STUDY ON UNCONFINED COMPRESSIVE … · Ashis Kumar Bera 60 Emirates Journal for Engineering Research, Vol. 18, No.1, 2013 of unconfined compression strength (UCSURSP) of pond ash

Emirates Journal for Engineering Research, 18 (1), 59-65 (2013) (Regular Paper)

59

STUDY ON UNCONFINED COMPRESSIVE STRENGTH OF POND ASH SOIL MIXTURE REINFORCED WITH JUTE GEOTEXTILES

Ashis Kumar Bera

Bengal Engineering and Science University, Shibpur , Howrah-711 103, India, E-mail: [email protected]

(Received June 2012 and Accepted February 2013)

قد تم تنفيذ سلسلة من االختبارات المعملية لدراسة قوة الضغط غير المحصورة لبرآة رماد تربة هذا البحث في ، في ةغير المحصوريقلل بشكل ملحوظ قيمة قوة ضغط ) ٪30٪ إلى 0(زيادة الرماد . مدعومة وغير مدعومة

مع اضافة طبقات . التغييرات فى قوة ضغط غير المحصورة ليست ملموسه) ٪40فوق (حين، مع اضافة برآة رماد قيم قوة الضغط غير المحصورة تزىد بشكل ) التربة، برآة الرماد، خليط رماد برآة تربة(من الجوت للعينات

ضغط التربة غير المحصورة بداللة قوة ضغط غير المحصورة للتنبؤ بقوة يوقد تم تطوير نموذج غير خط. ملحوظ لتربة غير مدعومة

In the present investigation a series of laboratory tests has been performed to study the unconfined compression strength of soil, pond ash and also pond ash mixed soil for both unreinforced and reinforced conditions. With increase in pond ash content (0 % to 30%) of the pond ash mixed soil, the value of unconfined compression strength decreases significantly, whereas, with addition of pond ash ( above 40 % ) the changes of unconfined compression strength of pond ash mixed soil is not appreciable. With introduction of jute geotextile layers of reinforcement to the samples ( soil, pond ash, and soil pond ash mixture ) the values of unconfined compression strength increases significantly. A non linear power model has been developed to predict the unconfined compression strength of soil pond ash mixture reinforced with jute geotextile layers of reinforcement in terms of unconfined compression strength of unreinforced soil pond ash mixture, number of layers of jute geotextile reinforcement and also pond ash content ( % ). Keywords: Unconfined Compressive Strength; Pond Ash; Jute Geotextile; Dry Unit Weight; Power Model.

1. INTRODUCTION

Nowadays pond ash/ fly ash have become an attractive construction material because of its self hardening character, which depends on the availability of free lime in it. Efforts have always been made by the researchers to make pertinent use of pond ash in road constructions in the localities, which exists in the vicinity of thermal power stations. Jute geotextile can reinforced the soils, which are usually weak in tension at the initial stages. Ramaswamy and Aziz[20] reported that after jute geotextile placed on the weak subgrade, the subgrade stiffens and becomes stronger on consolidation with time under the action of granular sub-base surcharge, self weight of pavement, construction rolling and traffic loads. They also reported that the gain in strength of the subgrade with time can well be compensated for the loss of strength of the jute fabric within the same time frame. For obtaining the maximum benefit of pond ash/ fly

ash mixed soil embankment, subgrade the introduction of jute geotextile reinforcement into the pond ash/ fly ash mixed soil is necessary. Initially jute geotextile provide strength to the newly constructed jute geotextile reinforced pond ash/ fly ash mixed soil structure, but with times the strength of jute geotextile decrease. Whereas with time the strength of pond ash/ fly ash mixed soil increases. A number of researchers studied the different engineering properties of fly ash mixed soil[ 16, 22, 12, 10, 23, 11, 18, 13 ]. Bera et al.[7] developed a nonlinear power model to predict the unconfined compression strength of reinforced pond ash. In the present investigation attempt has been made to study the unconfined compression strength of pond ash mixed soil reinforced with jute geotextile. An attempt also been made to develop a regression model for predicting unconfined compression strength ( RSPUCR ) of pond ash mixed reinforced soil in terms

Ashis Kumar Bera

60 Emirates Journal for Engineering Research, Vol. 18, No.1, 2013

of unconfined compression strength ( URSPUCS ) of pond ash mixed soil, pond ash content (PC) and also number of layers of reinforcement (N).

