5. Cellar ruin

________________________________________

5.1. Causes of failure of cellars and cavities

  5.1.1. natural causes of failure

  5.1.2. human causes

    5.1.2.1. inadequate technology used in the design of cellars

    5.1.2.2. change of surface load above cavities, appearance of overload.

    5.1.2.3. dynamic effects

    5.1.2.4. watering

    5.1.2.5. construction over cavities

    5.1.2.6. abandoning cellars and cavities without expertise

    5.1.2.7. lack of control of cellars and cavities.

5.2. The process of failure

  5.2.1. briefly on the rock mechanics of failure

  5.2.2. occurrence and course of failure in the underground space

    5.2.2.1. damage to sidewalls

    5.2.2.2. damage to the cavity ceiling,

    5.2.2.3. failure of the floor

  5.2.3. damage to nearby cavities

  5.2.4. intersections, junctions

  5.2.5 the problem of structures running up to the surface

________________________________________

5.1. Causes of failure of cellars and cavities

There are natural and artificial causes for the destruction of cellars and cavities. The latter are almost always due to human activity (some kind of intervention or even lack thereof).

5.1.1. Natural causes of failure

The most common cause of natural origin is the deterioration of rocks including cellars and cavities over time.

The reason for this is that by creating cellars and artificial cavities, we remove it from the natural rock body, which has several consequences:

- load conditions are rearranged,

- changes in impacts on previously undisturbed rock mass (eg flow of groundwater),

- chemical and biological effects,

- air gets to the previously intact rock body

- other extreme natural effects

Underground there are always - even today - geological processes that can affect cellars. Tectonic fractures cause many problems. Caverns that are built into sediments or sand from the Earth's modern age are rarely found, but they have often appeared in rocks formed hundreds of thousands or millions of years ago.

For example, the Táncsics Mihály Street section of the cavernous system under the Buda Castle, the fragmentation of which is clearly the responsibility of the tectonic movements. Traces of the fractures can be found in several places in the Miocene limestone limestone encircling the basement systems of Budafok and Kőbánya.

Ceiling break due to tectonic reasons (Buda Castle)

When examining this circumstance, the location and stratification of the rock surrounding the cavity must always be taken into account. The bearing capacity of vertical and horizontal layered rocks is different.

Cellar formation and the need for reinforcement in case of various rock layers (Buda Castle)

The cellars and cavities alter the flow of groundwater, because the passages collect the water. There are several possible consequences: the walls of the cavities are filled with water and damaged, and the flowing water can carry natural rock materials. In both cases, the strength of the structures is significantly reduced and may even be completely destroyed.

Cellars flooded with water under the Quarry

Water in cellars and cavities is causing and causing problems in many Hungarian settlements. In Eger, in Pécs, in the Buda Castle, in the Kőbánya cellar system, professionals have to contend with a lot of water with diverse chemical and physical properties.

At the entrance of the cavities near the surface, the effect of frost is also common. This is caused by the cold air entering the cellar during the cold winter weather, when the water on the ceiling cools below 0 degrees and freezes. In the early 1990s, we encountered polar-thickness ice columns at the entrance of the cave system under the Buda Castle, which made the entrance temporarily unusable.

Frost destroys structures and rocks.

Ice columns at the entrance of a railway tunnel

Excavation and use of the cavity may result in biological and chemical processes that significantly affect the condition. For example, the most common function of cellars is viticulture: the mildew of the walls has a good effect on the aging of the wine, but not so much on its condition and retention of strength.

The same is true for air entry: humidity is always present in the air, which can cause weathering in rocks. Layers of flue gas from the burning of torches and candles, used for lighting, have been used to destroy rocks by aggressive chemical action on the walls of cellars and cavities.

Freshwater limestone cooked with torch traces

Fortunately, seismic influences (earthquakes), which are rare in Hungary, can affect the condition of underground cavities. This is typically a problem in settlements that are otherwise endangered by earthquakes, but there is a type of rock, namely loess, which is capable of being damaged, even by smaller, non-human, earthquakes.

The relationship between cellar collapse and seismic effects has not yet been investigated in Hungary. The author of this website started these analyzes, which led to very interesting results.

"... every cellar collapses once ... one in 600 years, the other tomorrow morning ...

5.1.2. Causes of cellar damage due to human activity

Artificial causes always accelerate and intensify natural processes, and this leads to increased and rapid destruction of cellars and cavities.

