US3668368A

US3668368A - A process and apparatus for the prevention of ice formation in tunnels

Info

Publication number: US3668368A
Application number: US95452A
Authority: US
Inventors: Oddmund Moldskred
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-12-07
Filing date: 1970-12-07
Publication date: 1972-06-06
Anticipated expiration: 1989-06-06

Abstract

Processes and devices for the prevention of ice formation in tunnels, especially road and railway tunnels, mountain cuttings and the like, by the supply of heat from the outside to rock faces where the formation of ice normally occurs. More particularly, this involves installing electrical heating means distributed in a self-supporting manner in individual bores formed in a rock face substantially at right angles to a boundary surface with the air and heating a layer of rock between the air and rear-lying masses of rock to a temperature higher than the temperature at said boundary surface and lower than the temperature of said rear-lying rock masses.

Description

United States Patent Moldskred [54] A PROCESS AND APPARATUS FOR THE PREVENTION OF IC FORMATION IN TUNNELS [72] Inventor: Oddmund Moldskred, Brakehaugen, 5050 Nesttun, Norway [22] Filed: Dec. 7, 1970 [21] Appl.No.: 95,452

[52] U.S. Cl. ...2l9/213, 6l/45 R [5l] ..H05b 3/00 [58] Field ofSearch ..2l9/200, 201, 213, 345;

61/36 A, 45 B, 45 R; 299/l4 1451 June 6,1972

Primary Examiner-C. L. Albritton Allurneys- Kenyon& Kenyon Reilly Carr & Chapin s7 ABSTRACT Processes and devices for the prevention of ice formation in tunnels, especially road and railway tunnels, mountain cuttings and the like, by the supply of heat from the outside to rock faces where the formation of ice normally occurs. More particularly, this involves installing electrical heating means distributed in a self-supporting manner in individual bores formed in a rock face substantially at right angles to a boundary surface with the air and heating a layer of rock between the air and rear-lying masses of rock to a temperature higher than the temperature at said boundary surface and lower than the temperature of said rear-lying rock masses.

27 Claims, 6 Drawing Figures PATENTEDJUN s 1972 3, 668 368 SHEET 10F 2 INVENTOR: ODDM um: MOLDSKFPED 1 PROCESS APPARATUS'FORTHE PREVENTION OF ICE FORMATION IN TUNNEIS This invention relates, in general, to a process for preventingthe forrnationof ice in tunnels, especially road and railway tunnels, andsimilar mountain cuttings by supplying heat from the outside to that portion of the mountain where ice fon'nation occurs and devices for carrying out theprocess.

It has previouslybeen proposed, for-example,in US. Pat.

No. 2,018,293, toprovide a heating arrangement designed for an upwardly directed surface which is designed to betrodden on or driven on by heavy trafiic. The upwardly directed surface is adapted by heating of the ground to be kept free of snow and ice. The heating elements are, in such circumstances, arranged at a suitable level below the top surface inserted in a suitable road material and. are adapted to be supplied with a suflicient amount of heat to not only'prevent ice formation on the roadway but also to supply sufficient heat to continuously melt snow and possibly ice formations on the roadway. In orderto achieve the best possible heating efiect the heating elements are disposed in slings parallel to the surface which is to be heated. Such a solution is certainlynot practicable for tunnel walls and similar rock faces. Firstly, the placing of the heating elements in slings parallel to the surface which is to be heated gives, from a heat-technical view, an uneconomic solution .both in the case of heat elements ar ranged in a moulding layer outside the rock face which is to be heated and in the case of heatingelements arranged freely outside the rock face. in the first-mentioned instance, where the heating elements are to be inserted in a moulding layer.

over the whole tunnel archway .or the like, production and possible repair costs are prohibitively expensive without giving a satisfactory practical solution. The moulding shell which is erected outside the rock face cannot provide an effective seal against water leakage from rear-lying rock portions and will thus be subject to breaking up. Hitherto, experience with such moulding shells has not been especially good. In the second instance, where the heating elements are arranged free-lying outside the rock face, production and maintenance costs are certainly relatively low, but as a consequence of the outside air circulating past, the loss of heat to the outside air is disproportionately high.

in many mountain cuttings and overhangs, and in most tunnels for railand wheel-going vehicles in areas having especially lowwinter temperatures, ice formation presents a serious disadvantage and danger for the traffic. Such ice fon'nation is especially prominent in water-carrying crevices in the .heat capacity. Furthermore,

wards from the mass of the mountain, flowing,

and ice formation can be avoided in a relatively simple and easy manner.

