IJITE8March2564(1)(3).pdf

7/26/2019 IJITE8March2564(1)(3).pdf

1/14

IJITE Vol.03 Issue-03, (March, 2015) ISSN: 2321-1776

Impact Factor- 3.570

A Monthly Double-Blind Peer Reviewed Refereed Open Access International e-Journal - Included in the International Serial Directories

International Journal in IT and Engineering

http://www.ijmr.net.inemail id- [email protected] Page 104

STUDY OF SLOPE STABILITY OF ASH DYKE RAISINGS UNDER STATIC CONDITION

Nazimali N. Chinwala

Assistant Professor,

Civil Engineering Department, Parul Institute of Engg. & Tech., Waghodia, India

ACKNOWLEDGEMENT:

Author is very thankful to Essar Engineering Services - Hazirafor providing software facility forstability analysis of slopes.

ABSTRACT

There are more than 85 thermal power plants in India; of which majority are coal basedproducing approximately 100 million tons of coal ash yearly. With increased utilization of

generated ash through usage in concrete, brick making and other embankment constructions,

the utilization of the ash has increased considerably. However, the percentage of utilization is

still insufficient and for most of the power plants ash is deposited in form of ash-pond in the

vicinity of power plant as waste material covering several acres of valuable land. Moreover, for

new power plants the land acquisition is a major issue and with limited area, rapid vertical

expansions of Ash-dykes are inevitable. Present paper describes static analysis carried out on the

ash-dyke sections with various raising stages. Based on the state of the art practice in the India,

starter dyke section and subsequent raising geometry is selected. Using the in-situ test data

performed on the existing ash-dykes, geotechnical properties of the deposited ash ponds are

selected to perform the static analysis of the ash-dyke sections. A series of stability runs are

carried out to map the factor of safeties at various stages of ash-dyke raising. Sensitivity analysis

is carryout out to examine the influence of the geotechnical properties of the deposited ash in

the ash-dyke. Present study helps the geotechnical professionals to choose better geometries of

ash-dykes during planning stage to ensure sustainable performance.

KEY WORDS: Ash-dyke; static; slope stability; factor of safety; Sensitivity analysis.

7/26/2019 IJITE8March2564(1)(3).pdf

2/14

7/26/2019 IJITE8March2564(1)(3).pdf

3/14






(outflow point) are similar to those of silty soils. Gandhi S. R. (2005) published a paper Design

and Maintenance of Ash Pond for Fly Ash Disposal in which he explained various methods of

raising the dyke by describing its advantage and disadvantage. He also suggested that ash dykeshould be supervised regularly and necessary remedial measures should be taken and

highlighted important issues related to design, construction, operation and maintenance of ash

pond.

MATERIAL PROPERTIES

Material properties used for the study and analysis, were taken from the published project data

of site Rajpura Thermal Power Project, Punjab, and are as shown in Table 2. Typical cross

section used for the analysis is shown in Fig. 1:

Fig. 1: Typical layout of the section

Table 2: Material properties used for the analysis

Material No. & (Color) Soil TypeC

(KN/m2)

(KN/m3)

k (m/sec)

1

(Orange)Clayey Silt 90 0 18 1 x 10

-7

2

(Brown)Fill Material 35 0 17 1 x 10

-7

3

(Gold)Sand 0 36 17.8 1 x 10

-3

4(Light Blue)

Loose Flyash 0 29 12.2 1 x 10-5

5

(Grey)Compacted Flyash 0 32 14.2 1 x 10

-7

7/26/2019 IJITE8March2564(1)(3).pdf

4/14






OBJECTIVES

The focus of this research project was to design an optimum ash dyke and use fly ash forconstruction of ash dykes. More specifically the following two objectives were identified:

1) To design an ash dyke for optimum factor of safety by analyzing the dam section using finite

element based software SLIDE

2) To recommend the optimum design for the ash dyke by considering factor of safety in Static

condition.

ANALYSIS

For the analysis purpose, a three-stage dyke was considered stage wise by upstream method on

the starter dyke with different U/S and D/S slopes under different conditions by finite element

based software SLIDE by using Morgenstern-Price Method. Soil properties were assigned and

slope stability was carried out for Static condition, and the seepage study along with sensitivity

analysis was also carried out. In all the raisings of different slopes for the computation of slip

surface, Global Failure of ash dyke is taken into consideration.