Such reasons may include:

- defects in the construction of the cellar,

- overloads,

- dynamic loads, eg. road load, vibration,

- artificial cellars in close cellars,

- Insufficient water supply and drainage

- defects in structures over cavities

- improper abandonment and closure of unused cellars

- failure to check cellars

5.1.2.1.

Common causes of cellar damage include inadequate construction technology and the installation of inadequate structures

Basements were often carved by people who were not aware of the proper methods and technologies applicable to the particular rock environment. It is also a serious problem that in the old days the dimensioning of the possible reinforcing and supporting structures and the rules of their construction were not properly worked out, so they were built on the basis of experience.

Ruined arch (Kőbánya Old Hill Park)

A typical problem with built-in reinforcements is the improperly formed connection between artificial structures and natural rock. We have often encountered vaults, sidewalls, behind which space was not filled or not properly executed. As a result, the reinforcing structure does not physically contact the natural rock - it does not support it.

Making a regular space behind the arch

This has two consequences: the rock can move to different effects and unbalance the structure and, besides, the water between the rock and the wall also has a detrimental effect (pressure, soaking, chemical changes).

These defects usually occur within a short period of time after the basement has been designed, so repairing the basement, repairing the defective design, or even nearing the time of construction can occur. If not - and we find frequent examples of this - the damaged cellar remains, which can cause serious problems these days.

5.1.2.2.

The second most common cause of cellar damage is a change in the surface load above the cavities or the appearance of overload. This usually occurs when due diligence, soil mechanical testing or inadequate construction work is performed on a new building. It is also a problem if the cavities below the construction site are not known.

Until the 1970s (until the appearance of cellar problems in Pécs and Eger) this problem was not sufficiently addressed by professionals. In order to prevent problems occurring at that time, local regulations in most of our affected municipalities already provide specific criteria for areas endangered by cellars and artificial cavities.

5.1.2.3.

Besides the static load, the dynamic effects on the surrounding rocks of the cellars are not insignificant either. The most common of these is the impact caused by transport. In Hungary, 20-25% of broken cellars are located under the driveway. For cavities close to the surface, the vibration load can lead to particularly severe damage.

Soils without cohesion (sand, pebbles) also fail, causing slow but continuous spillage, which can lead to collapse, detachment and more than once.

Not really known, but dynamic loads also endanger cellars and cavities cut in hard rock.

Vibration measurements carried out at Buda Castle in 2004 showed that brittle, hard freshwater limestone (travertine) guides surface vibrations very well and transmits them to cellars and structures.

Vibration Measurement in the Buda Castle - The measuring probe at 16 Országház street

The result of the measurement

5.1.2.4.

Water is the most common cause of damage to cellar and cavity systems in the settlements.

According to the experiences of cellar protection experts, the majority of the water (90-95% in some settlements) gets into the cellars under the influence of human activity, from there into the cellars and cavities. There are two main reasons for this: inadequate condition of water pipes, sewage pipes and lack of drainage.

The greatest damage and the greatest danger to the underground areas is the defects of the faulty utility lines (water utilities).

Utility lines made in the past - primarily in the XX. Cast iron pipes laid in the first half of the 20th century, and asbestos cement pipes used in the 1950s and 1970s, are very rigid in their ability to absorb the movements of the surrounding soil. As a result, they move under tension as a result of very little movement, and cracks and fractures occur at their joints. From the minor injury, the water escapes, washing the underground conduit, which often flows into the cellar below. The pipe is no longer supported and after a while this rigid pipe wall can no longer be bridged, it suddenly explodes and the pressurized water floods the soil and the cavity there. Not only does the outflow of water flood the cavity below it, it often causes the surface to rupture by washing the soil.

Damage to cellars and cavities

This happened in 1994 in Pécs, in the Buda Castle, in July 1998 and in October 2004. In 1998, an asbestos-cement pipe under Dísz Square broke, resulting in hundreds of cubic meters of water flooding the 700-meter-long cellar system. The inflowing water washed away the reinforcing structures, materials and reinforcing works that were underway, and opened another previously unknown cave on the south side of the square. Luckily, he wasn't the victim of the incident.

Consequences of the Dísz Square Water Invasion (1997)

In 2004, the right rear wheel of a bus traveling through the Castle fell into a crash at Vienna Gate Square due to a pipe break, the bus had to be lifted by firefighters.

Cellar break in Vienna Gate Square (2004)

As a result of the disaster in Pécs, the exhibitions of the well-liked and highly visited mining museum were submerged and reopened only years later.

