US3858167A - Arrangement for determination of the continuity of thickness and of structural-tectonic elements of mineable layers, particularly of coal seams - Google Patents

Abstract

A transverse seam wave excited by the blast of charges of a directionally oriented blast base is used for determination of the continuity of thickness and of structural-tectonic elements of mineable layers. Direct elements of transverse seam waves and elements reflected from tectonic dislocations are picked up by pick-up devices and by their character the conditions of the structural-tectonic elements of the mineable layer may be determined.

Description

United States Patent 91 Stas etal.

[ Dec. 31, 1974 ARRANGEMENT FOR DETERMINATION OF THE CONTINUITY OF THICKNESS AND OF STRUCTURAL-TECTONIC ELEMENTS OF MINEABLE LAYERS, PARTICULARLY OF COAL SEAMS [75] Inventors: Bretislav Stas; Ludek Dlouhy;

Lubomir Siska; Adolf Skrabis, all of Ostrava, Czechoslovakia [73] Assignee: Vedeckovyzkumny uhelny ustav,

Ostrava-Radvanice, Czechoslovakia [22] Filed: June 12, 1972 [21] Appl. No.: 262,071

[30] Foreign Application Priority Data June 29, I971 Czechoslovakia 4774-71 [52] US. Cl 340/155 SW [51] Int. Cl G0lv H14 [58] Field of Search 340/155 SW [56] References Cited UNITED STATES PATENTS 3,352,375 11/1967 Krey ..l81/.5R

OTHER PUBLICATIONS Krey, Channel Waves As a Tool of Applied Geophysics In Coal Mining, 10/63, pg. 701-714, Geophysics, Vol. 28, N0. 5, Part 1.

Primary Examiner-Maynard R. Wilbur Assistant Examiner-N. Moskowitz [5 7 ABSTRACT A transverse seam wave excited by the blast of charges of a directionally oriented blast base is used for determination of the continuity of thickness and of i structural-tectonic elements of mineable layers. Direct elements of transverse seam waves and elements reflected from tectonic dislocations are picked up by pick-up devices and by their character the conditions of the structural-tectonic elements of the mineable layer may be determined.

3 Claims, 16 Drawing Figures PATENIED HEL3I m4 SHEET 1 [IF 5 PATENTEI] UEBB 1 I974 sum 2 OF I PATENTED 1 I974 3.858.167

SHEET 6 OF 7 '1 ARRANGEMENT FOR DETERMINATION .OF THE CONTINUITY OF THICKNESS AND OF STRUCTURAL-TECTONIC ELEMENTS OF MINEABLE LAYERS, PARTICULARLY OF COAL SEAMS BACKGROUND OF THE INVENTION The invention relates to a method and to an arrangement for making seismic measurements in mines in order to enable a quantitative and qualitative evaluation of the continuity of the thickness of a mineable layer, particularly of a coal seam within the worked part of the mine, furthermore to establish any existence and course of tectonic dislocations which disturb the seam within the measured section including a qualitative evaluation of the magnitudes of dislocation amplitudes of partial tectonic blocs in relation to the thickness of the seam and to determine the course of edges of places of the coal bloc, where sudden changes of the thickness or of physically mechanical properties of the proper mass of the coal seam are occuring.

A seismic reflex method is known for determining ruptures and dislocations within'the surface of deposited rock layers, particularly of coal seams of smaller thickness by means of boundary waves, which are generated and are propagated at the boundaries between thecoal seam and the rock cover and the beadrock. The motive components of these kinds of waves are oscillating perpendicularly to the surface of the coal seam, parallel with the direction of the main beam of the elastic wave and symmetrically with respect to the center of the coal seam. The exciting of boundary waves is accomplished by adisturbance at the center of the coal seam; generating thus a symmetric type of these waves. It has been found in the course of a further development of this method, that not symmetric boundary waves can be equally used for registration and evaluation of measuring results. The disturbance source is for this type of waves situated eccentrically to some boundary.

The geophones are for both described methods placed on the boundaries of the coal seam with the rock cover and the beadrock and registration of motive components is accomplished by couples of geophones situated in two horizonts'and are with respect to the center of the coal seam associated in couples and polarized in counterphase.