It is still another object of the invention to provide additional improvements in the heating and arrangements for performing the process.

A main concept of the present invention is the recognition of the factthat'themass of the mountain always has a relativelyhigh background temperature, that is to say of the order of magnitude of from2. to 8 C, and with an almost inexhaustible the mountain mass is a relatively goodheat conductor, of an order of magnitude of four times the heat conductivity of water. The consequence of this is that onlythe outermost layer of the mountain rock mass is cooled below 0- C. By cooling down the outer portion of the rock mass, there will thus alwaystake place a flow of heat from the rear-lying rock massesand this will involve the zero centigrade depth beinggdisplaced comparatively little inwards into the mountain, even after long cold periods. The present invention is based upon the afore-mentioned recognition, the aim being to utilize the stream of heat from the rear-lying rock masses as much as possible. The aim is only to heat the outer layer of a rock face to a temperature above zero, but nevertheless lower than the temperature of the rear-lying rock masses so that the flow of heat from such rear-lying masses is not turned but, on the contrary, so that such a flow of heat is maintained to a certain, though reduced, extent, the most substantial loss of heat at the outermost layer of all of the mountain only being compensated for, thereby preventing the formation of ice on the outer surface. The aim is to keep the water which trickles outnot only in the mountainbut also outside the latter.

A process according to the invention is characterized in that the exposed rock faces are heated by the placing of distributed heaters in a self-supporting manner in bores substantially at right angles to the main boundary surface to the air, a rock face between the air and the rear-lying rock masses being heated to a temperature higher than the temperature of the boundary surface to the air but lower than the temperature of the rear-lying rock masses, so that the heating can counteract the transport of heat from the rear-lying rock masses towards the main boundary surface to the air, and from the said layer towards the rear-lying rock masses. 7

In addition to the heat-technical advantages which are achieved according to the invention by introducing the distributed heaters substantially at right angles to the outer surface so as to heat thereby the rock masses to a certain layer depth, there are obtained by the method according to the inmountain, and loosened ice and stone blocks often cause significant material damage and can in certain circumstances be a risk'to human safety.

in general, problems arise with water dripping in tunnels and mountain cuttings, both in the winter and the summer. I The biggest disadvantages occur on conventional gravel or oil- 'gravelled roads but even on asphalt or concrete roads, the problems can be rather large since the constant dripping of I water hollows out the surface of the road and in addition the water is distributed over larger portions of the roadway. During the winter, such water dripping results in the build up of vention special constructional advantages. A series of bores can thus be bored out in the rock face with conventional boring equipment and thereafter the heaters can be mounted in such bores in a self-supporting manner so that there is obtained a simple and secure fixing of the heaters in a ready way. it should be clearly evident that the mounting of the heating unit can be carried out, according to the circumstances, in an especially easy and inexpensive manner.

It is preferred, according to the invention, that the heaters are disposed at a mutual distance of between 30 and cm, preferably about 50 cm. With a mutual distance of about 50 cm, there is achieved an especially uniform dispersion of the quantity of heat from the heaters over the whole area between the heaters. I

it is apparent that the quantity of heat supplied can be regulated by placing the heaters at larger or smaller distances from each other by respectively using stronger or weaker heating efl'ects from the heaters. An actual heating efiect can be, for example, about 50 W/m when heaters of 14 W areutilized. According to the invention a satisfactory heating effect is achieved with heaters of, for example, 7 W.

The present invention comprises furthermore devices for carrying out the method and such a device is characterized by electrical heating means dimensioned so as to be installed and received so as to be almost fully pushed directly in individual bores in the rock face in a self-supporting manner by means of suitable locating means.

