Indian Patents. 268353:A MULTI-POINT ANCHORING SYSTEM FOR GROUTED-TYPE BOREHOLE EXTENSOMETER FOR STRATA MOVEMENT MEASUREMENTS IN UNDERGROUND EXCAVATION

Title of Invention	A MULTI-POINT ANCHORING SYSTEM FOR GROUTED-TYPE BOREHOLE EXTENSOMETER FOR STRATA MOVEMENT MEASUREMENTS IN UNDERGROUND EXCAVATION
Abstract	A multi-point anchoring system has been disclosed which provides point-anchorage to a multi-point borehole extensometer using grouting technique. It essentially consists of an anchor carrying a cement capsule along with it and a device to rupture the capsule at the position of the anchorage. This rupturing of the capsule is done by a pivoted knife and thread pulling system.

Full Text	The present invention relates to a multi-point anchoring system for grouted-type borehole extensometer for strata movement measurements in underground excavation. The present invention particularly relates to a multi-point anchoring system for grouted-type borehole extensometers using quick or slow setting cement capsules. The multi-point anchoring system of the present invention provides point-anchorage to a borehole extensometer using grouting technique at plurality of points. This essentially consists of an anchor carrying a cement capsule along with it and a device to rupture the capsule at the position of each anchorage point. The rupturing system of the capsule consists of a pivoted knife and a pulling system by means of a thread. A safety arrangement system is provided for preventing the accidental breakage of the grouting capsule during insertion into the borehole along with the extensometer. In case of multiple anchoring, a protective pipe is provided to prevent the rods of preceding anchors from coming in contact with the grout of succeeding anchors. This invention will be particularly used in conjunction with borehole extensometers to study the movement of strata due to mining or any underground excavation and its process of grouting in the borehole for measurement of roof movement. Borehole extensometers are widely used in coal mines, metal mines, tunnels and caverns for measuring the relative ground movement occurring due to underground excavation. The measurement is taken from underground and as well as from surface. In general, mechanical type and grouted type anchors are used for anchoring one end of the extensometer rods to the rock mass inside a borehole. The mechanical type instruments are prone to slipping along the sides of the borehole especially when they are installed near blasting areas due to blast vibration. In case of grouted anchors the full column grouting of borehole is a tedious process. Extensive efforts have been devoted to the development of various devices for measuring ground movement in mine roofs, tunnels and other underground excavation works. To highlight the wide mining and tunneling usage and continual efforts, which have been made by other inventors to improve the performance of borehole extensometers, a few patent references are provided below for illustration. Reference may be made to U.S. patent no. 4,242,915 entitled "Extensometer anchor". This invention as illustrated in figure-1 of the drawings accompanying this specification, relates to the field of "Borehole" AND "Extensometer" AND "mine" which comprises of an extensometer anchor for use in a mine borehole. The anchor has an anchor body that, when in an operative mode, is placed in the borehole. Extending at least partially around the outer surface of the body are one or more grooves whose major plane is generally perpendicular to the length of the borehole. Seated within each groove is a compressible resilient anchor member, like a ring, which remains loaded by a retaining device, such as a cotter pin, extending through it. Upon being pulled from outside of the borehole, the retaining device unloads the compressed anchor which then moves to expand outwardly in the borehole and firmly anchor the anchor body and attached extensometer within the mine borehole. The main disadvantage of this system is that it may slip in the borehole due to a nearby blast vibration. More over this is only a mechanical device liable to slide during a borehole getting crushed due to rock stress which is not uncommon. Reference may be made to another U.S. patent no. 4,514,905 entitled "Convergence extensometer for measuring mine roof subsidence" wherein an extensometer for measuring changes in the vertical distance between the roof and floor of a mine opening comprising of a pair of rigid telescoping members, a tension spring securing said members to each other in a telescoping relationship, a hook for attaching a non-extensible cable to each of said members, and an indicator for determining telescopic movement of said members. The extensometer of this invention is utilized by securing one of said telescoping members to the roof of the mine and the other telescoping member to the floor of the mine with the axis of said members being disposed along the vertical. The telescoping members are secured, under tension, to the mine roof and floor by means of a non-extendible cable such as a steel cable. The indicator for determining the telescopic movement of the members may be a pair of lugs or flanges or other indicating marks, each member of which pair is affixed to a separate telescoping member. The device is illustrated in figure.2 of the drawings accompanying this specification. The main disadvantage of this system is that it may slip in the borehole due to a nearby blast vibration in the mine. Reference may be made to yet another U.S. patent no. 5,629,480 entitled "Rock extensometer". In this invention there is an extensometer for use in a borehole, which comprises a combination of linear motion transducers located with daisy wheel anchors, which may be attached together if desired with extension bars. Linkages are used to connect the transducers to the daisy wheel anchors. The transducers are set up to measure distance changes both axially along the hole or radially. The extensometer includes at least one axially measuring transducer, and at least two radially measuring transducers. The transducers change in value according to changes in borehole dimensions; the transducer values are monitored electrically. The main disadvantage of this system is that it may slip in the borehole due to a nearby blast vibration in the mine. The installing mechanism is difficult and cumbersome. Reference may be made to still another U.S. patent no. 4,463,611 entitled "Extensometer". In this invention a rod extensometer for measuring movements in rock structures and in foundations, the measuring rod system consists of a one piece flexible rod made of reinforced plastic and surrounded by an encasing tube and connected at one end to a fixed-point anchoring device and by its other end to a pick-up element for the measuring value. This design enables the rod extensometer to be inserted into a borehole at short notice and with very little loss of time. Furthermore, the rod can form a practically endless structure wound onto a delivery spool and thus stored and transported with ease and in a space-saving manner. The main disadvantage of this system is that it may slip in the borehole due to a nearby blast vibration in the mine. Moreover this extensometer cannot monitor the rock movement in a continuous manner and need to be activated during measurement time. The process of installation and grouting is difficult and cumbersome. Reference may be made to U.S. patent no. 4,719,803 entitled "Borehole extensometer" for monitoring relative mass displacements. In this device positionable in a borehole for monitoring relative mass displacements axially along the borehole between at least two spaced-apart anchor points, comprises at least two retrievable anchor members arranged in spaced-apart opposite relationship to define the at least two anchor points, the anchor members each having radially displaceable borehole wall contacting means and including mechanical means for radially