2. MATERIALS In the present investigation soil and pond ash have been used as construction materials and jute geotextiles as reinforcement.

2.1 Construction Materials

The soil sample used in the present investigation has been collected from the University Campus, West Bengal, India and pond ash collected from the ash pond of Kolaghat Thermal Power Station, India. The grain size distribution tests and also liquid limit, plastic limit tests for both the samples have been performed in the Soil Mechanics Laboratory of Civil Engineering Department of this University. Fig.1 shows the grain size distribution curves for soil and pond ash samples and in accordance with the ASTM D2487[2] the pond ash and soil are designated as SM and MH respectively. To determine the maximum dry unit weight and optimum moisture content ( OMC ) of the pond ash, soil and also soil pond ash mixture, compaction tests have been performed in the Soil Mechanics Laboratory in accordance with ASTM D698[1]. Fig. 2 shows the dry unit weight versus moisture content curves for pond ash, soil and also soil pond ash mixture. From the figure (Fig.2) it is found that with increase in pond ash content from 0 % to 100 %, the maximum dry unit weight decreases and optimum moisture content increases. Nicholson & Kashyap[18] also found the similar types of results in case of fly ash stabilization of tropical Hawaiian soils.

Figure1 Grain size distribution curves for construction materials ( Soil and pond ash )

Figure 2 Typical dry unit weight versus moisture content

curves for soil, pond ash, and soil pond ash mixture samples.

2.2 Jute geotextile reinforcement

Jute geotextile has been collected from local market at Kolkata, West Bengal, India. The engineering properties of Jute geotextile samples viz., mass per unit area, thickness, apparent opening size, and wide width tensile strength have been determined in accordance with ASTM D 5261[3], ASTM D5199[4], ASTM D 4751[5] , and ASTM D4595[6] respectively from the laboratory tests and are presented in the Table 1.

Table 1. Engineering properties of Jute geotextile

Engineering Properties Property Value Mass per unit area (gm / m2) 210

Thickness (mm) 1.10 Apparent opening size

(mm) 0.85

Breaking strength Warp ( kN / m ) Weft ( kN / m )

3.20 3.00

Elongation at break % Warp (Max) Weft (Max)

8.86 9.84

3 EXPERIMENTAL PROGRAMME AND TEST PROCEDURE To study the unconfined compression strength of unreinforced and reinforced soil, pond ash and soil pond ash mixture, two different series ( A and B ) of UCS tests have been planned (Table 2). Series A have been chosen to know the effect of pond ash contents (%) and also effect of dry unit weight on unreinforced soil pond ash mixture. In the series B has been chosen to study the effect of number of jute geotextile layers of reinforcement on reinforced soil pond ash mixture. In the present investigation the number of layers has been chosen (1 to 4) on the basis of the earlier researcher[7]. Before preparing the sample on pond ash soil mixture, both the soil and pond ash (in desired percentage) has

0 10 20 30 40 50Moisture content

10

12

14

16

18

20

Dry

uni

t Wei

ght

( kN

/ m

3 )

Pond ash content ( % )

0

20

50

80

100

0.001 0.010 0.100 1.000 10.000Particle Size ( mm )

0

10

20

30

40

50

60

70

80

90

100

% F

iner

Pond ash ( SM ) G = 2.21 Cc = 2.64 Cu = 6.25

Soil ( MH ) G = 2.62 Cc = 5.44 Cu = 11.11 LL = 56.5 % PL = 31.27 %

Study on unconfined compressive strength of pond ash soil mixture reinforced with jute geotextiles

Emirates Journal for Engineering Research, Vol. 18, No.1, 2013 61

been mixed thoroughly in dried condition. Depending on the desire moisture content require amount of water was mixed thoroughly with dry soil, pond ash and also soil pond ash mixture. The unreinforced and reinforced cylindrical soil, pond ash and soil pond ash mixed samples have been prepared in the metallic split mould having dimension 38 mm (dia.) × 76 mm (height). The samples have been compacted in the split mould, layer by layer with the help of a tamping rod. The size of the sample and methods of

preparation of the sample have been chosen on the basis of earlier researchers [14]. The weights of the prepared samples have been checked against the required unit weight and moisture content. The samples, having weight not within ±0.25% of the required weight, have been rejected[8]. The methods of placement of the reinforcement in to the reinforced samples and test procedure are already presented elsewhere[7].