The results of detection of tectonic dislocations by the described methods are summarized in a statistic analysis, where a 66 percent success of the prognosis is specified. As a limiting factor for the applicability of the seismic reflex method only a depth range is mentioned, equal to a hundredfold thickness of the coal seam. Another limitation of the application of this method according to published experiences is in that the inclination of the investigated tectonic dislocations with the surface of the coal seam must be larger than 30 in order to obtain a reflection capable to be registered. Reflections from disturbances having a smaller inclination than 30 are rather or even completely indistinct.

Another drawback of these methods is that they do not always render a clear indication of the first occurance of the reflected waves, which uses to be disturbed by complicated interferences, generated in the systems of couples of geophones coordinated in pairs and polarized in counterphase, due to loss of the time phase of boundary waves, which proceed along tracks of different lengths in the rock cover and beadrock of the coal seam, determined by the inclination of the tectonic disturbance. Due to difficulties with the determination of the first occurance of reflected waves, the accuracy of the location of the reflection elements in space is reduced. As a mean value for the error of location of the reflection element according to the depth range, the value of a :10 to 15 percent is generally indicated.

Both described methods are suitable for investigating coal seams of smaller thickness only. In case of coal seams of larger thickness, where there is no simultaneous access to the rock cover and to the bedrock for placing associated couples of geophones directly from the mine gallery, what holds true for coal seams of a thickness surpassing 3 metres, the described methods are from the point of view of operation and economy unsuitable and practically inapplicable.

SUMMARY OF THE INVENTION It is an object of this invention to reduce the drawbacks of known methods and arrangements for determining the continuity of mineable layers, of changes of their thickness, and of their structural and tectonic elements, particularly of coal seams, which have a reduced elasticity with respect to the surrounding rocks, forming their rock cover and bedrock. In accordance with this invention charges are placed in thecentral zone of the thickness of the coal seams in a multicomponent blast base directionally oriented, when by simultaneous discharge mirror symmetrical Rayleigh waves are generated with respect to the central part of the scam in the boundary surfaces with the rock cover and bedrock. By their mutual counterphase effect zones of increased tension in the central zone of the coal seam are created, parallel with the head of the Rayleigh waves. At the place of transformation of the increased tension into motive components having a transverse direction, oscillating within the plane of the coal seam parallel with the heads of Rayleigh waves, seismic pick-up devices for'registration of transverse oscillations of the mass of the coal seam are located in the central zone of the coal seam at the edge of the free surface created by partial interruption of the coal seam by a mine gallery.

The arrangement for executing this method comprises a generator of oscillations connected to the fuse of the charges and connected also to one input of a seismic amplifier, to a second input of which a source of DC voltage is applied. Groups of seismic pick-up devices distributed in a registration base are connected to other inputs. The output of the seismic amplifier is connected to a registration device, which in turn is connected to a time standard. The registration device and the time standard are energized from a supply source. The axis of maximum sensitivity of the geophones in the registration base are at an angle of 45 to with the direction of the main beam of the direct or reflected transverse seam wave and simultaneously parallel with the plane of the coal seam. The geophones are arranged in the pick-up device in two systems so that the axis of maximum sensitivity of the geophones of one partial system are perpendicular to the axis of maximum sensitivity of geophones of the second partial systern.

Advantages of the method and arrangement according to this invention show particularly in that they enable to determine the continuity of the thickness and details of structural-tectonic elements of the internal composition of a mineable layer, particularly of a coal seam. By using a transverse seam wave which has higher distinguishing properties and sensitivity in reaction to elastic inhomogenities, which disturb the continuity or thickness of the coal seam, than known boundary waves, the accuracy of results is increased. The transverse seam wave enables to follow tectonic dislocations having with the plane of the coal seam an inclination even less than 30. They enable furthermore to obtain reflections also from flat reverse faults, from edges of zones of a distinct change of the thickness of the coal seam or from zones ofa distinct change of elasticity of the mass of the coal seam, where no proper tectonic dislocation exists. Another advantage is the possibility to investigate coal seams of any inclination and of any thickness if there is the possibility to create a free surface within a zone of the coal seam at the place of the registration base. The substantial increase of the accuracy of measuring results enables an improved determination of the first occurances of waves of the transverse seam wave due to elimination of unwelcomed interferences, generated in systems of geophone couples coordinated in pairs and polarized in counterphase. Due to an efficient increase of the signal to noise ratio and of the sensitivity of registration, an increase of the depth range up to a four hundredfold of the thickness of the investigated coal seam for a reflection measuring method is enabled. If a radiation measuring method is applied, the range is more than a thousandfold of the thickness of the coal seam.

