Armfield S12-MKII, Инструкция по эксплуатации

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Armfield Instruction Manual
54
By substituting (H - s) for h this lead to the equation of Thiem.
(2)
Procedure
Cone of depression for a single well in an unconfined aquifer
For this experiment no cap is placed over the sand in the area of the well and the
sand surface should be horizontal and flat. Ensure that the drain valves for the two
cylindrical wells are both in the closed position. Connect the flexible piping from the
two French drains to the quick release connector on the two flow meters- these will
be used as inlet pipes not as drains for this experiment. Maintaining equal flow
through both flow meters, flood the sand until the water level in the manometer tubing
is just below the sand level in the tank. Open the drain valve beneath the well set
centrally between the manometer tapping points (the right-hand well when facing the
apparatus from the side holding the flow meters and manometer array). Adjust the
flow and drain valves to give a good draw-down at the well (as displayed on the
manometers) and steady conditions.
Graphs of water table elevation can be drawn from the manometer readings for
abstraction from the centrally placed well and, from these, a contour plan of the water
table surface may be prepared. So long as the coefficient of permeability k has been
determined by the method above, theoretical values for s can now be determined
from the equations provided and compared with the plotted experimental values.
Dupuit's formula in the form given in equation (1) can be used for small drawdowns in
the area close to the well (take value of R
o
equal to half the width of the catchment
tank), while Thiem's formula, equation (2), can be used for the more distant areas.
As in the other well experiments, Q
o
, the discharge must be measured. To do this,
the outflow pipe should be diverted into a measuring cylinder to collect the outflow
over a timed period. It will be necessary to balance the inflow valves so that the well
abstraction does not lead to a falling water table while readings of s and Q
o
are being
taken. It is also important to check that a water surface is visible in the standpipe to
ensure that the aquifer remains fully saturated in the region close to the wall.
Results
Volume
collected
I
Time to
collect
sec
Q
0
m
3
/s
H
m
Tapping
position
m
Manometer
readings
m
S
(=H-manometer
reading)