Table 2 Plan of unconfined compression strength test

Series Construction Material Dry unit weight

( kN / m3 ) Moisture content Number of

Reinforcement Layers A

Soil + 0 % pond ash

13.94 to 16.51

20.00 ( OMC )

UR

A Soil + 10 % pond ash 12.60 to 15.00 23.00( OMC ) UR A Soil + 20 % pond ash 12.59 to 15.10 23.20 ( OMC ) UR

A Soil + 30 % pond ash 13.13 to 15.07 23.50 ( OMC ) UR A Soil + 40 % pond ash 13.50 to 15.06 24.00 ( OMC ) UR A Soil + 50 % pond ash 12.90 to 15.20 24.20 ( OMC ) UR A Soil + 60 % pond ash 12.80 to 15.30 24.60 ( OMC ) UR A Soil + 70 % pond ash 12.30 to 14.60 25.00 ( OMC ) UR A Soil + 80 % pond ash 12.10 to 14.54 26.00 ( OMC ) UR A Soil + 90 % pond ash 11.94 to 14.52 26.50 ( OMC ) UR A 100 % pond ash 10.89 to 12.35 28.00 ( OMC ) UR B Soil + 0 % pond ash 15.94 (

maxdγ ), 20.00 ( OMC ) 1 to 4 B Soil + 10 % pond ash 14.94 (

maxdγ) 23.00( OMC ) 1 to 4

B Soil + 20 % pond ash 14.80( maxdγ ) 23.20 ( OMC ) 1 to 4 B Soil + 30 % pond ash 14.75(

maxdγ ) 23.50 ( OMC ) 1 to 4 B Soil + 40 % pond ash 14.70(



maxdγ ) 24.60 ( OMC ) 1 to 4 B Soil + 70 % pond ash 14.20( maxdγ ) 25.00 ( OMC ) 1 to 4 B Soil + 80 % pond ash 14.10( maxdγ ) 26.00 ( OMC ) 1 to 4 B Soil + 90 % pond ash 14.00(

maxdγ ) 26.50 ( OMC ) 1 to 4 B 100 % pond ash 11.93(

maxdγ ), 28.00 ( OMC ) 1 to 4

4 RESULTS AND DISCUSSIONS Figure 3 shows the plots of unconfined compression strength ( UCS ) versus dry unit weight curves for pond ash soil mixture with varying pond ash content ( 0 - 30 % ). The plots of unconfined compression strength ( UCS ) versus dry unit weight curves for pond ash soil mixture with varying pond ash content ( 40- 100 % ) is shown in Fig.4. Figure 5 shows the plots of unconfined compression strength versus pond ash content ( % ) curves for reinforced samples. The plots of unconfined compression strength versus number of layers of reinforcement curves for reinforced samples are shown in Fig.6. Based on experimental results discussions are made as follows:

Figure 3 UCS versus dry unit weight curves for pond ash

soil mixture with varying pond ash content ( 0- 30 % )

12 13 14 15 16 17Dry unit Weight ( kN / m 3 )

0

200

400

600

800

Unc

onfin

ed C

ompr

essi

on S

treng

th (

kN /

m 2

)


0

10

20

30

Ashis Kumar Bera


Figure 4 UCS versus dry unit weight curve for pond ash soil

mixture with varying pond ash content (40 - 100 %)

