Die Wirksamkeit der Kapillarsperre als Deponieoberflächenabdichtung

The principles of capillary barriers are well known from many
laboratory studies. A limited number of large-scale applications
are known, in particular for the sealing of past pollution and
demolition waste. This study investigates the suitability of a
capillary barrier for the sealing of a municipal landfill.
Laboratory tests have shown the fundamental applicability of the
selected materials. The sealing effect of the material combination
as a capillary barrier was examined in a large scale tipping trough
under step increasing hydraulic load and two differential slopes.
The materials showed drain capacities suitable for an effective
capillary barrier. For a long-term study under natural weather
conditions, two experimental fields with integrated large scale
lysimeters and slopes of 10 % and 26 % have been constructed on
site at the landfill. The lysimeter data of three subsequent years
were used for the analysis. After the growth of a closed cover of
vegetation the surface runoff was negligible. Only in wet years it
exceeded 2 % of the annual precipitation. In 2000 and 2001 the
evapotranspiration was between 55 % and 65 %. In the very wet year
2002, however, it was significantly below 50 %. The predominant
part of the lysimeter runoff was drained by the capillary layer.
Only heavy precipitation caused a relevant drain into the capillary
block. Except for the very wet year 2002 the effectiveness of the
whole system exceeded 95 % of the annual precipitation. As expected
the efficiency of the steeper lysimeter clearly surpassed 95 %. In
order to verify the possibility to reduce the effort for the
experimental determination of the efficacy of the capillary barrier
by numerical simulations, it was tried to calculate the measured
results by numerical models for the water balance layer and the
capillary barrier. The results show that in principle a realistic
prediction is possible. However, a reliable prediction of the
measured results can only be achieved by using parameters that were
calculated by inverse modeling for the unsaturated hydraulic
conductivity. Because of the high sensitivity of the model,
calculations with parameters predicted by standard methods did not
lead to plausible results, but overestimated the effectiveness of
the capillary barrier. Therefore it is not advised to substitute
large scale tipping experiments by numerical modeling. Although the
capillary barrier is not gas proof, the closed water coating above
the boundary to the capillary block largely restricts the movement
of gas. Laboratory experiments resulted in very low permeability
for gas through an aqueous capillary barrier. Measurements at the
experimental fields showed that the capillary barrier significantly
reduces the emission of gas at the surface compared to the
non-sealed landfill surface. However, under adverse air pressure
conditions low gas emissions are still measurable. Considering the
present investigations, the capillary barrier is a competitive and
secure alternative especially for the fracture-prone clay liner.
For demolition waste it can be used as single sealing. For
municipal waste, as in the underlying landfill of Bayreuth, the
combination with an additional sealing element, e. g. a synthetic
liner is recommended.