FIELD OF INVENTION

[001] The present subject matter described herein, relates to a method of strata monitoring and indicating movement of roof during process of coal mining. More particular, to a method for strata monitoring and indicating movement of roof in goaved out area during depillaring by means of a high visibility instrument i.e. an Auto Warning Tell Tale (AWTT).
BACKGROUND AND PRIOR ART AND PROBLEM IN PRIOR ART
[002] During the process of coal mining, depillaring with caving is considered as one of the most -risky operations in underground coal mining owing to the reason that it involves fall of ground in the goaved out area. Such falling of roof does not necessarily give enough prior physical indications. The conventional practice of monitoring any roof movement in the goaved out area in the coal mine during depillaring has been carried out using a wooden indicator prop at the goafedges, which is effective but has quite a number of limitations. The other physical symptoms are sounds from goaf, crushing of pillar sides/corners. However, strata monitoring and indication of roof movement is always dependent on the experience of individuals working in the mine dealing with those conditions for long time. Also, there is no distinctive visual indication with the bending of these indicator props under abutment load.
[003] With conventional free-standing support such as props, there is an obvious indication when they are carrying excessive load, the greater the load the greater the deformation. Furthermore, roof bolts however give no visual indication of any increase in load and therefore there is no indication of how close either the individual bolts or the system is to the stage of ultimate failure.
[004] Technical problem in the existing technologies: The Mine operator immediately vacate the pillar after blinking of the warning lights provided on the AWTT.
[005] Another technical problem in the existing technologies is the low percentage of extraction from the pillar due to unpredicted roof fall and blinking of warning lights provided on the AWTT.
[006] Another technical problem in the existing technologies is uneven time interval between blinking of warning lights provided on the AWTT and the roof fall over the extracted pillar area in the goaf.
[007] Therefore, in order to overcome the limitations of the existing provisions, there is a need in the art to provide an improved method for strata monitoring and indication of roof movements for ensuring safety of personnel and machinery during the mass extraction of coal pillars.
OBJECTS OF THE INVENTION
[008] It is therefore the object of the invention to overcome the aforementioned and other drawbacks in prior art used for strata monitoring and indication of roof movements for ensuring safety of personnel and machinery during the mass extraction of coal pillars.
[009] The principal objective of the present invention is to develop a method, which is more efficient and provides a higher visibility as compared to conventional methods of strata monitoring and estimating the caveability of roof over the extracted pillar area in the goaf.
[0010] Another object of the present invention is to develop a method, which is cost effective and economic simultaneously being suitable to the geological structural configurations of the coal mines.
[0011] These and other objects and advantages of the present subject matter would be apparent to a person skilled in the art after consideration of the following detailed description taken into consideration with accompanying drawings in which preferred embodiments of the present subject matter are illustrated.
SUMMARY OF THE INVENTION
[0012] One or more drawbacks of the conventional systems based on existing methods of providing warning of impending fall in goaf or similar technologies are overcome, and additional advantages are provided through a method for strata monitoring and indicating movement of roof in goaved out area during depillaring by means of a high visibility instrument, i.e., an Auto Warning Tell Tale (AWTT) as claimed in the present disclosure. Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be a part of the claimed disclosure.
[0013] In an embodiment of the present subject matter relates to a method for strata monitoring and indicating roof movements during mining of coal using an Auto Warning Tell Tale (AWTT), comprising steps of installing Auto Warning Tell Tale at all junction points in roof portion of a coal mine prior to initiation of depillaring process, monitoring and recording time interval (Tx) (in hours) between blinking of Auto Warning Tell Tale (AWTT) and completion of adjacent pillar extraction, monitoring and recording time duration (Ty) between completion of pillar extraction and falling or caving of roof, analysing recorded data and quantifying minimum time in hours taken by a roof to fall or cave subsequent to extraction of pillar, wherein, recording of data includes measurement of start of pillar extraction, completion of pillar extraction, blinking of Auto Warning Tell Tale (AWTT), caving or falling of roof of a coal mine and percentage of coal extracted per pillar in terms of date and exposure time in hours.
[0014] In another embodiment of the present subject matter, analysis of recorded data includes comparing the time interval (Tx) (in hours) between blinking of Auto Warning Tell Tale (AWTT) with area of exposure and time duration (Ty) (in hours) between completion of pillar extraction and falling or caving of roof.
