CN112985982B - Electrical method monitoring device suitable for true triaxial loading and use method thereof - Google Patents
Electrical method monitoring device suitable for true triaxial loading and use method thereof Download PDFInfo
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Abstract
The invention discloses an electrical monitoring device suitable for true triaxial loading, which comprises an electrode mounting plate fixed on a loading plate, wherein a plurality of threaded holes which are used for mounting an electrode body and are uniformly distributed in a rectangular array are formed in the electrode mounting plate, a plurality of wire grooves which are used for connecting the end points of threaded holes in the same row or in the same line in series are formed in one side surface, which is attached to the loading plate, of the electrode mounting plate, and the two ends of each wire groove respectively extend to the edge of the electrode mounting plate.
Description
Technical Field
The invention relates to the field of indoor mechanical and electrical characteristic experiments of coal rock masses, in particular to an electrical method monitoring device suitable for true triaxial loading and a using method thereof.
Background
At present, underground geotechnical engineering relates to underground mining, natural gas, petroleum and other energy exploitation, meanwhile, construction activities of tunnels and underground caverns are influenced, deep geotechnics bear forces in three orthogonal directions, and ground stress can be truly simulated under the condition of true triaxial loading in laboratories, namely maximum main stress, middle main stress and small main stress. The stress state of the underground rock soil can be disturbed under any mining conditions, the internal structure of the rock is changed, the electrical characteristics of the rock are changed, for example, the development of the fracture can cause the increase of the resistivity, and if the rock fracture is fully developed, the self strength is reduced, and dynamic disasters such as rock burst and the like can be generated under the high stress state. The magnitude and complexity of the foreign stress increase with the increase of the burial depth, and the damage forms are also complex and various, so that the research on the electrical characteristics of the whole process of coal rock damage under the three-dimensional confining pressure condition is very important.
The hydraulic fracturing technology which is one of the technical means for mining and utilizing deep environmental resources is very important, the technology improves the permeability of rock strata in oil extraction activity, the technology enables the coal strata to achieve the purposes of permeability increasing and pressure relieving in coal mining activity, the damage of the hydraulic fracturing technology to a target rock mass can also cause the change of the electrical characteristics of the rock mass, particularly, the fracturing liquid as a low-resistance body has obvious response in electrical method monitoring, and support is provided for the evaluation of the influence range of the electrical method monitoring hydraulic fracturing technology. Therefore, the study on the electrical characteristic change and crack propagation of the hydraulic fracturing process is also very important. In order to effectively simulate the electrical characteristics of rock disturbance damage and hydraulic fracture range monitoring in deep mining activities, many scholars study the electrical characteristics of coal rock bodies under the condition of triaxial loading.
In a sample of a rock fracturing experiment under a true triaxial condition, in order to achieve better research on a crack expansion rule and electrical characteristic change, many scholars mix similar materials according to the mechanical characteristics of coal and rock masses, pour the materials in a mould, bury an electrode or a probe in an unset sample, or perform hole digging and groove digging treatment on the basis of raw coal and raw rock so as to install the electrode and the probe. In this case, a simulation experiment is performed under a true triaxial loading condition, and thus, a crack propagation and electrical property change rule is expected. However, in such an operation mode, the physical structure and chemical properties of the coal rock are easily changed, the integrity of the coal rock is damaged, and large deviation is generated in the simulation of the field environment. And at present, the electrical characteristics of the coal rock mass under the condition of a single shaft or a true triaxial are measured, and due to the fact that the installation is inconvenient, a small number of probes or electrodes are mostly adopted for monitoring, the obtained data volume is small, and the change characteristics of the hydraulic fracturing process of the coal rock mass are difficult to comprehensively research. Chinese patent CN105716954A discloses a crack form electrical monitoring method for hydraulic fracturing simulation experiment, which adds a plurality of conductive graphite rod arrays during cement casting, injects fracturing fluid into the test piece after the formation and consolidation, and determines the crack development condition by measuring the resistance change of each resistivity, but this way makes the electrode unable to be recovered, resulting in material waste, and the measurement mode is more traditional, and it is difficult to obtain accurate data with high efficiency.