outwardly displacing the borehole wall contacting means to engage the borehole wall and thereby fix the anchor member in the borehole against the wall thereof. A linear displacement sensing means is arranged between the anchor members, the displacement sensing means being connected to one of the anchor members and including an elongated axially movable sensor element, the sensor element being normally biased in a direction toward the other anchor member for contact engagement therewith. Relative mass displacements are transmitted to the sensor element and are measured by the displacement sensing means as a variation in distance between the anchor members within the borehole. The main disadvantage of this system is that it may slip in the borehole due to a nearby blast vibration in the mine. Moreover this extensometer cannot monitor the rock movement in a continuous manner and need to be activated during measurement time. Therefore with reference US Patent No. 4242915, US Patent No. 4719803, as mentioned above where mechanical type friction gripping arrangement have been made. Further an extensometer with daisy wheel type of mechanical anchors have been designed in US Patent No. 5629480. Though these mechanical type of anchors are easier to install, the main disadvantage of these inventions is that they are prone to slipping along the sides of the borehole especially when they are installed near blasting areas due to vibration. This can lead to erroneous results. Places where heavy blasting are practiced in hard rocks such as large underground caverns and metal mines, it is necessary to grout the anchors using cement to secure a good holding of the anchors on to the rock. For grouted type of anchoring, especially in multi-point anchoring systems, the general practice has been to completely grout the borehole after exposing the anchors and giving protective covering to the rods. References may be made to US Patent No. 4463611 and US Patent No. 3483745. However the main disadvantage of these inventions is grouting the anchors in the borehole is very tedious process and in certain cases infeasible, when the boreholes are longer and upward. Grouting the anchors in an upward hole requires high-pressure cement injection. Cracks in the rock mass lead to leakage of the cement from the borehole and may not result in proper anchorage. Grouting in a down hole, though easier, cannot go beyond certain depth regime. Moreover, full installation of such grouted type borehole extensometers takes 2-3 days to allow the cement to dry up in the borehole. Such delay often results in the loss of important rock mass movement data. If this grouting operation can be done only at the anchor positions using quick setting cement capsules, it will be much easier and quicker to make such installation and to take a quick initial reading. In the past grouting anchors at selective places in the borehole has not been done for the installation of borehole to the best of our knowledge except for a single point anchoring system by borehole grouting (not by a cement capsule) in the reference SI 20088 (Republic of Slovenia). Hence, it is clear from the hitherto known prior art that there is a definite need to provide a borehole extensometer which can easily and reliably ensure a proper measurement system of strata movement in mine / tunnel excavations. The main object of the present invention is to provide a multi-point anchoring system for grouted-type borehole extensometer for strata movement measurements in underground excavation, which obviates the drawbacks of the hitherto known prior art as detailed above. Another object of the present invention is to provide a multi-point anchoring system for grouted-type borehole extensometers using quick or slow setting cement capsules, which obviates the drawbacks of the hitherto known prior art as detailed above. Yet another object of the present invention is to provide a multi-point anchoring system for grouted-type borehole extensometer for measuring strata movement in a mine / tunnel roof / side which obviates the drawbacks of the hitherto known prior art as detailed above. Still another object of the present invention is to provide a multi-point anchoring system for grouted-type borehole extensometer, which can be installed in any direction in an underground opening including upward and downward direction. Still yet another object of the present invention is to provide a multi-point anchoring system for grouted-type borehole extensometer, which will eliminate the problem of slippage during any ground vibration. A further object of the present invention is to provide a multi-point anchoring system for grouted-type borehole extensometer, which will eliminate the requirement of hydraulic or pneumatic grout pumps. A still further object of the present invention is to provide a multi-point anchoring system for grouted-type borehole extensometer, which will reduce the setting time of grouting in the borehole. Another object of the present invention is to provide a multi-point anchoring system for grouted-type borehole extensometer, which will require less manpower to install. The extensometer of the present invention consists of anchoring system of multi-point type and can be installed into boreholes drilled to any direction and having a diameter of the order of 49 to 75mm. Up to two anchors are possible in a 49mm diameter hole (AX size), and up to 5 anchors can be installed into 75mm (NX size) borehole. A triple anchoring system in an upward hole is shown in Figure. 3. The extensometer consists of two rubber discs with holes to accommodate various anchors, steel rods, plastic tubes and threads. The said two rubber discs are fitted by an anchor in a single set. In between two rubber discs there are cement capsule attached in the anchor rod by means of adhesive tapes. This cement capsule can be slit by a pivoted sharp edged knife riveted in the flat portion of the anchor. The knife can be operated by a long thread from outside the borehole. The knife is tied by a safety tape for inadvertent cutting of the capsule. After the cement capsule grouts the system the long steel rods attached with the bottom of the anchor transmits the strata movement to the sensor fitted at the lower ends. For multi-point anchoring in several strata there will be plurality of such sets. A circular lid covers the borehole by means of nut and bolt mechanism tightened with the borehole collar. Accordingly the present invention provides a multi-point anchoring system for a grouted type borehole extensometer for measurement of strata movement in underground excavation, which comprises a plurality of anchor sets, characterized in that each such anchor set consists of two rubber discs removably fixed at the two ends of an anchor rod having a flat portion wherein is provided a pivoted sharp edged knife capable of being remotely operated by means such as a long thread from outside a borehole, the said rubber discs capable of accommodating a cement capsule attached by means such as adhesive tape to the said anchor in such a manner that the said cement capsule can be slit by the said pivoted sharp edged knife, the said anchor being provided at the bottom with means for connecting extension steel rods capable of transmiting the strata movement to a sensor fitted at the lower end of the said extension rod. In an embodiment of the present invention, the rubber discs being provided with multiple holes capable of accommodating and allowing to pass through the anchor, extension steel rods, tubes and threads. In another embodiment of the present invention, the anchor is having threads at both the ends to removably fix the rubber discs by means such as nuts, washers. In yet another embodiment of the present invention, the anchor rod having a flat portion near the middle wherein is provided a sharp edged knife riveted to enable pivotal movement. In still another embodiment of the present invention, the knife is covered by a tape as a safety measure to prevent