[0015] In yet another embodiment of the present subject matter, the Auto Warning Tell Tale (AWTT) is coupled with measurements by Remote Reading Multipoint Extensometer (RRME).
[0016] In yet another embodiment of the present subject matter, the method comprises estimating the cavability of roof rocks and setting of a warning limit based on the results obtained after analysis of recorded data.
[0017] In yet another embodiment of the present subject matter, the method includes fixing the percentage of extraction of pillar with a safe withdrawal time allowance.
[0018] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.
[0019] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] It is to be noted, however, that the appended drawings illustrate only typical embodiments of the present subject matter, and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments. The detailed description is described with reference to the accompanying figures. In the figures, a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system or methods or structure in accordance with embodiments of the present subject matter are now described, by way of example, and with reference to the accompanying figures, in which:
[0021] Figure 1 illustrates a flow diagram representing steps involved in a method for strata monitoring and indicating movement of roof method in accordance with an embodiment of the invention;
[0022] Figure 2A illustrates a schematic view of the Auto Warning Tell Tale (AWTT) installed during pillar extraction by split and fender mining process in accordance with an embodiment of the invention;
[0023] Figure 2B illustrates a schematic view of the Auto Warning Tell Tale (AWTT) installed during pillar extraction by non-split mining process in accordance with an embodiment of the invention;
[0024] Figure 3 illustrates a schematic view of an Auto Warning Tell Tale Device;
[0025] Figure 4 illustrates a schematic view of an example of analysis of caving of roof or roof fall during the pillar extraction process, in accordance with an embodiment of the invention;
[0026] Fig. 5 illustrates blank data sheet for entry of data and calculation of data to help in taking decision for pillar extraction process, in accordance with an embodiment of the invention;
[0027] Fig. 6 illustrates an example for calculation of percentage of extraction during the pillar extraction process, in accordance with an embodiment of the invention; and
[0028] Fig. 7a and 7b illustrate graph completion vs fall, percentage of extraction vs time interval between blinking and fall, in accordance with an embodiment of the invention.
[0029] The figures depict embodiments of the present subject matter for the purposes of illustration only. A person skilled in the art will easily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.
DETAILED DESCRIPTION
[0030] The detailed description of various exemplary embodiments of the disclosure is described herein with reference to the accompanying drawings. It should be noted that the embodiments are described herein in such details as to clearly communicate the disclosure. However, the amount of details provided herein are not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the present disclosure as defined by the appended claims.
[0031] It is also to be understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and embodiments of the present disclosure, as well as specific examples, are intended to encompass equivalents thereof.
[0032] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a",” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.
[0033] It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may, in fact, be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
[0034] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
[0035] Auto-Warning Tell-Tale (AWTT) device provides a highly visible and immediate warning of excessive movement inside the coalmine. The device provides a real-time warning to the machine operators at the possible onset of caving. The present mechanised Pillar extraction process is much faster as compared to the conventional mining and hence dependency is more on usage of the device as it is difficult to rely only on physical conditions and indications such as sound from goaf and physical observations for the impending roof falls. Usage of AWTT device helps in immediately withdrawal of men and machine in a situation of any roof movements or caving. The AWTT device consists of LEDs that start blinking once a certain (predefined) deformation is measured by the AWTT device placed inside the goaf area. The intensity of blinking light can be seen deep inside the goaved out area.
[0036] These and other advantages of the present subject matter would be described in greater detail with reference to the following figures. It should be noted that the description merely illustrates the principles of the present subject matter. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present subject matter and are included within its scope.
[0037] As illustrated in Figure 1 to Figure 3, the present subject matter describes a method 100 for strata monitoring and indicating roof movements during mining of coal using an Auto Warning Tell Tale (AWTT). Figure 1 illustrates a method 100 for strata monitoring and indicating roof movements during mining of coal using an Auto Warning Tell Tale (AWTT). The order in which the method 100 is described is not intended to be construed as a limitation, and any number of the described method blocks can be combined in any appropriate order to carry out the method 100 or an alternative method. Additionally, individual blocks may be deleted from the method 100 without departing from the scope of the subject matter described herein.
[0038] At step 101, the method includes installing Auto Warning Tell Tale (AWTT) device at junction points in roof portion of a coal mine prior to initiation of depillaring process. The installation of AWTT device is performed manually by mining personnel working inside the coal mine fields.
