The enclosing
rocks of the risky domestic cellars are very
diverse, which significantly determines the development of the dangerous state
and therefore the prevention activities. Given that a general
description of the various types of rock can be found in the literature, I present their properties
in terms of their effect on underground cavities and cellars. 4.1. Major rock types that surround it 4.1.1. Pannonian sand and clay (Pécs, Érd-high shore, Eger) are typically low
stability, water sensitive and swell. Total dehydration and repeated soaking can cause
very serious damage to underground objects. Cavities created in the clay version are also exposed to
the risk of so-called foot swelling, which must be taken into account when dimensioning the support structures
and revising the cavities. The breakage of the cavities can
be flowing or blocky. In these materials the cellars were
often built with a supporting structure, an arch. 4.1.2. The air-contact surface of the cavity cut
into sedimentary limestone ("lime" limestone
and "sarmatian" limestone)
is damaged, mossed, and the rock loses its strength. Its
bending strength is low, so cracking
(sometimes only a few tens of meters)
of the ceiling formed during the
mining is almost inevitable. Typically,
large cracks and displacements occur in limestone, which at first cause
slow movements. They break down
in blocks. The problem
is the large size of the cavities
as well as
the installation (and thus overload) of the surface above
them. 110 km in Budafok and 32 km in Kőbánya can be found. Properties of Sarmatian
limestone: weight: γ = 2,0 - 2.07 t / m3 Uniaxial compressive strength: σc = 3.6 - 8.0 MPa Tensile strength:
σt = 0.3 MPa Shear strength:
τ = 0.52 - 0.58 MPa (source: KBFI-ALFA 1997, 2002) Sarmatian limestone is
mostly inhomogeneous: from lime slurry to hard limestone,
it can be found in all varieties.
As a result, the various layers
are easily separated, leading to discrete layers.
This phenomenon occurs primarily on the drawn
side of the rock body (in the lower plane
of the headstone, in the side walls
at the point
of protrusion). 4.1.3. The caverns of the freshwater limestone (Budapest I. district,
Eger) are typically naturally formed, and later received various functions (protection, storage) as a result of human activity. The rock forming the hollow of the
cavities is brittle and of low bending strength.
It is sensitive to road traffic
and vibration and transmits
vibration waves far. The rupture usually takes the form
of a coffin lid. The clay, marl,
which appears as an encrusting rock and is embedded between blocks, is water-sensitive and prone to swelling. Characteristics of freshwater
limestone: weight: γ = 2.5-2.6 t / m3 Uniaxial compressive strength: σc = 6.8 - 9.0 MPa Shear strength:
τ = 0.52 - 0.58 MPa (Source: FŐMTERV Rt.) 4.1.4. In the volcanic
rock tuffs (rhyolite tuff, rhyodacite tuff) the cavities
were formed primarily through the mining of building stone. The
tuffs are sensitive to water,
their strength in the air deteriorates greatly, and they are characterized by weathering. This phenomenon is found mainly in the surface-related entrance of the cellars. Like sedimentary rocks, tufts have
low tensile strength. The strength properties of tufts vary widely, depending
on their condition and location. Properties of the rhyodacite tuff (when dry): weight: γ = 1.33 - 1.45 t / m3 Uniaxial compressive strength: σc = 2.25 - 7.09 MPa Tensile strength:
σt = 0.52 - 0.97 MPa Shear strength: τ = 0.35 - 0.50 MPa (source: GEOSERVICE Gmk 1985) Characteristics of basalt
tufa (wet or air-dry): weight:: γ = 1.9 - 2.1 t / m3 Uniaxial compressive strength: σc = 7.35 - 11.08 MPa Tensile strength:
σt = 0.25 - 1.57 MPa (source: Réthelyi 1986) It is characteristic of the rhyodacite tuff that the
main constituents of the feldspar are converted to clay by
moisture. It is important to know
that it is not only groundwater
or rainwater that can cause
this, but also the vapors
that accumulate in the air space of the cellars. As
a result, their strength is significantly reduced, up to
20% of the original strength. The rock structure of the tuffs allows
the root of the vegetation to penetrate, and this factor also
contributes to the degradation of the vegetation. The cellars built
in the solid rock environment described above are characterized
by the fact
that the supporting structures (masonry, arches, entrance barriers) are made of materials
extracted from the cut. Therefore,
the process and time course of their failure is almost identical to that
of the parent rock - that is, it occurs
with it. Also typical of such solid cellar-driven
cellars is that the headstone above
them is usually of low thickness and has significant natural or artificial layers.
