Contribution to Research on Rock-Fill Dam Modelling Material

8/2/2019 Contribution to Research on Rock-Fill Dam Modelling Material

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Contribution to Research on Rock-fill Dam Modelling Material

Soldo Boo1 & tuhec Damir11

Faculty of Geotechnical Engineering, University of ZagrebHallerova aleja 7, 42000 Varadin, Croatia

[email protected], [email protected]

Abstract

The subject issue of this paper is the passage area of the intake canal in the Varadin HydroelectricPower Plant, that is, the area between the traditional rock-fill embankment and the machine-room being asolid object. In this passage area of rock-fill embankment and the concrete coating (joined with dilatations)there is a problem of water streaming in the contact zones, which may have adverse results (endangerstability). Useful information on the status of the structure and guidelines for further maintenance areobtained based on research done on the material, i.e. assessment of parameters of stability calculation

and sieving.

Key-words: water, Varadin Hydroelectric Power Plant, embankment, soil parameters.

Introduction

The subject issue of this research is the embankment material, because of water sieving through theintake canal embankment (from the canals with concrete walls) and because of its stability. The sievingleaves through dilatations (rubber sealing) of the concrete walls and through gravel embankment. Thegrain-size distribution and compactness of the material were examined by penetrating a dynamic probe tothe defined depth. The achieved outcomes resulted in creating correlations based on which the necessaryparametres for implementation of the sieving assessment and stability estimate were made. Testing of theintake canal embankment has been conducted for both banks.

Figure 1. A typical embankment canal profile


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Testing and Correlation of Soil Parametres

Water permeability, i.e. water permeability coefficient for non-coherent materials may be assessed based

on a grain-size diagram and using the Hazens empirical expression:( )tDCk ef += 03,07,0

2[m/day]

where:C = is the empirical coefficient of sands purity and homogeneity, a value that in case of pure andhomogenous sands varies from 1,200 to 800, and in case of dusty, clay and homogenous sands from

800 to 400. If size depends on porosity it is to be defined by Lange: ( )2640400 += nC

10D = effective diameter of grains defined by the grain-size curve.

t= water temperature in C.where n is porosity.For example, if the water temperature is t = 10 C and empirical coefficient of sand purity and

homogeneity is C = 1000, the Hazen empirical term became: )/(1000 210 daymDk = or

)/(16,1 210 smDk = . The water permeability coefficient for common soil types are: - gravel

scmk /1010 12 = ; - sand - scmk /1010 31 = ; - fine sands, mixtures comprising sands, silts,

and clays - scmk /1010 73 = ; - homogeneous clays - scmk /107

< .

Water permeability coefficient k may be also evaluated from figure 2, considering the data from the

granulometric curve, that is, the 10D diameter of the soil particles for which 10 % of the particles are finer

and the void ratio e .grain diameter

0.0

01

0.0

1

0.1

1

10

0.1 1 10

Promjer efektivnog zrna D 10 [mm]

Koeficijent

vodopropusnosti,

k[cm/s]

e=0.7

e=0.6

e=0.5

e=0.4

e=0.3

WaterPermabilicm/styCoefficientk[cm/s]

Effective Grain Size D10 [mm]

Figure 2. Relation diagram of effective grain size (D10) sieving (mm) and permeability coefficient k [cm/s]

(according to NAVFAC DM-7.1)


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Table 1 Porosity and pores coefficient for non-coherent and coherent materials.

Soil Type

Soil

Condition

Porosity

n [%]

Pore

Coefficiente [1]

tenuous 38 42 0.61 0.72Sandy Gravel

compact 18 25 0.22 - 0.33

tenuous 40 45 0.67 0.82Coarse to MediumSand compact 25 32 0.33 0.47

tenuous 45 48 0.82 0.82Uniform Fine Sand

compact 33 36 0.49 0.56

tenuous 45 55 0.82 1.22Coarse sand

compact 35 40 0.54 0.67

soft 45 50 0.82 1.00

plastic 35 40 0.54 0.67Dust

solid/firm 30 35 0.43 0.49

soft 50 55 1.00 1.22

plastic 35 45 0.54 0.82Clay (CL)

solid/firm 30 35 0.43 0.54

soft 60 70 1.50 2.30

plastic 40 - 55 0.67 1.22Clay (CH)

solid/firm 30 - 40 0.43 0.67

To evaluate water permeability k (water permeability coefficient) details of the embankment grain-sizedistribution were used.

The following diagram in figure 3 below show the results of grain-size testing. All tested samples werecollected from the piezometric bore-holes on the embankment crown, at level 192.054 m above sea, andat level 180.184 m above sea at the embankment toe.