inadvertent cutting of the cement capsule. In still yet another embodiment of the present invention, the extension steel rods are connected with the anchors by means of connectors to enable transmission of the strata movement to the sensors fitted at the bottom of each steel rod. In a further embodiment of the present invention, there is provided a borehole collar en suited at the mouth of the borehole. In a further embodiment of the present invention, there is provided a circular lid with holes for sensors and threads to cover the borehole by tightening by means of nut and bolts with the collar. In a still further embodiment of the present invention, there is provided a protective pipe to prevent the rods of preceding anchors from coming in contact with the grout of succeeding anchors. In figures 3 to 5(e) of the drawings accompanying this specification is illustrated an embodiment of the multi-point grouted type borehole extensometer of the present invention for measuring rock strata movement in an underground excavation. Figures 3 and 4 of the drawings illustrate the anchoring system of the present invention. In figure 3 is shown a multi-point anchoring system. A detailed cross section of the anchor and the knife is shown in figure 4. Figure 5 shows another view of the anchor behind the cement capsule. Sectional views of the rubber plates to be used with 1st, 2nd, 3rd, 4th and 5th anchors are shown in figures 5a, 5b, 5c, 5d and 5e, respectively. Each anchoring device consists of a quick setting cement capsule (1) attached to an anchor (3) (3/4" diameter torsion rod made of mild steel). The capsule has been supported by two rubber disks (2a) and (2b) one on the top (2b) and the other on the bottom (2a). Both the rubber disks (2a) and (2b) have a diameter equal to that of the borehole within a clearance of 1mm to allow movement of the anchor assembly during insertion. The bottom disk (2a) is fixed to the bottom of the anchor using a couple of washers (8a) and (8b) on bottom and top respectively and a nut (9a), which would be tightened on a male screw thread cut at the bottom of the anchor (3). The bottom portion of the anchor is further reduced in diameter to fix it to a %" diameter stainless steel rod (21) using a coupling (20). The top rubber disk (2b) is free to move in the down ward direction, but restricted to go upward using a similar washer (8c) and nut (9b) assembly. The cement capsule (1) will be resting on the bottom rubber plate (2a) and shall be tightly secured to the anchor (3) using 2 or 3 adhesive tapes (19). The position of the anchor with respect to the rubber plate can be decided depending on the borehole size and the number of anchors to be installed in the same borehole. The top rubber plate shall be resting on the top of the capsule and shall be free to move up and down subject to the top washer (8c) and nut (9b) assembly. The commercially available cement capsules manufactured in India for the purpose of roof bolting in coal mines have a diameter of 32mm and can be made to a length as required by the mining company. These capsules can have various setting time requirement for hardening of the cement formatting. Time duration of 30 minutes would be sufficient enough for inserting this anchoring system into a borehole of up to 20m length. However, if the time required for inserting all the anchors into the borehole is more than 1 hour, slow setting cement capsules may be used or cement and water may be mixed to form a slurry and filled into tubular plastic bags of 32mm diameter on the site just before installation of borehole extensometer. In such cases the setting time of anchors would be higher. The commercially available cement capsules in India are used in roof bolting operations by soaking them in water for a few minutes and after they absorbs water they are inserted into the boreholes and punctured by a steel rod (bolt). Following its rupture, the grout hardness in the hole within a duration of 30-60 minutes as specified by the manufacturer. In a quick setting cement capsule, the time between its taking out from water and puncturing it should be less than 10-15 minutes. However, this duration of curing can be increased by the manufacturer. The capsules (1) inserted into the borehole along with the anchors are ruptured at the point of anchorage by a knife (4). The sharp edge (15) of the knife (4) shall be facing the capsule (1). The knife (4) shall be pivoted to the anchor at its centre using a rivet (5). The anchor is usually circular in cross section; therefore a flat portion (17) is created on its surface where the knife (4) shall be fixed. A guide pin (6) shall be fixed adjacent to the blunt edge (16) of the knife to restrict its movement in that direction. A hole (14) shall be provided at the top end of the knife to enable a thread (7) to pass through it a couple of times. As the thread is pulled downwards or towards the collar of the borehole, the knife would swing in such a way that the sharp edge (15) of the knife cuts into the capsule, which is secured to the anchor. During insertion of the anchor into the hole, it may so happen that the thread (7) attached to the knife (4) may accidentally cut the capsule and spill the contents. To prevent this, a safety adhesive tape (16) shall be wound around the knife (4) and the anchor (3). Only when the thread is pulled with a sufficient force, the knife first cut across the adhesive taping before puncturing into the capsule. Figure 5 shows another view of the anchor behind the cement capsule. The thread shall be tied to the hole of the knife (14) with a single knot and shall be attached to the top rubber disc (8b) roughly in the middle by passing through the rubber disc (8b) and by putting a knot (23) on the top of the disc. When the thread is pulled, the top rubber disc squeezes the capsule (1) downward during its puncture. This will enable better evacuation of the contents on to the bottom rubber plate. Since the cement capsule has got a capacity of about 300-400 cm3, the grout would ensure an anchorage of about 10cm in the borehole. The other end of the thread (7) passes through the bottom plate through a 2-3mm diameter hole (11). After passing the thread (7), grease shall be applied to the hole to prevent the leakage of cement grout. When additional anchors are to be installed, similar anchoring systems are to be inserted into the borehole as shown in figure 3 of the drawings. In such case, the top and bottom rubber discs (2b and 2a respectively) of the subsequent anchors shall be provided with holes of 2-3mm diameter (11) for passing the threads (7) of the preceding anchors. After the threads (7) are passed through the holes (11), grease shall be applied to these holes (11) to make sure that the cement grout won't leak through it. Sectional views of the rubber plates to be used with 1st, 2nd, 3rd, 4th and 5th anchors are shown in figures 5a, 5b, 5c, 5d and 5e, respectively. Moreover, holes with a plastic pipe (10) of about Vz" diameter tightly passing through the top and bottom rubber plates shall be provided for passing the stainless steel rods (21) attached to the preceding anchors. The plastic pipes (10) will ensure free movement of the stainless steel rods through the succeeding anchoring system. The plastic pipes (10) would also prevent the grout of the succeeding anchors to come in contact with the stainless steel rods (21). The collar (12) of the borehole shall be grouted on to the mouth of the borehole before the insertion of the multi-point anchoring system. The threads (7) of all the anchors shall be made to pass through a hole of 4-5mm diameters in the circular lid (13). When all the anchors are positioned and the threads passed through the lid (13) the collar of the borehole (12) shall be closed using the circular lid (13) with nuts and bolts assembly (22). Now, the cement capsules are ruptured by pulling the threads one by one. After the specified setting time of the cement capsules, the circular lid (13) shall be