4.1 Unconfined compression strength of soil, pond ash and also soil pond ash mixture

Figs.3 - 4 shows the unconfined compression strength versus dry unit weight curves with varying pond ash contents 0 % to 30 % and 40 % to 100 % respectively. From the curves (Fig.3) it is observed that with increase in dry unit weight of the soil and soil pond ash mixture (up to 30 %) samples the UCS increases. From the curves (Fig.3) it is also observed that with increase in pond ash content (0 % to 30 %) the values of UCS decreases for any dry unit weights under study. It is may be due to that with increase in pond ash content, the soil pond ash mixture became less clayey. Similar types of results have been obtained in case of fly ash stabilization of tropical Hawaiian soils[18]. Whereas in case of Fig.4 it is observed that with increase in pond ash content from 40 % to 100 %, decreases of UCS values are insignificant for all dry unit weights ( under study ) . It is may be due to that above 40 % pond ash content in the soil pond ash mixture, the clay content became very less (less than 9.2 %). As a result above 40 % pond ash content in the soil pond ash mixture, the cohesive strength of the soil pond ash mixture may be negligible contribution to develop unconfined compression strength.

4.2 Unconfined compression strength of jute geotextile reinforced pond ash mixture

From the previous section it is found that with increase in pond ash contents in soil pond ash mixture samples, the values of UCS decreases. Nicholson & Kashyap[18] also reported that increase in fly ash contents (0 % to 25 % ) in case of fly ash stabilization of tropical Hawaiian soils tested at one day, the values of UCS decreases. But with time the values of UCS of fly ash stabilization of tropical Hawaiian soils increases significantly. A number of researchers[21,15] also reported that with time the fly ash samples gaining strength significantly. So, jute getextile can be used as reinforcement to the pond ash mixed soil. Though, with time the strength of jute

geotextile decreases, as it is biodegradable reinforcing material. Ranganathan[19] reported that once a road has been fully constructed and is in use, the jute geotextile becomes superfluous and hence the biodegradability of jute does not pose problems for their end use. Fig. 5 shows the plots of UCS versus number of layers of reinforcement curves for soil, pond ash and also soil pond ash mixture. From the figure (Fig. 5) it is found that with increase in number of layers up to 4, the value of UCS increases for all types of samples ( soil, pond ash and also soil pond ash mixture). Fig.6 shows the plots of UCS of soil pond ash mixture versus pond ash content (%) curves. From the curves (Fig.6) it is also observed that with increase in pond ash content in the soil pond ash mixture samples, the values of UCS decreases for unreinforced case as well as reinforced case (reinforcement layers 1 to 4). But rate of decrease is became less with introduction of number of layers of reinforcement. It is may be due to that with introduction of horizontal layers of reinforcement to soil pond ash mixture samples, the frictional forces developed between the reinforcement and soil pond ash mixture samples.

Figure .5 Unconfined compression strength versus number of layers curves for reinforced samples

Figure.6 Unconfined compression strength versus pond ash content ( % ) curves for reinforced samples

10 11 12 13 14 15 16 Dry unit Weight ( kN / m 3 )

0

200

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600

800U

ncon

fined

Com

pres

sion

Stre

ngth

( kN

/ m

2 )


40

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10 20 30 40 50 60 70 80 90 100Pond ash content ( % )

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ompr

essi

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th (

kN /

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1

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4

No. of Layers ( N )

Unreinforced

0 1 2 3 4 5 6 7 8Number of layers ( N )

0

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ompr

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5 NUMERICAL MODEL FOR PREDICTING RSPUCS

Unconfined compression strength of reinforced soil pond ash mixture depends on a number of factors such as percent of pond ash content, dry unit weight, number of layers of reinforcement (N) etc. A number of researchers[17,7] have been tried to develop the mathematical model to predict the unconfined compression strength of reinforced fly ash. In the present investigation a non linear power model have been developed to predict the unconfined compression strength of reinforced soil pond ash mixture ( RSPUCR ) in terms of unconfined compression strength of soil pond ash mixture, pond ash content (%) and also number of layers of reinforcement. Multiple regression analysis has been performed to develop this model. The details of the multiple regression methods have been presented elsewhere[9]. The power model is so developed to predict the RSPUCR as follows:

( ) ( )PCURSPRSP NUCSUCS 995266.0)(24063.97 2307.0241571.0 ××= ..(1)

