US3887235A

US3887235A - Assembly for hydraulic extraction of sheet-like mineral deposits sectioned into panels by a system of passageways

Info

Publication number: US3887235A
Application number: US441481A
Authority: US
Inventors: Manfred Koppers
Original assignee: Rheinstahl AG
Current assignee: Rheinstahl AG
Priority date: 1973-02-15
Filing date: 1974-02-11
Publication date: 1975-06-03
Anticipated expiration: 1992-06-03
Also published as: PL98946B1; CA999312A; DE2307413C2; AU6465474A; DE2307413B1; FR2217524B1; FR2217524A1; GB1426854A

Abstract

The assembly has a supporting structure for high pressure hydraulic nozzles, the supporting structure including a single shield-like structural member, having a channel cross-section open toward the working face, and which is rigid against bending and extends, parallel to the working face, between two roadways. Winch drag means extend along the two roadways and act on respective opposite end portions of the structural member to move the latter in the direction of advance of the workings. High pressure nozzles are mounted on the flange edge portions of the supporting structure projecting toward the working face, being positioned at fixed locations and being adjustable perpendicularly to their discharge axes. Alternatively, a carrier mounting the high pressure nozzles is movable longitudinally of the supporting structure to travel parallel to and along the entire length of the working face. The supporting structure is inclined in the backward direction, toward the old works, for permitting the caving-in roof to slide down toward the old works. The supporting structure also is divided longitudinally into a roof portion and a base portion, the two portions being adjustable relative to each other. Conveyors extending along the roadways receive the dislodged portions of the mineral deposit, such as coal, and convey the same to a collecting area. The supporting structure furthermore may be designed as a conveying trough discharging into the conveyors.

Description

United States Patent Koppers 1 June 3, 1975 1 ASSEMBLY FOR HYDRAULIC EXTRACTION OF SHEET-LIKE MINERAL DEPOSITS SECTIONED INTO PANELS BY A SYSTEM OF PASSAGEWAYS [75] Inventor: Manfred Koppers, Duisburg,

Germany [73] Assignee: Rheinstahl AG, Germany [22] Filed: Feb. 11, 1974 [21] Appl. No.: 441,481

[30} Foreign Application Priority Data Feb. 15, 1973 Germany 2307413 [56] References Cited UNITED STATES PATENTS 6/1959 Milik 299/19 X 3,284,138 11/1966 Binaut 299/34 3,306,665 2/1967 Lobbe 299/34 FOREIGN PATENTS OR APPLICATIONS 672,336 5/1952 United Kingdom 299/17 Primary Examiner-Ernest R. Purser Attorney, Agent, or Firm-McGlew and Tuttle 5 7] ABSTRACT The assembly has a supporting structure for high pressure hydraulic nozzles, the supporting structure including a single shield-like structural member, having a channel crosssection open toward the working face, and which is rigid against bending and extends, parallel to the working face, between two roadways. Winch drag means extend along the two roadways and act on respective opposite end portions of the structural member to move the latter in the direction of advance of the workings. High pressure nozzles are mounted on the flange edge portions of the supporting structure projecting toward the working face, being positioned at fixed locations and being adjustable perpendicularly to their discharge axes. Alternatively, a carrier mounting the high pressure nozzles is movable longitudinally of the supporting structure to travel parallel to and along the entire length of the working face. The supporting structure is inclined in the backward direction, toward the old works, for permitting the caving-in roof to slide down toward the old works. The supporting structure also is divided longitudinally into a roof portion and a base portion, the two portions being adjustable relative to each other. Conveyors extending along the roadways receive the dislodged portions of the mineral deposit, such as coal, and convey the same to a collecting area. The supporting structure furthermore may be designed as a conveying trough discharging into the conveyors.

17 Claims, 5 Drawing Figures ASSEMBLY FOR HYDRAULIC EXTRACTION OF SHEET-LIKE MINERAL DEPOSITS SECTIONED INTO PANELS BY A SYSTEM OF PASSAGEWAYS FIELD AND BACKGROUND OF THE INVENTION This invention relates to an assembly for the hydraulic extraction of sheet-like mineral deposits sectioned by a passageway system into blocks or panels which are limited laterally by two roadways extending in the advance direction of the workings, the assembly including a hydromechanically acting device having at least one high pressure nozzle mounted on a supporting structure so as to be capable of dislodging the working face extending between the two roadways. More particularly, the present invention is directed to an improved assembly of this type.

