LABORATORY MODEL TESTS TO EFFECT OF DENSITY TO FILL MATERIAL ON THE PERFORMANCE OF A MODEL REINFORCED SOIL WALL

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LABORATORY MODEL TESTS TO EFFECT

OF DENSITY TO FILL MATERIAL ON THE

PERFORMANCE OF A MODEL

REINFORCED SOIL WALL

Srihars ha. Baditala

Assistant Professor, Department of Civil Engineering,

Assosa University, Assosa, Ethiopia

Yohannes Feyissa Beyisho

Dean for engineering and technology faculty,

Assosa University, Assosa, Ethiopia

ABSTRACT

The effective functioning of reinforced earth structures is very much

dependent on the quality of materials and construction. Many times, due to

poor quality of the materials used and poor quality control measures

exercised, the density of the reinforced soil fill is not up to the design

requirements, leading to underperformance or distress of the reinforced soil

walls. Therefore, it becomes necessary to evaluate the level of

underperformance vis-à-vis that of relative compaction. In view of this, in the

present study, a series of laboratory experiments were carried out on a model

soil wall of 300 mm high with vertical face, prepared at different density states

of 95%, 80% and 70% of MDD of IS HCT. The wall was subjected to

monotonic load applied through a model square footing of size (B) equal to 50

mm on the surface at an offset distance of 1(B). Similar tests were carried out

on the soil wall reinforced with a Woven Geotextile in wrap around form; to

study the effect of density on the performance of reinforced soil wall. The

results indicated proportionality between relative compaction level and

performance of soil wall without and with reinforcement.

Key words:

Reinforced Earth Structures, Density of Soil Fill, Relative

Compaction, Offset Distance

Cite this Article:

Sriharsha. Baditala and Yohannes Feyissa Beyisho,

Laboratory Model Tests To Effect of Density To Fill Material On The

Performance of A Model Reinforced Soil Wall.

International Journal of Civil

Engineering and Technology

,

7

(3), 2016, pp.365–372.

1. INTRODUCTION

Tremendous increase in infrastructure development in India during the past decade

has increased the reinforced soil applications manifolds. Apart from design, the

effective functioning of these reinforced soil walls (RSW), is also dependent on the

quality of materials used and the control on quality exercised during construction.

Any slackness on these two issues results in low relative compaction, which in turn

results in underperformance or distress of the reinforced soil walls. It is a known fact

that, remediation of such walls adds to cost and affect project completion schedules. It

is therefore necessary to understand the role of in-situ dry density of the reinforced

soil fill on the performance of reinforced soil walls, such that, the performance of the

reinforced soil fill can be predicted in advance. Essentially, efforts are made in this

study, in this direction.

1.1. Review of Literature

Considerable research has been carried out on the behaviour of reinforced soil walls.

Juran, I. and Christopher, B.,

(

1988), studied the behavior of soil wall reinforced with

different materials viz., woven polyester, geo-textile strips, plastic grids, and

non-woven materials. Ho, S.K., and Kerry Rowe, R., (1996), studied the effect of

geometric parameters. Vafaeian, M. and Abbaszadeh, R., (2008), have studied model

studies on soil wall reinforced with three types of cotton papers. They studied the

effect of tensile strength of the reinforcement, the number of layers, the vertical

spacing, the offset distance of the load applied on the surface and concluded that, the

failure surface was found to be an arc of a circle when stiffer reinforcement is used

and that for weaker reinforcement was almost a straight line. They also concluded

that, the performance of the RSW was better when tensile strength of the

reinforcement was higher and number of reinforcement layers was higher. However,

limited studies were carried out on the effect of density on performance of RSW,

which has been addressed in the present study.

2. METHODOLOGY

The methodology includes collection and characterisation of the materials;

performing monotonic load tests; analysis and interpretation of test results and

drawing observations and conclusions.

2.1. Characterization of Silty Sand

The Silty Sand used in this study (locally called as Morum) is collected from

Mahaboob nagar district of Telangana state. The index and engineering properties of

soil are summarised in Table 1.