Where, URSPUCS =Unconfined compression strength of

unreinforced soil pond ash mixture

=RSPUCR Unconfined compression strength of soil pond ash mixture reinforced with jute geotextile layers of reinforcement. N =Number of layers of jute geotextile reinforcement PC = pond ash content ( % ). Figure.7 shows the plots of observed RSPUCR

versus predicted RSPUCR . From the figure (Fig.7) it

found that all the predicted values are within 10% error. For knowing the efficiency of the model the values of multiple coefficient of determination ( R2 ), standard error ( Es ) have been presented in the figure 7. Table 3 presents the comparison of RSPUCR (Predicted, using additional data not used in developing the model) and corresponding observed

RSPUCR for validation of the model. The above model (Eq.1) may be helps to estimate the values RSPUCR . However, further refining of these models may be done with more data bases containing the varying types of soils, pond ash and also varying types of jute geotextile reinforcements.

Figure.7 Observed unconfined compression strength versus predicted unconfined compression strength

Table 3 Comparison of RSPUCR (Predicted, using additional data not used in developing the model)

and corresponding observed RSPUCR .

URSPUCS ( kN / m2)


Number of reinforcement Layers

( N )

RSPUCR

(kN / m2) ( Observed )

RSPUCR

( kN / m2) ( Predicted )

170 90 4 360 302 210 30 2 350 360 290 10 2 380 428 280 60 2 330 335

6 CONCLUSIONS Based on the experimental results and discussions made, the following conclusions may be drawn:

• With increase in dry unit weight of soil, pond ash and also soil pond ash mixture the values of unconfined compression strength (UCS) increases.

• The value of unconfined compression strength (UCS) of soil pond ash mixture decreases significantly with increase in pond ash content to soil up to 30 %. But pond ash content with in the range of 30 % to 100 %,

the change in the values of unconfined compression strength is insignificant.

• With introduction of jute geotextile layers of reinforcement to the soil pond ash mixture samples, the values of unconfined compression strength increases irrespective of addition of pond ash content ( % ) to soil pond ash mixture .

• The proposed nonlinear power model may be use full for practicing engineers to estimate the RSPUCR in the field. However, further refining of the model is necessary with more databases containing the varying

100 1000 10000Observed unconfined compression strength ( kN / m 2 )

100

1000

10000

Pred

icte

d un

conf

ined

com

pres

sion

stre

ngth

( kN

/ m

2 )

0 % Variation line+10 % Variation line

-10 % Variation line

R2= 0.910 Es= 0.036 kN/R2

n = 40

Ashis Kumar Bera


types of soils, pond ash and also varying types of jute geotextile reinforcements.

Nomenclature UCS Unconfined compression strength ( kN / m2 )

RSPUCR Unconfined compression strength of pond ash mixed reinforced soil in terms of unconfined compression strength ( kN / m2 )

URSPUCS Unconfined compression strength of pond ash mixed soil (kN / m2 )

PC Pond ash content ( %) N Number of layers of reinforcement. n Number of observations

maxdγ Maximum dry unit weight 2R Multiple coeficient of determination sE Estimation of standard error

REFERENCE 1. ASTM D 698 “Standard test method for

laboratory compaction characteristics of soil using standard effort (600kN-m/m3)”, American Society of Testing Materials, Philadelphia, PA.

2. ASTM D2487 “Standard practice for classification of soils for engineering purposes (Unified Soil Classification System)”, American Society of Testing Materials, Philadelphia, PA.

3. ASTM D 5261. “Standard Test Method for Measuring Mass per Unit area of Geotextiles”. American Society of Testing Materials, Philadelphia, PA.

4. ASTM D 5199. “Standard Test Method for Measuring the nominal Thickness of Geosynthetics”. American Society of Testing Materials, Philadelphia, PA.

5. ASTM D 4751. “Standard Test Method for Determining Apparent Opening Size of Geotextile”. American Society of Testing Materials, Philadelphia, PA.

6. ASTM D 4595. “Standard Test Method for Tensile Properties of Geotextile by the Wide Width Strip Method”. American Society of Testing Materials, Philadelphia, PA.

