Title of Invention

A RETRIEVABLE ELECTRO-MECHANICAL BROEHOLE EXTENSOMETER

Abstract

A retrievable electro-mechanical borehole extensometer which comprises measuring point anchor(s) (14) having threading on both the ends , characterised in that one end of the said anchor being fixed to one or more extension rods (15) through coupling (17) depending upon the depth of measurement desired, each set of said extension rod(s) and coupling (s) being covered by a rigid pipe (16) in such a manner so as to allow free movement of the extension rod, each of the said such set of anchor, coupling(s), extension rod(s), rigid pipe is passed through a hole in a globular spacer (18) of diameter little less than the borehole (11) diameter, the said globular spacer having a plurality of such holes for allowing multiple measuring anchors to the placed at various depths without touching each other, the complete set consisting of a plurality of measuring point anchor, globular spacer, coupling(s), extension rod(s) and rigid pipe being kept firmly inside a borehole (11), in which measurements are to be taken, by means of a guide pipe (12) matching borehole (11), the guide pipe being provided at its top end with a annular collar (19) having at least two guide pipe anchors (13), the top ends of the extension rods being fixed to a set of known linear variable differential transducer (LVDT) housed in the mouthpiece (21) for measuring the rock displacements.

Full Text

This invention relates to a retrievable electro-mechanical borehole extensometer useful for monitoring rock mass movement at various depths in side the rock mass in a borehole. This invention particularly relates to an improved groutable type electro-mechanical borehole extensometer with retrievable extension rods and having air vent for providing air lock free grouting. The Borehole Extensometer, is an instrument installed in a borehole for monitoring several parameters, such as, (i) deep seated movement of rock mass at one or several locations around an underground opening, (ii) joint seperation around an underground opening, (iii) ground subsidence over a depillared mine working, (iv) surface settlement, (v) settlements of surface structures (vi) stability of rock slopes,etc. The current borehole extensometer is depicted in Fig. 1 of the drawings accompanying this specification. Two measuring points depicted by anchors (2) have been shown in Fig.l. Various components and corresponding numbers marked on the figure 1 in the drawings are as follows: 1. Borehole in which the current extensometer is installed 2. Anchor 3. Extension rod for transferring the movement upto the borehole mouth 4. PVC pipe to cover the extension rods 5. Collar head with guide pipe 6. Hollow space in guide pipe to house Linear Variable Differential Transducer (LVDT) 7. LVDT cable exit 8. Observation arrangements 9. Cap with handle 10. Grout The current borehole extensometer has the problem of jumbling of extension rods inside the borehole (1). The movement of the rock mass, therefore, is not correctly transferred to the surface. To overcome this problem, spacers (18) has been designed and developed in the present invention. The other problem in current borehole extensometer is that once the extensometer is installed its range can not be increased. This is because of the accessibility up to the LVDTs' which are housed in a hollow space (6) in guide pipe (5) pushed in the borehole (1). This problem has also been removed in the present invention. The third problem in the current borehole extensometer is that once the extensometer is installed it can not be reused. Its use is thus discouraged for short-term monitoring on cost considerations resulting into the loss of useful information. The main object of the present invention is to provide a retrievable electro-mechanical borehole extensometer which obviatss the drawbacks of the hitherto known borehole extensometers. Another object of the present invention is to provide a retrievable electro-mechanical borehole extensometer having both direct readout and electrical readout facilitites. Yet another object of the present invetion is to provide spacers to avcid touching of one set of extension rod and anchor from the other set of rod and anchor. Still another object of the present invention is to provide anchor which overcomes the grouting problems of deepest monitoring point in the vertically upward hole. This electro-mechanical borehole extensometer of present invention is first of its kind in the World. The Retrievable Electro-Mechanical Boerehole Extensometer of the present invention is depicted in Figs. 2, 3 and 4 of the drawings accompanying this specification. In Fig. 2 only two anchors have been shown because of clarity. However, upto eight anchors can be fixed. Various components and corresponding numbers marked on the figures in the drawings are as follows: 11. Borehole in which the extensometer is to be installed 12. Guide pipe 13. Guide pipe anchor 14. Anchor to be