opened and a suitable mouthpiece shall be attached to the collar for the measurement of the rods position using any electrical/mechanical sensors. If quicker setting cement capsules are used, the user may not get enough time to install all the anchors at a time. In such case, the anchors can be installed one by one. This could be done using the following procedure: The entire anchorage system for one anchor can be assembled at the site before the capsule (1) is taken out from water. Moreover, the collar of the borehole is also made ready and one nut-bolt assembly (22) of the circular lid (13) already tightened prior to soaking the cartridge. The circular lid (13) can now be rotated with respect to the nut-bolt assembly (22) to open and close the borehole mouth. The capsule (1) after taking out from water is now fixed between the top (2b) and bottom (2a) rubber discs by two adhesive tapes (19) and the single anchor system is inserted into the borehole. This can be done in a few minutes. The mouth of the borehole can be partially closed by rotating the circular lid (13) with the thread (7) passing through the partially open portion of the borehole mouth. When the thread (7) is pulled, the capsule (1) is broken and the grout surrounds the anchor and is fixed to the borehole wall by about 30 minutes duration. After the specified hardening time, the borehole mouth is fully opened by rotating the circular lid (13) with respect to the nut-bolt assembly (22). The rod of the first anchor can now be found rigid. The second anchorage system has to be assembled at the site before the capsule is soaked. When the capsule is taken out from water, it is quickly fixed in its position with two adhesive tapes (19) and the second anchoring system is inserted into the borehole by passing the rod of the first anchorage system through the protective plastic pipe (10) of the second anchorage system. Subsequent anchors can also be installed in the similar fashion. The novelty of the multi-point anchoring system for grouted type borehole extensometer using quick setting cement capsules of the present invention for measuring rock strata movement in an underground excavation, resides in its usefulness for grouting of plurality of anchors in several rock layers, through simple cost-effective constructional features and ease of installation requiring less manpower, less electricity cost and having low cost of manufacture. Another novelty of the present invention is that it does not require very skilled labour in installation. It will also take less time to install, which may be at par with the state of the art extensometers used else where. Yet another novelty of the present invention is that this extensometer ensures good grouting at the anchor point as a result there will be a homogeneous strength in the grout to bind the anchor and the rock layers at predetermined distance. Still another novelty of the present invention is that this extensometer will prevent slippage of the anchors during any blast vibration. Yet still another novelty of the present invention is that the design of the extensometer is such that it will prevent inadvertent slit of the cement capsule at unwanted place. The novelty of the multi-point anchoring system for grouted type borehole extensometer using quick setting cement capsules of the present invention for measuring rock strata movement in an underground excavation, has been realized by the non-obvious inventive step of providing in combination a set of anchors with independent grout materials in form of quick setting capsules in between a pair of rubber discs fitted at the two ends of an anchor. The capsule can be slit at any predetermined position inside the borehole. The anchor is designed in a noble manner by flattening a part of it to accommodate the sharp knife, which can be operated by means of long thread from outside the borehole. There is a safety tape tying the knife to prevent inadvertent cutting of the capsules or the thread. In the hitherto known prior art, there are no such sharp knife which act as cutters/mixers of the grout material inside the borehole. The presence of several such anchors enables anchoring of the extensometer at several points independently at predetermined place. The main advantages of the novel multi-point anchoring system of the present invention as described herein above are as follows: 1. The multi-point anchoring system described above has got applicability in a gamut of rock mechanics applications including underground metal mine, underground coal mines, tunnels and caverns. 2. Since the anchors are grouted, error caused by slippage of anchors due to blasting vibration in the vicinity of the extensometer is avoided. Therefore it ensures error free readings. 3. Easier and quicker to install in comparison to the existing full column grouted type multi-point borehole extensometers. 4. Since the grouting is selective and only at the anchors, it can easily be installed in deeper holes. 5. Applicability in boreholes drilled upwards as well as downwards. 6. Faster installation allows the user to start the measurement of rock mass deformation much earlier. 7. It requires less manpower to make the installation. 8. A hydraulic or pneumatic pump is not necessary for the grouting of the anchors. Minimal facilities are needed at the installation site. 9. All the parts involved in the anchoring system are easily and commercially available and therefore easy to manufacture and would be cheaper. We claim: 1. A multi-point anchoring system for a grouted type borehole extensometer for measurement of strata movement in underground excavation, which comprises a plurality of anchor sets (3), characterized in that each such anchor set consists of two rubber discs(2a,2b) being removably fixed at the two ends of an anchor rod having a flat portion wherein is provided a pivoted sharp edged knife(4) so as to remotely operated by means such as a long thread from outside a borehole, the said rubber discs accommodating a cement capsule(l) attached by means such as adhesive tape (19) to the said anchor in so that the said cement capsule being slit by the said pivoted sharp edged knife (15), the said anchor being provided at the bottom with means for connecting extension steel rods (21) so as to transmit the strata movement to a sensor fitted at the lower end of the said extension rod. 2. A multi-point anchoring system as claimed in claim 1, wherein the rubber discs being provided with multiple holes for accommodating and allowing to pass through the anchor, extension steel rods, tubes and threads. 3. A multi-point anchoring system as claimed in claim 1-2, wherein the anchor is having threads at both the ends to removably fix the rubber discs by means of nuts (9a, 9b), washers (8a,8b). 4. A multi-point anchoring system as claimed in claim 1-3, wherein the anchor rod having a flat portion near the middle wherein is provided a sharp edged knife riveted to enable pivotal movement. 5. A multi-point anchoring system as claimed in claim 1-4, wherein the knife is covered by a tape as a safety measure to prevent inadvertent cutting of the cement capsule. 6. A multi-point anchoring system as claimed in claim 1-5, wherein the extension steel rods are connected with the anchors by means of connectors to enable transmission of the strata movement to the sensors fitted at the bottom of each steel rod. 7. A multi-point anchoring system as claimed in claim 1-6, wherein is provided a borehole collar(12) suited at the mouth of the borehole. -18- • 8. A multi-point anchoring system as claimed in claim 1-7, wherein is provided a circular lid(13) with holes for sensors and threads to cover the borehole by tightening by means of nut and bolts with the collar. 9. A multi-point anchoring system as claimed in claim 1-8, wherein is provided a protective pipe(lO) to prevent the rods of preceding anchors from coming in contact with the grout of succeeding anchors. Dated this 17"^ March 2006 (Chetan Kumar) Scientist, IPMD,CSIR -19-