[0039] At step 102, the method includes monitoring and recording data and time interval (Tx) (in hours) between blinking of warning lights provided on the Auto Warning Tell Tale (AWTT) and completion of pillar extraction. Once the process of de-pillaring has been initiated for extraction of coal from the coal mine, the method 100 involves monitoring and recording of gap between blinking of AWTT device at different frequencies as per the functioning of the AWTT device and completion of pillar extraction.
[0040] At step 103, the method includes monitoring and recording data and time interval (Ty) between completion of pillar extraction and falling of roof or caving of roof. Herein, the gap between the stage of completion of extraction of pillar up to the falling or caving of roof is monitored and recorded;
[0041] At step 104, the method includes analysing the recorded time interval (Tx) and the recorded time interval (Ty) and recorded data. Herein, the time interval data, i.e., Tx and Ty are analysed for further processing.
[0042] At step 105, the method includes determining time period (Tz) between the blinking of warning lights of the AWTT and the fall or cave of roof of the pillar on basis of the recorded time interval (Tx) and the recorded time interval (Ty). On the basis of the analysed data, a minimum time in hours taken by a roof to fall or cave subsequent to extraction of pillar. This step includes calculation of minimum time taken by the roof to fall or cave after the pillar extraction work has been completed.
[0043] As shown in the blank data format sheet of Fig. 5, the essential data recorded includes Start and completion of pillar, the AWTT blinking, the date and time of fall. From this data the interval between P completion vs fall, AWTT blinking vs fall and AWTT blinking vs P completion is recorded. The interval between P completion vs fall (Ty) is plotted against blinking vs fall (Tz). The standard design method considers minimum time interval of 8 hours which is to be maintained for Ty. This plot gives the understanding of any early fall with respect to P completion.
[0044] Further, on the basis of existing data, the roof layers are categorised as easily caveable, moderately caveable and difficult to cave based on caveability studies done prior to depillaring process. Tx and Tz helps in understanding the behaviour of roof with respect to caving. More duration means difficult to cave, less duration means easily caveable, and standard duration of 8 hours means moderately caveable roof.
[0045] At step 106, the method includes determining (106) minimum time interval (Tc) taken by roof to cave after extraction of pillar for subsequent pillars based on determined time period (Tz) and the recorded data. Wherein, the recorded data during step of recording (102, 103) includes percentage (%) of coal extracted from each pillar and area of exposure in extracted pillar.
[0046] The present method considers minimum time interval of 8 hours which is to be maintained for Ty for safe extraction. Whenever the duration Ty is less than 8 hours the percentage of extraction by reducing slice length or number of slice (leaving coal in the pillar) is followed. Continued monitoring establishes the result due to reduction of percentage of extraction helping in controlling early fall.
[0047] In an embodiment, the method includes analysing of recorded data includes comparing the time interval (Tx) (in hours) between blinking of Auto Warning Tell Tale (AWTT) with area of exposure and time duration (Ty) (in hours) between completion of pillar extraction and falling or caving of roof of the pillar.
[0048] In an embodiment, the Auto Warning Tell Tale (AWTT) device is coupled with Remote Reading Multipoint Extensometer (RRME) to determine the caveability of the roof of the pillar.
[0049] At step 107, the method includes estimating the caveability of roof of the pillar based on the determined time period (Tz) and the recorded data.
[0050] The caveability index is determined prior to depillaring using Impact Split Method. It categorises roof layers as easily caveable, moderately caveable and difficult to cave. This caveability is calibrated based on actual monitoring by AWTT & RRME. Roof falls within 8 hours of P completion or AWTT blinking (whichever is earlier) is considered as easily caveable whereas duration more than this is considered as moderately caveable. Delay in caving more than 48 hours is considered as difficult to cave roof.
[0051] At step 108, the method includes setting of a warning limit of the AWTT device based on the roof layers sagging with respect to the percentage of extraction per pillar obtained on the basis of analysed recorded data and time interval (Tx, Ty, Tz).
[0052] The AWTT blinking limit is reset based on the strata behaviour. An early fall demands lowering of AWTT limit to give enough prior warning, whereas delay in fall demands for increasing the limit of warning. Similarly percentage of extraction also influences the pattern of caving. More extraction results in early fall whereas less extraction results in delay in fall. As explained earlier with pillar extraction in the working example.
[0053] The time interval between P completion vs fall (Ty) and Blinking vs fall (Tz) are plotted with percentage of extraction to understand how more extraction from pillar results in early fall after P completion and vice versa.
