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6. Cellar collapse, cellar damage on the surface 6.1. The appearance
of the bending zone, the subsidence
of the soil surface
6.1.1. Facilities in the
bending zone
6.1.2. The appearance of subsidence
of the soil surface due to
the curvature of the bending zone
6.1.3. damage to engineering facilities and roads due to
subsidence of the soil surface
6.1.4. Movement of tall
structures in the bending zone
6.1.5. Damage to buildings due to
soil subsidence 6.2. Penetration
of the collapse zone to the
surface (rupture) 6.3. Collapse
due to top-down forces (rupture) Over the past 35 years, more than 370 Hungarian settlements have been struggling with the damage
caused by cellars and caverns beneath their territory. Abandoned and poorly maintained cellars, artificial caverns and caves are constantly
being damaged. These processes date back to the
18th-19th centuries. They also appeared on
the surface in the 20th century, but the damage
was more frequent and more severe in the 20th century. In the second half of the 20th century, urbanization accelerated. The technical-technical reason for this is primarily
the expansion of towns and settlements, the higher built-in
ratio and, last but not least, the multiplication
of road traffic. The damage to artificial cavities
and cellars was discussed in the previous chapter. When the support
structures of the cavity are damaged
to such an extent that it
is no longer able to be compensated for by the
rock or soil above it, the
damage also appears on the
surface. This can be a slow process,
but most of the time it is rapid, sudden, and not infrequently a disaster for human life or material goods. These damages have long been
known to deep-water mining professionals. Their scientific knowledge and analysis has a large body of literature, as it is still
a problem for the inhabitants of the areas and settlements
above the former mines. It is important to know that
Hungary was at the forefront in this field as
well: engineers working in the mining areas of Selmecbánya and then of
Tatabánya-László were already
in the 19th century. At the end of the
20th century, At the beginning of the 20th century, they dealt with
this problem and devised methods which were used
throughout the continent. Significant work was also done
by Hungarian engineers to investigate
and repair surface damage related to tunnel construction.
In the most densely built-up settlement in the country, countless buildings sank during the construction
of metro lines 2 and 3 in
Budapest, so this had to be dealt with.
The appearance of damage caused by cellars
and artificial cavities is similar to the
latter activity, but the damage
is eliminated by the procedures applied in mining. 6.1. The appearance of the bending zone,
the subsidence of the soil surface Damage to subterranean cavities is most often manifested by the subsidence
of the soil surface. The reason for this is that
the components of the soil move
downwards due to gravity. This
depression is greatest above the axis
or center of the cavity, and decreases with distance. This gives rise
to a form of turtle, commonly used in the technical
language: sinking hoop.
Sinking hump over basement corridor
Sinking hump over cellar space Over the last
100-150 years, many theories and calculation methods have been
developed to investigate the subsidence of soil above artificial cavities. Their detailed description can be found in the literature. The essence
of the theories is to describe the
shape of a sink (a so-called
sinking dip) as a body of rotation, the dimensions of which can then
be calculated mathematically. The rate of descent is influenced by many factors.
The most important of these
are: - underground depth
of the cavity - the extent of the cavity - the boundary surfaces of the cavity, or
the condition of the built-in structures - rock quality
and soil quality (fracture or boundary
angle, consistency, boundary stresses, stratification, etc.) above and within the cavity, - hydrological
conditions of the cavity and its surroundings - static and dynamic loads on
the cavity and the surrounding rock environment etc By default, theories only consider
the extent, depth and boundary of the rock (soil) above the cavity.
Some of these are:
Theories for calculating subsidence In the case of cellars, artificial cavities, these calculation methods are sufficient
to estimate what and how much
subsidence is expected over
a given object. Of course, when it
comes to dimensioning a support structure, more serious calculations are needed, but that
is a special branch of engineering science… It is important to note that
the sinkhole does not only
have a latitude (as shown in the
diagrams of the calculations). The dent follows the shape
of the underground space, the cut, and its
impact zone is not only perpendicular
to the axis
of the cut, but also at
the end of the cellar. This effect is a problem for cellars
that, although not under a building, run close to
it. Such cases occur in the settlements where the individual
cellars are made on steep
terrain (such as a hillside) and they reach the mountain.