In many Hungarian settlements, the drainage of sewage into sewers is still not complete or complete: in these places, the waste water entering the clearing shafts soaks the cellars. Where the sewage network is of poor quality or aged, waste water can also reach the surface. And the greater the difference in the number of properties with running water and the corresponding drainage, the more this process becomes apparent. Hungary has made significant steps in this area in the last two decades, but there are still settlements where a significant part of the dwellings are not connected to the sewage system, but the water supply system has been fully completed.

The damage caused by wastewater is exacerbated by the fact that the water discharged from the sewers is chemically very aggressive. Therefore, it dissolves and damages the boundary rocks, which are damaged faster than possible.

Due to the above, the experts considered the reconstruction of water supply and sewage networks important in addition to the prevention of cellar hazards in several settlements. This is how the sewage and water networks of Eger, Pécs and the Buda Castle were completely renovated.

Inadequate surface drainage is also a problem. In countless settlements of our country this is not properly solved, and as a result, the underground waters cause serious damage to the underground cavities. Since the start of institutional cellar emergency response activities, ie four decades ago, many municipalities have been experiencing this problem, which often results in catastrophes, which are generally echoed in the public awareness.

5.1.2.5.

Almost every reason described above occurs as a result of special human activity. When under construction, endangered by cellars, human negligence often results in underground structures being damaged by static or dynamic overloading of their masonry, ceilings, or water from the surface.

Such an event probably led to the collapse of the Rákóczi cellar in Sárospatak in 2009, when work began on excavating clay soils above the cellar and then leaving the pit open for a long time. The pit was soaked by the fragmented tufa layer beneath it, so its physical properties changed: weathering occurred and friction between smaller and larger pieces decreased. This eventually led to the interlocking pieces unable to hold each other, collapsing with the layers above them.

Sárospatak

The soaked work pit that may have contributed to the damage to the Rákóczi Basement

Explanatory diagram of the failure

5.1.2.6.

It has been known to professionals since the commencement of the cellar hazard prevention work that our cellars and underground caverns have been abandoned and dismantled over the past centuries without any expertise. Even today, this fact makes it difficult to protect against damage. In the mid-1990s, practitioners working in this field could claim that 90-95% of domestic cellar systems are known. Unfortunately, this rate has not improved much in the past two decades: despite the huge amount of work, excavation, and recent investigations, there are always new, unknown cavities, and newer settlements are showing up. Our big cities - Eger, Pécs, Budapest districts - have been able to sacrifice historical comprehensive maps, records, records, but the scarce financial resources of small settlements have not made it possible. And the truth is, these documents aren't very well written for smaller settlements ...

XIX. century map of the quarry-old hill limestone quarry and cellar system

5.1.2.7.

A similar problem is the lack of regular inspection and monitoring of cellars and cavities. In larger settlements the control and follow-up is solved. But small settlements cannot pay enough attention to this, partly because of the lack of material resources and partly due to the lack of specialists.

There is also a lack of systematic solution for the management and maintenance of cellar systems, which in many cases leads to the occurrence of havaria events.

5.2. the process of failure

When investigating the damage of cellars, we apply rock-engineering solutions in mining and civil engineering.

5.2.1. briefly on the rock mechanical components of the failure

The minerals and crystal structures that make up the rock undergo the physical (fracture, displacement, water uptake) and chemical (clayey, chemical composition) changes described in the previous chapter. These changes lead to a deterioration of their existing strength properties, leading to damage to the cellars.

This is dealt with in a separate discipline of mining and geotechnics. One of the hardest subjects in mining engineering, geologist training, hundreds and hundreds of colleagues sweat in rock engineering exams at our technical colleges. In practical life, few can tell the subject matter specialists themselves, though that would be the basis for any activity underground.

This site is primarily intended for those who are interested in the topic, or who have such problems. Those who are generally laymen ... so I tried to delve into the details as much as needed to understand the processes that interest us.

There is a Chinese saying: a drawing says more than a thousand words. Therefore, as an introduction to the chapter, I present here a highlighted figure from the material of a leading company specialized in the field of mining mechanics, mining areas, which presents nothing more than the distribution of stresses occurring underground. I will refer to this drawing many times later ...

Voltage distribution around a square cross section in limestone

5.2.2. the process of the destruction of cellars and artificial cavities

Cellars and cavities do not exist by themselves - their condition is determined by the rocks that surround them. During their examination, they should have separate sides, separate ceilings and separate floors.