Disclosure of Invention
Aiming at the technical defects, the invention aims to provide an electrical method monitoring device suitable for true triaxial loading and a using method thereof.
In order to solve the technical problems, the invention adopts the following technical scheme:
the invention provides an electrical monitoring device suitable for true triaxial loading, which comprises an electrode mounting plate fixed on a loading plate, wherein a plurality of threaded holes which are uniformly distributed in a rectangular array and used for mounting an electrode body are formed in the electrode mounting plate, a plurality of wire grooves used for connecting the end points of threaded holes in the same row or the same line in series are formed in one side surface of the electrode mounting plate, which is attached to the loading plate, two ends of each wire groove respectively extend to the edge of the electrode mounting plate, the electrode body comprises a metal probe, a probe cap is nested at the upper end of the metal probe, a spring is compressed between the upper end surface of the metal probe and the top surface of the inner cavity of the probe cap, two inverted r-shaped sliding grooves are symmetrically arranged on the side surface of the probe cap, two sliding bolts which are matched with the inverted r-shaped sliding grooves and used for limiting the downward maximum displacement of the probe cap are arranged on the side surface of the metal probe, and a wire hole communicated with the inner cavity of the probe cap is formed at the top end of the probe cap, the outer wall of the probe cap is provided with external threads matched with the threaded hole, the metal probe is connected with a lead, and the lead passes through the inner cavity of the probe cap and the lead hole and then extends to the edge of the electrode mounting plate along the wire groove.
Preferably, the height of the sliding bolt on the side edge of the metal probe does not exceed the outer diameter of the probe cap.
Preferably, the electrode mounting plate and the probe cap are made of high-strength metal materials, the surfaces of the electrode mounting plate and the probe cap are subjected to insulation paint spraying treatment, the electrode mounting plate is rectangular, and chamfers are arranged at the edges of the electrode mounting plate and the probe cap.
Preferably, the electrode mounting plate is fixedly connected with the loading plate through bolts, and threaded holes for the bolts to pass through are respectively formed in four corners of the electrode mounting plate and the loading plate.
Preferably, the threaded hole is filled and compressed by adopting a hole bolt, the hole bolt is made of a high-strength metal material, and the surface of the hole bolt is subjected to insulating paint spraying treatment.
The invention also provides a using method of the electrical monitoring device suitable for true triaxial loading, which specifically comprises the following steps:
s1: determining the material and the dimension specification of the rock sample for the experiment;
s2: determining the number and the size of the electrode mounting plates according to the dimension specification and the experimental scheme of the rock sample, determining the arrangement mode and the number of the electrode bodies on the electrode mounting plates, and marking the mounting positions and the serial numbers of the electrode bodies;
s3: installing the electrode bodies in the threaded holes according to the position requirement, and enabling the metal probe of each electrode body to be higher than the plane of the electrode installation plate;
s4: the lead is connected with the metal probe, passes through the spring and the lead hole, is led out from the threaded hole and extends to the edge of the electrode mounting plate along the wire groove;
s5: filling and flattening the hole plugs without the electrode bodies by using the hole plugs, wherein the mounting heights of the hole plugs are flush with the surface of one side of the electrode mounting plate, and then fixing the electrode mounting plate on a loading plate by using bolts;
s6: placing a rock sample in a true triaxial loading cavity, connecting a lead with an electrical method instrument, opening the electrical method instrument, starting loading confining pressure by a loading plate, and maintaining stability when the pressure reaches a designed axial pressure sigma 1, a maximum horizontal pressure sigma 2 and a minimum horizontal pressure sigma 3;
s7: continuously increasing the axial pressure sigma 1, and carrying out an overall process electrical method monitoring experiment of true triaxial loading fracture of the rock sample;
s8: and after the rock sample is unstably damaged, stress loading is finished, confining pressure of the loading plate is removed, then the electric method instrument is closed to take out the rock sample, the electrode mounting plate is disassembled, the electrode body is recovered, the fracture effect is analyzed and evaluated, and the electric method monitoring experiment of true triaxial loading damage is completed.