[0054] The roof layer(s) sagging/convergence is indicated by blinking of AWTT once it attains the predefined warning limit. Usually AWTTs are set at 5 mm as standard warning limit. The blinking by this instrument indicates sagging of the roof layers within 10 m horizon from the roof. The other associated physical indications during sagging includes formation of tensile cracks in the roof, crushing of adjacent pillar corners, bending of bearing plates of the roof bolts, and bending of indicator props installed in the middle of breaker line support. Reduction in percentage of extraction of coal standing on pillars (in comparison to the designed percentage) results in providing restriction to the roof layers to cave, which increases blinking time giving enough prior indication.
[0055] At step 109, the method includes determining (109) percentage of extraction from a pillar and safe withdrawal time allowance during production.
[0056] Percentage of extraction from pillar is show in working example below. The core of the analysis is maintaining minimum of 8 hours duration between P completion & caving. Spot decisions are taken based on the nature of fall. Early fall demands reduction of percentage of extraction whereas delay in fall demands for increase percentage of extraction.
[0057] The percentage of extraction of the pillar during designing considers many parameters including physico-mechanical properties of coal & roof rocks, depth, height of extraction etc. For an example, referring fig. 6, showing the design with area of extraction in green colour and coal left out in purple colour. The percentage of extraction is estimated from the coal won against total coal in the pillar. In the above figure, the total area of solid pillar is 19 m x 19 m = 361 m2. Each small square in the figure denotes 1 m x 1m area. Total area left is 88 m2. The designed percentage of extraction is {(361 m2 – 88 m2) x 100/361 m2} i.e., about 76%.
[0058] The recording of data in the method 100 includes measurement of the following parameters: (a) start of pillar extraction, (b) completion of pillar extraction, (c) blinking of Auto Warning Tell Tale (AWTT), (d) caving or falling of roof of a coal mine and (e) percentage of coal extracted per pillar by measuring date and exposure time in hours.
[0059] The analysis of recorded data in the method 100 includes comparing the time interval (Tx) (in hours) between blinking of Auto Warning Tell Tale (AWTT) with area of exposure and time duration (Ty) (in hours) between completion of pillar extraction and falling or caving of roof.
[0060] The Auto Warning Tell Tale (AWTT) is coupled with Remote Reading Multipoint Extensometer (RRME).
[0061] In practical situations, the AWTT has anchor at 10 m in the roof horizon and any sagging beyond predefined limit (generally 5 mm) within this 10 m is indicated by this instrument. The limitation of AWTT here is it do not from which horizon within 10 m sagging has happened. To know more about this RRME with four anchors at different horizons is installed. The movement of 5 mm or more captured by AWTT is analysed against RRME readings indicating movement of layers in the above horizon. As indicated in figure 4 the left most column is the predetermined caveability index (green for easily caveable, yellow for moderately caveable and red for difficult to cave). This caveability is calibrated based on monitoring by AWTT & RRME to establish the actual caveability.
[0062]
[0063] The anchor height of the AWTT is required to be set at 10.0 m in the roof horizon of the pillar inside the coal mine. The warning limit being on conservative side is set as 5 mm in usual mining operations. The action level is revised when monitoring data from the panel is gained. It is required to have minimum 8 hours of time interval between the completion of pillar extraction and the associated roof fall or caving of roof in the goaf.
[0064] Figure 4 illustrates an example of analysis of caving of roof or roof fall during the pillar extraction process by an application of the present method. Herein, the monitoring and recorded data as obtained from the AWTT device and Remote Reading Multipoint Extensometer (RRME) is compared with time and area of exposure prior to the caving of roof in the goaf. This further helps in re-assessment of percentage of pillar extraction for improved efficacy and inferring safe time interval for withdrawal of men and machine to ensure maximum and safe coal extraction from the coal mines.
Working Experimental Example:
[0065] Referring graphs provide in figure 7a and 7b which illustrates a qualitative analysis and is associated with many parameters. When the show two graphs are compared vertically the following points are understood:
• In P1, the % of extraction was 87 % (being the first pillar more extraction was done than the design) resulted in early fall (as designated by the graph showing interval between P completion vs fall as 28 hours and Blinking vs fall as 2 hours).
• Later in P2 the percentage of extraction was reduced which resulted in more time interval between P completion vs fall (87 hours) and blinking vs fall (13 hours).