Full Text

The present invention relates to a multi-point anchoring system for grouted-type borehole extensometer for strata movement measurements in underground excavation. The present invention particularly relates to a multi-point anchoring system for grouted-type borehole extensometers using quick or slow setting cement capsules.
The multi-point anchoring system of the present invention provides point-anchorage to a borehole extensometer using grouting technique at plurality of points. This essentially consists of an anchor carrying a cement capsule along with it and a device to rupture the capsule at the position of each anchorage point. The rupturing system of the capsule consists of a pivoted knife and a pulling system by means of a thread. A safety arrangement system is provided for preventing the accidental breakage of the grouting capsule during insertion into the borehole along with the extensometer. In case of multiple anchoring, a protective pipe is provided to prevent the rods of preceding anchors from coming in contact with the grout of succeeding anchors.
This invention will be particularly used in conjunction with borehole extensometers to study the movement of strata due to mining or any underground excavation and its process of grouting in the borehole for measurement of roof movement.
Borehole extensometers are widely used in coal mines, metal mines, tunnels and caverns for measuring the relative ground movement occurring due to underground excavation. The measurement is taken from underground and as well as from surface. In general, mechanical type and grouted type anchors are used for anchoring one end of the extensometer rods to the rock mass inside a borehole. The mechanical type instruments are prone to slipping along the sides of the borehole especially when they are installed near blasting areas due to blast
vibration. In case of grouted anchors the full column grouting of borehole is a tedious process.
Extensive efforts have been devoted to the development of various devices for measuring ground movement in mine roofs, tunnels and other underground excavation works. To highlight the wide mining and tunneling usage and continual efforts, which have been made by other inventors to improve the performance of borehole extensometers, a few patent references are provided below for illustration.
Reference may be made to U.S. patent no. 4,242,915 entitled "Extensometer anchor". This invention as illustrated in figure-1 of the drawings accompanying this specification, relates to the field of "Borehole" AND "Extensometer" AND "mine" which comprises of an extensometer anchor for use in a mine borehole. The anchor has an anchor body that, when in an operative mode, is placed in the borehole. Extending at least partially around the outer surface of the body are one or more grooves whose major plane is generally perpendicular to the length of the borehole. Seated within each groove is a compressible resilient anchor member, like a ring, which remains loaded by a retaining device, such as a cotter pin, extending through it. Upon being pulled from outside of the borehole, the retaining device unloads the compressed anchor which then moves to expand outwardly in the borehole and firmly anchor the anchor body and attached extensometer within the mine borehole. The main disadvantage of this system is that it may slip in the borehole due to a nearby blast vibration. More over this is only a mechanical device liable to slide during a borehole getting crushed due to rock stress which is not uncommon.
Reference may be made to another U.S. patent no. 4,514,905 entitled "Convergence extensometer for measuring mine roof subsidence"
wherein an extensometer for measuring changes in the vertical distance between the roof and floor of a mine opening comprising of a pair of rigid telescoping members, a tension spring securing said members to each other in a telescoping relationship, a hook for attaching a non-extensible cable to each of said members, and an indicator for determining telescopic movement of said members. The extensometer of this invention is utilized by securing one of said telescoping members to the roof of the mine and the other telescoping member to the floor of the mine with the axis of said members being disposed along the vertical. The telescoping members are secured, under tension, to the mine roof and floor by means of a non-extendible cable such as a steel cable. The indicator for determining the telescopic movement of the members may be a pair of lugs or flanges or other indicating marks, each member of which pair is affixed to a separate telescoping member. The device is illustrated in figure.2 of the drawings accompanying this specification. The main disadvantage of this system is that it may slip in the borehole due to a nearby blast vibration in the mine.
Reference may be made to yet another U.S. patent no. 5,629,480 entitled "Rock extensometer". In this invention there is an extensometer for use in a borehole, which comprises a combination of linear motion transducers located with daisy wheel anchors, which may be attached together if desired with extension bars. Linkages are used to connect the transducers to the daisy wheel anchors. The transducers are set up to measure distance changes both axially along the hole or radially. The extensometer includes at least one axially measuring transducer, and at least two radially measuring transducers. The transducers change in value according to changes in borehole dimensions; the transducer values are monitored electrically. The main disadvantage of this system is that it may slip in the borehole due to a nearby blast vibration in the mine. The installing mechanism is difficult and cumbersome.
Reference may be made to still another U.S. patent no. 4,463,611 entitled "Extensometer". In this invention a rod extensometer for measuring movements in rock structures and in foundations, the measuring rod system consists of a one piece flexible rod made of reinforced plastic and surrounded by an encasing tube and connected at one end to a fixed-point anchoring device and by its other end to a pick-up element for the measuring value. This design enables the rod extensometer to be inserted into a borehole at short notice and with very little loss of time. Furthermore, the rod can form a practically endless structure wound onto a delivery spool and thus stored and transported with ease and in a space-saving manner. The main disadvantage of this system is that it may slip in the borehole due to a nearby blast vibration in the mine. Moreover this extensometer cannot monitor the rock movement in a continuous manner and need to be activated during measurement time. The process of installation and grouting is difficult and cumbersome.
Reference may be made to U.S. patent no. 4,719,803 entitled "Borehole extensometer" for monitoring relative mass displacements. In this device positionable in a borehole for monitoring relative mass displacements axially along the borehole between at least two spaced-apart anchor points, comprises at least two retrievable anchor members arranged in spaced-apart opposite relationship to define the at least two anchor points, the anchor members each having radially displaceable borehole wall contacting means and including mechanical means for radially outwardly displacing the borehole wall contacting means to engage the borehole wall and thereby fix the anchor member in the borehole against the wall thereof. A linear displacement sensing means is arranged between the anchor members, the displacement sensing means being connected to one of the anchor members and including an elongated axially movable sensor element, the sensor element being normally biased in a direction toward the other anchor member for contact
engagement therewith. Relative mass displacements are transmitted to the sensor element and are measured by the displacement sensing means as a variation in distance between the anchor members within the borehole. The main disadvantage of this system is that it may slip in the borehole due to a nearby blast vibration in the mine. Moreover this extensometer cannot monitor the rock movement in a continuous manner and need to be activated during measurement time.
Therefore with reference US Patent No. 4242915, US Patent No. 4719803, as mentioned above where mechanical type friction gripping arrangement have been made. Further an extensometer with daisy wheel type of mechanical anchors have been designed in US Patent No. 5629480. Though these mechanical type of anchors are easier to install, the main disadvantage of these inventions is that they are prone to slipping along the sides of the borehole especially when they are installed near blasting areas due to vibration. This can lead to erroneous results. Places where heavy blasting are practiced in hard rocks such as large underground caverns and metal mines, it is necessary to grout the anchors using cement to secure a good holding of the anchors on to the rock.
For grouted type of anchoring, especially in multi-point anchoring systems, the general practice has been to completely grout the borehole after exposing the anchors and giving protective covering to the rods. References may be made to US Patent No. 4463611 and US Patent No. 3483745. However the main disadvantage of these inventions is grouting the anchors in the borehole is very tedious process and in certain cases infeasible, when the boreholes are longer and upward. Grouting the anchors in an upward hole requires high-pressure cement injection. Cracks in the rock mass lead to leakage of the cement from the borehole and may not result in proper anchorage. Grouting in a down hole, though