7. Bera A.K., Chandra, S.N., Ghosh, A., and Ghosh, A. ( 2009 ) “Unconfined compression strength of fly ash reinforced with jute geotextiles” , Journal of Geotextiles and Geomembranes, 27 ( 5 ): 391-398.

8. Bera A.K., Ghosh, A., and Ghosh, A. ( 2009 ) “Shear strength response of reinforced pond ash” , Journal of Construction and Building Materials, 23 ( 6 ): 2386- 2393.

9. Bera, A.K., Ghosh, A., and Ghosh A. ( 2005 ) “Regression model for bearing capacity of square footing on reinforced pond ash”.

Geotextiles and Geomembranes, 23 ( 3 ) : 261-285.

10. Bin-Shafique, S., Edil, T., Benson, C.H., and Senol, A. ( 2004 ) “Incorporating a fly ash mixed layer in to pavement design- case study”. Geotechnical Engineering, Institutions of Civil Engineers, London, 157 ( GE4 ) : 239-249.

11. Cokca, E. ( 2001 ) “Use of class C fly ashes for the stabilization of expansive soil”. Journal of Geotechnical and geoenvironmental engineering, 127 ( 7 ): 568-573.

12. Edil, T.B., Acosta, A.H., and Benson, C.H. (2006) “Stabilizing soft fine grained soils with fly ash”. Journal of Materials of Civil Engineering, ASCE, 18( 2 ) :283-294.

13. Ferguson, G. ( 1993 ) “Use of self cementing fly ashes as a soil stabilization agent”. Geotechnical Special Publication No. 36, ASCE, New York, 1 - 14.

14. Ghosh, A., Subbarao, C. ( 2007 ) “Strength characteristics of Class F fly ash modified with lime and gypsum”. Journal of Geotechnical and Geoenvironmental Engineering Div. ASCE, 133( 7 ): 757 – 766.

15. Gray, D.H., Lin, Y.K., (1972 ) “Engineering properties of compacted fly ash”. Journal of Soil Mechanics and Foundation Engineering Div. ASCE, 98 ( 4 ):361 – 380.

16. Jongpradist, P., Jumlongrach, N., Sompote, Y., Somchai, C. ( 2010 ) “Influence of fly ash on unconfined compressive strength of cement-admixed clay at high water content”, Journal of Materials in Civil Engineering, ASCE, 22 (1): 49-58.

17. Kaniraj, S.R., Havanagi, V.G. ( 2001 ) “Behavior of cement-stabilized fibre-reinforced fly ash–soil mixtures”. Journal of Geotechnical and Geoenvironmental Engineering, ASCE 127 (7):574-584.

18. Nicholson, P.G., and Kashyap, V. (1993) “Fly ash stabilization of tropical Hawaiian soils”. Fly Ash for Soil Improvement, Geotechnical Special publication No. 36, ASCE, New York, 15- 29.

19. Ranganathan, S.R., ( 1994 ) “Development and potential of jute geotextiles”. Journal of Geotextiles and Geomembranes 13: 421 – 433.

20. Ramaswami, S., Aziz, M. ( 1989 ) “ Jute geotextile for roads”. International Workshops on Geotextile, India, 137-143.

21. Raymond, S. ( 1958 ) “Utilization of pulverized fuel ash”. Civil Engineering and Public Works Review. London, Vol.53, pp. 1013 -1016.

22. Solanki, P., Khoury, N., and Zaman, M.M.,



(2009) “Engineering properties and moisture susceptibility of silty clay mixed with lime, class C fly ash, and cement kiln dust”. Journal of Materials in Civil Engineering, ASCE, 21 (12 ): 749-757.

23. Trzebiatowski, B., Edil, T., and Benson, C.H (2004) “Case study of subgrade stabilization using fly ash” State Highway 32. Recycled Materials in geotechs, GSP No. 127, A. Aydilek and J.Wartman ( eds. ), ASCE, Reston Va., 123-136.

Documents

STUDY ON UNCONFINED COMPRESSIVE … · Ashis Kumar Bera 60 Emirates Journal for Engineering Research, Vol. 18, No.1, 2013 of unconfined compression strength (UCSURSP) of pond ash