In the case of multiple adjacent or intersecting
subterranean spaces, the subsidence dents add up, which
results in a larger-than-normal
subsidence in a given rock environment. The following
movement zones are formed in the
soil above the cavities:
A - bending zone B - fragmented
zone C - collapse zone In the bending zone, the
curvature of the surface can cause
damage and the ground does not
always collapse - but the buildings
and engineering facilities above it can
cause serious damage. If the fractured
zone comes close to the
surface, the magnitude and timing of any breakdown is unpredictable. The behavior of the collapse zone
is clear: the cavity of the cavity
cannot hold the mass above, collapses.
It is important to know that
the failure of zones affects each
other. As the collapse zone
grows, the fractured zone also gets higher,
with unforeseeable consequences. But the opposite is also possible: once the fractured
zone reaches the foundations of the surface structures,
the load will damage the
collapse zone. 6.1.1. Facilities in the bending zone The shifting of the
bending zone affects both the
buildings above and the utilities there.
Examining their damage is one of the most important subtasks of the emergency response activity. It is easy to see that
pipelines that fall into the
bending zone are more susceptible to damage. In the
event that they cannot absorb
soil movement (such as old cast
iron pipes, asbestos cement pipes), their breaking is almost inevitable. The joints of such utilities are also endangered:
old cast iron casings, various joints of eternit pipes are brittle and prone to fracture
due to their
age. Building foundations
and their associated fixtures (such as utilities) may
also be damaged. These may be damaged
or broken when the base
of the building is moved or tilted. 6.1.2. The appearance of subsidence on the
surface due to curvature of the bending zone
The appearance of the spatial descent
must be examined at the five (+ 1) points of the sinking
field. Elements of the sinking dip 1st dent roof 2. upper curvature field between the saddle
and the slope 3. dip slope with inflection
point 4. lower curvature field between the slope
and the turtle 5. turtle The surface of the soil on
the roof is unchanged, however, it is to be expected
that the dents will spread,
resulting in the outward displacement of the slope and the
curvature fields and the expansion of the turtle.
Disaster due to
unexpected appearance and widening of sinking (Nachterstedt , Germany 2009) In the upper curvature field, the surface
of the soil undergoes rock pulling at the top and compression at the bottom. Upward
opening V-shaped cracks appear. These lead to damage
to the structures
and buildings placed on it and to
the entry of rainwater. This increases the damage. Buildings are typically most sensitive to this type
of soil surface subsidence. Typical upwardly expanding cracks appear on
the walls of buildings that run in the direction
of the slope.
Building in semi-saddle
position It is more difficult to trace, but
the same reason is due to
the sinking of the corners. This
occurs when most of the building stands on unmoving ground
and the sinkhole is formed only on
the small width of the facade.
This damage is more difficult to detect
because several other damage processes
to the building (such as underwater
washing, roof overloading, building next to it) result
in similar corner breaks. On the slope
of the ditch, the soil-forming rocks and blocks slip. These slippages
can be up to several decimetres.
The structures on the slope of the
dip will tilt, tilt towards the turtle,
or even slip. In the lower curvature field, the soil
or rock suffers from compression at the top and pulling at the
bottom. This leads to an inverted
"V" opening of the
rock above the soil and the cellar,
further breaking the cavity ceiling.
This is because the frictional force for stability
between the rock blocks here is significantly reduced or eliminated.
Building in the
lower curvature field Buildings in the lower curvature field and buildings show characteristic downward cracks, which are
mainly visible on the wall
next to the
doors and windows. Special mention should
be made of the fact that the
roof, which is opposite to the
sinking slope, is also sinking, which
results in the so-called saddle position. In the saddle position, the soil surface
suffers from pulling at the
top and compression at the bottom. It
also creates upward V-shaped cracks and splits, with the consequences
described earlier.
Building in saddle
position It can be seen from the
above - and it has long been known
to those skilled in the art - that structures and buildings on sunken
soil surface suffer severe damage
if their sinking is uneven, but on one
side of the block containing it, and not on
the other. 6.1.3. damage to
civil engineering structures
and roads due to subsidence Soil deflection
and sinking can result in sinking up to several
decimeters. This may pose a serious
problem for sheet-shaped structures on the surface.
