Umwelt-Geräte-Technik GmbH | Eberswalder Str. 58 | D-15374 Müncheberg | Tel.: +49 (0) 33 43 2 - 89 575 |
6.3
Filling the hood
The immersion depth “T” of the air intake pipe should be about 2 cm more than the dis-
tance between soil surface and air outlet “Hk”. Thus the hydraulic pressure “zero” appears
narrow under the soil surface.
Open [V1] slowly. Thereby the overflow chamber [3] gets filled with water. In doing so the
hose connection 2 should be completely de-aerated. Remaining air bubbles may be re-
moved by moving the hose connection and lifting or tipping the infiltration reservoir as long
as it is assured that the hood isn`t moved.
The Water in the infiltration reservoir is set to a negative pressure. As long as the system is
airtight the overflow chamber won`t overflow. If the overflow chamber overflows please
check that all Valves are closed and none of the 2 gaskets at the connection faces of the
hose connection or the gasket of the socket for the air intake pipe is missing or damaged.
Open Valve “K” and suck air off the hose connection 1 [9] (pipette bulb) till the water level
in the standpipe [4] reaches center scale. Following close valve “K” and keep it closed.
Slowly open the aeration valve “V2”. Thereby the space under the hood is set to a negative
pressure and the water flows over the overflow chamber. Now the filling of the hood
started.
Shut [V2] as soon as the water table has reached the mark on the hood. Thus the infiltration
flow raises the underpressure until the aeration of the Mariotte water supply system starts.
Once the aeration started the the underpressure under the hood remains at a steady state.
He is determined and controlled by the immersion depth “T” of the air intake pipe. On sites
with poor infiltration the underpressure under the hood might not be enough to start the
aeration. In this case evacuate additional air through the valve [V3] to keep the negative
pressure under the hood at the desired value.
The negative pressure Us at the U-tube manometer should always be higher than the water
table Hs on the scale of the standpipe.
6.4
Choosing the effective water tension
The effective water tension “h” on the soil surface is calculated irrespective to the regula-
tion directly out of the water level “Hs” in the standpipe and the negative pressure “Us” at
the U-tube manometer.
s
s
U
H
h
( h< 0 !! )
(13)
It is advisable to start the test with water tension “Zero“to record the saturated hydraulic
conductivity
The scale values at the hood (Hs) and at both brackets of the U-tube manometer “Us”
should be recorded.