STARTER DYKE

For the static stability analysis the starter dyke was taken of three different slopes i.e. D/S (1:2)

U/S (1:2), D/S (1:2) U/S (1:1.5) and D/S (1:2.5) U/S (1:2). The height of starter dyke was kept as

6m. The top width was also kept as 6m. Fig. 2 shows the analysis of Starter dyke with D/S (1:2)

U/S (1:2) slopes and Table 3 shows FOS for different slopes in starter dyke.

Fig. 2: Starter Dyke D/S (1:2) U/S (1:2) (FOS = 2.337)

7/26/2019 IJITE8March2564(1)(3).pdf

5/14






Table 3: FOS for different Slopes of Starter dyke

Starter Dyke FOS in StaticCondition Remarks

D/S (1:2) U/S (1:2) 2.337 D/S Slope

D/S (1:2) U/S (1:1.5) 2.334 D/S Slope

D/S (1:2.5) U/S (1:2) 2.674 D/S Slope

RAISINGS

Starter Dyke with D/S (1:2) U/S (1:2) Slopes

For starter dyke with D/S (1:2) U/S (1:2) slopes different raisings (Stage I, Stage II, and Stage III)were done with slopes D/S (1:2) U/S (1:2) respectively. Fig. 3 shows typical analysis of Stage III

stability analysis. The result of Stage I and Stage II analysis is shown in Table 4.

Fig. 3: Starter Dyke D/S (1:2) U/S (1:2), Stage I D/S (1:2) U/S (1:2), Stage II D/S (1:2) U/S

(1:2), Stage III D/S (1:2) U/S (1:2) (FOS = 2.214)

For starter dyke with D/S (1:2) U/S (1:2) slopes different raisings (Stage I, Stage II, and Stage III)

were done with slopes D/S (1:2.5) U/S (1:2.5) respectively. Fig. 4 shows typical analysis of Stage

III stability analysis. The result of Stage I and Stage II analysis is shown in Table 4.

7/26/2019 IJITE8March2564(1)(3).pdf

6/14






Fig. 4:Starter Dyke D/S (1:2) U/S (1:2), Stage I D/S (1:2.5) U/S (1:2.5), Stage II D/S

(1:2.5) U/S (1:2.5), Stage III D/S (1:2.5) U/S (1:2.5) (FOS = 2.24)

For starter dyke with D/S (1:2) U/S (1:2) slopes different raisings (Stage I, Stage II, and Stage III)

were done with slopes D/S (1:3) U/S (1:3) respectively. Fig. 5 shows typical analysis of Stage III


Fig. 5: Starter Dyke D/S (1:2) U/S (1:2), Stage I D/S (1:3) U/S (1:3), Stage II D/S (1:3)

U/S (1:3), Stage III D/S (1:3) U/S (1:3) (FOS = 2.552)

Starter Dyke with D/S (1:2) U/S (1:1.5) Slopes

For starter dyke with D/S (1:2) U/S (1:1.5) slopes different raisings (Stage I, Stage II, and Stage III)


7/26/2019 IJITE8March2564(1)(3).pdf

7/14







Fig. 6: Starter Dyke D/S (1:2) U/S (1:1.5), Stage I D/S (1:2) U/S (1:2), Stage II D/S (1:2)





Fig. 7: Starter Dyke D/S (1:2) U/S (1:1.5), Stage I D/S (1:2.5) U/S (1:2.5), Stage II D/S(1:2.5) U/S (1:2.5), Stage III D/S (1:2.5) U/S (1:2.5) (FOS = 2.255)

7/26/2019 IJITE8March2564(1)(3).pdf

8/14









Fig. 8: Starter Dyke D/S (1:2) U/S (1:1.5), Stage I D/S (1:3) U/S (1:3), Stage II D/S (1:3)


Starter Dyke with D/S (1:2.5) U/S (1:2) Slopes

For starter dyke with D/S (1:2.5) U/S (1:2) slopes different raisings (Stage I, Stage II, and Stage III)



7/26/2019 IJITE8March2564(1)(3).pdf

9/14






Fig. 9: Starter Dyke D/S (1:2.5) U/S (1:2), Stage I D/S (1:2) U/S (1:2), Stage II D/S (1:2)U/S (1:2), Stage III D/S (1:2) U/S (1:2) (FOS = 2.284)




Fig. 10: Starter Dyke D/S (1:2.5) U/S (1:2), Stage I D/S (1:2.5) U/S (1:2.5), Stage II D/S

