2
observed for a goaf thickness equal to four times the mining
height, and a stiffness ratio between goaf and the rest of the
strata equal to 1 on 10.
Three different time series of satellite images are used
in the study of upsidence (radar-interferometry or InSAR
(interferometry with synthetic aperture radar)). The first two
series, i.e., the European C-band ERS1/2 and ENVISAT-
ASAR satellite images, were made available for research
through a research proposal of the European Space Agency
(ESA) (Devleeschouwer et al. 2008). These two series cover
the periods from August 1992 through December 2000
(87 cycles of 35 days), and from December 2003 through
October 2010 (72 cycles of 35 days), respectively. The
third and most recent time series is made available through
the European Ground Motion Service project (EGMS),
which receives funding from the European Commission’s
Copernicus program (Costantini et al. 2021). The latter is
based on the Sentinel-1 (S1) satellite mission, which was
launched in 2014, and it systematically collects interfero-
metric C-band SAR image stacks with global coverage at
short revisit time (temporal resolution of 6 days). The
observations available via the EGMS website cover the
period from early January 2016 through end of December
2021 (i.e., a period of 6 years).
This paper discusses three topics. First, the emphasis is on
surface movements over long time periods. Measurements
along a survey line of about 2.5 km are presented over a
total period of 65 years, i.e., from the start of mining a
first longwall panel in the area until approximately 40 years
after mining the last panel, of which more than 30 years are
situated after the closure of the mine. The recently available
EGMS data extend previously published results by more
than 10 years (Vervoort 2021c). Second, the focus is on
the phase of upsidence and, more specifically, on the period
covered by the EGMS data, i.e., about 30 years after the
closure of the mine. A comparison is made with previously
published results (Vervoort and Declercq 2017). Since the
EGMS data also includes horizontal east-west movements,
the latter are also presented and discussed for the same site.
Third, examples are presented of damage to buildings and
infrastructure observed above the same mined zone after
the mine closure.
SURFACE MOVEMENTS DURING THE
ACTIVE LIFE OF A MINE AND THE
FOLLOWING DECADES
Data are presented for a total observation period of 65 years
(Figure 1). Figure 1a shows the measuring line with a total
length of almost 2.5 km (Vervoort 2021c). The vertical
movements were measured in comparison to a reference
point approximately 900 m further northeast than point A
along the same road, i.e., A-B-C. These levelling data were
supplemented with recent remote sensing observations by
satellites (Figure 1b). Information on the mining in the
vicinity of the measuring line is included in Figure 1a. The
first panels were mined in year 0, at the beginning of the
monitoring period. The line is in the northern part of the
mine. The mining extends to just north of point B. So,
point A is situated above the virgin zone, north of the min-
ing. Below point E, the sum of the mining heights of the 9
longwalls is 11.2 m, i.e., the largest value of the four points
above the mined zone. The last panel was mined in year 27.
Four years later (year 31) the mine was closed.
The phase of subsidence lasted until years 33 (Point
E) and 35 (Points B, C and D). Below points B and E,
the last panel was mined more than 10 years earlier (year
22 vs. 33 and 35). Below B and C, it is 8 years earlier (27
vs. 35). When interpreting these moments, the large inter-
val between measurements must be taken into account.
However, the phase of subsidence lasts much longer than
the often-assumed period of 3 to 5 years. If the under-
ground infrastructure and rock mass had not been sub-
merged after the closure, the phase of subsidence would
most likely have continued. In other words, the change
in direction of movement (from downward to upward)
around year 35 most likely means that the upward move-
ment becomes larger than the additional downward move-
ment. Comparing the total uplift to date, i.e., recorded up
to year 65 (period of 30 to 32 years), with the maximum
subsidence recorded, a ratio is calculated between 5.4%
(Point D) and 20% (Point B). For points C and E, this
ratio is 6.6% and 10.3%, respectively.
On the scale of Figure 1b, one might get the impres-
sion that there is no more surface movement after 65 years.
However, when zooming in on the last 6 years (Figure 2 the
EGMS satellite data), there is still a clear trend of upward
movement. Above the mined zone, an additional move-
ment of 10 to 15 mm over the period of 6 years is observed,
i.e., an annual rate of approximately 2 mm. Although in
the Campine basin it was observed that the extension of
the upsidence or uplift zone towards the north and south
increases with time after the mine closure (Vervoort 2021a),
one must still be cautious when interpreting the trend for
point A after year 3 (Figure 2a).
observed for a goaf thickness equal to four times the mining
height, and a stiffness ratio between goaf and the rest of the
strata equal to 1 on 10.