The heater can be designed so as to be received in the bore inserted in a heat-conducting moulding mass which is introduced directly into the bore, according to a first embodiment. According to a second embodiment the heater can be enclosed in an outer jacket of elastic, heat-conducting material so as to be receivable as a unit in the borein a self-supporting manner.

By heating the tunnel archway or similar overhanging rock face by the aforesaid method and/or by means of the aforesaid devices of the invention, it has been possible to avoid the formation of ice on the tunnel archway or the overhanging rock face with a relatively small amount of heat, but as a consequence of the dripping of water from the heated tunnel archway or the overhanging rock face, there have resulted, nevertheless, some difficulties due to the build up of ice on the ground below the tunnel archway or below the overhanging rock face.

According to another embodiment of the invention a process for preventing the formation of ice in tunnels and similar rock faces by supplying heat from the outside to the rock face comprises covering the exposed rock face in a tunnel archway or in a similar rock face against the outside air with a cloth, fluid-tight and, preferably, also gas-tight facing material to form a liquid-conducting layer and a temperature barring or blocking layer between the rock face and the cloth material, the latter, with a suitable intermediate space, being anchored to the rock face via electrical heating means which are fixed in individual bores in the rock face.

By the afore-mentioned solution, the water dripping from the rock face can be led in a controlled manner to the fringes of the roadway in the tunnel or the like and, if desired, can be led away in a frost-proof drainage ditch or another suitable collecting means. Furthermore, by means of the said facing, a substantial flow of cold air past the covered rock face can be avoided so that the need for heat to avoid the formation of ice on the covered rock face can be additionally strongly reduced.

The process according to the invention is from the procedural point of view especially advantageous in that the heating means are first secured in the rock face with free outwardly projecting coupling ends and thereafter the cloth material is threaded in position on the coupling ends and finally secured in place by arranging current-conducting means outside the cloth material in current-conducting connection with the coupling ends associated with the heating means.

It is preferred to utilize relatively rigid current-conducting means between the distributed heaters, the current-conducting means serving as supporting means and/or carrying means for the cloth material. In this way, the possible formation of ice which will occur on the stoppage of current or for other reasons in the layer between the cloth material and the covered rock face, is collected up in an effective manner by the cooperating support of the cloth material and the currentconducting means. Similarly stones which have come free from the covered mountain portion can be gathered up in the cloth material.

Moreover, it is preferred to utilize a cloth material with a light-reflecting surface directed outwardly from the covered rock face. In this way, there can be combined in one and the same construction, the afore-mentioned advantages with an especially favorable light-technical solution. It should be understood that the term cloth in this specification also embraces an appropriate cloth-like material.

A device for carrying out the process according to the invention is characterized by a cloth, fluid-tight and preferably also gas-tight facing material being anchored, with a suitable intermediate space, to the rock face via electrical heating means which are fixed in bores in the rock face to form a liquid-conducting layer and a temperature barring or blocking layer between the rock face and the cloth material.

It is preferred to employ current-conducting means consisting of rigid current-conducting rails of metal, preferably of reinforcing steel, which are welded to or are fastened in current-conducting connection to the heating means in another suitable way. I

F urthermore,it is preferred that the heaters consist of a baror loop-shaped heating element of metal rod, such as reinforcing steel, inserted in a heat-conducting moulding mass directly in a bore in the rock face.

In order that the invention can be more clearly understood, convenient embodiments thereof will now be described, by way of example, with reference to the accompanying drawings in which:

FIG. 1 is a section through a tunnel,

FIG. 2 is a section showing a detail of a portion of the tunnel roof of FIG. 1 with heating cartridges inserted,

FIG. 3 is a diagram showing the temperature distribution along the line A A of FIG. 2 with and without the supply of extra heat,

FIG. 4 is a section of a tunnel having heaters located only in the uppermost portion of the tunnel archway,

FIG. 5 is a vertical section illustrating a detail in the slit between two current-conducting means and a heater and an associated cloth material, and

FIG. 6 is a section at right angles to the section of FIG. 2.

