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Proceedings of International Conference on Advances in Architecture and Civil Engineering (AARCV 2012), 21st – 23rd June 2012 489

Paper ID TRA122, Vol. 1

ISBN 978-93-82338-01-7 | © 2012 Bonfring

Abstract--- When the fluid is ground water, the terms

coefficient of permeability (k) is essential to determine. If

water is present in the soil mass at or near an excavation

elevation, then the water that will flow into the excavation

must be accounted for. The greater the coefficient of

permeability, the greater the volume of water that must be

controlled. Therefore the value of coefficient of permeability

will impact both design and construction of soil subgrades for

pavements. Permeability value depends on the soil's

triangular textural and unified classification. The optimum

content for stabilizing soil with fly ash and rice husk ash was

obtained on the basis of California bearing ratio (CBR) test.

This mixing of admixtures to soil changes the permeability

along with other strength properties. In order analyse the

effect of admixtures on the permeability of stabilized soil, an

laboratory study was conducted on these mixes in the present

study. Various other properties like CBR, Atterbergs limits,

optimum moisture content & maximum dry density, grain size

distribution were also analyzed.

Keywords--- Permeability, California bearing ratio (CBR),

fly ash, rice husk ash, soil

I. INTRODUCTION

A. General

NY given mass of soil consists of solid particles of

various sizes with interconnected void spaces. The

continuous void spaces in a soil permit water to flow from a

point of high energy to a point of low energy. Permeability is

defined as the property of a soil that allows the seepage of

fluids through its interconnected void spaces. In order to

obtain a fundamental relation for the quantity of seepage

through a soil mass under a given condition by Darcy’s law.

Darcy’s Law states that under steady conditions of flow

through beds of sands of various thicknesses and under

various pressures, the rate of flow is always proportional to the

hydraulic gradient. This principle has been found to be

generally valid for the flow of water in soils, except at high

Aditya Kumar Anupam, Research Scholar, Transportation Engineering

Group, Indian Institute of Technology Roorkee, Uttarakhand, India

Praveen Kumar, Faculty, Transportation Engineering Group, Indian

Institute of Technology Roorkee, Uttarakhand, India

G.D Ransinchung R.N, Faculty, Transportation Engineering Group, Indian

Institute of Technology Roorkee, Uttarakhand, India

velocities when turbulence occurs. Darcy’s law is expressed

mathematically as

υ = ki

where q is the total rate of flow through the cross-sectional

area A, and k is the so called coefficient of permeability.

The proportionality constant (k) is referred to as the

hydraulic conductivity, which describes the ability of a porous

material to allow the passage of a fluid, and is not a

fundamental property of soil, but depends upon a number of

factors. Particle size distribution has a significant effect on the

material’s permeability, in which the smaller the particles, the

smaller the voids between them, and therefore the

permeability decreases. On the other hand, particle shape and

texture influences permeability. Irregular shape and rough

surface texture tend to reduce the flow rate of water through

the soil. Void ratio, which is dependent on the way soil is

placed or compacted, may affect the flow characteristics in

soils and it is used essentially in the formulas used to calculate

the permeability. Another factor in controlling the hydraulic

conductivity is the degree of saturation. Entrapped air in the

soil can block flow lines between particles, thereby

appreciably reducing the permeability. The temperature factor

affects the physical properties of water such as water

viscosity, an increase in temperature causes a decrease in the

viscosity of water, i.e. the water becomes more fluid, which

tends to affect the measured permeability. For laboratory tests

the standard temperature is usually 20°c (see Head, K. H.,

1992 the second edition).

Different techniques are available to determine soil

hydraulic conductivity (K). The degree of permeability is

determined by applying a hydraulic pressure difference across

a soil sample, which is fully saturated and measuring the

consequent rate of flow of water (Head, K. H., 1992).

