PSI - Issue 5

K Bouzelha et al. / Procedia Structural Integrity 5 (2017) 77–84 K Bouzelha et al./ Structural Integrity Procedia 00 (2017) 000 – 000

81 5

The slip circle considered in this study is the possible critical rupture arc with radius R and passing through the foot of the slope . The angles α o and β o defining this critical circle (See Fig. 1) are obtained as a function of the upstream slope β and the internal friction angle φ of embankment material using the abacus of Costet et al. (1983). These values are given in table 3.

Table 3. C alculation parameters . Symbol Designation

Value 20,00 18,43 22,00 17,92

Unit

φ β

Internal friction angle

inclination angle of upstream slope

(°) (°) (°)

α o β o

Calculation parameter of the slip circle (Fig. 1) Calculation parameter of the slip circle (Fig. 1)

The considered random variable in this probabilistic analysis is the acceleration coefficient of the seismic zone (A) is generated by a lognormal distribution law (fig.3). This latter is defined from database containing 45 accelerometers registered during Boumerdes earthquake of 21 May 2003 by the National Earthquake Engineering Research Center in central zone of Algeria. The coefficient of variation that represents the distribution of the random variable realizations is evaluated at 0,664.

0.6

Histogram Lognormal

0.5

0.4

0.3

Density

0.2

0.1

0

0

1

2

3

4

5

6

Seismic acceleration

Fig. 3. Generation of random variable.

5. Resultants et discussion

The deterministic analysis of the upstream slope stability of the studied embankment is conducted initially without taking into account seismic effect and the saturation line (AGC, 2008). The results summarized in table 4 show that the obtained safety coefficient value is higher than the admissible value (F s =1.40) according to the Maghreb guide of the design of small dams (PNUD, 1987).

Table 4 : Safety factor Fs without taking into account seismic effect. Symbol Designation Value

Unit

M s

Stabilizing Moment Overturning moment

540,432 272,307

t.m t.m

M m

F s

Safety factor

1.98

We have analyzed the upstream slope stability of the embankment under seismic effect by considering different seismic zones. The results illustrated in Table 5 show that safety coefficients are higher than the admissible value and they decrease from the low seismicity zone to the high seismicity zone.