• Similarly, another example of reducing % of extraction to 48% in P 13 resulted in delay of P completion vs fall (197 hours) and blinking vs fall (34 hours).
• In this way it helps in controlling the early roof fall by reducing percentage of extraction
Technical advantages:
[0066] With the present method implemented by means of the AWTT device, safety of men & machine deployed in the depillaring panel remains assured.
[0067] With the present disclosure, due to visual indications it becomes easy to identify any roof movements inside the coal mine without any need of a skilled personnel.
[0068] With the present system, there is no additional requirement of cables or similar systems.
[0069] With the present disclosure, it is easy to install and set up the AWTT device that helps in setting site-specific warning limit based on the analysis and does not necessarily requires setting up of a fixed warning limit.
[0070] With the present disclosure, it is possible to take on the spot decisions for further cutting slices or nooks or withdrawal of men & machine by the miners or operators based on the visual indication provided by the AWTT device.
[0071] With the present disclosure, the AWTT device installed in any geologically disturbed area would further give additional warning in case of deterioration of roof in real-time.
[0072] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances, where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”
[0073] It will be further appreciated that functions or structures of a plurality of components or steps may be combined into a single component or step, or the functions or structures of one-step or component may be split among plural steps or components. The present invention contemplates all of these combinations. Unless stated otherwise, dimensions and geometries of the various structures depicted herein are not intended to be restrictive of the invention, and other dimensions or geometries are possible. In addition, while a feature of the present invention may have been described in the context of only one of the illustrated embodiments, such feature may be combined with one or more other features of other embodiments, for any given application. It will also be appreciated from the above that the fabrication of the unique structures herein and the operation thereof also constitute methods in accordance with the present invention. The present invention also encompasses intermediate and end products resulting from the practice of the methods herein. The use of “comprising” or “including” also contemplates embodiments that “consist essentially of” or “consist of” the recited feature.
[0074] Although embodiments for the present subject matter have been described in language specific to structural features, it is to be understood that the present subject matter is not necessarily limited to the specific features described. Rather, the specific features and methods are disclosed as embodiments for the present subject matter. Numerous modifications and adaptations of the system/component of the present invention will be apparent to those skilled in the art, and thus it is intended by the appended claims to cover all such modifications and adaptations which fall within the scope of the present subject matter.

We claim:

1. A method (100) for determining caveability and percentage of extraction of coal during mining using instrumentation including an Auto Warning Tell Tale (AWTT) device, the method comprising steps of:
installing (101) the Auto Warning Tell Tale (AWTT) device at all junction points in roof portion of a coal mine prior to initiation of depillaring process;
monitoring and recording (102) data and time interval (Tx) (in hours) between blinking of warning lights provided on the Auto Warning Tell Tale (AWTT) and completion of pillar extraction;
monitoring and recording (103) data and time interval (Ty) between completion of pillar extraction and falling or caving of roof of the pillar;
analysing (104) the recorded time interval (Tx) and the recorded time interval (Ty) and recorded data; and
determining (105) time period (Tz) between the blinking of warning lights and the fall or cave of roof of the pillar on basis of the recorded time interval (Tx) and the recorded time interval (Ty);
determining (106) minimum time interval (Tc) taken by roof to cave after extraction of pillar for subsequent pillars based on determined time period (Tz) and the recorded data;
wherein, the recorded data during step of recording (102, 103) includes percentage (%) of coal extracted from each pillar and area of exposure in extracted pillar.
2. The method as claimed in claim 1, wherein analysing (104) of recorded data includes comparing the time interval (Tx) (in hours) between blinking of Auto Warning Tell Tale (AWTT) with area of exposure and time duration (Ty) (in hours) between completion of pillar extraction and falling or caving of roof of the pillar.
3. The method as claimed in claim 1, wherein the Auto Warning Tell Tale (AWTT) device is coupled with Remote Reading Multipoint Extensometer (RRME) to determine the caveability of the roof of the pillar.
4. The method as claimed in claim 3, wherein the method comprises:
estimating (107) the caveability of roof of the pillar based on the determined time period (Tz) and the recorded data; and
setting (108) of a warning limit of the AWTT device based on the roof layers sagging with respect to the percentage of extraction per pillar obtained on the basis of analysed recorded data and time interval (Tx, Ty, Tz).
5. The method as claimed in claim 1, wherein the method includes:
determining (109) percentage of extraction from a pillar and safe withdrawal time allowance during production.