Examples are road surfaces, traffic lanes. A further
major problem is that the pavement of the roads and the
concrete foundation beneath them are
not, or only
to a limited extent, capable of absorbing the stresses caused
by bending. Larger dents cause
the base to break, causing
the casing to fail. Asphalt is flexible to a certain extent,
but if the
foundation beneath it is damaged, it will be damaged
by increased speed as a result
of traffic. The surface of asphalt, which is fractured by parallel crevices, is a common sight on the
roads of communities threatened by cellar
danger. This indicates that a sinking trough has formed beneath the roadway, along
which the pavement slipped and its surface continuity
was interrupted. The cracks always indicate
the direction of the cavity below,
parallel to its axis. The resulting
cracks cause traffic problems, but it is even
more problematic that the rainwater flows through them under
the cover, soaking it (or
freezing it in cold weather conditions).
Road pavement failure due to
sinking above the basement 6.1.4. Movement of tall
structures in the bending zone Sinking dents are the biggest
problem in tall buildings (chimneys, power-tower columns, high-rise buildings). These tend to
fall - which causes the appearance
of off-center forces, and it is a serious problem that the
wires hang on one side or
are tensioned on the opposite
side, which can lead to the
wire breaking.
Power line column
tilt 6.1.5. Damage to
buildings due to soil surface
subsidence Soil subsidence causes the most damage to buildings. In the case of buildings,
the damage described above both reduces the
value in use and endangers the safety
of use. The forms of the appearance of damage have been
presented above in the case of the
individual motion fields of the sinking
dip. In addition to the cracks
described there, damaged buildings may include the
following: - movement of
doors and windows becomes difficult or impossible - connections
to utility lines are broken - deformation
of the space causes the walls
to break apart, causing the support of the slabs to
be damaged or displaced, - the walls under the
arches open, which can even
lead to the arch breaking, - in the case of slabs with
lining bodies, the dents formed
by the cellar
running parallel to the slab beams
cause the beams to rotate,
causing the lining bodies to
slide out - the beams of traditional
"I" iron beams are opened in the
upper bending area or in the
saddle position, the beams of the
vault fall out, - the walls of buildings tilt as a result of the sinking. Tilting the wall will cause
some damage: cracks will appear
on the wall,
and the tilting wall will not
only be subjected to pressure but
also to bending,
which can cause it to
fail quickly.
Damage to building structures due to sinking 6.2. Penetration of the collapse zone
to the surface
(rupture) A rupture is called when the
ceiling of a cavity falls into a cavity
and the rock or soil above it
and the artificial structures are no longer able to
hold their own weight and therefore fall into the
cavity. The rupture process can only
be followed from the bottom, so
it takes a lot of energy to
defend against it. That is why
this is the most dangerous process in the vicinity of cellars, artificial cavities. It was
the cause of many major disasters. Damage to buildings
or roads is difficult to prevent
and repair. 6.3. Collapse by
top-down forces In Hungary, it
is very common that a cavity protrudes
below the surface, but it
is covered by an existing spatial structure (rock, possibly road, building). This is most often the case
with unknown, closed, masonry cellars.
Demolition of a building (Eger 1970) In this case, a disaster occurs when, for
various surface effects (road traffic,
dynamic loads), the bridging loses
its hold and collapses. In our historic towns and districts the accessories
of the old cellars are the chimneys
that lead from the cellars to
the surface. Where cellars were
used for storage or possibly
for housing, the chimneys provided
ventilation. We see this kind
of thing in every cellar that has a problem.
Ventilation chimney of brewery cellar (Budapest – 10. disrict,
Kőbánya)
Cross-section of the cave with a surface
well in the Buda Castle The problem
is that most of the chimneys were just
obscured by our ancestors, or maybe built
on them. In many cases in the
Buda Castle such horns were broken.
There was something after 50-60 years. This was
also the reason for the
bus accident at Vienna Gate Square, but in the Trinity Square
(opposite the Matthias Church), for example,
there was a short period of three sinking that
could be attributed to this cause.
Sinking of the floor covering due to a horn
leading to the surface (Buda Castle, Holy Trinity
Square 2002) Damage to horns can be prevented
by examining them from below,
which requires serious knowledge. Cellar safety specialists
also need to pay particular
attention to this because the
rock near the falling chimney is often damaged, leading to an increase
in surface appearance.
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