[t is well known to break coal from its solid position, between the roof and the floor, by means of water jets produced in so-called hydraulic monitors. The monitors comprise a nozzle through which water is forced by a pump to form a hydraulic jet, and the energy inherent in the jet and striking the coal or other mineral is used to dislodge the same. The work is effected with relatively low water pressures and large water volumes. The nozzles are mounted on the ends of lance-shaped poles held by the operator and directed against the working face (cf. Report E5, Institut National de l industrie Charbonniere, Liege, 1963).

It is also known to mount such nozzles on posts, such as jack columns, or on an auxiliary frame, as disclosed, for example, in Report 59l5, Bureau of Mines, 1961.

In accordance with an originally used method, the hydromechanical working is practiced in such a manner that, in sloping or half-sloping seams, sectional entries are driven in the coal from a rise, at lateral spacings of to l5 m and with a drop of 5, as suggested, for example, in Glueckauf, 1968, p. 289. The panels extending between two sectional levels are worked, in the homeward direction, with monitors. The roof is intended to remain unsupported. However, and disadvantageously, this condition cannot be met, or can be met only with great difficulties. The extracted coal is removed with the aid of the backwater, in principle downwardly to a collecting point, and with or without chutes.

In another known method, an advance borehole is made in the seam from a sloping, upwardly driven bottom level up to a top level, and then, starting from above, the borehole is enlarged downwardly by means ofa monitor. The seam thus can be worked along a face extending up to 20 m. In such a case, the monitor is supplied from a pump installed at the bottom level, through piping, and can be swung from a mid position to both sides. As in the method mentioned above, difficulties due to the nature of the roof arise from an irregular fall-in of the roof into the cleared space. By leaving pillars of coal, scuh caving-in can partly be avoided. However, the pillars of coal are lost for exploitation.

There are further known monitors having nozzles working under high pressure and demonstrating good cutting performances, as disclosed in Coal Age," of March 1972, and Water-Jet Mining of Coal" by Nicholas P. Chironis. The high pressure nozzles have a passage diameter of approximately 1 mm and the water is fed under a pressure of I000 to 7000 atm, which results in an up to double sonic velocity. With such nozzles, it is possible to cut rocks, from marble to the hardest rocks such as granite. ln coal mining, the nozzles are known as Summers Jets, and are mounted in an arrangement usual with a coal planer. Five nozzles are substituted for the cutter of the coal planer, and the arrangement permits working thicker coal seams than possible with a planer. Additional nozzles are provided on the thus equipped planer head, both for undercutting and top cutting the coal seam, and for ripping the already cut-out layer horizontally. To reduce the friction losses in high pressure piping, the hydraulic pressure producing pump is directly coupled to the machine and travels therewith along the face. Such workings require a roof supporting structure behind the conveyor, permitting an access to the face and serving as an anchorage for the conveyor and the working machine. Appropriate shifting mechanisms also are necessary. A disadvantage is that, because of the water splashing about, the supporting and shifting mechanisms become contaminated with coal particles and their operational capability is affected.

From a report published by the Bureau of Mines in March 1968, it is known to mount a monitor on a conventional loader and to work cavities in the seam with this mechanism. However, this method requires supporting or anchoring the roof behind the machine.

Finally, German Pat. No. l,274,544 discloses a conveyor means movable in the working direction and capable of carrying along a hydromechanical planer.

SUMMARY OF THE lNVENTlON The present invention is based on the coal mining method using high pressure nozzles, and is directed to making the process of extracting coal and other minerals more economical by providing an assembly with which sheet-like deposits, sectioned by passageways into panels, can be worked in a width extending over several panels while the roof, in the area of headways and roadways, is left to cave-in continuously during the homeward working, with the working team at the working face being reduced to a minimum.

The invention presupposes that the respective portion of the seam is opened, as usual, from a bottom headway, and is sectioned into panels by mutually parallel roadways extending perpendicular thereto and leading to a top passageway which is parallel to the bottom headway. The work is to be performed in a retreating long wall method in the direction from the bottom headway to the top passageway. However, the conditions of the deposit may be different from one deposit to another, and the method is to be conformed to the particular deposit.

in accordance with the invention, in an assembly of the type mentioned above, the supporting structure includes a single shield-like structural member having a channel cross-section and which is rigid against bending and with the channel cross-section opening toward the working face. The structural member extends parallel to the working face between two roadways, and is movable in the direction of the working advance by drag means acting on the opposite ends of the structural member and extending along the roadways. High pressure nozzles are distributed over the entire length of the structure and mounted at fixed locations on the flange edge portions of the supporting structure projecting against the working face. Alternatively, a device movable parallel to and along the entire length of the working face, and equipped with high pressure nozzles, is mounted on the supporting structure.