Preferably, in the step 3, one end of the metal probe in each electrode body, which extends out of the electrode mounting plate, is 3-5 mm higher than the plane of the electrode mounting plate.
The invention has the beneficial effects that:
1. the electrode mounting plate designed by the invention is arranged between a rock sample and a loading plate, has the functions of load transmission and compression resistance insulation, and is convenient for multi-position flexible installation of the electrode body through the threaded holes which are arranged at equal intervals transversely and longitudinally, so that the electrical property change characteristics of the rock sample can be monitored comprehensively and three-dimensionally;
2. the wire groove can provide space for a wire, so that the wire is prevented from being deformed and damaged by compression, the hole bolt can improve the flatness of the electrode mounting plate, and the uniform stress in the rock sample loading process is ensured;
3. the side surface of a probe cap in the electrode body is provided with an inverted r-shaped sliding chute, so that the metal probe can conveniently slide axially and be damaged and replaced, the spring has a buffer effect on the metal probe contacting a rock sample, and the metal probe can be stably attached to the surface of the rock sample through the elasticity of the spring;
4. the size of the electrode mounting plate and the number of the threaded holes are not fixed, the electrode mounting plate can be manufactured according to the specification of the loading cavity and the size of a rock mass sample, but the electrode body corresponds to the threaded holes, so that the electrode body can be recycled;
5. the edge of the electrode mounting plate is provided with the chamfer, so that safe displacement of the true triaxial loading edge loading plate is facilitated, and space is provided for leading the wire out of the loading cavity.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a front view of an electrode mounting plate and an electrode body mounted in a true triaxial loading chamber in a loading failure experiment according to embodiment 1 of the present invention;
fig. 2 is a top view of the position where the electrode mounting plate and the electrode body are mounted in the true triaxial loading chamber in the hydraulic fracturing experiment provided in embodiment 2 of the present invention;
fig. 3 is a front view of the electrode mounting plate and electrode body combination provided in embodiment 1 of the present invention;
fig. 4 is a left side view of the electrode mounting plate and electrode body combination provided in embodiment 1 of the present invention;
fig. 5 is a top view of the combination of the hole bolt and the electrode mounting plate and the electrode body provided in example 1 of the present invention;
fig. 6 is a schematic structural diagram of a metal probe provided in embodiment 1 of the present invention.
