2D PLAXIS 2D version 8.2 is a user friendly geotechnical program intended for two- dimensional analysis of deformation