A particular advantage of the assembly embodying the invention is that, in service, only a few operations need to be performed in the roadways by a working team which, consequently, can be reduced to a very small number. Because the supporting structure also protects the headway along the working face against falling rocks, the entering of this space, for inspection and the like, is safe. Another advantage of the supporting structure is that the nozzles and, if provided, the guides can be protected against coal deposits. While maintaining the dimensions of the basic component parts, the height of the supporting structure can be varied, that is, it can be adapted to the thickness of the seam, To prevent the supporting structure from running onto coal or the like which has not been removed, the lower edge of the structure, projecting toward the coal face, is provided with transition pieces of plastic or steel conforming to the floor, Well known auxiliary ventilation devices are used for the ventilation of the roadways and the workings.

Another advantageous feature of the invention is that, analogously to sheet piling, the upper flange of the supporting structure is inclined rearwardly, that is, in the direction of the old works, for sliding away of the caved-in roof.

At its middle part from top to bottom, the supporting structure may be divided by a longitudinal joint. In one embodiment of the invention, the thus formed lower part and upper part are hinged together and may swing about the line of this joint. In another embodiment, the upper part has two cheeks engaging over the lower part, and the two parts are vertically adjustable relative to each other.

In accordance with another advantageous feature of the invention, the opposite end portions of the upper part of the supporting structure, extending into the roadway, are provided with respective skidlike arms pro ecting in the advance direction of the workings and connected to a device for vertical adjustment so that the upper part, and thereby the entire supporting structure, can be pivoted about an axis extending longitudinally thereof.

In accordance with a further development of the invention, high pressure nozzles are mounted along the entire length of the edge portions of both the upper and lower parts of the supporting structure, projecting against the working face. Because the nozzles are capable of cutting not only the coal but also stone, the opening necessary for the advance of the supporting structure is cleared in any case, despite possible bulges or other irregularities protruding from the overlying straturn or the bedrock.

In another advantageous embodiment of the invention, the high pressure nozzles are displaceable, per pendicularly to their central axes, and/or are inclinable to the central axis in all directions. Due to this mobility or orientability of the nozzles. intersecting cutting planes, such as continuous slits, may be obtained, by which the seam is dislodged into blocks. Thus, the coal face may be undercut as well as separated from the roof in the same manner as with a conventional mechanical cutter. A working mode analogous to the operation of a planer is also possible, To minimize the distance between the pressure producing pump and the nozzles, in accordance with the invention, the pump is located ei ther directly on the supporting structure or on a sliding planer head carrying the nozzles.

In order to reduce the dimensions of the pumps as much as possible, the invention further comtemplates a program-controlled operation of the nozzles, particularly in the embodiment where the nozzles are mounted directly on the supporting structure. The program may be set up, for example, so that the first nozzle works along a partial distance. is then switched off, the following nozzle works the next partial distance, is then switched off, and so on. Instead of a single nozzle, a plurality of nozzles working in groups may be put into operation in the different parts.

In another advantageous embodiment of the invention, the nozzles are mounted on a sliding carriage movable along the supporting structure and operating as a planer. The nozzles may be disposed in different ways on the head of this carriage, for example, directed against the coal face or parallel thereto, and the nozzles may also be made orientable in the horizontal plane.

In accordance with a further development of the invention, the sliding or planer head has a U-shaped cross-section The flanges are directed toward the coal face and provided with adjustable nozzles of which some are oriented parallel and some are oriented per pendicular to the roof or the floor.

For collecting and transporting the extracted material, the lower part of the supporting structure is shaped, in accordance with the invention, as a conveyor trough. The coal cut or broken off is entrained by the back flowing water and delivered to the conveyors in the roadways. This transportation may be assisted by flushing nozzles provided on the sliding head and oriented in the travel direction thereof. Instead of flushing nozzles, a scraper conveyor, movable with the planer head or separately driven, may assist the conveying of the material. To obtain a trouble-free transfer of the material onto the conveyors in the roadways, the conveyors advantageously are designed as bottom belt conveyors.

