8
DISCUSSION AND CONCLUSIONS
The main conclusion of the presented research is that sur-
face movements above longwall mining last much longer
than the often assumed 3 or 5 years. One can even ask if
it will ever stop completely (Vervoort 2020a). Or in other
words, the goaf volumes and the rock mass surrounding
the goaf volumes will always behave differently than the
unaffected strata outside the mining concession. Results are
presented for the Campine coal district, Belgium. The latter
is characterized by irregular multi-seam mining over large
depth intervals. These features are also observed in other
European coal basins. However, for longwall mining in a
single seam at shallow depth, the same conclusions may not
necessarily be valid. The new insights into the long-term
surface movements over coal longwall panels are a direct
result of the availability of satellite remote sensing data. The
latter cover large areas, and the time series are available over
long periods of time. The frequency of measurements as
a function of time is high, as is the spatial distribution of
reflectors or data points. This can never be matched by con-
ventional leveling campaigns. For the latter, it is virtually
impossible to find the necessary funding, time and motiva-
tion, if successive measurements yield comparable results.
The satellite time series showed that with movements of a
few mm a year, the trend of movement only becomes clear
if the time series covers five years or more.
The second conclusion is that after all underground
activities have ceased and underground access is sealed off,
the flooding of the underground infrastructure, goaf vol-
umes and surrounding (non-collapsed) strata results in upsi-
dence or uplift. In other words, the additional movements
are now upward instead of on-going downward move-
ments. The most recent available data, namely the EGMS
time series of Interferometric C-band SAR Sentinel-1
images, indicate beyond doubt that this upward movement
continues thirty years after the mine closure. A comparison
between the vertical movements above the mined zone and
the zones to the north and south shows that the observed
(a)
(b) (c)
Figure 7. Examples of damage to masonry of large building, observed after the closure of the coal mines. a.
Pictures b &c. On-going vertical (b) and horizontal (c) surface movement during the period 2016–2021 (average,
minimum and maximum values of four neighboring data points)
DISCUSSION AND CONCLUSIONS
The main conclusion of the presented research is that sur-
face movements above longwall mining last much longer
than the often assumed 3 or 5 years. One can even ask if
it will ever stop completely (Vervoort 2020a). Or in other
words, the goaf volumes and the rock mass surrounding
the goaf volumes will always behave differently than the
unaffected strata outside the mining concession. Results are
presented for the Campine coal district, Belgium. The latter
is characterized by irregular multi-seam mining over large
depth intervals. These features are also observed in other
European coal basins. However, for longwall mining in a
single seam at shallow depth, the same conclusions may not
necessarily be valid. The new insights into the long-term
surface movements over coal longwall panels are a direct
result of the availability of satellite remote sensing data. The
latter cover large areas, and the time series are available over
long periods of time. The frequency of measurements as
a function of time is high, as is the spatial distribution of
reflectors or data points. This can never be matched by con-
ventional leveling campaigns. For the latter, it is virtually
impossible to find the necessary funding, time and motiva-
tion, if successive measurements yield comparable results.
The satellite time series showed that with movements of a
few mm a year, the trend of movement only becomes clear
if the time series covers five years or more.
The second conclusion is that after all underground
activities have ceased and underground access is sealed off,
the flooding of the underground infrastructure, goaf vol-
umes and surrounding (non-collapsed) strata results in upsi-
dence or uplift. In other words, the additional movements
are now upward instead of on-going downward move-
ments. The most recent available data, namely the EGMS
time series of Interferometric C-band SAR Sentinel-1
images, indicate beyond doubt that this upward movement
continues thirty years after the mine closure. A comparison
between the vertical movements above the mined zone and
the zones to the north and south shows that the observed
(a)
(b) (c)
Figure 7. Examples of damage to masonry of large building, observed after the closure of the coal mines. a.
Pictures b &c. On-going vertical (b) and horizontal (c) surface movement during the period 2016–2021 (average,
minimum and maximum values of four neighboring data points)