Consequences of the destruction of rocks:

on the side walls

- spit out

- appearance of cracks

- disk detachments

- breaking of blocks

- Freaking out then falling

- water intrusion

on the ceiling

- appearance of cracks

- disk detachments

block blocks

- collapse

- rupture

- soaking, water intrusion

on the floor

- flooding

- swelling of the sole

It is clear that the failure of the side walls and ceiling is similar, but their causes are very different.

Given that most of the processes outlined above follow each other, the damage is described below.

5.2.2.1.

See 5.2.1 for damage to sidewalls. may be caused by any of the effects listed in section.

When designing cellars, our ancestors paid far less attention to the safety of the sidewalls than to the ceiling. The dangerous cellars were usually made without a built-in sidewall. only a small percentage of built masonry. This is partly justified as the cellar is already carved into material that stops on its own. However, the effects detailed above have damaged the sidewalls as well as the cellar ceilings, though often not as spectacular.

There are two types of pressure on the sidewalls: the vertical pressure may cause the natural rock mass to bend (obviously, this means bending towards the cellar space), or cracks or fractures appear.

In the case of sidewalls, it is imperative to note that the horizontal pressure is exerted by the rocks until they are less than their tensile strength. If this value is exceeded, the wall or its elements will move. This rarely appears in the displacement of the entire wall surface, but rather in the detachment of individual pieces. Depending on the quality of the wall and the magnitude of the compressive force, the separation can be plate or block. The detachment of rocks will be concave, and the remaining rock will move toward the inside of a pillar, block of rock, until it reaches a depth where the fracture stress is greater than the fracture force.    

The process is significantly accelerated by a variety of physical and chemical effects (wetting, water pressure, frost, chemicals from water and air, etc.).

Swelling of the clay floor beneath the side walls may cause the wall to come under pressure and try to circumvent it. This process is known from mines but also occurs in near-surface cavities. If the rock blocks (layers of soil) above the sidewall are plastic or not heavy, the pressure on the sidewall will raise the layers above it, or possibly the surface above the basement itself. At greater depths or when carrying heavy loads to the sidewall (eg arches), the sidewall bends toward the free surface, which also appears in the form of sheet peelings.

Distribution of stress on the sidewalls and soles of a typical cellar profile

This process results in a significant reduction in the load-bearing capacity of the sidewall and, if it is displaced, also reduces the stability of the attached reinforcing structures. The fall of rock material is often dangerous, as it often causes a sudden explosive separation of rock material from the sidewall or ceiling. There is a known coal mine where some quarries had to be abandoned because the miners were unable to work because of the fossilized pieces of rock.

The relationship between the damage to the sidewall and the collapse of the ceiling above is clearly observed under the Buda Castle.

Buda marl over the freshwater limestone quilt (Buda Castle, Dísz tér 15.)

The Buda marl is a good load-bearing, volatile material, but when it is given water, its texture becomes soapy, its load-bearing capacity is reduced to 30-35% of the original. One of the main damages to the cellar system under the Buda Castle was the natural waters and the water from public utilities for a long time. As a result of the watering, the marl forming the sidewalls of the cavities was destroyed, and large pieces of rock became detached.

The process was intensified in the XX. In the 20th century, road traffic increased, bringing significant dynamic loads to the bottom. As a result of these effects, the internal width dimensions of the cavities increased and the span of the limestone supporting the cavity ceiling became larger. After a while, limestone was no longer capable of absorbing the resulting bending force, causing cracks and tearing. By the second half of the 1980s, the damage had become such that traffic restrictions had to be introduced in Buda Castle. At that time, buses with heavy loads on the road and on the ground were replaced, and since then no other heavy vehicles have been allowed to enter the Castle.

5.2.2.2. Damage to the ceilings of cellars and artificial cavities.

Underground rocks are at rest, and rock mechanics call this a primary state. At any point, we examine the mass so formed, and find that it is laden with the weight of the mass of the earth, the mass of the rock. This weight is very high, depending on the material and condition of the rock, it can be 1.6-2.8 tons per cubic meter.

Because rocks, even the hardest rocks, are not completely rigid, they produce a certain amount of compression, or tension.

Ceiling break

When a cavity is formed in a rock, this tension appears on the ceiling of the cavity, trying to move its material towards the open space, that is, the cavity.