Description of reference numerals:
1. loading a cavity by true triaxial; 2. a loading plate; 3. a water injection pipe; 4. an electrode mounting plate; 5. a bolt; 6. a rock sample; 7. a threaded hole; 8. a wire slot; 9. a hole bolt; 10. chamfering; 11. an electrode body; 12. a metal probe; 13. a spring; 14. a probe cap; 15. an inverted r-shaped chute; 16. a wire guide hole; 17. an external thread; 18. a wire; 19. a sliding bolt; 20. an electrical method instrument; 21. a seal ring; 22. a hole sealing section.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Embodiment 1: the rock sample 6 is subjected to an electrical method detection experiment of a failure process under a true triaxial condition, as shown in fig. 1 and fig. 3-6, the rock sample 6 with the size of 500 x 500mm is selected; determining the length, width and thickness of the electrode mounting plates 4 to be 500 × 20mm according to the size of the rock sample 6, determining 4 positions of the 4 electrode mounting plates 4 which are respectively mounted on the front end face, the rear end face, the left end face and the right end face of the rock sample 6, and respectively arranging 15 × 15 threaded holes 7 of 225 in each electrode mounting plate 4 in the transverse direction and the longitudinal direction;
aiming at the electrode mounting plates 4 on the front end face and the rear end face of the rock sample 6, 15 electrode bodies 11 are respectively arranged on the 4 th column, the 8 th column and the 12 th column on the transverse position of the electrode mounting plates 4, the total number of the electrode bodies 11 is 90, and the serial numbers of the electrodes are marked on the two electrode mounting plates 4 in sequence, wherein the serial numbers of the electrodes are 1-90;
for the electrode mounting plates 4 on the left end face and the right end face of the rock sample 6, 15 electrode bodies 11 are respectively arranged on the 4 th column, the 8 th column and the 12 th column of the transverse position of the electrode mounting plates, 90 electrode bodies 11 are in total, and the serial numbers are marked continuously and are 91-180, so that the total number of the required electrode bodies 11 is 180;
when the electrode body 11 is assembled, the lead wire 18 firstly passes through the lead wire hole 16 of the probe cap 14 and the spring 13 and is connected with the metal probe 12, then the spring 13 is inserted into the probe cap 14, and the sliding bolt 19 of the metal probe 12 is installed along the opening end of the inverted-r-shaped chute 15, so that the metal probe 12 can move up and down along the inverted-r-shaped chute 15.
A lead 18 is inserted through the threaded hole 17 with the corresponding number, the electrode body 11 is installed from one side of the contact surface of the electrode installation plate 4 and the rock sample 6, each metal probe 12 is kept higher than the end surface of the electrode installation plate 4 by 3mm when the electrode body 11 is installed, the lead 18 penetrates through a lead hole 16 after being connected with the metal probes 12 and is led to the edge of the electrode installation plate 4 along a wire groove 8, then the threaded hole where the electrode body 11 is not arranged is filled and leveled by using a hole bolt 9, the electrode installation plate 4 is installed on the loading plate 2 by using a bolt 5, and the lead 18 is connected with an electrical instrument 20;
placing a rock sample 6 in a true triaxial loading cavity 1, insulating the upper surface and the lower surface of the rock sample 6, starting an electrical method instrument 20, applying confining pressure by a loading plate 2 to ensure that axial pressure sigma 1 is 50MPa, maximum horizontal pressure sigma 2 is 45MPa, minimum horizontal pressure sigma 3 is 40MPa, and keeping the axial pressure sigma 1, the maximum horizontal pressure sigma 2 and the minimum horizontal pressure sigma 3 stable;
and then continuing increasing the axial pressure until the rock sample 6 is unstable and cracked, stopping stress loading, further collecting electrical parameters of the whole process of an elastic stage, a plastic stage and the like under the triaxial loading of the 500 x 500mm rock under a true triaxial condition, removing confining pressure when a fracturing experiment is completed, closing the electrical instrument 20, processing and analyzing data, taking out the rock sample 6, then detaching the electrode mounting plates 4 at 4 positions, and recovering, cleaning and airing the electrode body 11 so as to be convenient for next use.