Permeability is measured using permeameter device (flexible

wall or rigid wall) by constant head test or variable (falling)

head test. Constant head permeability test is conducted on

highly permeable soil like gravel or sand following ASTM

D2434-68 Standard Test Method for Permeability of Granular

Soils (Constant Head). It consists of applying a constant head

(h) on the sample surface and measuring the time needed for

collecting a known amount of water at the tail end. The

permeability can be calculated using the equation

Permeability Study on Fly Ash and Rice Husk Ash

Admixes with Subgrade Soil for Pavement

Construction

Aditya Kumar Anupam, Praveen Kumar, G.D Ransinchung R.N

A



ISBN 978-93-82338-01-7 | © 2012 Bonfring

where,

k = coefficient of permeability (cm/sec), from constant head

test

Q = quantity of water discharged, cm3

t = total time of discharge, sec

A = cross-sectional area of soil sample, cm2

L = length of the sample (cm), and

h = Head causing flow (cm)

Variable head permeability test is conducted on relatively

less permeable soils like fine grained soils. The falling head

permeability test determines the permeability of a material by

measuring the time required for water level to fall from a

known initial head (h1) to a known final head (h2). The

permeability is then calculated using the equation

where,

k = coefficient of permeability (cm/sec), from falling head test

a = cross-sectional area of reservoir (cm2)

L = length of specimen (cm)

A = cross- sectional area of specimen (cm2)

h1, h2 = water levels (cm), and

Δt = time required for water falling from h1 to h2 (sec)

Various researchers have attempted to measure the

coefficient of permeability of subgrade (clayey) materials

using laboratory test procedures. Some of the test procedures

used and results obtained are summarized below.

According to work done by Tavenas, F., et al. (1983),

permeability tests in the triaxial cell present many advantages:

(1) cells of any dimensions can be built easily to accommodate

varying sizes of specimens thus reducing the problem of

specimen representativity (2) the possibility to test the clay

under effective stresses and back pressures equivalent to the

in-situ condition is a distinct advantage and (3) both falling

head and constant head tests may be performed. Another

observation by Tavenas, F. et al. is that the use of high

gradients minimizes the errors due to leakage and volume

changes of the specimen. Besides, the complete permeability

results may be obtained within a practical time frame. He

concluded also that as i (hydraulic gradient) increases, the

velocity of the water passage through the specimen will

increase and not the material's hydraulic conductivity. One

more valuable outcome of Tavenas, F., et al. (1983), is that

due to the very low permeability of clays, the measurement of

(K) implies the observation of very small flows over extended

periods of time. The identification and, if possible, the

elimination of errors on the observed flow are key

requirements for the accurate evaluation of the permeability of

clays. Another study by Mesri, G. and Olson, R. E. (1970) was

concentrated on the factors that affect the evaluation of the

coefficients of permeability. They observed that the

coefficients of permeability of clays are controlled by

variables that may be classified as mechanical and physico-

chemical. The mechanical variables of main interest are the

size, shape, and the geometrical arrangement of the clay

particles. The coefficient of permeability maximized if the

flow channels consist of many small channels and a relatively

few large ones, through which the main flow occurs. Physico-

chemical variables exert great influence on the coefficient of

permeability by controlling the tendency of the clay to

disperse or to form aggregates. A major disadvantage of lab

tests is the small sample size. The sample size is only a very

small percentage of the overall volume, making the

representativeness of the samples questionable in light of a

possible scale-dependency of hydraulic conductivity. Thus,

there is little value in using small specimens to assess field

hydraulic conductivity. This observation was similar to the

work conducted by Benson, C. H., et al. 1997, who pointed

out that small specimens are too small to adequately represent

the network of pores controlling field-scale hydraulic

conductivity.

The fact of the matter is that measured permeability is

controlled by so many factors such as air bubbles, degree of

saturation less than 100 %, migration of fines, temperature

variations which change the fluid viscosity, unavoidable

disturbance, dependency upon properties of pore fluid, and/or

small sample size which does not provide representative

specimen to the field conditions.

II. MATERIAL SELECTION

A. Soil

Clay of medium compressibility (A-7-6) soil is used for

this study. The index properties such as liquid limit, plastic

limit, plasticity index and other important soil properties as

per AASHTO and United States soil classification systems are

presented in Table 1. Figure 1 presents the grain size

distribution curves of this soil.

Table1: Physical Properties of Soil

Properties Values

Optimum moisture content (%) 17

Dry density (gm/cc) 1.85

Specific gravity 1.99

Liquid limit (%) 46

Plastic limit (%) 21

Plasticity index 25

Unified soil classification CL

AASHTO soil classification A-7-6

Type of soil Clay of medium

compressibility



ISBN 978-93-82338-01-7 | © 2012 Bonfring

Figure 1: Grain size Distribution Curve of Soil

B. Fly Ash (FA)

Fly ash is a waste by-product from thermal power plant,

which use coal as a fuel. Fly ash contains substantial amounts

of silicon dioxide (SiO2) and calcium oxide (CaO). Fly ash is a

non-crystalline pozzolanic and slightly cementitious material.