Table 1 Properties of Silty Sand

Parame ter Value

Gravel sized part icles 16.4 % Sand sized partic les 78% Fine gra ined particles 5.6%

Consistency Non plastic

MDD (IS HCT) 2.03 g/cc

OMC (IS HCT) 9.60 %

Classification

2.2. Characteristics of Woven Geotextile

The woven geotextile used in this study is shown in Fig. 1 and its characteristics are

indicated in Table 2

Figure 1 A view of the woven geotextile

Table 2 Characteristics of Woven Geotextile

Property Value

Type of geosynthetic Polypropylene slit film tape woven geotextile

Co mme rcia l na me SKAPS W-250 Mass per unit area 170 (g/sqm)

Thickness 0.425 (mm)

Grab Tensile strength 1.11 (kN) Grab e longation 15 (%) Puncture resistance 4.005 (kN)

2.3. Test set up

The experimental test set up is shown in Fig 1. The PC controlled Tri-axial test

facility is utilised to conduct the model plate load tests. The application of load is by

hydraulic control system and the load is measured by an electronic load cell with a

sensitivity of 1 kg. The settlement is measured by electronic Linear Voltage

Differential Transducer (LVDT) of ± 50 mm range. The PC controlled facility is run

by software that enables to give the operating conditions as input. The facility logs the

load and settlement observations continuously and provides online display of the

progress of the mechanism.

2.4. Model test tank & Model footing

A model test tank of size 300mmx750mmx600mm is used. The tests are carried out

using model footing of size 50 mm such that the width of the tank 300 mm and depth

300 mm, will be more than or equal to 5B, such that the boundary effects are avoided.

The model footings are made of 25mm thick aluminium plates with a rough base.

2.5. Scheme of experiments

The investigations are carried out systematically as per the scheme of experiments,

which includes determining the resistance to the load applied at an offset distance of 1

(B), on the soil wall prepared at three different relative compactions viz., 70%, 85%

and 95% ; without and with woven geotextile in wrap around form.

3. RESULTS

3.1. Pertaining to un-reinforced soil wall

The results of monotonic load tests on un-reinforced soil wall represented in terms of

bearing pressure versus settlement are presented in Fig. 3 and the typical failure is

depicted in Fig. 4.

Figure 3 Variation in Bearing Pressure with Settlement pertaining to Unreinforced Soil Wall

Figure 4 A view of failure of Unreinforced Soil Wall at 70% relative compaction, with load applied at an offset distance of 1B

0 50 100 150 200 250 300 350 0 2 4 6 8 10 B e a ri n g P re ss u re ( k P a ) Settlement

70% rela tive compa ction 80% rela tive compa ction 95% rela tive compa ction

3.2. Pertaining to reinforced soil wall

The results of similar monotonic load tests carried out on soil wall reinforced with

woven geotextile in wrapped around form ; compacted at three specified relative

compactions; subjected to the load applied at an offset distance of 1.0 B ; is presented

in Fig. 5 and a typical view of failure is shown in Fig. 6.

Figure 5 Variation in Bearing Pressure with Settlement pertaining to Reinforced Soil Wall

Figure 6 A view of failure of the reinforced soil wall at a relative compaction of 70%, with load applied at an offset distance of 1B

4. OBSERVATIONS

4.1. Pertaining to unreinforced soil wall

Based on the analysis of test results pertaining to monotonic load tests on

unreinforced soil wall, the following observations are made:

1. As it can be seen from Fig. 3, the nature of bearing pressure versus settlement curve, in general is elasto-plastic. A closer examination reveals the fact that, complete failure without considerable plastic deformation was observed specifically at lower relative compaction of 70%.

2. As depicted in Fig. 4, the mode of failure included separation and collapse of plastic zone formed on the unsupported vertical face. The rupture surface was found to be curvilinear akin to a paraboloid.