(1:2.5) U/S (1:2.5), Stage III D/S (1:2.5) U/S (1:2.5) (FOS = 2.505)



7/26/2019 IJITE8March2564(1)(3).pdf

10/14







Fig. 11: Starter Dyke D/S (1:2.5) U/S (1:2), Stage I D/S (1:3) U/S (1:3), Stage II D/S (1:3)


SENSITIVITY ANALYSIS

For the sensitivity analysis in static condition, for Starter dyke D/S (1:2) & U/S (1:1.5), Stage I D/S

& U/S (1:2.5) slopesthe properties of flyash which are taken into consideration for loose flyash

(Material 4), and Compacted flyash (Material 5) are given in the Table 5 and the graphs of

comparison of unit weights v/s FOS and Phi v/s FOS for different materials are shown in Figures12 and 13.

Table 5: Ash properties taken into consideration in Sensitivity analysis

7/26/2019 IJITE8March2564(1)(3).pdf

11/14






11 12 13 14 15 16

2.6

2.8

3.0

3.2

FactorofSafety

Unit Weight (kN/m3)

Loose Ash

Compacted Ash

Fig. 12: Comparison of Unit weights v/s FOS for Loose and Compacted ash in Static

condition

26 28 30 32 34

2.5

3.0

3.5

FactorofSafety

Phi (deg)

Loose Ash

Compacted Ash

Fig. 13: Comparison of Phi v/s FOS for Loose and Compacted ash in Static condition

CONCLUSION

1) In Static condition the ash dyke constructed using upstream method gives factor of safety

above 2.137 for all different types of slopes which are found to be safe.

2) For the Sensitivity analysis in Static condition, for Starter dyke D/S (1:2) & U/S (1:1.5), Stage I

D/S & U/S (1:2.5) slopes the value of FOS decreases from 2.86 to 2.8 and 2.92 to 2.8 for loose

ash and compacted ash respectively with increase in the unit weight from 10.5 to 16 KN/m3

inboth compacted ash and loose ash. While, the value of FOS increases from 2.78 to 2.92 and 2.81

to 2.89 for loose ash and compacted ash respectively with increase in the value of phi from 26

to 35 for both compacted ash and loose ash.

7/26/2019 IJITE8March2564(1)(3).pdf

12/14






REFERENCES

1.

IS 78941975: Stability Analysis of Earth Dams, Bureau of Indian Standards, New Delhi.

2.

Journal of Geotechnical Engineering ASCE. Vol. 110, No GT6, pp. 701-718.

3. Sherard J. L., Dunnigan L. P., and Talbot J. R. (1984), Basic Properties of Sand and Gravel

Filters, Journal of Geotechnical Engineering ASCE. Vol. 110, No GT6, pp. 684-699.

4.

Gandhi S. R. and Mathew G. V. (1996), Granular Filter for Ash Dykes, Proceeding, Indian

Geotechnical Conference, Vol. 1, pp. 532535.

5. Gandhi S. R., Dey A. K. and Selvam S. (1999), Blast Densification of Pond Ash, Fly Ash

Disposal and Deposition: Beyond 2000 AD.

6. Sridharan A., Pandian N. S., and Srinivas S. (1999), Shear Strength Characteristics of Pond

Ash for Use as Structural Fills, Fly Ash Disposal and Deposition: Beyond 2000 AD.

7. Gupta K. K., Raju V. S., and Manoj Datta (1999), Gradation, Compaction and Strength of

Coal Ash, Fly Ash Disposal and Deposition: Beyond 2000 AD.

8. Gandhi, S. R. (2005), Design and Maintenance of Ash Pond for Fly Ash Disposal,

Proceeding, Indian Geotechnical Conference, Vol. 1, pp. 8590.

9.

Choudhary A. K., Jha J. N. and Verma B. P. (2009), Construction of an Ash Pond with

Waste Recycled Product, Fly Ash and Locally Available Soil - A Case Study,

Proceeding, IGC2009, Guntur, pp. 565-568.