0

10

20

30

40

50

60

70

80

90

100

110

0.001 0.01 0.1 1 10 100

Promjer zrna D [mm]

postota

kmasezrna

TL1 (0 - 12.6 m) TL1 (12.6 - 14 m) TL1 (14.3 - 15.0 m) TL2 (0 - 3.0 m) TL2 (3 - 4 m)

grain diameter

massgra

inpercentage

Figure 3. Grain-size diagram of the left embankment samples


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The diagram enables reading the effective grain diameter, that is, of the D10 for the material in the left partof the embankment. For this material the effective grain diameter ranges from D10=0.2, in the embankmentfrom the crown to the toe. In the under-toe area, the effective grain diameter may, from the diagram, be

estimated to D10=0.02 mm. Subsequently, the water permeability coefficient kmay be solved using theabove formulae: for the material (in the embankment) D10=0.20 mm in the embankment scmk2104 =

or daymk 25 and for the material (in the foot) D10=0.02 mm in the embankment scmk 4104 = or

dayk /35.0= . For the dust layer the water permeability coefficient is scmk 51025.1 = or

daymk 011.0 .

Number of impacts of the related dynamic probe correlates with the number of NSPT impacts. This testdiffers from the Standard Penetration Test (SPT), there is a correlation between number of impacts, that isthe dynamic and the standard. Bibliography shows there are several parameter correlations based on thenumber of impacts in the Standard Penetration Testing. One such correlation is shown in Table 2.

Table 2 Correlation of the number of impacts and relative compactness, dry volume weight, pore

coefficient and internal friction angle (J.E. Bowles, 1979)

NSPT Soil Type rD

[%]

d [kN/m3] e [%] [%]

< 42035

Low PlasticityDust ML

255075

13.514.015.0

1.000.900.80

273133

< 82545

Dusty SandSM

255075

15.015.516.5

0.800.740.62

293235

< 103050

Poorly GraduatedSandSP

255075

16.016.517.5

0.650.600.52

293336

< 153065

Well GraduatedSandSW

255075

17.018.019.0

0.570.490.43

303437

< 205070

Poorly GraduatedGravel

GP

255075

18.519.020.5

0.470.390.33

323538

< 285590

Well GraduatedGravel

GW

255075

20.021.022.0

0.360.280.22

323640

Based on such processing of the results the statistics showed the compactness status. For example, if wesplit the statistics into compactness categories the resulting compactness conditions are as follows: highlytenuous, tenuous, medium compact, compact, highly compact. The resulting 5 compactness classes are:

highly tenuous (NDPH=0-1; NSPT=0-4), tenuous (NDPH=1-4; NSPT=4-10), medium compact (NDPH=4-13;NSPT=10-30), compact (NDPH=13-24; NSPT=30-50) and highly compact (NDPH>24; NSPT>50).

To evaluate embankment conditions the statistics was made of the number of impacts on the 10 cmpenetration depth. Testing was done on 10 probes up to 15 m deep. Figure 4 shows typical outcomes ofnumber of impacts and their frequency.


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0

5

10

15

20

25

30

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38

N [1]

U[%]

Figure 4. Correlation of the number and frequency of impacts in % (12 class example)

Based on the presented results we can conclude that there is high percentage of zones where materialconditions include highly tenuous, tenuous and medium compact materials. In the passage area there isalso material with high content of dust under the largest swale (piezometric bore-drill). The calculationparameters of stability and sieving were estimated as described.

Conclusion

Based on the soil grain-size testing and other correlations of parameters resulting from field research the

following soil parameters have been defined: water permeability coefficients and parameters necessary inassessing stability. Implementation of the resulting parameters in software intended to stability andsieving produced a highly logical image. Both the presentation of sieving and of calculating stabilityresulted in creating the in-situ status, for example the most common water level, and the stability obviouson the embankment.

References

Bowles, I.E., 1979: Foundation Analysis and Design, Second Edition, McGraw-Hill Book Company, NewYourk.

Geotehniki fakultet, 2004: Elaborat o procjeivanju i stabilnosti nasipa dovodnog kanala HEV,

Varadin. (Faculty of Geotechnical Engineering, 2004: Study on Sieving and Stability of the Intake CanalEmbankment at the Varadin Hydroelectric Power Plant)

GeoTechnik, d.o.o, 2002: Report of Infiltration water Intake Performed at the Hydroelectric Power Plant,Varadin.

Hep Varadin, 2002: Hydroelectric Power Plant Varadin Groundwater Levels Report, Varadin.

NAVFAC, 1986: Soil Mechanics, Geotechnical Directory, Design Manual 7.1., Alexsandria, Virginia.

Slope/W - Seep/W, 2004: Geotechnical Engineering Software for Windows, Groundwater SeepageAnalysis, Finite-element Method, Geo-Slope International Ltd. Calgary, Canada.

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Contribution to Research on Rock-Fill Dam Modelling Material