Embodiment 2: an electrical monitoring experiment of a rock sample 6 in a hydraulic fracturing process under a true triaxial condition is shown in fig. 1, 3-6;
selecting a rock sample 6 with the size of 300 x 300mm, processing and drilling a central hole with the diameter of 20mm and the depth of 200mm, adopting a water injection pipe 3 with the pipe diameter of 18mm, and installing a high-strength sealant and a sealing ring 21 in the central hole to form a hole sealing section 22;
determining the length, width and thickness of the electrode mounting plates 4 to be 300 × 20mm according to the rock sample 6, selecting 5 electrode mounting plates 4 to be respectively mounted at 5 positions of the front end face, the rear end face, the left end face, the right end face and the lower end face of the rock sample 6, and respectively arranging 9 × 9 threaded holes 7 in the transverse direction and the longitudinal direction of each electrode mounting plate 4;
aiming at an electrode mounting plate 4 on the front end face of a rock sample 6, respectively arranging 9 electrode bodies 11 on the 3 rd column and the 7 th column in the transverse position of the electrode mounting plate 4, and then sequentially marking electrode serial numbers 1-18 on the electrode mounting plate 4;
for the electrode mounting plate 4 on the rear end face of the rock sample 6, 9 electrode bodies 11 are respectively arranged on the 3 rd row and the 7 th row of the transverse position of the electrode mounting plate and are marked with serial numbers of 19-36;
for the electrode mounting plate 4 on the left end face of the rock sample 6, 9 electrode bodies 11 are respectively arranged on the 3 rd row and the 7 th row in the longitudinal direction, and the serial numbers are edited to be 37-54;
aiming at an electrode mounting plate 4 on the right end face of a rock sample 6, respectively arranging 9 electrode bodies 11 on a longitudinal 3 rd row and a longitudinal 7 th row, and editing serial numbers to be 55-72;
for the electrode mounting plate 4 on the lower end face of the rock sample 6, 9 electrode bodies 11 are arranged in the 7 th row at the transverse position 3, and the serial numbers are edited to be 73-90, so that the total number of the required electrode bodies 11 is 90.
Sequentially mounting the electrode body 11 in threaded holes 7 with the number of 1-90 of the five electrode mounting plates 4 according to the number, passing a lead wire 18 through the threaded holes 7 with the corresponding number, mounting the electrode body 11 from the side of the contact surface of the electrode mounting plate 4 and the rock sample 6, and keeping each metal probe 12 higher than the side surface of the electrode mounting plate 4 by 3mm when mounting the electrode body 11; all the leads 18 are led to the edge of the electrode mounting plate 4 along the wire grooves 8, then the hole bolts 9 without the electrode bodies 11 are filled and leveled by using the hole bolts 9, the electrode mounting plate 4 is mounted on the loading plate 2 by using the bolts 5, and the leads 18 are connected with an electrical method instrument 20;
placing a rock sample 6 in a true triaxial loading cavity 1, insulating the upper surface of the rock sample 6, starting an electrical method instrument 20, applying confining pressure by using a loading plate 2, and keeping the axial pressure sigma 1 equal to 30MPa, the maximum horizontal pressure sigma 2 equal to 25MPa, the minimum horizontal pressure sigma 3 equal to 20MPa stable; then inputting high-pressure water into the water injection pipe 3, and collecting the electrical parameters of the whole process of fracture initiation, crack propagation and the like of the 300-300 mm rock hydraulic fracturing under the true triaxial condition;
when the fracturing experiment is completed, stop water injection earlier, then unload confined pressure, close electrical method instrument 20 again, handle the analysis to data, take out rock sample 6, dismantle 5 electrode mounting panels 4 of position again, retrieve and wash and dry the electrode body 11 to use next time.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (7)
1. An electrical method monitoring device suitable for true triaxial loading is characterized by comprising an electrode mounting plate (4) fixed on a loading plate (2), wherein the electrode mounting plate (4) is provided with a plurality of threaded holes (7) which are used for mounting an electrode body (11) and are uniformly distributed in a rectangular array, one side surface of the electrode mounting plate (4) attached to the loading plate (2) is provided with a plurality of wire grooves (8) used for connecting end points of the threaded holes (7) in the same row or the same line in series, two ends of each wire groove (8) respectively extend to the edge of the electrode mounting plate (4), the electrode body (11) comprises a metal probe (12), the upper end of the metal probe (12) is nested with a probe cap (14), a spring (13) is compressed between the upper end surface of the metal probe (12) and the top surface of an inner cavity of the probe cap (14), and two inverted r-shaped chutes (15) are symmetrically arranged on the side surface of the probe cap (14), the metal probe (12) side is equipped with two with the smooth bolt (19) that are used for restricting the downward maximum displacement of probe cap (14) of falling r shape spout (15) adaptation, probe cap (14) top is opened has a wire guide (16) that communicates its inner chamber, be equipped with external screw thread (17) with screw hole (7) adaptation on the outer wall of probe cap (14), metal probe (12) are connected with wire (18), wire (18) extend to electrode mounting panel (4) edge along wire casing (8) after passing probe cap (14) inner chamber and wire guide (16).