On the base of these properties it can be converted into

meaningful wealth as an alternative construction material in

civil engineering works. Fly ash is collected from NTPC

Dadri, Ghaziabad, India, during the burning of pulverized coal

to produce steam for generation of energy in thermal power

stations was collected for the study. The collected fly ash,

characterized for physical and chemical properties are reported

in Table 2.

Table 2: Physical and Chemical Properties of Fly Ash

Physical Properties Chemical Properties

Property Value Constituents % by

weight

Type

Class F or

low lime

fly ash

Ignition loss 7.6

Specific

gravity 2.27 SiO2 61

Liquid limit 47 Al2O3 16.9

Plastic limit Non-plastic Fe2O3 7.24

Optimum

moisture

content (%)

26 CaO 3.74

Maximum dry

density (g/cm3) 1.6 MgO 2.4

Specific

surface (cm2/g) 4,220 Na2O3 2.7

Lime reactivity

(kg/cm2) 50 K20 1.04

Loss on

ignition (%) 7.6 SO3 1.51

C. Rice Husk Ash (RHA)

Rice husk ash is a predominantly siliceous material

obtained after burning of rice husk in a boiler or an open fire.

Lime reactivity test conducted on this ash indicate the fully

burned rice husk ash exhibits greater reactivity. This waste

material having pozzolonic properties can be utilized in the

stabilization for road construction. For this study, rice husk

ash was obtained from paddy mill, Roorkee. It was fine

grained siliceous in nature light weight and grey in color. The

physical properties are given in Table 3.

Table 3: Properties of Rice Husk Ash

Sr. No. Properties Values

1 SiO2 (%) 72.24

2 CaO (%) 4.12

3 MgO (%) 1.7

4 Fe2O3 + Al2O3 7.2

5 Specific Gravity 1.87

6 Lime Reactivity (kg/cm2) 34

III. LABORATORY INVESTIGATION AND INTERPRETATION

OF RESULTS

A. Standard Proctor Test

The geotechnical properties of soil (CBR, permeability,

etc.) are dependent on the moisture and density at which the

soil is compacted. Generally, a high level of compaction of

soil enhances the geotechnical parameters of the soil, so that

achieving the desired degree of relative compaction necessary

to meet specified or desired properties of soil is very

important. The aim of the Proctor test (moisture-density test)

was to determine the optimum moisture contents (OMC) and

maximum dry densities (MDD) of both untreated compacted

and treated stabilized soil-mixtures. In order to obtain these

parameters, heavy compaction test was employed for the

mentioned mixture proportions as per IS: 2720 (Part 8). The

results for OMC and MDD for soil stabilized with fly ash and

rice husk ash are as shown in Figure 3 and Figure 4

respectively.

0

20

40

60

80

100

0.001 0.01 0.1 1

Pe

rce

nt

Fin

er

(%)

Partical Size (mm)



ISBN 978-93-82338-01-7 | © 2012 Bonfring

Addition of FA & RHA alters the compaction

characteristics of soil sample. The dry density decreases and

moisture content increases for both the cases (Figs.3 & 4).

Typically, higher the concentration of FA & RHA, the greater

the alterations to the compaction characteristics are. The

increase of moisture contents is approximately linear with the

ash content. Increase of moisture content is more pronounced

for RHA than FA for having more surface area than FA. The

moisture increase is due to the hydration effect and the affinity

for more moisture during chemical reaction process. Decrease

in density is directly attributed to the flocculation/aggregation

and the formation of cementitious products.

B. California Bearing Ratio (CBR) Test

The California bearing ratio (CBR) is a penetration test for

evaluation of the mechanical strength of road sub-grade and

base courses. This test was conducted after 4 days of soaking

in water as per IS 2720 (Part 16). The results revealed from

the laboratory study are presented in Fig. 5.

Figure 5 shows the trend of improvement of CBR values

for both FA and RHA admixed soil samples. The rate of gain

of soaked CBR values are approximately linear for both the

cases. This trend is better maintained for soil sample admixed

with FA than the one of RHA. The increase of soaked CBR

value for RHA admixed soil sample showed linear

relationship with the ash content up to 30% after which this

increase is slackened. However, these CBR values are more

than that of 30% ash content. The increase of CBR value is

attributed to the formations of adhesive hydrated compounds

like calcium silicate hydrate and calcium aluminates hydrate

gels within the soil mass when fine soil particles comes in

contact with calcium ions, alumina and silica present in FA

and RHA.