A further advantage of the object of this invention is a simplification of the systems of locating and interconnecting of the geophones. As the location is accomplished in a single level, there is no need of counterphase polarization of geophone couples. Advantageous is also the reduction of the number of geophones, having as consequence a reduction of the failure rate, of the work needed, of time consumption and of costs for preliminary and boring work.

DESCRIPTION OF DRAWINGS In the attached drawings examplary embodiments of the method and of arrangements according to this invention for determining the continuity of the thickness and of structural-tectonic elements of mineable layers are indicated, particularly of coal seams, whereby FIG. la and 112 show principles of generation of the course and effects of a transverse seam wave, FIG. 2a, 2b, 2c, 2a and 2e the placing of charges in a coal seam in order to generate a transverse seam wave for different thickness of the coal seam and different relative spacial position ofa mine gallery and of the central zone of the coal seam. FIG. 3a, 3b, 3c and 3a show optimum arrangements of multicomponent blast bases directionally orientated for generation of a transverse seam wave having its maximum energy in the required direction. FIG. 4a and 4b indicate an optimum spacial orientation of a seismic pick-up device and the axis of maximum sensibility of the geophones. FIG. 5 is an example of utilizing a transverse seam wave for determining the continuity of a coal seam in a block limited by galleries and for investigation of tectonics in its field of interest by measuring from a single survey mine gallery. FIG. 6 shows a fundamental outlay of an arrangement for determining the continuity of a coal seam and for investigation of tectonic dislocations. FIG. 7 indicates the principle of a tectonic pick-up device.

DESCRIPTION OF PREFERRED EMBODIMENTS When determining the continuity of the thickness and of the structurally tectonic elements of a coal seam and the course and extent of tectonic dislocations, which are disturbing this coal seam, a transverse seam wave 14 (see FIG. la) is generated in the required direction, originating by a counterphase energetic effect of mirrorsymmetrical rock-cover and bedrock Rayleigh waves which are propagated along the rock-cover boundary 7 and along the bedrock boundary 8 of the coal seam 1. This coal seam 1 having the thickness 2 is situated in a carbon rock massif between the rock cover 3 and the bedrock 4. Due to an excitation generated in point 5 of the central zone 6 of the coal seam l, in their phases mirror-symmetrical rockcover Rayleigh waves 9 and a bedrock Raleigh waves 10 with opposite polarity of motive components are excited in the rock-cover boundary 7 and in the bedrock boundary 8, said waves oscillating in counterphase perpendicularly to the plane of the coal seam 1, parallel with the perpendicular component z and symmetrically with respect to the central zone 6 of this coal seam I, being propagated along the rock-cover boundary 7 and the bedrock boundary 8 in direction of the main beam 24 of the transverse seam wave 14 parallel to the longitudinal component x. I

In compression zones 11 and particularly in the compression zone, formed by the head 15 of rock cover Rayleigh waves 9 and bedrock Rayleigh waves 10, motive components 12 of longitudinal direction are generated, oscillating parallel with the plane of the coal seam and with the direction of the main beam 24 of the transverse seam wave 14 in the longitudinal component x and furthermore a zone of increased pressure in the mass of the coal seam l is generated, distributed around its central zone 6, parallel with the head 15a and 15b respectively of the rock cover Rayleigh wave 9 and the bedrock Rayleigh wave 10 (see FIG. lb) and also with the plane of the coal seam l and perpendicular to the direction of the main beam 240 and 24b of the transverse seam wave 14, parallel with the transverse component y which are propagated in direction of the longitudinal component .r at the propagating speed of the rock cover and bedrock Rayleigh waves 9, 10, whereby the change-over of the compression condition to motive components 13a, 13b of a transverse direction takes place on the edges of free surfaces, formed by partial interruption of the coal seam l by the mine gallery 16a at the place of the registration base 17, said motive components 13a, 13b of a transverse direction, oscillating parallel with the plane of coal seam 1 perpendicularly to the direction of the main beam 24a, 24b of the transverse seam wave 14 which is direct or reflected parallel with the transverse component y with maximum amplitudes at the center of the compression zones 11.