In the tunnel of FIG. 1, the low air temperature t causesa cooling of the mass of rock which has a temperature in the deeper layers, that is to say at a certain distance from the tunnel surface. The air temperature in the tunnel can, disregarding extreme values, go down to -10 to 20 C, while the temperature in the heart of the mountain will be up to 10 C at the actual mountain depths. This temperature is dependent, however, upon the region and the height above sea-level. There wilLthus occur a flow of heat energy in towards the tunnel opening, that is to say in the direction of the arrow of FIG. 1.

In FIG. 2, there is shown a section of a tunnel roof with, an arrangement for preventing ice formation in the form of heating cartridges 11 which are inserted in holes 12 in the rock. The holes are bored in advance in the usual way and can be from 15 to 30 cm deep and have a diameter of from 2.5 to 5 cm, depending upon the dimensions of the heating cartridges.

The main portion of the heating cartridges 1 1 is the barshaped portion 13 which receives the heating element. The bar-shaped portion 13 is preferably of cylindrical form and fits in the bore in the rock. The heating cartridge 11 comprises besides a coupling head 14, the individual heating cartridges being coupled to the electrical supply system in an appropriate series or parallel coupling by means on connection leads 15.

The heating element per se, which is not shown, can be designed in a number of known ways, for example as a stocking of resistance wire.

In view of the low surface temperature which has necessarily shown itself, the heating element can be enclosed in a cheap and easily made insulation material. The outer jacket of the heating cartridge is advantageously formed from an elastic and shock-resistant material, such as rubber. The design of the coupling portion and other details of the cartridge is conventional and will, therefore, not be discussed further here.

The outer surface of the heating cartridge can be made elastic, for example, by arranging yielding ribs with a slightly larger diameter than the light opening of the hole 12, whereby the heating cartridge can be held in place without special auxiliary means. However, the best results can be achieved if it is cast in a moulding material 16 as shown. In this way, air pockets between the heating cartridge and the rock which can reduce the heat transfer are avoided. The moulding material serves simultaneously as a binding agent and holds the heating cartridge securely in position.

By virtue of the good heat-conducting relationship between the source of heat and the heat consumer, that is to say between the heating cartridge and the air of the tunnel, the arrangement according to the invention operates with a low thermal inertia. The heating element only needs to be coupled in, in the time-space in which the temperature is at its lowest. The consumption of energy and the operation expensescan, therefore, be reduced to a low level.

The cost of procuring the heating equipment and especially mounting the latter will be low just the same since the heating .Figure,

cartridges can be produced by machine and hence reasonably and the mounting only involves the boring of holes and introduction of heating cartridges and the setting up of supply lines. The necessary control equipment can be very limited.

The controlcan be based in a known manner on a thermostatic coupling. For example, a thermostat or a combination of thermostats can be. employed, which besides reacting at the temperature of the air in the tunnel or on the outside, also takes into account the temperature at one or more predetermined locations in the mountain.

In FIG. 3 there is illustrated a schematic temperature diagram which shows the operation of the invention. In the curve a shows the temperature distribution along the line A A in FIG. 2 in the original case without the supply of extra heat, and curve b the corresponding temperature distribution with heaters coupled .in. As will be evident, it is possible, by means of the heaters according to the invention, to 1 bringthe boundary area between the mountain and the air in the tunnel or on the outside up to a temperature above 0 C without significantly heating large portions of the mass of rock and of the air at the side of the mountain.

According to experience, from 100 to 150 W/m is sufiicient to maintain even the most exposed portions ice-free.

With a heating element which develops about 50 W a distance of about 70 cm betw een the heaters in a square pattern will give in most instances a sufficient yield.