attached to extension rod 15. Stainless steel extension rod or movement transferring element 16. Rigid pipe to cover extension rod 17. Extension rod coupling 18. Ball shaped Spacer (18a) hole for air duct (18b) hole for clamping the anchor (18c) holes for other extension rods (18d) hole for grout pipe (18e) clamping screw 19. Annular Collar of guide pipe 20. Arrangement to facilitate the grouting of deepest anchor 21. Kouthpiece housing LVDT and other measuring arrangements 22. Protection cap having spring loaded arrangement 23. Bottom annular collar in the mouthpiece Accordinglythe present invention provides a retrievable electro-mechanical borehole extensometer which comprises measuring point anchor (14) having threading on both the ends Accordingly the present invention provides a retrievable electro-mechanical borehole extensometer which comprises measuring point anchor(s) (14) having threading on both the ends , characterised in that one end of the said anchor being fixed to one or more extension rods (15) through coupling (17) depending upon the depth of measurement desired, each set of said extension rod(s) and coupling (s) being covered by a rigid pipe (16) in such a manner so as to allow free movement of the extension rod, each of the said such set of anchor, coupling(s), extension rod(s), rigid pipe is passed through a hole in a globular spacer (18) of diameter little less than the borehole (11) diameter, the said globular spacer having a plurality of such holes for allowing multiple measuring anchors to the placed at various depths without touching each other, the complete set consisting of a plurality of measuring point anchor, globular spacer, coupling(s), extension rod(s) and rigid pipe being kept firmly inside a borehole (11), in which measurements are to be taken, by means of a guide pipe (12) matching borehole (11), the guide pipe being provided at its top end with a annular collar (19) having at least two guide pipe anchors (13), the top ends of the extension rods being fixed to a set of known linear variable differential transducer (LVDT) housed in the mouthpiece (21) for measuring the rock displacements. In an embodiment of the present invention the deepest measuring anchor may be provided with an extension rod at the bottom/farther end (20) for fixing an air vent. In another embodiment of the present invention a grout pipe may be provided with the measuring anchor of the deepest measurement point. In yet another embodiment of present invention the top ends of the extension rods may be passed through a common globular spacer. The following steps should be followed for installing the borehole extensometer of the present invention: STEP l: The guide pipe (12) is inserted in the borehole (11) and embedded with the rock mass by grouting the guide pipe anchors (13) attached to the annular collar (19) of the guide pipe. STEP 2: The extension rod (15) is attached to anchor (14) with the help of coupling (17), and the rigid pipe (16) is pushed over the extension rod leaving anchor (14) exposed. The other end of rigid PVC pipe, which covers the extension rod, is inserted in the hole having clamping arrangement (18b) of the spacer (18). The spacer is then clamped to the rigid pipe near the junction of the anchor and the PVC pipe. Clamping is done by tightening the screw (18e) provided for this purpose on the ball shaped spacer (18) as shown in Fig. 3. The anchor (14) is then inserted in the borehole. Both the extension rods and the rigid PVC pipes are made available in small pieces of varying lengths for adjusting the position of anchors (14) in the borehole. Using the extension rod coupling (17), the next piece of extension rod is attached to the exposed end of the extension rod and the extension rod is again covered with the rigid pipe. Thick rigid pipe pieces have arrangement at its two ends for joining the subsequent pieces of pipe. This way, by fixing the extension rods and covering it with rigid pipes, the anchor is placed at the desired position inside the borehole. The other end of the extendion rod is kept above the guide pipe annular collar. All the anchors are fixed at the desired locations in this manner. While inserting the second anchor i.e. anchor no. 2, it must be kept in mind that extension rod end of anchor 1 i.e. the previously installed anchor should pass through one of the holes of spacer (18c) and anchor no. 2 will pass through the clamping hole (18b). Finally, at the time of fixing anchor no. 5, the extension rod ends of earlier installed 4 anchors would pass through the 4 holes (18c) of the spacer and anchor no. 5 would pass through the clamping hole of the spacer (18b). Therefore, the number of spacers used in one instrument is equal to the number of anchors. The diameter of holes in the spacer (18b and 18c) is kept slightly more than the outer diameter of the rigid pipe (16) for smooth sliding of spacer over rigid pipe. This type of spacer has solved the problem of jumbling of extension rods inside