2. An electro-mechanical monitoring device adapted for true triaxial loading according to claim 1, wherein the height of the sliding pin (19) on the side of the metal probe (12) does not exceed the outer diameter of the probe cap (14).
3. An electrical method monitoring device suitable for true triaxial loading according to claim 1, wherein the electrode mounting plate (4) and the probe cap (14) are made of high-strength metal material and the surfaces of the electrode mounting plate and the probe cap are subjected to insulation painting treatment, the electrode mounting plate (4) is rectangular and the edges of the electrode mounting plate are provided with chamfers (10).
4. The electrical method monitoring device suitable for true triaxial loading according to claim 1, wherein the electrode mounting plate (4) and the loading plate (2) are fixedly connected through bolts (5), and threaded holes (7) for the bolts (5) to pass through are respectively formed at four corners of the electrode mounting plate (4) and the loading plate (2).
5. An electrical method monitoring device suitable for true triaxial loading according to claim 4, wherein the threaded hole (7) without the electrode body (11) is filled and pressed by a hole plug (9), and the hole plug (9) is made of high-strength metal material and the surface of the hole plug is subjected to insulation painting treatment.
6. The use method of the electrical method monitoring device suitable for true triaxial loading according to claim 5, comprising the following steps:
s1: determining the material and the dimension specification of the rock sample (6) for the experiment;
s2: determining the number and the size of the electrode mounting plates (4) according to the dimension specification and the experimental scheme of the rock sample (6), determining the arrangement mode and the number of the electrode bodies (11) on the electrode mounting plates (4), and marking the mounting positions and the serial numbers of the electrode bodies (11);
s3: the electrode bodies (11) are arranged in the threaded holes (7) according to the position requirement, and the metal probe (12) of each electrode body (11) is higher than the plane of the electrode mounting plate (4);
s4: the lead (18) is connected with the metal probe (12) and passes through the spring (13) and the lead hole (16), and then the lead (18) is led out from the threaded hole (7) and extends to the edge of the electrode mounting plate (4) along the wire groove (8);
s5: filling and leveling up the threaded hole (7) without the electrode body (11) by using a hole bolt (9), wherein the installation height of the hole bolt (9) is flush with the surface of one side of the electrode installation plate (4), and then fixing the electrode installation plate (4) on the loading plate (2) by using a bolt (5);
s6: placing a rock sample (6) in a true triaxial loading cavity (1), connecting a lead (18) with an electrical method instrument (20), opening the electrical method instrument (20), starting loading confining pressure by a loading plate (2), and maintaining stability when the pressure reaches a designed axial pressure sigma 1, a maximum horizontal pressure sigma 2 and a minimum horizontal pressure sigma 3;
s7: continuously increasing the axial pressure sigma 1, and carrying out an overall process electrical method monitoring experiment of true triaxial loading fracture of the rock sample;
s8: and after the rock sample (6) is destabilized and damaged, the stress loading is finished, the confining pressure of the loading plate (2) is removed, then the electric method instrument (20) is closed to take out the rock sample (6), the electrode mounting plate (4) is disassembled, the electrode body (11) is recovered, the fracture effect is analyzed and evaluated, and the electric method monitoring experiment of the true triaxial loading and damage is completed.
7. The use method of the electrical monitoring device suitable for true triaxial loading according to claim 6, wherein in step 3, the end of the metal probe (12) in each electrode body (11) extending out of the electrode mounting plate (4) is 3-5 mm higher than the plane of the electrode mounting plate (4).
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