That which is indicated here in the embodiment for tunnels also serves substantially for exposed mountain areas, such as mountain cuttings and the like. In certain instances, constructional-problems can occur with the protection of leads and other projecting constructional components against mechanical stress, but this does not involve the principle of the invention. 1

Therefore, it is possible with the invention to procure an effective and reasonable frost-protection in tunnels, mountain cuttings and the like while maintaining installation and operative costs low. Besides, the arrangement according to, the invention is, by virtue of its simple construction, pendable. By appropriate design of the heaters, possible necessary repairs can be made simple.

tightly up under the face. Preferably, the cloth material is fixed relatively tightly stretched out between adjacent end pins of the heater. The cloth material 27 can be layed out in suitable widths of the passage, for example, by laying out in the longitudinal direction of the tunnel and by overlapping along the edges in such a manner that it is ensured that the water which trickles out from the rock face is conveyed along the side of the cloth material which faces inwards to the side of the mountain. If desired, special fastening means can be used to secure the cloth material on the end pins 25, 26 just up under the bore hole and, at the same time, to provide a sealing off between the end pins and the cloth material. If desired, there can also be obtained a fluidand gas-tight sealing between the adjacent and overlapping breadths of cloth material by sticking together the breadths of cloth material or in another suitable way, but the latter is not regarded as necessary under normal conditions, since a free overlapping is especially de- Referring to FIGS. 4, 5 and 6, a section ofa tunnel has heaters 20 which are connected to each other in a star coupling by means of current-conducting means 21 shown in FIG. 1 by reference numerals 21a, 21b and 210, so that there are correspondingly formed three separate circuits which can be combined according to need. If desired, the central point in the star coupling can be connected to a fourth current conductor so that the three circuits can be coupled in and coupled out independently of each other.

In the preferred embodiment which is illustrated in FIGS. 2 and 3, the heater 20 consists of reinforcing steel having a diameter of 6-8 mm, while the current-conducting means 21 correspondingly consist of reinforcing steel having a diameter of 12 mm.

In 'the rock face 22,.there is formed a bore 23 having a diameter of 35 mm and a length of about 300 mm. In the bore 23, there is inserted in a heat-conducting moulding material, the heater 20. The heater 20, which has a total length of about 1,100 mm extends with

endpins

25, 26 at the opposite ends about 50 mm outside the bore, while that within the bore in which the all predominant length of the heater is received, extends U-shaped in a double-folded loop 26 so that a concentrated heating within the bore is achieved. Another advantage in position on the end pins 25, 26 and pushing this relatively 7 5 'material and the rock face lying within.

, archway,

usually sufficient.

The cloth material can be light-reflecting on that side of the cloth material which faces away from the tunnel archway. By means of such a light-reflecting lining of the tunnel archway,

light-technical advantages are achieved in a ready manner, in addition to the advantages which are obtained with respect to the drainage of water and the reduction of the need for heat for heating the rock face which is covered by the cloth material. By making the cloth material of suitable fiber-reinforced plastic material, sufficient strength can be obtained in the material to catch stones which possibly are loosened or broken away from the covered mountain portion.

After the cloth material is arranged in position on the rock face which is to be covered, the fixing end pins 25, 26 of the heater project freely outwards from the cloth material and are ready to have mounted thereon current-conducting means 21 The bar stumps can, if desired,.be preformed so that the cloth material is held directly against the side of the rock along the current-conducting means or can, if desired, after mounting be pushed or pressed against the side of the mountain. In this way, there can be formed more or less separate drain chambers between parallel series of current-conducting means having minimal air communication between neighboring chambers so as to provide a stationary air layer between the cloth By allowing the current-conducting means to extend transversely of the tunnel there can be correspondingly formed drain water conduit means between the tunnel archway and the cloth material in the said chambers between parallel series of current-conducting means. In the construction of FIG. 1, the rows of current-conducting means are within their respective spheres of the tunnel archway or are arranged in each of the current circuits mainly in a direction transversely of the tunnel. The current-conducting means which extend along .the tunnel do not need to be pressed inwards against the rock face as are the transverse current-conducting means but can extend rectilinear ly or, if desired, slightly outwardly arched so as to permit the formation of drain water conduit means between the rows of the remaining current-conducting means.

By utilizing current-conducting means and heaters of reinforcing steel, an eflective support of the cloth material can be obtained and of possible loosened stones which are caught by the cloth material. (Even rather large stone blocks can be caught by the network of reinforcing steel which the currentconducting means and heaters form. Even if the network of reinforcing steel is deformed or destroyed as a consequence of such a block of stone comingloose from the tunnel archway, the falling of the stone block down on to the roadway and the causing of damage can at any rate be prevented.)

