Guidelines for Safety Inspection of Dams - Central Water Commission

Code
No.
I
II
Table III
Minimum Desired Values of Factors of Safety
[as per Code IS 7894 of 1975]
Loading
Conditions
Construction
condition with or
without partial
pool. *
Reservoir partial
pool.
Slope most
likely to be
critical
Upstream &
downstream
Upstream
Pore Pressure
Assumption
To be accounted for
the Hilf's method.
Weights of material
in all zones above
phreatic line to be
taken as moist and
those below as
buoyant.
Type of
shear
strength
test to be
adopted
Minimum
desired
factor of
safety
QR * 1.0
RS +
III Sudden drawdown
Max.head water to
(a) min.with tail water
at max.
Upstream As given in 5.4.2 ** RS +
Max.tail water to
(b) min. with reservoir
full
Downstream As given in 5.4.5 ** RS +
IV
Steady seepage
with reservoir full
Downstream As given in 5.5.2 ** RS +
Steady seepage
V with sustained
rainfall
Downstream As given in 5.6.1 ** RS +
VI
Earthquake
condition:
(a) Steady seepage Downstream As given in Case IV RS +
(b) Reservoir full Upstream As given in Case II RS +
1.3
1.3
1.3
1.5
1.3
1.0 Ψ
1.0 Ψ
Note: These factors of safety are applicable for the method of analysis mentioned in the Code.
* Where the reservoir is likely to be filled immediately after completion of dam, construction
pore pressure would not have dissipated and these should be taken into consideration. This
is to be adopted for failure planes passing through impervious foundation layer.
+ S Test may be adopted only in cases where the material is cohesionless and free draining.
Ψ Values are according to IS:1893-1984 “Criteria for earthquake resistant design of
structures (3 rd rev.).
** These refer to the Code.
Q Test = Unconsolidated undrained test
R Test = Consolidated undrained test and
S Test = Consolidated drained test.
23