3. The variation in resistance against applied loads with variation in relative compaction is presented in Fig. 7. It can be seen that, higher the relative compaction, higher is the

0 500 1000 1500 2000 2500 3000 0 5 10 15 20 25 30 B e a ri n g P re ss u re ( k P a ) Settlement (mm) 70% rela tive compa ction 80% rela tive compa ction 95% rela tive compa ction

resistance offered against the applied load. The relationship is well represented by a second order polynomial or by a power equation.

Figure 7 Variation in Bearing Pressure at failure with Relative Compaction pertaining to Unreinforced Soil Wall

4.2. Pertaining to Reinforced soil wall

The observations pertaining to the reinforced soil wall are as presented below:

1. The nature of bearing pressure versus settlement curve, for reinforced soil wall, is also elasto-plastic, as seen in Fig. 5. Interestingly, when reinforced, complete failure was not observed even at lower relative compaction of 70%.

2. As shown in Fig. 6, the reinforced soil wall sustained deformation, but not undergone complete failure, as it happened in unreinforced soil wall.

3. As it can be observed in Fig. 8, resistance to the applied load is increasing with increase in relative co mpaction. The relationship is well represented by 2nd order polynomia l as well as power equation; simila r to that for unreinfo rced soil wall.

Figure 8 Variation in Bearing Pressure at failure with Relative Compaction pertaining to Reinforced Soil Wall

y = 11.906x - 856.59 R² = 0.9338 y = 4E-25x13.647 R² = 0.9725 y = 0.4636x2 _{- 64.954x + 2279.5} R² = 1 y = 6E-05e0.1647x R² = 0.9569 -50 0 50 100 150 200 250 300 350 400 60 70 80 90 100

B

ea

ri

ng P

re

ss

ur

e

at

f

ai

lur

e,

kP

a

Relative Compaction, (%) y = 59.029x - 4076.3 R² = 0.9529 y = 4E-12x7.3667 R² = 1 y = 1.9187x2 _{- 259.07x + 8902.8} R² = 1 y = 0.3333e0.0895x R² = 0.9978 0 200 400 600 800 1000 1200 1400 1600 1800 60 70 80 90 100

B

ea

ri

ng Pr

es

sur

e

at

f

ai

lur

e,

kP

a

Relative Compaction, (%)

4.3. Observations pertaining to general comparison

The behaviour of unreinforced and reinforced soil wall is compared one-to-one and

the following observations are drawn:

1. It is clearly seen from Fig. 9 that, at any relative compaction, a definite increase in resistance offered against the applied load is seen when the soil wall is reinforced.

Figure 9 Comparison of Bearing Pressure at failure soil wall with and without reinforcement 1. The variation of percentage increase in the resistance with relative compaction, is

shown in Fig. 10. As established in earlier research, weaker the soil, higher is the percentage increase when reinforced.

Figure 10 Variation of Percentage increase in Bearing Pressure at failure due to reinforcement

5. CONCLUSIONS

Based on the experimental investigations carried out in this study, the following

important conclusions are drawn:

1. This study clearly established that, higher the dry density of the fill material, higher is the resistance offered against the applied loads. This was observed in both Unreinforced Soil Wall and Reinforced Soil Wall.

0 200 400 600 800 1000 1200 1400 1600 1800 70 80 95

Un-reinforced Soil Wall Reinforced Soil Wall

B e a ri n g P re ss u re a t fa il u re , k P a

Rela tive Compa ction, (%)

0 1000 2000 3000 4000 5000 70 80 95 P er ce nt age i nc re as e

2. A definite increase in resistance to the applied loads was observed when soil wall is reinforced. For the materials used and for the test conditions adopted in this paper, the increase was in the range 449 % to 3827 %. This emphasizes the importance of reinforcement in soil walls.

3. The mode of failure in Unreinforced Soil Wall was consisting of separation and collapse of a zone of soil near the face of wall. This was contained when reinforced. Hence, this study showed that, collapse of soil wall can be effectively contained when reinforced.

4. On the whole, this study clearly brought out the mechanisms of failure of soil walls when subjected to applied loads without and with reinforcement. This study is useful to the designers and practitioners in prediction of the impact of under compaction on the behavior of reinforced soil wall.

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