With possible repairs, the current-conducting means can be readily clipped off and welded on anew as required. If it is desirable, for one or another reason, to install further heaters in the rock face in addition to the originally mounted heaters, the latter can be readily freed without making substantial provisions in the original equipment.

During operation, there can be employed single phase or multi-pha'se alternating current having for example up to 48 V voltage. The heaterscan be designed to yield respectively for example -1000 W all according to the heat need at the individual location. The control equipment for the heating installation can be done quite simply and can, for example, be based on a thermostatic coupling. For example, there can be utilized a thermostat or a combination of thermostats, which besides reacting at the temperature of the air in the tunnel or in the open, also take account of the temperature at one or more predetermined locations in the mountain. if desired control of the connection and'disconnection of the various circuits 21a, 21b and 210 can be pulsating, alternate or continuous current feed, all according to need and controlled by suitable known control means.

A distance between the heaters of about 50 cm has been found to be especially favorable from a heat economic viewpoint. However, it is apparent that the distance between the heaters can vary according .to desire and need and correspondingly there can be employed stronger or weaker heat yields from each heater for example by employing thinner or thicker reinforcing steel in the heaters. If desired, provision can also be made for obtaining a certain heat emission from the current-conducting means, but this heat effect is little relative to the heat effect from the heaters in that the reinforcing steel in the current-conducting means can be dimensioned sufficiently liberally relative to the reinforcing steel in the heaters. I It will be appreciated that the true scope of the invention is not limited by the aforesaid embodiments which have been described purely by way of example. For instance, the invention can also embrace a device which only difiers from one described above in that the heating means are replaced by insert means interconnected by metal rail means which simply form a support network beneath the fluid-tight cloth facing material and are not connected to a source of electric current.

What I claim is:

1. In a process for the prevention of the formation of ice in tunnels, especially road and railway tunnels, and mountain cuttings and thelike by the supply of heat from the outside to rock faces where ice formation normally occurs, the improvement which comprises installing electrical heating means distributed in a self-supporting manner in individual bores formed in a rock face substantially at right angles to a boundary surface with the air and heating a layer of rock between the air and rear-lying rock masses to a temperature higher than the temperature at said boundary surface and lower than the temperature at said rear-lying rock masses, whereby the transport of heat from the latter towards said boundary surface and from said layer of rock to said rear-lying rock masses is substantially counteracted.

2. A process according to claim 1, which comprises placing the heating means at a mutual distance of between 30 and 100 3. A process according to claim 2, wherein the distance is about 50 cm. Y

4. A process according to claim 1, which comprises spacing from but anchoring indirectly to the rock face a fluid-tight cloth facing material by way of the heating means to form between said rock face and said facing material a liquid-conducting and temperature-barring layer.

5. A process according to claim 4, wherein the material is gas-tight.

6. A process according to claim 4, which comprises initially securing in the rock face heating means having outwardly projecting fixing means and thereafter threading the facing material into position on said fixing means and finally ensuring facing that said facing material is in current-conducting connection with said fixing means.

7. A process according to claim 4, which comprises utilizing relatively rigid current-conducting means between the distributed heating means to support the facing material.

8. A process according to claim 4, which comprises utilizing a facing material having a light-reflecting surface directed outwardly from the covered rock face.

9. A device which comprises insert means dimensioned for direct and almost complete introduction in individual bores formed in a rock face, locating means for ensuring self-supporting mounting of said insert meansin said bores, a fluidtight cloth facing material spaced from but anchored indirectly to the rock face by way of the insert means to form between said rock face and said facing material a liquid-conducting and temperature-barring layer and metal rail means interconnecting said insert means to form 'a supporting network beneath facing material.

10. A device according to claim 9, wherein the metal wall means are made of reinforcing steel.

11. A device according to claim 9, wherein the facing material has a light-reflecting surface directed outwardly from the covered rock face.