Three different time series of satellite images are used
in the study of upsidence (radar-interferometry or InSAR
(interferometry with synthetic aperture radar)). The first two
series, i.e., the European C-band ERS1/2 and ENVISAT-
ASAR satellite images, were made available for research
through a research proposal of the European Space Agency
(ESA) (Devleeschouwer et al. 2008). These two series cover
the periods from August 1992 through December 2000
(87 cycles of 35 days), and from December 2003 through
October 2010 (72 cycles of 35 days), respectively. The
third and most recent time series is made available through
the European Ground Motion Service project (EGMS),
which receives funding from the European Commission’s
Copernicus program (Costantini et al. 2021). The latter is
based on the Sentinel-1 (S1) satellite mission, which was
launched in 2014, and it systematically collects interfero-
metric C-band SAR image stacks with global coverage at
short revisit time (temporal resolution of 6 days). The
observations available via the EGMS website cover the
period from early January 2016 through end of December
2021 (i.e., a period of 6 years).
This paper discusses three topics. First, the emphasis is on
surface movements over long time periods. Measurements
along a survey line of about 2.5 km are presented over a
total period of 65 years, i.e., from the start of mining a
first longwall panel in the area until approximately 40 years
after mining the last panel, of which more than 30 years are
situated after the closure of the mine. The recently available
EGMS data extend previously published results by more
than 10 years (Vervoort 2021c). Second, the focus is on
the phase of upsidence and, more specifically, on the period
covered by the EGMS data, i.e., about 30 years after the
closure of the mine. A comparison is made with previously
published results (Vervoort and Declercq 2017). Since the
EGMS data also includes horizontal east-west movements,
the latter are also presented and discussed for the same site.
Third, examples are presented of damage to buildings and
infrastructure observed above the same mined zone after
the mine closure.
SURFACE MOVEMENTS DURING THE
ACTIVE LIFE OF A MINE AND THE
FOLLOWING DECADES
Data are presented for a total observation period of 65 years
(Figure 1). Figure 1a shows the measuring line with a total
length of almost 2.5 km (Vervoort 2021c). The vertical
movements were measured in comparison to a reference
point approximately 900 m further northeast than point A
along the same road, i.e., A-B-C. These levelling data were
supplemented with recent remote sensing observations by
satellites (Figure 1b). Information on the mining in the
vicinity of the measuring line is included in Figure 1a. The
first panels were mined in year 0, at the beginning of the
monitoring period. The line is in the northern part of the
mine. The mining extends to just north of point B. So,
point A is situated above the virgin zone, north of the min-
ing. Below point E, the sum of the mining heights of the 9
longwalls is 11.2 m, i.e., the largest value of the four points
above the mined zone. The last panel was mined in year 27.
Four years later (year 31) the mine was closed.
The phase of subsidence lasted until years 33 (Point
E) and 35 (Points B, C and D). Below points B and E,
the last panel was mined more than 10 years earlier (year
22 vs. 33 and 35). Below B and C, it is 8 years earlier (27
vs. 35). When interpreting these moments, the large inter-
val between measurements must be taken into account.
However, the phase of subsidence lasts much longer than
the often-assumed period of 3 to 5 years. If the under-
ground infrastructure and rock mass had not been sub-
merged after the closure, the phase of subsidence would
most likely have continued. In other words, the change
in direction of movement (from downward to upward)
around year 35 most likely means that the upward move-
ment becomes larger than the additional downward move-
ment. Comparing the total uplift to date, i.e., recorded up
to year 65 (period of 30 to 32 years), with the maximum
subsidence recorded, a ratio is calculated between 5.4%
(Point D) and 20% (Point B). For points C and E, this
ratio is 6.6% and 10.3%, respectively.
On the scale of Figure 1b, one might get the impres-
sion that there is no more surface movement after 65 years.
However, when zooming in on the last 6 years (Figure 2 the
EGMS satellite data), there is still a clear trend of upward
movement. Above the mined zone, an additional move-
ment of 10 to 15 mm over the period of 6 years is observed,
i.e., an annual rate of approximately 2 mm. Although in
the Campine basin it was observed that the extension of
the upsidence or uplift zone towards the north and south
increases with time after the mine closure (Vervoort 2021a),
one must still be cautious when interpreting the trend for
point A after year 3 (Figure 2a).