Tanking of tunnels is now often specified when inflows exceed as little as 1
L/s/km with a unit distance of 100 m.
To demonstrate inflows over a 100 m segment of a tunnel are less than 0.1 L/s
with a standard error of 0.01 L/s by timed, gravity filled, volume measurement
up and downstream of the segment, the measuring cylinder volume (L) must exceed
10 Q, where Q is the flow in L/s, and the number measurements taken and averaged
must exceed 20 . If a standard error of 0.02 L/s is acceptable then 5Q2
measurements must be taken and averaged.
If gravity filling is not possible then the number, n, of repeat pumped
container measurement required is given by:
is the 100 m section leakage
is the volume filling time
is the standard error of volume measurement
Z is the standard normal
K is a coefficient dependent on
physical measurement conditions
Based on analysis of field data an indicative coefficient of variation of
volume measurement is ~0.05.