the borehole. In this system the extension rods are joined together with the clockwise rotation whereas the attachment of extension rod with the anchor requires anticlock-wise rotation. This reverse direction of rotation enables retrieval of the extension rods at a later stage when the purpose of the instrument is fulfilled. STEP 3: After installing the anchors, the borehole is grouted using a grout mixture of cement-water slurry. The purpose behind covering the extension rods with rigid pipes is to keep the extension rods free to transfer the movement of the anchor (14) to the borehole annular collar (or in other words the movement of the rock mass because the anchor is grouted with the rock mass). STEP 4: After the grout is set, each extension rod is connected to the mouth piece (21) having magnetic sensor of the linear variable differential transducer (LVDT). Finally, the guide pipe collar (19) is clamped to the bottom annular collar of the mouth piece (23). This way the mouth piece is attached to the rock mass and the instrument is made ready for observations. STEP 5: Using mechanical readout, the distances between the reference points and the extension rod head fitted inside the mouthpiece are measured regularly to calculate relative displacements of the anchors (14). Using electrical readout, the movements of the magnetic sensors with respect to the fixed LVDTs are measured. Since magnetic sensors are attached to the rods used for mechanical observation and the LVDTs are attached to the mouthpiece which is the refernce point, both the electrical and the mechanical readout will provide the same relative displacement values. The present invention has the provisions of repairing or replacing the LVDTs, if found faulty and of increasing the range of the instrument, if the movements are found to be more than the set range. The main advantages of the Retrievable Electro-Mechanical Borehole Extensometer of the present invention are as follows: (i) Jumbling of extension rods in boreholes is eliminated to improve the reliability of the system. (ii) Except the grout pipe, guide pipe, rigid pipe and the anchors, all other components can be retrieved from a borehole for reuse. (iii) The design eliminates the problem of grouting of the deepest anchor in specially vertically upward boreholes. (iv) Design facilitates accessibility to increase the measurement range at a later stage. (v) It provides both direct mechanical readout and remote electrical readout facilities. (vi) It is possible to check the reliability of the electrical system before approach facility to the instrument is with drawn. Claim: 1. A retrievable electro-mechanical borehole extensometer which comprises measuring point anchor(s) (14) having threading on both the ends, characterised in that one end of the said anchor being fixed to one or more extension rods (15) through coupling (17) depending upon the depth of measurement desired, each set of said extension rod(s) and coupling (s) being covered by a rigid pipe (16) in such a manner so as to allow free movement of the extension rod, each of the said such set of anchor, coupling(s), extension rod(s), rigid pipe is passed through a hole in a globular spacer (18) of diameter little less than the borehole (11) diameter, the said globular spacer having a plurality of such holes for allowing multiple measuring anchors to the placed at various depths without touching each other, the complete set consisting of a plurality of measuring point anchor, globular spacer, coupling(s), extension rod(s) and rigid pipe being kept firmly inside a borehole (11), in which measurements are to be taken, by means of a guide pipe (12) matching borehole (11), the guide pipe being provided at its top end with a annular collar (19) having at least two guide pipe anchors (13), the top ends of the extension rods being fixed to a set of known linear variable differential transducer (LVDT) housed in the mouthpiece (21) for measuring the rock displacements. 2. An extensometer as claimed in claim 1 wherein the deepest measuring anchor is provided with an extension rod at the bottom/farther end for fixing an air vent (20). 3. An extensometer as claimed in any of the claims 1 to 2 wherein a grout pipe is provided with the measuring anchor of the deepest measuring point. 4. An extensometer as claimed in any of the claims 1 to 3 wherein the top ends of the extension rods are passed through a common globular spacer (18). 5 A retrievable electro-mechanical borehole extensometer substantially as herein described with reference to figures 2,3 and 4 of the drawings accompanying this specification.

Documents:

2632-del-1996-abstract.pdf

2632-del-1996-claims.pdf

2632-del-1996-complete specification (granted).pdf

2632-del-1996-correspondence-others.pdf

2632-del-1996-correspondence-po.pdf

2632-del-1996-description (complete).pdf

2632-del-1996-drawings.pdf

2632-del-1996-form-1.pdf

2632-del-1996-form-19.pdf

2632-del-1996-form-2.pdf

2632-del-1996-form-4.pdf