The mass of rock forming the headstone bridges the cavity and therefore, to a certain thickness, acts as a two-legged support. In the two-legged bracket, a bending stress occurs, which, as is known, means that a tensile force is applied at the top (press belt).

Drawn and pressed belt of bent support

The tensile strength of various rocks is much lower than their compressive strength. There are materials with little or no cohesion, which have little or no ability to absorb bending and tensile forces.

Resistance to such effects is not only influenced by the quality of the rock. Layers above the cavity, when the stresses applied to them are higher than their boundary voltages, are destroyed. The failure occurs where the two voltages are of the same magnitude. It is well-known that in the two-support brackets (beams, slabs) serving as the supporting structure, the maximum stress occurs in the middle of the carrier (see voltage diagram).

Failure to do so will cause loosening and collapse of aggregates with little or no cohesion (eg granular rocks). Generally, the process begins immediately after folding out and is relatively fast under unchanged conditions.

In the case of cohesive rocks, the tensile stress causes the deposition to be layered (plate) or block. Divorced blocks fall down over time, and their course is difficult to predict: in some cases, the deposited rock masses remain in place for a long, long time, and in other cases, often in an accident-prone state, this process occurs rapidly.

Plate detachment in limestone

The above depends on a number of factors such as the material of the cooker, the distance bridged, the size and speed of the loads on the headstock, and so on.

Ideally, even in a non-cohesive and solid rock block, this process known as rupture lasts until a sloping or arched surface, usually bounded by a parabolic plane, is formed at the site of the falling portions, close to the natural boundary of the rock. it can retain the layers above it. This type of rupture is referred to in many ways, the most well-known in Hungary being the "coffin cover".

Theoretical drawing of the main rupture

However, ruptures rarely stop in this state. The situation becomes severe when the rupture continues towards the surface, reaching a layer or layer with insufficient self-retention. In this case, the ruptured ceiling together with the natural and artificial (built-in elements) above it collapses into the damaged cavity, causing severe damage.

The above process occurs particularly rapidly when the rock material forming the headstone is cracked.

The two processes add up, the cellar, the cavity ceiling breaks and collapse occurs. This process usually takes place in a very short period of time and is significantly influenced by the various effects discussed in the previous section, such as the dynamic load or the dissolving or rock abrasion effect of groundwater.

Not really studied and processed, but similar to the one described in clay soil failure. In the case of clay ceilings, the block bridging the block may be assumed to be a two-pillar support having the same height as the clay layer. But clay and its processes raise several issues that we cannot deal with with conventional solutions in soil mechanics, petrology.

1. the shear stress of the clay is not clearly defined (depends also on waterlogging and swelling, or on the speed of loading)

2. blocks made of clay material exhibit completely different properties in the dry state and in the wet state, sometimes with conflicting properties,

3. constant shear stress should be expected even when the soil is moving slowly,

4. not only friction but also adhesion can occur in the clay mass, causing, in some cases, effects contrary to the general rock mechanical processes

5. shrinkage and separation cracks in the clay block and its surface change forces that are very difficult to predict in advance

6. if the clay absorbs water, the swelling pressure may cause the ground pressure to increase several times its original size.

7. the moisture content of the clays can change in positive and negative directions over a very short period of time, resulting in a temporal change in the above

The clay block thus acts as a bridgehead over the open cavity, a two-pillar support. As with the various effects mentioned above, it suffers the greatest damage at half the span. There is a crack in it, which causes bending. The deflection in the middle will be greatest. At the same time, due to plasticity, some internal forces may be rearranged, for example, water will flow towards the sloping portion, and the degree of crack expansion may also move in a negative direction (i.e., the crack may close).

In these cases, the tear, collapse, is unpredictable, and the flow of the block may occur: the water collected as a lens over the tiled clay layer may soak the clay below, leading to a change in consistency and breaking into the cellar space. This process, known as the mud sluice, has been the cause of numerous mine accidents in the past.

Mud Flush in a Broken Cellar (Buda Castle, Dísz tér)

Predicting the breakage of the heating system and the calculation applied

Many researchers have developed a number of methods for predicting the displacement of rock bodies above the rocks formed in rocks. The simplest method of calculation in engineering practice is the one used in tunnel construction based on the Protodyanokov theory developed during the Soviet metro construction.

Protodjanokov, who developed his theory on granular soils, assumes that an open cavity will form a vault surrounded by parabolic arches. The height of the vault can be calculated as follows:

Drawing of the Protodjanokov theory

If the plane of the ceiling of the cavity is within this value of "h", it shall be expected to break to the surface.