The transverse seam wave 14 is reflected from a teetonic dislocation l8 interrupting the coal seam 1. Charges 19 (FIG. 2a to 2e) for exciting a disturbance are located in the central zone 6 of the coal seam 1 into bores 20 bored from the mine gallery 16 at an angle 21 so that the central zone 6 of the coal seam l is thereby bases in lines 23a, 23b, perpendicular to the direction of the main beam 24 a of the direct transverse seam wave 14 or of the main beam 24b of the reflected transverse seam wave 14, or at an angle 21a, 21b within an angular sector from 45 to 135 with respect to the supposed course of the tectonic dislocation 18. In order to rectify the main beam 24 of the transverse seam wave 14 into the required direction optimum systems of distribution of bores 20 are selected (FIG. 3b to 3d) in multicomponent blast bases 22. The suitability of any system depends on the actual complexity of seismogeological conditions of the locality and on the difficulty of the problem to be solved.

The maximum differentiating ability of the registration with respect to the direction of the main beam 24 of the transverse seam wave 14 is achieved by placing the seismic pick-up devices 25 into the central zone 6 of the coal seam l and simultaneously so, that the axis 32a, 32b of maximum sensitivity of the geophones 26a, 26b (FIG. 4a, 4b) are parallel with the plane of the coal seam l and simultaneously so, that the main beam 24 of the transverse seam wave 14 strikes the axis 32a, 32b of maximum sensitivity of the geophones 26a, 26b perpendicularly or within an angular sector at 45 to 135 with respect to the axis 32a, 32b of maximum sensitivity of the geophones 26a, 26b.

Suitable conditions of incidence of the main beam 24 of the transverse seam wave 14, coming from any direction, on the axis 32a, 32b of maximum sensitivity of the geophones 26a, 26b are secured by the application of seismic pick-up devices 25, where the geophones 26a, 26b are arranged in two systems so, that the axis 32a of maximum sensitivity of geophones 26a of one partial system are perpendicular to the axis 32b of maximum sensitivity of geophones 26b of the second partial system, where the particular partial system of geophones 26a or 26b is switched on for registration purposes, on the axis 32a or 32b of maximum sensitivity the main beam 24 of the transverse seam wave 4 impinges within an angular sector from 45 to 135 either with respect to the axis 32a of maximum sensitivity of geophones 26a, or with respect to axis 32b of maximum sensitivity of geophones 26b.

The application of the tranverse seam wave 14 for determining the continuity of a coal seam in a coal block 30 limited by mine galleries 16a, 16b, 16c and for following the tectonics in its field of interest by measuring from one survey gallery 16c is shown in FIG. 5.

If the propagation ofa tranverse seam wave 14 which is direct or reflected by sections 28a, 28b and 28d of a tectonic dislocation 18 in beam sectors 27a, 27b and 27d is observed, it can be said, that the amplitude of fault of the tectonic dislocation 18 in sections 28a, 28b and 28d is larger than 30 percent of the thickness of the coal seam l of the coal block 30 but smaller than the whole thickness of the coal seam 1. If an undistrurbed reception of the transverse seam wave 14 is obtained in the beam sector 27c, it can be said, that the continuity of thickness of the coal seaml of the coal block 30 is maintained within the whole range of the beam sector 27c. If only reflection elements 31c, 31d, 3le and 31f of the transverse seam wave 14 reflected from the tectonic dislocation are received, it can be said, that the magnitude of its amplitude of fault is larger than 30 percent of the thickness of the coal seam l in the coal block 30. The reflection elements 31a, 31b correspond to reflections of the transverse seam wave 14 from the edges of the zone of a distinct change of the thickness of the coal seam l in the pressure zone 29. If no passage of a direct or reflected seam wave within the beam sectors 27a, 27b is detected, it can be said, that the amplitude of fault of the tectonic dislocation 18 in sectors 28e, 28f is larger than the thickness of the coal seam l, or the elasticity of the mass of the coal seam l in the beam sector 27f is affected by inhomogenities or by a substantial reduction of the thickness of the coal seam l, which prevents the passage of a direct or reflected seam wave.