C. Permeability test

Permeability is a measure of the ease in which water can

flow through a soil volume. It is one of the most important

geotechnical parameters. However, it is probably the most

difficult parameter to determine. In large part, it controls the

strength and deformation behaviour of soils. It directly affects

the quantity of water that will flow toward an excavation,

design of subgrade on permeable foundations and design of

the clay layer for a landfill liner. For fine grained soil as use in

this study falling head permeability test is done. The

permeability test results for soil admixed with FA and RHA

are shown in table 4.

Table 4: Permeability Results of Soil Admixed with FA and

RHA

Percentage

of Soil

Percentage

of Ash

Permeability (cm/sec)

FA RHA

100 0 8.61×10-10 8.61×10-10

95 5 1.5×10-9 6.41×10-8

90 10 6.5×10-9 2.71×10-8

85 15 4.8×10-8 8.4×10-7

80 20 3.27×10-7 6.47×10-6

75 25 8.6×10-7 5.8×10-6

70 30 4.7×10-6 6.14×10-5

65 35 2.57×10-5 7.48×10-4

0 100 7.5×10-2 1.5×10-2

As shown in the table permeability value of soil is

8.61×10-10 which is very low with respect to drainage

capability of pavement subgrade layer. Hence there is a need

to increase the permeability of the subgrade soil for better

drainage. Admixing 20% of FA to the soil increases the

permeability to 3.27×10-7 and 15 % of RHA to the soil

increases the permeability to 8.4×10-7 providing an effective

drainage for subgrade soil. Further addition of FA and RHA to

the soil keeps on increasing the permeability.

IV. CONCLUSIONS

Clayey soil selected for this study had poor drainage

condition. In order to improve the drainage its permeability

needs to be increased. This experimental study was aimed to

analyze the effect of admixing FA and RHA on the

permeability of clayey soil for improving its drainage

properties.

The additions of FA to the soil shows increase in OMC

from 17 to 26 % for and decrease in dry density from 1.88 to

1.52 gm/cc at varying ash content from 0 to 35 %. Similar

results are revealed for soil-fly ash admixture.

The addition of fly ash and rice husk ash to the soil

increases CBR linearly. However, in case of soil-RHA

mixture the rate of increment is nearly constant after 30 % of

ash content. This shows that 30 % of RHA can be considered

as an optimum content for soil stabilization.

Based on the extensive experimental study carried out, it

was noticed that the permeability of soil increased on

admixing FA and RHA, thereby improving the drainage of

pavement subgrade layer.



ISBN 978-93-82338-01-7 | © 2012 Bonfring

From this study, the FA and RHA may be effectively

utilized in soil to improve the permeability and thus improving

drainage of subgrade layer.

REFERENCES

[1] Anupam A. K., Kumar P. and R.N. Ransinchung G.D, “A comparative

study of sugar cane bagasse ash & fly ash for use in pavement

construction” international conference of highway engineering,

Thailand, Bangkok, pp.469-474 ,April 2012.

[2] Benson, C. H., and Trast, J. M., “Hydraulic Conductivity of Thirteen

Compacted Clays”, Clays and Clay Minerals, Vol. 43, No. 6, pp. 669-

681, 1995.

[3] FHWA, 2006. Geotechnical aspects of pavements, Report FHWA

NHI05037, Federal Highway Administration, Washington D. C

[4] Head, K. H., “Manual of Soil Laboratory Testing”, Vol. 2: Permeability,

Shear Strength and Compressibility Tests, New York: Halsted Press,

1992-2nd edition.

[5] IRC, 2001. Guidelines for the design of flexible pavements, IRC:

372001, The Indian Roads Congress, New Delhi.

[6] Kumar, P. and Singh, S. P. (2008). “Fiber-reinforced fly ash subbases in

rural roads.” Journal of Transportation Engineering ASCE, Vol. 134 (4),

171-180.

[7] Mesri, G., and Olson, R. E., “Mechanics Controlling the Permeability of

Clays”, Clays and Clay Minerals, Vol. 19, pp. 151-158 (1971).

[8] Tavenas, F., Leblond, P., Jean, P. and Leroueil, S., “The Permeability of

Natural Soft Clays. Part I: Methods of Laboratory Measurement”, CAN.

GEOTECH. J. VOL. 20, pp. 629-644, (1983).