The method shall be applied taking into account:

- we must assume that the relocation will take place,

- for stratified soils it is not necessary to calculate the vault parameters separately for each layer, only the properties of the layer directly above the cavity need to be considered,

- swelling of clay in clay soils is also to be expected,

- practice has shown that the theory can be well applied at depths between b / 2tg <H <b / tg.

Ceiling collapse

To a large extent, the above-described rupture process can also lead to a collapse of the cellar ceiling from above. It is easy to see that the thinned teal will not be able to hold the mass above it, so its weight will lead to its collapse.

Excessive thinning of the head, which may result from the dismantling of the rock body above the cavity (eg as a result of construction work), also leads to collapse.

The examination of top cracks is similar to the tests in the field of supporting structures, the directions of forces and supports can be recorded according to the method used there, except that the quality and condition of the soil must always be taken into account. The procedures followed here are in the field of soil mechanics, and the literature and civil engineering practice deal with them in an inexhaustible amount.

The above processes do not only appear in the ceiling of the natural state (unsupported) bordered by the flat slab. In many places, the ceilings were already arched. Not everywhere because, for example, where the extraction of building materials was the reason for cutting cellars, they did not do so because it would have meant less material to extract. Anyway, it was believed that hard, usable building stone would stop at a horizontal lower plane. In fact, the beech-miners quarryers explicitly believed that the ceiling of the cavity should not be carved, because it would weaken it.

The vaulted ceilings are deformed into an ellipse by the effects detailed above: the upper part is pressed in, the two ends resting on the sidewall move horizontally outwards. This is because the minor axis of the ellipse will be smaller than the original diameter and the major axis will be smaller.

In the former case, as long as the boundary voltage of the rock is greater than the voltage from the top, the arch stops in place. However, if this limit is exceeded, the arch will first be damaged (similar to those described above), detachments from the bottom will begin, and then, if the voltage is not reduced, will collapse.

The displacement of the lateral support of the arches causes the sidewalls to move, and the height of the arch itself decreases. This also reduces its carrying capacity - the two processes reinforce each other until the arch is completely destroyed.

5.2.2.3. damage to the cellar base

In the case of cellars and near-surface storage areas, we do not have to expect foot-swelling or failure similar to deep-mine mines. The cause of the process is the tension on the floor, which causes it to move towards the open space, that is to say the cut space. As a result, the floor folds in the middle and fractures. Not only clay soils, but also sand or even solids (such as limestone) can cause this damage.

In the case of near-surface cavities, the same forces are exerted on the sole as in mines. This can be well observed in the voltage diagram presented above.

However, this force is significantly lower than in the case of underground mines, but the situation changes when the rock environment is wet and the cavity is wet.

The presence of water in rocks and structures will definitely increase the stresses in it.

In the case of domestic cellars and cavities it is common to say that even in the case of cellars cut into solid rock, the floor itself is of soft material, most often clay or some variation thereof (eg marl). As is known, these materials undergo significant changes upon wetting. On the one hand, their strength is reduced and, on the other hand, these materials tend to swell. Both effects can lead to a significant increase in flooring.

In underground mines, this phenomenon causes not only a static problem, but also hinders, for example, traffic and material transport.

In cellars and cavities, this process is particularly problematic because it causes the sidewalls and built-in supporting structures to move, not infrequently losing their stability.

Further damage to the flooring is due to the physical presence of water - it is difficult for the clay to absorb moisture, and the water in the enclosed cellar space will remain for a very long time, even for years, without proper measures. This leads to long-term damage to the rock material surrounding the cavity, to the built-in structures, and even to related structures (eg above the cellar).

He was well aware of the problems of cellars that had been flooded in Eger, Pécs or even Kőbánya for years.

The flooded cellars and caves in the Buda Castle after the water pipe breaks mentioned earlier in the chapters were not accessible for a long time, and the work in them could only be done after pumping for weeks.

5.2.3. damage to close cellars

The underground caverns of our settlements are characterized by the fact that underground caverns have been created over the centuries without any system or expertise. As a result, the running of cellar passages, both horizontally and in height, is irregular and often fails to meet basic safety standards.