12. A device according to claim 9, wherein the facing material is gas-tight.

13. A device according to claim 9, wherein the insert means are positioned at a mutual distance of between 30 and cm.

14. A device according to claim 13, wherein the distance is about 50 cm.

15. A device as set forth in claim 9 wherein said insert means is a heating means and which further comprises current-conducting means interconnecting said heating means to a source of electric current.

16. A device according to claim 15 further including a heat conducting molding material about said heating means.

17. A device according to claim 15, wherein said heating means are enclosed in outer jackets of elastic heat-conducting material so as to be self-supportingly receivable in their respective bores as a unit.

18. A device according to claim 17, wherein said heating means include an elastic shock-resistant portion for securing said means to the wall of a bore and for producing a heat-conducting contact with the bore.

19. A device according to claim 15 further including a fluidtight cloth facing material secured to said heating means in spaced relation to the rock face to form between said rock face and said facing material a liquid-conducting and temperature-barring layer.

20. A device according to claim 19, wherein the currentconducting means comprise rigid metal rails arranged beneath the facing material in the form of a supporting network therefor.

21. A device according to claim 20, wherein the rigid metal rails are made of reinforcing steel.

22. A device according to claim 19, wherein the heating means comprise metal rod heating elements having a form selected from bar and loop shapes.

23'. A device according to claim 22, wherein the metal rod is U-shaped in a double loop with outer end legs projecting freely outwards to form fixing means in which the cloth material is threaded and to which the current-conducting means are secured.

24. A device according to claim 22, wherein the metal rod heating elements are made of reinforcing steel.

25. A device according to claim 19, wherein the material has a light-reflecting surface directed outwardly from the covered rock face.

26. A device according to claim 15, wherein the heating means are positioned at a mutual distance of between 30 and 100 cm.

27. A device according to claim 26, wherein the distance is about 50 cm.

facing

Claims

1. In a process for the prevention of the formation of ice in tunnels, especially road and railway tunnels, and mountain cuttings and the like by the supply of heat from the outside to rock faces where ice formation normally occurs, the improvement which comprises installing electrical heating means distributed in a self-supporting manner in individual bores formed in a rock face substantially at right angles to a boundary surface with the air and heating a layer of rock between the air and rear-lying rock masses to a temperature higher than the temperature at said boundary surface and lower than the temperature at said rearlying rock masses, whereby the transport of heat from the latter towards said boundary surface and from said layer of rock to said rear-lying rock masses is substantially counteracted.

2. A process according to claim 1, which comprises placing the heating means at a mutual distance of between 30 and 100 cm.

3. A process according to claim 2, wherein the distance is about 50 cm.

5. A process according to claim 4, wherein the facing material is gas-tight.

6. A process according to claim 4, which comprises initially securing in the rock face heating means having outwardly projecting fixing means and thereafter threading the facing material into position on said fixing means and finally ensuring that said facing material is in current-conducting connection with said fixing means.

9. A device which comprises insert means dimensioned for direct and almost complete introduction in individual bores formed in a rock face, locating means for ensuring self-supporting mounting of said insert means in said bores, a fluid-tight cloth facing material spaced from but anchored indirectly to the rock face By way of the insert means to form between said rock face and said facing material a liquid-conducting and temperature-barring layer and metal rail means interconnecting said insert means to form a supporting network beneath facing material.

12. A device according to claim 9, wherein the facing material is gas-tight.

13. A device according to claim 9, wherein the insert means are positioned at a mutual distance of between 30 and 100 cm.

14. A device according to claim 13, wherein the distance is about 50 cm.

19. A device according to claim 15 further including a fluid-tight cloth facing material secured to said heating means in spaced relation to the rock face to form between said rock face and said facing material a liquid-conducting and temperature-barring layer.

20. A device according to claim 19, wherein the current-conducting means comprise rigid metal rails arranged beneath the facing material in the form of a supporting network therefor.

23. A device according to claim 22, wherein the metal rod is U-shaped in a double loop with outer end legs projecting freely outwards to form fixing means in which the cloth material is threaded and to which the current-conducting means are secured.

25. A device according to claim 19, wherein the facing material has a light-reflecting surface directed outwardly from the covered rock face.

27. A device according to claim 26, wherein the distance is about 50 cm.