easier, cannot go beyond certain depth regime. Moreover, full installation of such grouted type borehole extensometers takes 2-3 days to allow the cement to dry up in the borehole. Such delay often results in the loss of important rock mass movement data.
If this grouting operation can be done only at the anchor positions using quick setting cement capsules, it will be much easier and quicker to make such installation and to take a quick initial reading. In the past grouting anchors at selective places in the borehole has not been done for the installation of borehole to the best of our knowledge except for a single point anchoring system by borehole grouting (not by a cement capsule) in the reference SI 20088 (Republic of Slovenia).
Hence, it is clear from the hitherto known prior art that there is a definite need to provide a borehole extensometer which can easily and reliably ensure a proper measurement system of strata movement in mine / tunnel excavations.
The main object of the present invention is to provide a multi-point anchoring system for grouted-type borehole extensometer for strata movement measurements in underground excavation, which obviates the drawbacks of the hitherto known prior art as detailed above.
Another object of the present invention is to provide a multi-point anchoring system for grouted-type borehole extensometers using quick or slow setting cement capsules, which obviates the drawbacks of the hitherto known prior art as detailed above.
Yet another object of the present invention is to provide a multi-point anchoring system for grouted-type borehole extensometer for measuring
strata movement in a mine / tunnel roof / side which obviates the drawbacks of the hitherto known prior art as detailed above.
Still another object of the present invention is to provide a multi-point anchoring system for grouted-type borehole extensometer, which can be installed in any direction in an underground opening including upward and downward direction.
Still yet another object of the present invention is to provide a multi-point anchoring system for grouted-type borehole extensometer, which will eliminate the problem of slippage during any ground vibration.
A further object of the present invention is to provide a multi-point anchoring system for grouted-type borehole extensometer, which will eliminate the requirement of hydraulic or pneumatic grout pumps.
A still further object of the present invention is to provide a multi-point anchoring system for grouted-type borehole extensometer, which will reduce the setting time of grouting in the borehole.
Another object of the present invention is to provide a multi-point anchoring system for grouted-type borehole extensometer, which will require less manpower to install.
The extensometer of the present invention consists of anchoring system of multi-point type and can be installed into boreholes drilled to any direction and having a diameter of the order of 49 to 75mm. Up to two anchors are possible in a 49mm diameter hole (AX size), and up to 5 anchors can be installed into 75mm (NX size) borehole. A triple anchoring system in an upward hole is shown in Figure. 3. The extensometer consists of two rubber discs with holes to accommodate various anchors,
steel rods, plastic tubes and threads. The said two rubber discs are fitted by an anchor in a single set. In between two rubber discs there are cement capsule attached in the anchor rod by means of adhesive tapes. This cement capsule can be slit by a pivoted sharp edged knife riveted in the flat portion of the anchor. The knife can be operated by a long thread from outside the borehole. The knife is tied by a safety tape for inadvertent cutting of the capsule. After the cement capsule grouts the system the long steel rods attached with the bottom of the anchor transmits the strata movement to the sensor fitted at the lower ends. For multi-point anchoring in several strata there will be plurality of such sets. A circular lid covers the borehole by means of nut and bolt mechanism tightened with the borehole collar.
Accordingly the present invention provides a multi-point anchoring system for a grouted type borehole extensometer for measurement of strata movement in underground excavation, which comprises a plurality of anchor sets, characterized in that each such anchor set consists of two rubber discs removably fixed at the two ends of an anchor rod having a flat portion wherein is provided a pivoted sharp edged knife capable of being remotely operated by means such as a long thread from outside a borehole, the said rubber discs capable of accommodating a cement capsule attached by means such as adhesive tape to the said anchor in such a manner that the said cement capsule can be slit by the said pivoted sharp edged knife, the said anchor being provided at the bottom with means for connecting extension steel rods capable of transmiting the strata movement to a sensor fitted at the lower end of the said extension rod.
In an embodiment of the present invention, the rubber discs being provided with multiple holes capable of accommodating and allowing to pass through the anchor, extension steel rods, tubes and threads.
In another embodiment of the present invention, the anchor is having threads at both the ends to removably fix the rubber discs by means such as nuts, washers.
In yet another embodiment of the present invention, the anchor rod having a flat portion near the middle wherein is provided a sharp edged knife riveted to enable pivotal movement.
In still another embodiment of the present invention, the knife is covered by a tape as a safety measure to prevent inadvertent cutting of the cement capsule.
In still yet another embodiment of the present invention, the extension steel rods are connected with the anchors by means of connectors to enable transmission of the strata movement to the sensors fitted at the bottom of each steel rod.
In a further embodiment of the present invention, there is provided a borehole collar en suited at the mouth of the borehole.
In a further embodiment of the present invention, there is provided a circular lid with holes for sensors and threads to cover the borehole by tightening by means of nut and bolts with the collar.
In a still further embodiment of the present invention, there is provided a protective pipe to prevent the rods of preceding anchors from coming in contact with the grout of succeeding anchors.
In figures 3 to 5(e) of the drawings accompanying this specification is illustrated an embodiment of the multi-point grouted type borehole
extensometer of the present invention for measuring rock strata movement in an underground excavation.
Figures 3 and 4 of the drawings illustrate the anchoring system of the present invention. In figure 3 is shown a multi-point anchoring system. A detailed cross section of the anchor and the knife is shown in figure 4. Figure 5 shows another view of the anchor behind the cement capsule. Sectional views of the rubber plates to be used with 1st, 2nd, 3rd, 4th and 5th anchors are shown in figures 5a, 5b, 5c, 5d and 5e, respectively.
Each anchoring device consists of a quick setting cement capsule (1) attached to an anchor (3) (3/4" diameter torsion rod made of mild steel). The capsule has been supported by two rubber disks (2a) and (2b) one on the top (2b) and the other on the bottom (2a). Both the rubber disks (2a) and (2b) have a diameter equal to that of the borehole within a clearance of 1mm to allow movement of the anchor assembly during insertion. The bottom disk (2a) is fixed to the bottom of the anchor using a couple of washers (8a) and (8b) on bottom and top respectively and a nut (9a), which would be tightened on a male screw thread cut at the bottom of the anchor (3). The bottom portion of the anchor is further reduced in diameter to fix it to a %" diameter stainless steel rod (21) using a coupling (20). The top rubber disk (2b) is free to move in the down ward direction, but restricted to go upward using a similar washer (8c) and nut (9b) assembly.
The cement capsule (1) will be resting on the bottom rubber plate (2a) and shall be tightly secured to the anchor (3) using 2 or 3 adhesive tapes (19). The position of the anchor with respect to the rubber plate can be decided depending on the borehole size and the number of anchors to be installed in the same borehole. The top rubber plate shall be resting on
the top of the capsule and shall be free to move up and down subject to the top washer (8c) and nut (9b) assembly.
The commercially available cement capsules manufactured in India for the purpose of roof bolting in coal mines have a diameter of 32mm and can be made to a length as required by the mining company. These capsules can have various setting time requirement for hardening of the cement formatting. Time duration of 30 minutes would be sufficient enough for inserting this anchoring system into a borehole of up to 20m length. However, if the time required for inserting all the anchors into the borehole is more than 1 hour, slow setting cement capsules may be used or cement and water may be mixed to form a slurry and filled into tubular plastic bags of 32mm diameter on the site just before installation of borehole extensometer. In such cases the setting time of anchors would be higher.