In many of our settlements it can be stated that when making the cellar branches, the makers did not take into consideration the existing cellars and passages. Even where a specialist did this job, it was not easy to keep close to two passages, but where the non-specialist was working or the owners were trying to expand an existing cellar, the danger was even greater. In Eger, Budafok, as well as in Pécs, basement branches running from different properties, either side by side or behind each other, run without any system, not infrequently separated by walls or ceilings of just a few decimeters. Weakened ceilings and sidewalls cannot support the load above them, and collapses and cracks are common.

Cellar branches and cavities that are close together threaten the stability of adjacent cavity boundary structures.

Damage to adjacent cavities occurs in three ways:

a, the horizontal support of the cellar sidewalls is eliminated, which eventually leads to their fall

b, in more serious cases - and we have often seen examples of this - the block separating the two spaces becomes so thin that it is no longer able to hold the weight of the rock above it: it collapses (falls out, collapses). Simply put, there is a certain minimum limit for the thickness of each rock material within which it can support the loads it is carrying. This indicator depends on its natural characteristics (boundary voltage, cohesion, etc.), the load on it and last but not least its free height. The stability of boundaries created by ignoring them is not sufficient to fulfill their function.

c, the previously described rupture of the crowns of adjacent spaces superimposes (adds), by which the natural permeation over the cavities becomes much larger and reaches the exterior sooner.

Voltage distribution in the rock field around parallel cellar branches

The problem of the cellar branches above and below each other is more difficult to find out. The reason for this is that in addition to the frequent rock break-throughs and punctures caused by careless work, the damage is caused by very complex and difficult to observe rock physical effects.

In the case of vertically close cellar branches and cellars, the side walls and ceilings of the object above can cause serious damage to the structures of the space below.

The reason for this is that the loads from the main cellar of the upper cellar are not evenly distributed, but the walls provide a concentrated, linear load to the rock mass below them. While the distributed load can be borne by the structures of the lower cavity, such concentrated load is no longer certain.

5.2.4. intersections, junctions

For intersections and junctions, similar processes occur. Not only intersections in the traditional sense, but also cases where a section runs into or starts from a larger waiter.

At the point of contact of two or more cavities, the self-retaining capacity of the structures is reduced and the loads are concentrated.

If the voltage diagrams of the sections, shown earlier, are arranged by juxtaposing them (or their simplified scheme), it is easy to see that the stresses on the sidewalls add up for both the lateral and the main load.

The degree of damage depends not only on the usual parameters: the smaller the angles of the cavities are crossed or touched, the greater the failure rate.

This phenomenon typically occurs around the connection point on the side walls. There is almost no underground cellar system in Hungary where our specialists would not have encountered this phenomenon.

In the case of joints and intersections, damage to ceilings is also common. The forces acting on each other, like each other, are also concentrated, leading to their damage.

Our ancestors were more or less aware of this fact. During the excavation of the cellar system under the Óhegy Park in Kőbánya, it was discovered that in the passage system made without artificial support, the intersection of the sections was avoided, so that in the main section there were no two section joints.

Nor is it the case that the ceilings of the cavities are arched: there is an annular tension in the tangent arches, which moves the rock material towards the free space delimited by the arches;

Arched intersection (Kőbánya, Óhegy Park)

Construction of arch support at intersection

5.2.5. the problem of structures running to the surface

The surface horns that once served as vents or wells contribute greatly to the endangering of some of our historic neighborhoods and cities.

In the Buda Castle there are more than 120 such former wells.

The caves of the castle were used by the man of the Middle Ages as the primary source of water. He raised the water at the bottom of the cavities and used it in his household. This was especially important during the siege - the establishment and settlement of the Buda Castle was in fact due to the water in the caves of the Castle Hill. ARC. King Béla did not establish his new capital on the much higher and more defensible Gellért Hill after the Tartar invasion because there was no water essential for city life.

Horns have been used for centuries. When the water level decreased due to the installation, the wells were followed by the wells, so the existing caves at the bottom of the castle caves were formed. Later, during the storage and escape function of the caves, the horns leading to the surface were used for ventilation, but not infrequently for traffic.

During the construction of the traffic routes, the upper opening of the chimneys was walled and covered during the construction of buildings. However, in the XX. The increased burden of the 20th century led to the destruction of negligently constructed closures.

Almost every year since the early 1990s, there has been a rupture of the horn, there have been years when there are more.

Such a breakdown led, for example, to the discovery of caves on Vienna Gate Square or several on Trinity Square.

But similar vent chimneys in Budafok, Eger and Pécs have caused and are causing many problems.