7/26/2019 IJITE8March2564(1)(3).pdf

13/14






Table 4: FOS for all slopes in Static condition

Starter Dyke Stage I Stage II Stage III

FOS in

Static

Condition

Remarks

D/S(1:2) U/S(1:2) 2.337 D/S Slope

D/S(1:2) U/S(1:2) D/S & U/S (1:2) 2.753 Global Failure

D/S(1:2) U/S(1:2) D/S & U/S (1:2) D/S & U/S (1:2) 2.526 Global Failure

D/S(1:2) U/S(1:2) D/S & U/S (1:2) D/S & U/S (1:2) D/S & U/S (1:2) 2.214 Global Failure

D/S(1:2) U/S(1:2) 2.337 D/S Slope

D/S(1:2) U/S(1:2) D/S & U/S (1:2.5) 2.785 Global Failure

D/S(1:2) U/S(1:2) D/S & U/S (1:2.5) D/S & U/S (1:2.5) 2.706 Global Failure

D/S(1:2) U/S(1:2) D/S & U/S (1:2.5) D/S & U/S (1:2.5) D/S & U/S (1:2.5) 2.24 Global Failure

D/S(1:2) U/S(1:2) 2.337 D/S Slope

D/S(1:2) U/S(1:2) D/S & U/S (1:3) 2.841 Global Failure

D/S(1:2) U/S(1:2) D/S & U/S (1:3) D/S & U/S (1:3) 2.839 Global Failure

D/S(1:2) U/S(1:2) D/S & U/S (1:3) D/S & U/S (1:3) D/S & U/S (1:3) 2.552 Global Failure

D/S(1:2)

U/S(1:1.5)2.334 D/S Slope

D/S(1:2)

U/S(1:1.5)D/S & U/S (1:2) 2.645 Global Failure

D/S(1:2)U/S(1:1.5)

D/S & U/S (1:2) D/S & U/S (1:2) 2.43 Global Failure

D/S(1:2)

U/S(1:1.5)D/S & U/S (1:2) D/S & U/S (1:2) D/S & U/S (1:2) 2.137 Global Failure

D/S(1:2)

U/S(1:1.5)2.334 D/S Slope

D/S(1:2)

U/S(1:1.5)D/S & U/S (1:2.5) 2.691 Global Failure

D/S(1:2)

U/S(1:1.5)D/S & U/S (1:2.5) D/S & U/S (1:2.5) 2.609 Global Failure

D/S(1:2)U/S(1:1.5)

D/S & U/S (1:2.5) D/S & U/S (1:2.5) D/S & U/S (1:2.5) 2.255 Global Failure

D/S(1:2)

U/S(1:1.5)2.334 D/S Slope

D/S(1:2)

U/S(1:1.5)D/S & U/S (1:3) 2.744 Global Failure

7/26/2019 IJITE8March2564(1)(3).pdf

14/14






D/S(1:2)

U/S(1:1.5)D/S & U/S (1:3) D/S & U/S (1:3) 2.742 Global Failure

D/S(1:2)

U/S(1:1.5)D/S & U/S (1:3) D/S & U/S (1:3) D/S & U/S (1:3) 2.475 Global Failure

D/S(1:2.5)U/S(1:2)

2.674 D/S Slope

D/S(1:2.5)

U/S(1:2)D/S & U/S (1:2) 3.01 Global Failure

D/S(1:2.5)

U/S(1:2)D/S & U/S (1:2) D/S & U/S (1:2) 2.733 Global Failure

D/S(1:2.5)

U/S(1:2)D/S & U/S (1:2) D/S & U/S (1:2) D/S & U/S (1:2) 2.284 Global Failure

D/S(1:2.5)

U/S(1:2)2.674 D/S Slope

D/S(1:2.5)U/S(1:2)

D/S & U/S (1:2.5) 3.07 Global Failure

D/S(1:2.5)

U/S(1:2)D/S & U/S (1:2.5) D/S & U/S (1:2.5) 2.911 Global Failure

D/S(1:2.5)

U/S(1:2)D/S & U/S (1:2.5) D/S & U/S (1:2.5) D/S & U/S (1:2.5) 2.505 Global Failure

D/S(1:2.5)

U/S(1:2)2.674 D/S Slope

D/S(1:2.5)

U/S(1:2)D/S & U/S (1:3) 3.14 Global Failure

D/S(1:2.5)U/S(1:2)

D/S & U/S (1:3) D/S & U/S (1:3) 3.091 Global Failure

D/S(1:2.5)

U/S(1:2)D/S & U/S (1:3) D/S & U/S (1:3) D/S & U/S (1:3) 2.64 Global Failure

IJITE8March2564(1)(3).pdf

Documents

Transcript of IJITE8March2564(1)(3).pdf