The commercially available cement capsules in India are used in roof bolting operations by soaking them in water for a few minutes and after they absorbs water they are inserted into the boreholes and punctured by a steel rod (bolt). Following its rupture, the grout hardness in the hole within a duration of 30-60 minutes as specified by the manufacturer. In a quick setting cement capsule, the time between its taking out from water and puncturing it should be less than 10-15 minutes. However, this duration of curing can be increased by the manufacturer.
The capsules (1) inserted into the borehole along with the anchors are ruptured at the point of anchorage by a knife (4). The sharp edge (15) of the knife (4) shall be facing the capsule (1). The knife (4) shall be pivoted to the anchor at its centre using a rivet (5). The anchor is usually circular in cross section; therefore a flat portion (17) is created on its surface where the knife (4) shall be fixed. A guide pin (6) shall be fixed adjacent to
the blunt edge (16) of the knife to restrict its movement in that direction. A hole (14) shall be provided at the top end of the knife to enable a thread (7) to pass through it a couple of times. As the thread is pulled downwards or towards the collar of the borehole, the knife would swing in such a way that the sharp edge (15) of the knife cuts into the capsule, which is secured to the anchor. During insertion of the anchor into the hole, it may so happen that the thread (7) attached to the knife (4) may accidentally cut the capsule and spill the contents. To prevent this, a safety adhesive tape (16) shall be wound around the knife (4) and the anchor (3). Only when the thread is pulled with a sufficient force, the knife first cut across the adhesive taping before puncturing into the capsule. Figure 5 shows another view of the anchor behind the cement capsule.
The thread shall be tied to the hole of the knife (14) with a single knot and shall be attached to the top rubber disc (8b) roughly in the middle by passing through the rubber disc (8b) and by putting a knot (23) on the top of the disc. When the thread is pulled, the top rubber disc squeezes the capsule (1) downward during its puncture. This will enable better evacuation of the contents on to the bottom rubber plate. Since the cement capsule has got a capacity of about 300-400 cm3, the grout would ensure an anchorage of about 10cm in the borehole. The other end of the thread (7) passes through the bottom plate through a 2-3mm diameter hole (11). After passing the thread (7), grease shall be applied to the hole to prevent the leakage of cement grout.
When additional anchors are to be installed, similar anchoring systems are to be inserted into the borehole as shown in figure 3 of the drawings. In such case, the top and bottom rubber discs (2b and 2a respectively) of the subsequent anchors shall be provided with holes of 2-3mm diameter (11) for passing the threads (7) of the preceding anchors. After the threads (7) are passed through the holes (11), grease shall be applied to
these holes (11) to make sure that the cement grout won't leak through it. Sectional views of the rubber plates to be used with 1st, 2nd, 3rd, 4th and 5th anchors are shown in figures 5a, 5b, 5c, 5d and 5e, respectively.
Moreover, holes with a plastic pipe (10) of about Vz" diameter tightly passing through the top and bottom rubber plates shall be provided for passing the stainless steel rods (21) attached to the preceding anchors. The plastic pipes (10) will ensure free movement of the stainless steel rods through the succeeding anchoring system. The plastic pipes (10) would also prevent the grout of the succeeding anchors to come in contact with the stainless steel rods (21).
The collar (12) of the borehole shall be grouted on to the mouth of the borehole before the insertion of the multi-point anchoring system. The threads (7) of all the anchors shall be made to pass through a hole of 4-5mm diameters in the circular lid (13). When all the anchors are positioned and the threads passed through the lid (13) the collar of the borehole (12) shall be closed using the circular lid (13) with nuts and bolts assembly (22).
Now, the cement capsules are ruptured by pulling the threads one by one. After the specified setting time of the cement capsules, the circular lid (13) shall be opened and a suitable mouthpiece shall be attached to the collar for the measurement of the rods position using any electrical/mechanical sensors.
If quicker setting cement capsules are used, the user may not get enough time to install all the anchors at a time. In such case, the anchors can be installed one by one. This could be done using the following procedure:
The entire anchorage system for one anchor can be assembled at the site before the capsule (1) is taken out from water. Moreover, the collar of the borehole is also made ready and one nut-bolt assembly (22) of the circular lid (13) already tightened prior to soaking the cartridge. The circular lid (13) can now be rotated with respect to the nut-bolt assembly (22) to open and close the borehole mouth. The capsule (1) after taking out from water is now fixed between the top (2b) and bottom (2a) rubber discs by two adhesive tapes (19) and the single anchor system is inserted into the borehole. This can be done in a few minutes. The mouth of the borehole can be partially closed by rotating the circular lid (13) with the thread (7) passing through the partially open portion of the borehole mouth. When the thread (7) is pulled, the capsule (1) is broken and the grout surrounds the anchor and is fixed to the borehole wall by about 30 minutes duration.
After the specified hardening time, the borehole mouth is fully opened by rotating the circular lid (13) with respect to the nut-bolt assembly (22). The rod of the first anchor can now be found rigid. The second anchorage system has to be assembled at the site before the capsule is soaked. When the capsule is taken out from water, it is quickly fixed in its position with two adhesive tapes (19) and the second anchoring system is inserted into the borehole by passing the rod of the first anchorage system through the protective plastic pipe (10) of the second anchorage system. Subsequent anchors can also be installed in the similar fashion.
The novelty of the multi-point anchoring system for grouted type borehole extensometer using quick setting cement capsules of the present invention for measuring rock strata movement in an underground excavation, resides in its usefulness for grouting of plurality of anchors in several rock layers, through simple cost-effective constructional features
and ease of installation requiring less manpower, less electricity cost and having low cost of manufacture.
Another novelty of the present invention is that it does not require very skilled labour in installation. It will also take less time to install, which may be at par with the state of the art extensometers used else where.
Yet another novelty of the present invention is that this extensometer ensures good grouting at the anchor point as a result there will be a homogeneous strength in the grout to bind the anchor and the rock layers at predetermined distance.
Still another novelty of the present invention is that this extensometer will prevent slippage of the anchors during any blast vibration.
Yet still another novelty of the present invention is that the design of the extensometer is such that it will prevent inadvertent slit of the cement capsule at unwanted place.
The novelty of the multi-point anchoring system for grouted type borehole extensometer using quick setting cement capsules of the present invention for measuring rock strata movement in an underground excavation, has been realized by the non-obvious inventive step of providing in combination a set of anchors with independent grout materials in form of quick setting capsules in between a pair of rubber discs fitted at the two ends of an anchor. The capsule can be slit at any predetermined position inside the borehole. The anchor is designed in a noble manner by flattening a part of it to accommodate the sharp knife, which can be operated by means of long thread from outside the borehole. There is a safety tape tying the knife to prevent inadvertent cutting of the capsules or the thread. In the hitherto known prior art, there
are no such sharp knife which act as cutters/mixers of the grout material inside the borehole. The presence of several such anchors enables anchoring of the extensometer at several points independently at predetermined place.
The main advantages of the novel multi-point anchoring system of the present invention as described herein above are as follows:
1. The multi-point anchoring system described above has got
applicability in a gamut of rock mechanics applications including
underground metal mine, underground coal mines, tunnels and
caverns.
2. Since the anchors are grouted, error caused by slippage of
anchors due to blasting vibration in the vicinity of the extensometer
is avoided. Therefore it ensures error free readings.
3. Easier and quicker to install in comparison to the existing full
column grouted type multi-point borehole extensometers.
4. Since the grouting is selective and only at the anchors, it can easily
be installed in deeper holes.
5. Applicability in boreholes drilled upwards as well as downwards.
6. Faster installation allows the user to start the measurement of rock
mass deformation much earlier.
7. It requires less manpower to make the installation.
8. A hydraulic or pneumatic pump is not necessary for the grouting of
the anchors. Minimal facilities are needed at the installation site.
9. All the parts involved in the anchoring system are easily and
commercially available and therefore easy to manufacture and
would be cheaper.