A uniform advance of the supporting structure is obtained, in accordance with the invention, by measuring the distance between the supporting structure and a fixed point, marked out in each of the respective roadways, with the aid of an echo sounding device, and by controlling the two drag mechanisms or winches in ac' cordance with the measured values, for example, by means of a computer.

An object of the invention is to provide an improved assembly for hydraulic extraction of a sheet-like mineral deposit,

Another object of the invention is to provide such an assembly making the process of extracting coal and other minerals more economical.

A further object of the invention is to provide such an assembly in which, in service, only a few operations need be performed by a working team which can be re duced to a very small number.

Yet another object of the invention is to provide such an assembly in which protection is provided for inspection of the working face of the coal seam.

For an understanding of the principles of the invention, reference is made to the following description of typical embodiments thereof as illustrated in the ac companying drawings,

BRIEF DESCRIPTION OF THE DRAWINGS In the Drawings;

FIG. 1 is a plan view of a mining field portion to be worked;

FIG. 2 is a perspective view of one embodiment of a supporting structure in accordance with the invention, and in which the upper and lower parts are hingedly interconnected;

FIG. 3 is a perspective view of another embodiment of the supporting structure in which the upper part is displaceable vertically with respect to the lower part and in which the working direction can be varied by means of a skid-like arm projecting from the upper part;

FIG. 4 is a perspective view of an embodiment of the invention in which the supporting structure comprises a planer head; and

FIG. 5 is a view, similar to FIG. 4, showing another shape of the planer head.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1, the field portion to be worked is opened by a longwall entry 1 and by conveyor roads 2 extending perpendicularly to entry 1. Between adjacent conveyor roads 2, a coal block or panel 3 is left in solid position, this block or panel having a working face indicated at 4. In front of the working face 4, a supporting structure 5 is positioned to extend along the working face within the longwall entry 1, with the advance direction of the working being indicated by the arrow 6. The end portions of supporting structure 5 project into conveyor roads 2. Drag means 7, such as cables or chains, extend along the conveyor roads 2 between winches 8 and the end portions of supporting structure 5. Winches 8 are anchored in con veyor roads 2. In the illustrated example, the anchorage means is a beam 9 extending through a hole or bore formed in the solid panel 3 and projecting into conveyor roads 2. However, winches 8 also may be fixed in position by anchoring structures such as props, foot pieces, and head pieces.

Supporting structure 5 is equipped with devices for dislodging the coal and permitting the working of a panel 3 along its entire width. Behind supporting structure 5, the roofis left to cave-in in a direction of the old work 10, and the same applies to the head ends of the conveyor roads 2. The supporting structure 5 may be coupled with similar supporting structures operating in adjacent panels. The supporting structures also effect transportation of the extracted material to the conveyors 11, which are preferably bottom belt conveyors, mounted in roadways 2. In case of level differences at the transfer point, appropriate intermediate conveyors advantageously are used. Because panels 3 are worked in the homeward direction, and the conveyor roads 2 become correspondingly shorter, induced ventilation 12 is provided for the workings.

To enable winches 8 to haul in drag means 7 uniformly, that is, to assure continuously the right position of the supporting structure 5, echo sounding control elements are provided on the end portions of the supporting structure, or at fixed points in the conveyor roadways 2, and these control elements continuously check the distance between the ends of the supporting structure and the fixed points, and feed the values into jecting in the direction of working face 4. The top surface of upper part III is inclined toward the old works 10 so that the caving-in roof may slide down thereover. Supporting structure 5 is designed to be rigid against bending over the entire length of the working face 4. In the embodiment illustrated in FIG. 2, the two parts I and III of supporting structure 5 are connected to each other by pivot joints 14. By means of an adjusting mechanism 15, extension I] of part I and the flange of the upper part II] can be spread apart so as to adjust their mutual spacing to the given thickness of the seam. Supporting structure 5 rests against the footwall or floor of the seam.

FIG. 3 illustrates another possibility of adjusting the working direction of supporting structure 5. In its vertical portion, upper part III of supporting structure 5 is formed with a groove or recess opening downwardly and having its lateral cheeks engaging over the lower part I, so that both parts I and III can be adjusted vertically with respect to each other by means of an adjusting mechanism 151. On its portion projecting into conveyor road 2, part III is provided with a cantilever arm Illa which is pin-connected to a leg IIIb resting against the floor of conveyor road 2. A power cylinder Illc is mounted diagonally between cantilever arm "Ia and leg IIIb so as to bridge the pin connection. Thus, by actuating cylinder lllc, the entire supporting structure 5 is turned about its longitudinal axis while rolling on the curved surface 5a.

Nozzles 16 are mounted on the free end portions of the extension I] and the upper part III of supporting structure 5, and directed against coal face 4, as shown in FIG. 2. Nozzles 16 are high pressure nozzles which are displaceable in all directions perpendicularly to their central axes as indicated by arrows l7, and which are orientable in the widest desired range, as indicated by arrows 18.

The same nozzles also may be located in any plane between the extension II and the upper part III, and mounted for pivotal movement perpendicularly to the roof and the floor. To avoid extreme performances of the pumps, the nozzles may be controlled sequentially, for example, by first putting into operation single nozzles or a group of nozzles at one end of the supporting structure 5. After dislodging the working face 4 along the first working zone, the respective nozzles are shut off and the following nozzle or group of nozzles is put into operation, etc.

The extracted coal falls into a trough 19 provided in lower part I of supporting structure 5. Also, during advance of supporting structure 5, fallen coal is shoved into trough 19 over the upper surface of extension I],

shaped as an inclined platform or ramp 20. In trough 19, the coal is conveyed by the back water to the ends of the supporting structure 5 and from there to the conveyors 11 extending along the roadways 2. To aid the transportation of the material, longitudinally displace able, single-chain, pusher conveyors 21 may be utilized in trough 19.

In the embodiment of the invention shown in FIG. 4, a hydraulic planer head 23 is mounted for longitudinal displacement along guides 22 of supporting structure 5. Like a conventional planer equipped with a cutting edge, hydraulic planer head 23 projects into a recess formed in seam 3, and nozzles 161 separate slices of coal from the seam and have a height equal to the distance between the roof and the footwall. To facilitate the coal transportation to the conveyors 11 in roads 2, flushing nozzles 24, acting in the transport direction, are provided on hydraulic planer head 23.

In the embodiment ofthe invention shown in FIG. 5, a channel shaped hydraulic planer head 231 is mounted for movement along guides 221 of supporting structure 5, for traveling in the longitudinal direction of the latter along working face 4. Head 231 comprises a lower flange 25 and an upper flange 26, the two flanges being equipped with nozzles 162 which are disposed so as to be effective both in planes parallel to the roof or floor and in planes perpendicular thereto. Thus, the coal face is both undercut and separated from the roof and, in addition, cut into pieces.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

1. In an assembly for hydraulic extraction ofa sheetlike mineral deposit, which has been sectioned by a system of passageways into panels limited laterally by roadways extending parallel to the direction of advance of the workings, by a hydromechanically operating device including at least one high pressure hydraulic nozzle mounted on a supporting structure and adapted to dislodge the working face of the deposit, extending between the roadways, by a high pressure jet of hydraulic fluid; the improvement comprising, in combination, said supporting structure including a single rectilinear shield-like structural member, having a channel crosssection open toward said working face, and which is rigid longitudinally against bending and extends, parallel to said working face, between two roadways; drag means extending along the two roadways and acting on respective opposite end portions of said structural member to move the latter in said direction of advance; and a plurality of high pressure hydraulic nozzles movably mounted on said structural member for discharging high pressure jets of hydraulic fluid against said working face over the entire length thereof.

2. In an assembly for hydraulic extraction, the improvement claimed in claim I, in which the upper flange of said channel cross-section structural member is inclined downwardly and rearwardly of said direction of advance to permit the caving-in roof to slide downwardly and rearwardly therealong.

3. In an assembly for hydraulic extraction, the improvement claimed in claim 1, in which said nozzles are sequentially operable in groups each including at least one nozzle.

4. In an assembly for hydraulic extraction, the improvement claimed in claim 1, including an echo sounding device operable to measure the distance between said structural member and respective fixed points in each of said two roadways; and means operable, as a function of the measured values, to control the operation of said drag means in moving said structural member in said direction of advance.

5. In an assembly for hydraulic extraction, the improvement claimed in claim I, in which said high pressure nozzles are mounted at fixed locations on the flange edge portions of said supporting structure projecting toward said working face and are distributed along the entire length of said working face.

6. In an assembly for hydraulic extraction, the improvement claimed in claim 5, in which said nozzles are displaceable in all directions perpendicular to their central axes.

7. In an assembly for hydraulic extraction, the improvement claimed in claim 1, in which said structural member is divided, at its mid height, along a longitudinal parting line, into an upper part and a lower part; and means providing for movement of said upper and lower parts relative to each other.

8. In an assembly for hydraulic extraction, the improvement claimed in claim 7, including means pivotally interconnecting said upper and lower parts at said parting line for relative angular adjustment thereof.

9. In an assembly for hydraulic extraction, the improvememt claimed in claim 7, in which said upper part has a longitudinally extending channel-shaped groove embracing a longitudinally extending and upwardly projecting portion of said lower part; and means operable to displace said upper part relative to said lower part.

10. In an assembly for hydraulic extraction, the improvement claimed in claim 7, in which said structural member has end portions projecting into said roadways; each end portion of at least the upper part of said structural member having a skid-like projecting arm ar ticulated to a supporting leg engaging the floor of the associated roadway; and actuator means interconnecting said projecting arm and said supporting leg and operable to pivot said structural member about an axis extending longitudinally thereof.

11. In an assembly for hydraulic extraction, the improvement claimed in claim 1, including a device mounting said high pressure nozzles; and means mounting said device on said supporting structure for traveling therealong parallel to the entire length of said working face.

12. In an assembly for hydraulic extraction, the improvement claimed in claim 11, in which said device comprises a hydromechanically acting planer head.

13. In an assembly for hydraulic extraction, the improvement claimed in claim 12, in which said planer head is projectable into a recess of the mineral deposit seam; and additional nozzles mounted on said planer head and having discharge directions parallel to said working face.

14. In an assembly for hydraulic extraction, the improvement claimed in claim 12, in which said planer head is channel-shaped including a lower flange extending in the zone of the floor and an upper flange extending in the zone of the roof; said flanges being equipped with respective adjustable nozzles directed parallel, respectively, to the floor and to the roof and directed, respectively, perpendicular to the floor and to the roof.

15. In an assembly for hydraulic extraction, the improvement claimed in claim 12, in which the lower part 10 extending along said roadways and receiving the removed material.

17. In an assembly for hydraulic extraction, the improvement claimed in claim 15, including a scraper conveyor. adapted to the cross-sectional shape of said conveying trough. movable along said conveying trough.

Claims

1. In an assembly for hydraulic extraction of a sheet-like mineral deposit, which has been sectioned by a system of passageways into panels limited laterally by roadways extending parallel To the direction of advance of the workings, by a hydromechanically operating device including at least one high pressure hydraulic nozzle mounted on a supporting structure and adapted to dislodge the working face of the deposit, extending between the roadways, by a high pressure jet of hydraulic fluid; the improvement comprising, in combination, said supporting structure including a single rectilinear shield-like structural member, having a channel cross-section open toward said working face, and which is rigid longitudinally against bending and extends, parallel to said working face, between two roadways; drag means extending along the two roadways and acting on respective opposite end portions of said structural member to move the latter in said direction of advance; and a plurality of high pressure hydraulic nozzles movably mounted on said structural member for discharging high pressure jets of hydraulic fluid against said working face over the entire length thereof.

2. In an assembly for hydraulic extraction, the improvement claimed in claim 1, in which the upper flange of said channel cross-section structural member is inclined downwardly and rearwardly of said direction of advance to permit the caving-in roof to slide downwardly and rearwardly therealong.

5. In an assembly for hydraulic extraction, the improvement claimed in claim 1, in which said high pressure nozzles are mounted at fixed locations on the flange edge portions of said supporting structure projecting toward said working face and are distributed along the entire length of said working face.

10. In an assembly for hydraulic extraction, the improvement claimed in claim 7, in which said structural member has end portions projecting into said roadways; each end portion of at least the upper part of said structural member having a skid-like projecting arm articulated to a supporting leg engaging the floor of the associated roadway; and actuator means interconnecting said projecting arm and said supporting leg and operable to pivot said structural member about an axis extending longitudinally thereof.

15. In an assembly for hydraulic extraction, the improvement claimed in claim 12, in which the lower part of said structural member is formed with a conveying trough extending longitudinally thereof.

16. In an assembly for hydraulic extraction, the improvement claimed in claim 15, including nozzles mounted on that portion of said planer head extending above said conveying trough and discharging obliquely toward said conveying trough for conveying the removed material by flushing it along said conveying trough toward said roadways; and respective conveyors extending along said roadways and receiving the removed material.