The reason for the small thickness
is that most of the cavities were made
for material extraction, ie the extraction man was trying to
extract as much material as
possible from the site. A typical example of this, as well as
the size of the natural and artificial fillings, is the cellar system
located under the Old Hill Park in Budapest's
X. district. The quarry, formerly used for
quarrying and then clay mining, has been filled with communal
rubbish and building debris
since the 1960s. The 12, sometimes 18 meters thick, filling places a significant load on the
headstone of the deep cellars, which
are barely 0.8 to 1.2 meters thick.
The rock environment
of the cellar passages with filling Budapest, Kőbánya Cellar
system in Óhegy Park In such a thin
rock body, which is loaded with headstone, bending forces cause vertical cracks and, on its lower plane,
discrete deposits. This process can
also be found in cellars cut into
freshwater limestone and tuff.
Disc separation Budapest, Kőbánya 4.1.5. More than one
third of our country's territory is covered by loess
soils. Our loess can be divided
into three types. The so-called typical loess (which is typically found in Transdanubia, the Somogyi and Tolna hills, along the Danube,
on the Balaton extension) is the most problematic soil type in terms of both cellar damage
and construction. Loess
bank breaks in large areas (eg Dunaföldvár,
Dunaújváros, the eastern basin of Lake Balaton) are known, and each year the level
requires one or two deaths
due to improper
construction of the loess. The most damaging feature
of a typical loess is its collapse. This
process usually starts with water.
The main reason for the collapse lies
in the structure of the loess. It
contains SiO2 as its main constituent, along with feldspar,
carbonates and mica. Typical loess in our country consists of dust and sand carried
and deposited by the wind in the
Holocene (that is, very close to
our time in geological history). Changes in the Ice Age, during
the warmer periods, resulted in vegetation settling on the loess,
with tubules left in place of dead bodies, making
the loess macroporous. Water or a significant load causes these
tubes to collapse and lime to dissolve. This causes the loess
to suffer up to 55-60% volume
change (collapse). In loess, collapse occurs on vertical
and oblique free surfaces, which is why the
entrance part of the cellars is endangered. In such cases, the
cellars are dug deeper and deeper into the stomach
of the mountain. Bertalan Andrásfalvy
describes in his study of the Páty Cellar Mountain that a cellar carved in a loess is known to have entered its full length
under a manhole, as it was
originally. Loess on the surface is characterized by blocky breaks, and cellars have coffin-shaped
tears and detachments. The latter lead to a severe, often fatal
disaster. The destruction of the
loess cavities is rapid. One day, there
are only a few cracks that
can break in a few hours or
a day. From the point of view of cellar hazard prevention,
it is important to know that
although some of the cellar passages
cut in the old days have been
destroyed today, the collapses never
fill the underground space in their entirety and, therefore, sinking or cracking
is not excluded. The other two types of Hungarian loess, the good
loess on the soil, and the
properties of the infused loess prevalent
in the Great Plain, differ from the
above and do not pose the
same risk as the typical
loess. But the cellars established
in them have the same damage
as the clay
cellars discussed earlier.
The entrance
of the cellar carved into a loess
with a broken wall Kalazno, Tolna County 4.2. Occurrence of some
major rock types (look in hungarian page)
4.3. Relationships between
the surrounding rock environment of cellars and the appearance of cellar damage The following factors
should be considered when determining the appearance of cellar damage and how to treat
it: 1. The maximum depth of underground cavities and cellars subject to cellar
hazard prevention is approximately 25 m, therefore, in
addition to rock examination in mining, the methods of engineering (civil engineering) soil mechanics and geotechnics should be applied. The reason for this
is that most of the endangered cellars are made of materials
(eg clay, loess, spill rocks)
that deep-water mining does not encounter. 2. The shear strength
of rocks surrounding cellars and cavities is significantly reduced by the cracks
in them and the softer materials that fill them
(typically clay). 3. Moisture content
of the surrounding rocks is also a factor that reduces
stability. Soaking moisture or pressurized
water in the rock affects stability. 4. In Hungary, the so-called
so-called Qualification for the classification
of rock bodies is currently
developed in engineering practice. The application of RMR
is the generally accepted method. The essence of RMR is to measure, classify, and then aggregate the following six
properties of boundary rocks: - uniaxial rock compressive
strength (σc) - rock body breakdown index (RQD) - distance of the
rock body (Jn) - state of articulation
surfaces (Jr) - water conditions,
groundwater and groundwater
(Jw) - direction and location
of partitions (Or) Taking into account
the above with different weights, it sets
5 classes of rocks and assigns them different
types of support and freely extending cut lengths. The method is primarily
designed to drive new cuts, but
can be used with some additions
and modifications to test existing cellars, cavities without support structures, and to determine the
work to be performed. The author of this
site has prepared a modified
version of the RMR method for existing cellars.
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