- The application of a tranverse seam wave 14 for determining the course of tectonic dislocations in the field of interest of the mine can be also accomplished from a single mine gallery 16c (see FIG. 5 without the galleries 16a, 16b). In that case it is possible to register on the registration basis 17 reflection elements 31d, 3le and 31f of a transverse seam wave 14, reflected from a tectonic dislocation l8 and excited from blast bases 22a, 22b, 22h.

The determination of the continuity of a coal scam I and of the course'of tectonic dislocations in a coal block 30 is according to this invention accomplished by means of an arrangement (see FIG. 6) where a generator 33 of oscillations connected to one input of aseimic amplifier 35 is connected to the fuse 34 of the charges, arranged in the blast base 22 of the mine gallery 16a. A source 36 of DC voltage is connected to a second input of the seismic amplifier 35. Groups of seismic pick-up devices arranged in the registration base 17 in the mine gallery 16c are connected to other inputs of the seismic amplifier 35. The output of the seismic amplifier 35 is connected with a registration machine 37, which itself is connected to time standard 38. The registration machine 37 and the time standard are connected to a supply source 39.

The geophones 26a, 26b are in the seismic pick-up device 25 (see FIG. 7) arranged in two systems so, that the axis 32a of maximum sensitivity of the geophones 26a are perpendicular to the axis 32b of maximum sensitivity of geophones 26b. The required sensitivity of the seismic pick-up device .25 is achieved by increasing the number of geophones 26a, or 26b respectively, connected in series and oriented with conformingly situated axis 32a or 32b of maximum sensitivity.

We claim I l. Arrangement for determination of the continuity of thickness and of structural-tectonic elements of mineable layers, particularly of coal seams, having a reduced elasticity with respect to surrounding rocks,

- forming their rock cover and bedrock, providing a multicomponent blast base directionally orientated, composed of charges arranged along a line forming an angle of 45 to with respect to the direction of the main beams of a transverse seam wave, a fuse for discharge of said charges, a generator of oscillations, a registration base composed of a number of seismic pick-up devices, said seismic pick-up devices arranged at the edge of a free surface, created by partial interruption of the coal seam by a mine gallery, a seismic amplifier having a number of inputs and at least one output, a registration device, a time standard, a DC voltage source for the seismic amplifier and a supply source for energizing the registration device and the time standard, the generator of oscillations connected to the fuse for disimum sensitivity of which are at an angle between 45 to with respect to the main beam of the direct or reflected transverse seam wave generated by the blast and simultaneously parallel with the plane of the coal seam (l).

3. Arrangement as set forth in claim 2 where the geophones of the seismic pick-up device are arranged in two partial systems, the axis of maximum sensitivty of one partial system being perpendicular to the axis of maximum sensitivity of the second partial system.

l l l l

Claims (3)

1. Arrangement for determination of the continuity of thickness and of structural-tectonic elements of mineable layers, particularly of coal seams, having a reduced elasticity with respect to surrounding rocks, forming their rock cover and bedrock, providing a multicomponent blast base directionally orientated, composed of charges arranged along a line forming an angle of 45* to 135* with respect to the direction of the main beams of a transverse seam wave, a fuse for discharge of said charges, a generator of oscillations, a registration base composed of a number of seismic pick-up devices, said seismic pick-up devices arranged at the edge of a free surface, created by partial interruption of the coal seam by a mine gallery, a seismic amplifier having a number of inputs and at least one output, a registration device, a time standard, a DC voltage source for the seismic amplifier and a supply source for energizing the registration device and the time standard, the generator of oscillations connected to the fuse for discharge of the charges, the generator of oscillations connected to a first input of the seismic amplifier, to a second input of the seismic amplifier the DC voltage source being connected, other inputs of the seismic amplifier connected to groups of seismic pick-up devices, the output of the seismic amplifier connected to the registration device, which in turn is connected to the time standard, both being energized from the supply source.

2. Arrangement as set forth in claim 1, the seismic pick-up devices comprising geophones, the axis of maximum sensitivity of which are at an angle between 45* to 135* with respect to the main beam of the direct or reflected transverse seam wave generated by the blast and simultaneously parallel with the plane of the coal seam (1).

3. Arrangement as set forth in claim 2 where the geophones of the seismic pick-up device are arranged in two partial systems, the axis of maximum sensitivty of one partial system being perpendicular to the axis of maximum sensitivity of the second partial system.

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