We claim:
1. A multi-point anchoring system for a grouted type borehole extensometer for measurement of
strata movement in underground excavation, which comprises a plurality of anchor sets (3),
characterized in that each such anchor set consists of two rubber discs(2a,2b) being removably
fixed at the two ends of an anchor rod having a flat portion wherein is provided a pivoted sharp
edged knife(4) so as to remotely operated by means such as a long thread from outside a
borehole, the said rubber discs accommodating a cement capsule(l) attached by means such as
adhesive tape (19) to the said anchor in so that the said cement capsule being slit by the said
pivoted sharp edged knife (15), the said anchor being provided at the bottom with means for
connecting extension steel rods (21) so as to transmit the strata movement to a sensor fitted at
the lower end of the said extension rod.
2. A multi-point anchoring system as claimed in claim 1, wherein the rubber discs being
provided with multiple holes for accommodating and allowing to pass through the anchor,
extension steel rods, tubes and threads.
3. A multi-point anchoring system as claimed in claim 1-2, wherein the anchor is having threads
at both the ends to removably fix the rubber discs by means of nuts (9a, 9b), washers (8a,8b).
4. A multi-point anchoring system as claimed in claim 1-3, wherein the anchor rod having a flat
portion near the middle wherein is provided a sharp edged knife riveted to enable pivotal
movement.
5. A multi-point anchoring system as claimed in claim 1-4, wherein the knife is covered by a
tape as a safety measure to prevent inadvertent cutting of the cement capsule.
6. A multi-point anchoring system as claimed in claim 1-5, wherein the extension steel rods are
connected with the anchors by means of connectors to enable transmission of the strata
movement to the sensors fitted at the bottom of each steel rod.
7. A multi-point anchoring system as claimed in claim 1-6, wherein is provided a borehole
collar(12) suited at the mouth of the borehole.
-18-
•
8. A multi-point anchoring system as claimed in claim 1-7, wherein is provided a circular lid(13)
with holes for sensors and threads to cover the borehole by tightening by means of nut and bolts
with the collar.
9. A multi-point anchoring system as claimed in claim 1-8, wherein is provided a protective
pipe(lO) to prevent the rods of preceding anchors from coming in contact with the grout of
succeeding anchors.
Dated this 17"^ March 2006
(Chetan Kumar)
Scientist,
IPMD,CSIR
-19-

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Patent Number

268353

Indian Patent Application Number

768/DEL/2006

PG Journal Number

35/2015

Publication Date

28-Aug-2015

Grant Date

27-Aug-2015

Date of Filing

22-Mar-2006

Name of Patentee

COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH

Applicant Address

ANUSANDHAN BHAWAN, RAFI MARG, NEW DELHI - 110001, INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	LOUI JOHN PORATHUR	CENTRAL MINING RESEARCH INSTITUTE BARWA ROAD, DHANBAD, JHARKHAND, INDIA-826001
2	PAUL BISWAJIT	CENTRAL MINING RESEARCH INSTITUTE BARWA ROAD, DHANBAD, JHARKHAND, INDIA-826001

PCT International Classification Number

E21B 49/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA