Device and test method for quickly and accurately orienting and pasting strain gauges on ASR method specimens

Abstract

The present invention provides a device and a test method for quickly and accurately orienting and pasting strain gauges on ASR method specimens, which relates to the field of rock engineering and includes a production unit for manufacturing strain rosettes and a quick positioning unit for pasting the strain rosettes on a rock core to be measured; the production unit includes a shaping mold, the shaping mold includes an upper mold and a lower mold, a pouring hole is arranged on the upper mold, a first arc surface with the same radian as the contact surface of the rock core to be measured is formed by the convexity of the upper surface of the lower mold, and longitudinal marking lines and transverse marking lines are also arranged on the upper surface of the lower mold, a plurality of transverse marking lines are arranged in parallel, and the longitudinal marking lines are arranged perpendicular to the transverse marking lines; the quick positioning unit includes a quick installation ring and a high-pressure air source, the quick installation ring includes an inner ring and an outer ring arranged concentrically, the inner ring and the outer ring form a sealed ring cavity, three fitting holes are arranged on the inner ring, and the included angle between any two adjacent fitting holes in the radial direction is 120°, and the ring cavity is communicated with the high-pressure air source.

Description

Technical Field

[0001] The present invention relates to the field of rock mass engineering, and particularly to a device and a test method for quickly and accurately orienting and pasting strain gauges on ASR method specimens. Background Art

[0002] In-situ stress refers to the internal stress that rock masses in the earth's crust possess in their natural state. The change of the crustal stress environment is the most direct cause leading to crustal deformation, fracture, folding, and even earthquake occurrence. At the same time, in-situ stress is a necessary prerequisite for determining the geomechanical properties of engineering rock and soil, conducting surrounding rock stability analysis, and realizing the scientific excavation design and decision-making of geotechnical engineering. The in-situ stress state is of great significance for studying a series of scientific issues such as earthquake induction, regional crustal stability evaluation, oil well borehole wall stability, rock burst, and plate movement. The natural in-situ stress field can currently only be obtained by on-site measurement methods to determine the stress state within the rock mass, and unlike other materials, it cannot be obtained through theoretical calculation.

[0003] The Anelastic Strain Recovery method (also known as the ASR method) is a three-dimensional in-situ stress measurement method developed in recent years. Its principle is to assume that rocks have rheological properties and are an isotropic viscoelastic composite. When the core is drilled and removed from the original in-situ stress field, stress recovery will occur. First, the elastic strain recovery is completed instantaneously, and subsequent is the slow anelastic strain recovery. As Figure 1 shown, the amount of anelastic strain recovery is related to the load before unloading, so the in-situ stress can be deduced from the anelastic recovery amount of the core.

[0004] The ASR method can be used in combination with the borehole breakout method and the hydraulic fracturing method to mutually confirm and supplement more abundant data for in-situ stress measurement. In addition, compared with other methods, the ASR method can meet the research needs of continuously increasing deep stress state measurements, has high accuracy, a wide application range, and low test costs. Currently, both domestic and foreign ASR methods face the problem of missing anelastic strain data for at least five or six hours and at most more than ten hours from the time the core is taken out to the time of measurement. The first few hours after the core is just taken out from the rock mass are the stage when the anelastic strain changes the fastest. The earlier the measurement starts after the core is taken out, the more complete the anelastic strain data obtained, and the more accurate the in-situ stress corresponding to the rock mass. Therefore, the data during this period is crucial and greatly affects the correctness and accuracy of the data. However, the correct and effective pasting of strain gauges by traditional methods is not only cumbersome and time-consuming but also depends on the proficiency of the staff, which greatly hinders the practical application of the ASR method in in-situ stress measurement in deep wells, deep earth, and deep seas, and also hinders the popularization of the ASR method for in-situ stress measurement technology to a deeper and more practical stage. Summary of the Invention

[0005] The present invention provides a device and a test method for quickly and accurately orienting and pasting strain gauges on ASR method specimens, aiming to solve the problems in the prior art that the pasting of strain gauges is cumbersome, time-consuming, and depends on the proficiency of operators.

[0006] To achieve the above object, an embodiment of the present invention provides a device for quickly and accurately orienting and pasting strain gauges on ASR method specimens, including a manufacturing unit for manufacturing strain rosettes and a quick positioning unit for pasting the strain rosettes on the rock core to be measured;

[0007] The manufacturing unit includes a shaping mold, which includes an upper mold and a lower mold. The upper mold is provided with a pouring hole. The upper surface of the lower mold protrudes to form a first arc surface with the same radian as the contact surface of the rock core to be measured. The lower surface of the upper mold fits the shape of the upper surface of the lower mold. The upper surface of the lower mold is also provided with a longitudinal marking line and a transverse marking line. A plurality of the transverse marking lines are arranged in parallel, and the longitudinal marking line is perpendicular to the transverse marking line;

[0008] The quick positioning unit includes a quick installation ring and a high-pressure air source. The quick installation ring includes a concentric inner ring and outer ring. The inner ring and the outer ring form a sealed ring cavity. The inner ring is provided with three fitting holes, and the angle between any two adjacent fitting holes in the radial direction is 120°. The ring cavity is communicated with the high-pressure air source.

[0009] Preferably, a protruding portion protruding from the inner ring to the outer ring in the radial direction of the inner ring is further formed on the outer side wall of the inner ring. The angle between any two adjacent protruding portions in the radial direction of the inner ring is 120°. The protruding portion is provided with a fitting channel having the same shape as the fitting hole, and the fitting hole is located at the end of the fitting channel;

[0010] The outer ring is provided with a nozzle, and the nozzle is collinear with the fitting channel and the fitting hole, and the nozzle is communicated with the high-pressure air source.

[0011] Preferably, the quick positioning unit further includes a mounting bracket, which includes a chassis. The chassis is provided with a fixing structure for fixing the rock core to be measured. The chassis is also provided with a plurality of columns. The columns are provided with clamping units. The clamping units are slidably arranged on the columns and can be fixed at any position on the columns. The clamping units are used for clamping the outer ring.

[0012] Preferably, the device for quickly and accurately orienting and pasting strain gauges on ASR method specimens further includes a lead wire holder, which is detachably arranged on the upper mold and is used for supporting the lead wires of the strain rosette.

[0013] Preferably, the device for quickly and accurately orienting and pasting strain gauges on ASR method specimens further includes a core sampler. The front end of the core sampler has the same shape as the pouring hole. The front end of the core sampler protrudes to form a convex head, and the convex head has a second arc surface that is consistent with the radian of the core to be measured.

[0014] A test method using the aforementioned device for quickly and accurately orienting and pasting strain gauges on ASR method specimens is characterized by including the following steps:

[0015] S1. Making strain rosettes: Before drilling the core, obtain the radian of the core contact surface according to the drilling equipment, and make strain rosettes according to the obtained radian. Each strain rosette includes a pair of strain gauge groups, and each strain gauge group includes a pair of strain gauges. The two strain gauges of one strain gauge group are fixed in an "I" shape, and the two strain gauges of the other strain gauge group are vertically fixed at positive 45° and negative 45°. Drop flexible glue into the pouring hole to fix the positions of the strain gauges. After the flexible glue cures, take out the strain rosette.

[0016] S2. Loading the strain rosettes: Put the made strain rosettes into the fitting hole, keep the side of the strain rosette with strain gauges facing the center of the inner ring, and apply glue to the side of the strain rosette facing the center of the inner ring. Connect the annular cavity to the high-pressure gas source.

[0017] S3. Pasting the strain rosettes: Drill the core to be measured from the rock mass, and sleeved the quick installation ring on the core to be measured. Turn on and maintain the high-pressure gas source. The strain rosettes are bonded to the side of the core to be measured under the action of the high-pressure gas source. After the bonding is completed, remove the quick installation ring.

[0018] S4. Measuring the inelastic strain of the core to be measured: Connect the lead wires of each strain rosette to the leads of the strain gauge. Keep the pore pressure and temperature of the core to be measured unchanged during the measurement. The strain gauge continuously measures the inelastic strain value of the core to be measured and records it.

[0019] S5. Conducting a creep test, process the core to be measured to a length of 100 mm and retain the strain rosettes. Conduct a 48-hour creep test on the processed core under a uniaxial compression constant load, and obtain the inelastic strain recovery compliance in the shear and volume deformation modes.

[0020] S6. Calculate the magnitude and direction of the in-situ stress of the area corresponding to the core through the obtained inelastic strain recovery compliance and inelastic strain values in the shear and volume deformation modes.

[0021] Preferably, in step S1, an adhesive is attached to the upper surface of the lower mold. The strain gauges of the strain gauge group fixed in an "I" shape are composed of a first strain gauge and a second strain gauge. The first strain gauge is horizontally attached to the upper surface of the lower mold along the horizontal marking line through the adhesive, and the second strain gauge is vertically attached to the upper surface of the lower mold along the vertical marking line through the adhesive, and the second strain gauge is perpendicular to the end of the first strain gauge;

[0022] The strain gauge group vertically pasted at +45° and -45° is composed of a third strain gauge and a fourth strain gauge. The included angle between the third strain gauge and the vertical marking line is -45°, and the included angle between the fourth strain gauge and the vertical marking line is +45°. The third strain gauge and the fourth strain gauge are attached to the upper surface of the lower mold through the adhesive.

[0023] Preferably, a sample is drilled from the rock mass, and the sample is intercepted to form a core to be measured. The length of the core to be measured is not less than 20 cm.

[0024] The surface of the core is treated, cleaned, and air-dried to ensure that the strain rosette group is fully bonded to the core.

[0025] Preferably, in step S4, the lead wires of each strain gauge of the formed strain rosette are connected to the male head of the DuPont terminal. The wiring of the strain gauge is connected by the female head of the DuPont terminal. The male head and the female head are connected together. The surface of the core is wrapped with plastic wrap, and then sealed with a plastic bag. The sealed core is placed in a constant temperature water bath;

[0026] The strain gauge is connected to an uninterruptible power supply to ensure that there is no power outage during the measurement of the inelastic strain compliance. The measurement period is 5 - 7 days.

[0027] Preferably, in step S5, the axial and radial strain gauges in each strain rosette are connected to obtain the radial inelastic recovery strain and the axial inelastic recovery strain, and the inelastic strain recovery compliance of the shear and volume deformation modes is calculated.

[0028] The above solution of the present invention has the following beneficial effects:

[0029] In this application, by adopting the method of prefabricating the strain rosette, the method of pasting the strain gauges on the core to be measured is advanced to before taking out the core to be measured. The relative positions of the strain gauges are determined in advance using the horizontal and vertical marking lines of the shaping mold to make the strain rosette, and then the strain rosette is attached to the core to be measured using the rapid positioning unit, which shortens the time for pasting the strain gauges, ensures the integrity of the inelastic strain data, and thus obtains more accurate in-situ stress of the rock mass.

[0030] Other features and advantages of the present invention will be described in detail in the subsequent specific implementation section. Description of the Drawings

[0031] Figure 1 is the time-strain curve after rock unloading;

[0032] Figure 2 is a schematic diagram of the present invention;

[0033] Figure 3 is a schematic diagram of a shaping mold;

[0034] Figure 4 is a schematic diagram of a strain rosette;

[0035] Figure 5 is an internal schematic diagram of a quick installation ring;

[0036] Figure 6 is a schematic diagram of a mold extractor;

[0037] Figure 7 is a schematic diagram of strain rosette pasting.

[0038]

Description of the reference numerals

[0039] 1 - production unit, 11 - upper mold, 12 - lower mold, 111 - pouring hole, 112 - first arc surface, 121 - longitudinal marking line, 122 - transverse marking line

[0040] 2 - quick positioning unit, 21 - quick installation ring, 211 - inner ring, 212 - outer ring, 213 - fitting hole, 214 - protrusion, 215 - fitting channel, 216 - air nozzle

[0041] 22 - installation bracket, 221 - chassis, 222 - fixing structure, 223 - support column, 224 - clamping unit

[0042] 3 - leg wire holder, 31 - leg wire support rod, 32 - leg wire cross beam, 33 - coil

[0043] 4 - mold extractor, 41 - convex head, 42 - second arc surface

[0044] A - strain rosette, A0 - strain gauge group, A1 - first strain gauge, A2 - second strain gauge, A3 - third strain gauge, A4 - fourth strain gauge. Detailed implementation manners

[0045] To make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the accompanying drawings and specific embodiments.

[0046] As Figure 2-6As shown in the figure, an embodiment of the present invention provides a device for quickly and accurately orienting and pasting strain gauges on ASR method specimens, including a manufacturing unit 1 and a quick positioning unit 2. Among them, the manufacturing unit 1 is used to manufacture a strain rosette A composed of multiple strain gauges. The manufacturing unit 1 includes a shaping mold, which includes an upper mold 11 and a lower mold 12. A pouring hole 111 penetrating the upper mold 11 is provided on the upper mold 11, and the pouring hole 111 is waist-shaped; a first arc surface 112 is formed by the upward convexity of the upper surface of the lower mold 12, and the first arc surface 112 is consistent with the side curvature of the core to be measured. The lower surface of the upper mold 11 fits the shape of the upper surface of the lower mold 12. When the upper mold 11 and the lower mold 12 are closed, the lower surface of the upper mold 11 and the upper surface of the lower mold 12 achieve surface fitting. A longitudinal marking line 121 and a transverse marking line 122 are also provided on the upper surface of the lower mold 12. A number of transverse marking lines 122 are arranged in parallel, and the longitudinal marking line 121 is perpendicular to the transverse marking line 122. These two marking lines provide positioning for the strain gauges.

[0047] Preferably, threaded holes are respectively provided on the upper mold 11 and the lower mold 12, and the upper mold 11 and the lower mold 12 are fastened by bolts to ensure that the relative positions between the upper mold 11 and the lower mold 12 do not move relative to each other during the curing process of the strain rosette A.

[0048] The aforementioned quick positioning unit 2 includes a quick installation ring 21 and a high-pressure gas source (not shown in the figure). The quick positioning unit 2 is used to be sleeved on the core to be measured and quickly attach the strain rosette A to the side of the core to be measured, improving the pasting efficiency of the strain rosette A. The quick installation ring 21 includes an inner ring 211 and an outer ring 212. The inner ring 211 and the outer ring 212 are concentrically arranged, and there is a certain distance between the inner ring 211 and the outer ring 212 in the radial direction. Annular sealing plates are provided on the upper and lower bottom surfaces of the inner ring 211 and the outer ring 212 to form a closed annular cavity between the inner ring 211 and the outer ring 212. A fitting hole 213 is provided on the side wall of the inner ring 211, and the included angle between any two adjacent fitting holes 213 in the radial direction of the inner ring 211 is 120°. The shape of the fitting hole 213 is the same as the shape of the pouring hole 111. The connecting line of the centers of the fitting holes 213 is parallel to the axis of the core to be measured. The high-pressure gas source is connected to the annular cavity to provide high-pressure gas for the annular cavity.

[0049] In some embodiments of the present application, three convex portions 214 are provided on the outer side of the side wall of the inner ring 211. Each convex portion 214 protrudes from the inner ring 211 to the outer ring 212 along the radial direction of the inner ring 211. A linear fitting channel 215 is provided on the convex portion 214, and the fitting channel 215 is communicated with the fitting hole 213. Preferably, the thickness of the convex portion 214 is the same as the thickness of the strain rosette A formed by pouring.

[0050] The high-pressure gas source is connected to a gas nozzle 216, which is arranged on the outer ring 212, and the gas nozzle 216, the fitting channel 215, and the fitting hole 213 are collinear.

[0051] Furthermore, the present application further includes a leg wire holder 3, which is detachably arranged on the upper mold 11. The wire holder is used to support the leg wires of the strain rosette A.

[0052] Specifically, the leg wire holder 3 includes leg wire support rods 31, leg wire cross beams 32, and wire binding coils 33. The upper mold 11 is provided with insertion holes or screw holes, and the leg wire support rods 31 are detachably arranged in the insertion holes or screw holes. The leg wire cross beams 32 are arranged on the leg wire support rods 31, and several wire binding coils 33 are arranged on the leg wire cross beams 32. The leg wires of the strain rosette A are accommodated through the leg wire support, preventing the leg wires from being entangled with the strain gauges during pouring.

[0053] Preferably, the upper surface of the lower mold 12 is provided with a bottom hole groove, which corresponds to the position of the insertion hole or screw hole. The bottom end of the leg wire support rod 31 is located in the bottom hole groove. On the one hand, the bottom hole groove is used to support the leg wire support rod 31, and on the other hand, the hole bottom groove is used to reduce the atmospheric pressure on the upper mold 11 and the lower mold 12, ensuring the smooth opening of the upper mold 11 and the lower mold 12.

[0054] In some embodiments of the present application, the device for quickly and accurately orienting and pasting strain gauges for ASR method specimens further includes a mold extractor 4. The front end of the mold extractor 4 has the same shape as the pouring hole 111. The front end of the mold extractor 4 protrudes forward to form a convex head 41, which has a second arc surface 42, and the radian of the second arc surface 42 is the same as the radian of the contact surface of the core to be measured. A handle is arranged at the rear end of the mold extractor 4.

[0055] In this embodiment, when using the mold extractor 4, align it with the pouring hole 111 of the upper mold 11. Under the abutment of the convex head 41, the strain rosette A in the pouring hole 111 is pushed out of the pouring hole 111, and the second arc surface 42 ensures that the surface of the strain rosette A is not damaged.

[0056] In some embodiments of the present application, the quick positioning unit 2 further includes a mounting bracket 22. The mounting bracket 22 includes a chassis 221. A fixing structure 222 for vertically fixing the core to be measured is arranged on the chassis 221. Several support columns 223 are also arranged on the chassis 221. A clamping unit 224 is arranged on the support columns 223. The clamping unit 224 is slidably arranged on the support columns 223 and can be fixed at any position on the support columns 223. The clamping unit 224 is used to clamp the outer ring 212 to maintain the position of the quick installation ring 21 fixed on the core to be measured, preventing it from moving during the pasting process of the strain rosette A. The clamping unit 224 detachably clamps the quick installation ring 21.

[0057] Preferably, the fixing structure 222 adopts a three-jaw chuck.

[0058] In this embodiment, the diameter of the inner ring 211 is larger than the diameter of the core to be measured. The difference between the diameter of the inner ring 211 and the diameter of the core to be measured is less than or equal to the thickness of the strain rosette A, which facilitates the removal of the quick installation ring 21 from the core to be measured after the strain rosette A is bonded.

[0059] In the device for quickly and accurately orienting and pasting strain gauges on ASR method specimens provided in this application, a strain rosette A consistent with the contour of the core to be measured is made by using a shaping mold. When the strain rosette A is made, it is arranged along the horizontal marking line 122 and the vertical marking line 121, so that after the strain rosette A is made, the strain gauges inside are fixed according to the preset positional relationship. When the strain rosette A is fixed on the core to be measured, it is not necessary to adjust the position of each strain gauge individually, achieving the purpose of quickly pasting a single strain rosette A.

[0060] At the same time, this application uses a high-pressure gas source to push the strain rosette A to move. Under the action of the high-pressure gas source, the strain rosette A moves along the fitting channel 215 towards the core to be measured and is bonded to the core to be measured, achieving the purpose of simultaneously fixing multiple strain rosettes A on the core to be measured, shortening the fixing time of multiple strain rosettes A, and reducing the loss of inelastic strain.

[0061] In addition, the high-pressure gas source can also bond and maintain the bonding of the strain rosette A on the core to be measured by continuously ventilating, ensuring that the strain rosette A is fully fixed on the core to be measured.

[0062] This application also provides a test method, which uses the aforementioned device for quickly and accurately orienting and pasting strain on ASR method specimens, and includes the following steps:

[0063] S1. Making the strain rosette A: Before core drilling, obtain the radian of the core contact surface according to the drilling equipment, and make a shaping mold according to this radian. The first arc surface 112 on the lower surface of the upper mold 11 and the upper surface of the lower mold 12 of this shaping mold is the same as the radian of the core contact surface.

[0064] At least one pouring hole 111 is provided on this shaping mold, and each pouring hole 111 is used to make a strain rosette A. In this embodiment, three pouring holes 111 are provided on the shaping mold, and three strain rosettes A can be made at one time. Each strain rosette A includes a pair of strain gauge groups A0, and each strain gauge group A0 includes a pair of strain gauges. The two strain gauges of one strain gauge group A0 are fixed in an "I" shape, and the two strain gauges of the other strain gauge group A0 are fixed perpendicularly at positive 45° and negative 45°. Drop flexible glue into the pouring hole 111 to fix the positions of the strain gauges. After the flexible glue cures, remove the strain rosette A.

[0065] Specifically, a corresponding strain gauge group A0 is arranged in each pouring hole 111. One strain gauge group A0 is composed of a first strain gauge A1 and a second strain gauge A2, and the other strain gauge group A0 is composed of a third strain gauge A3 and a fourth strain gauge A4. When manufacturing the strain rosette A, an adhesive is coated on the upper surface of the lower mold 12. The first strain gauge A1 is bonded along the horizontal marking line 122 on the upper surface of the lower mold 12, and the second strain gauge A2 is bonded along the vertical marking line 121 on the upper surface of the lower mold 12, and the second strain gauge A2 is arranged at one end of the first strain gauge A1.

[0066] The included angle between the third strain gauge A3 and the vertical marking line 121 is -45°, and the included angle between the fourth strain gauge A4 and the vertical marking line 121 is +45°. After the two strain gauge groups A0 are fixed, flexible epoxy resin glue is dropped into the pouring hole 111.

[0067] The horizontal marking line 122 and the vertical marking line 121 are used to fix the relative positions of the respective strain gauges. Compared with the existing method of engraving marking lines on the core surface to fix the strain gauges, in this application, the step of fixing the relative positions of the strain gauges is advanced to before drilling the core to be measured, reducing the loss of inelastic strain during the fitting of the strain gauges.

[0068] After the flexible epoxy resin glue is cured, it can fix the relative positions of the respective strain gauges. The strain rosette A is ejected from the pouring hole 111 of the upper mold 11 by using the mold extractor 4.

[0069] Due to curing with flexible epoxy resin glue, the strain rosette A has a certain flexibility, and the flexible epoxy resin glue has a certain deformation ability, which is convenient for fixing the strain rosette A on the core to be measured.

[0070] S2. Loading the strain rosette A: The manufactured strain rosette A is placed into the fitting hole 213 from the direction of the inner ring 211, and the side of the strain rosette A with strain gauges is kept facing the center of the inner ring 211. Glue is coated on the side of the strain rosette A facing the center of the inner ring 211, and the annular cavity is connected to the high-pressure gas source.

[0071] S3. Pasting the strain rosette A: Drill the core to be measured in the rock mass, and sleave the quick installation ring 21 on the side core of the tire. Open and maintain the high-pressure gas source. The strain rosette A is bonded to the side of the core to be measured under the push of the high-pressure gas source. After the bonding is completed, the quick installation ring 21 is removed. The strain rosette A is fixed on the core to be measured as shown. Figure 7 shown.

[0072] In this step, a sample is drilled in the rock mass, and the test is cut into a core to be tested. The length of the core to be tested is not less than 20 cm. At the same time, the surface of the core to be tested is treated, which includes but is not limited to washing the oil particles on the core to be tested with clean water before pasting, wiping it with a paper towel, and then washing it with alcohol and air-drying it; if the patch area of ​​the core to be tested is rough and uneven, the core to be tested can also be polished to facilitate the firm pasting of the strain rosette A.

[0073] In this step, the strain rosette A is pasted on the same horizontal plane of the core to be tested, and one strain rosette A is pasted every 120°, so that the inelastic strain values ​​in 12 directions can be obtained.

[0074] S4. Measure the inelastic strain of the core to be tested: connect the leg wires of each strain rosette A to the lead wire of the strain gauge, keep the pore pressure and temperature of the core to be tested constant during the measurement, and the strain gauge continuously measures and records the inelastic strain value of the core to be tested.

[0075] In this step, the legs of each strain gauge in the strain gauge flower A are pre-connected to the male end of the DuPont terminal, and the wiring of the strain gauge is pre-connected using the female end of the DuPont terminal. When obtaining the inelastic strain, the female end and the male end are connected together accordingly.

[0076] Before the measurement, the surface of the core to be measured is wrapped with plastic wrap, and then the outer layer of the plastic wrap is sealed with a plastic bag. Under the dual protection of the plastic wrap and the plastic bag, it is placed in a water bath to keep the pore pressure unchanged during the measurement. The water bath uses a constant temperature water bath to maintain the temperature of the core to be measured during the measurement. In order to achieve 5-7 days of uninterrupted measurement, the strain gauge is electrically connected to an uninterruptible power supply such as a UPS.

[0077] S5. Conduct creep test: After the inelastic strain value measurement is completed, the core to be tested is taken out of the constant temperature water bath, and the fresh-keeping bag and plastic bag are removed. The core to be tested is processed to a length of 100 mm, and the strain rosette A on the core to be tested is retained. The processed core is subjected to a creep test under uniaxial compression and constant load for 48 hours, and the inelastic strain recovery compliance under shear and volume change modes is obtained.

[0078] In this step, the strain gauge is connected to the axial and radial strain gauges in each strain rosette A to obtain the radial inelastic recovery strain and axial inelastic recovery strain after the core is unloaded for 5 days after processing, saving the time for pasting the axial and radial strain gauges later. The inelastic strain recovery compliance in the shear and volume deformation modes is calculated based on the radial inelastic recovery strain and the axial inelastic recovery strain.

[0079] S6. The inelastic strain recovery compliance and inelastic strain value under the shear and volume deformation modes are obtained and brought into MATLAB to calculate the magnitude and direction of the ground stress in the area corresponding to the core.

[0080] Conventionally, 18 strain gauges are used to measure the core strain by the pasting method, which has 9 independent directions, that is, there are two strain gauges in each direction. Although it can ensure the stability of data, on the one hand, it wastes strain gauges, and on the other hand, each strain gauge needs to be pasted separately, increasing the workload. Moreover, the deviation of the pasting direction may be caused by human factors, which will affect the acquisition of effective inelastic strain data in the early stage to a certain extent. In this application, 12 strain gauges are used to obtain 12 independent directions (three of which are the same), meeting the requirement of at least six independent directions. While ensuring that each strain rosette has a 120° interval, it can be pasted at one time, and all 12 strain gauges are pasted on the core to be measured.

[0081] In addition, the strain rosette A is made before obtaining the core to be measured, and the strain rosette A is pasted on the core to be measured as a whole at one time. By using the pre-made strain rosette A to quickly paste it on the core to be measured, the integrity of the inelastic strain data is ensured, and the in-situ stress of the rock mass can be obtained more accurately.

[0082] The above is the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A device for quickly and accurately orienting and pasting strain gauges on ASR method specimens, characterized in that, it includes: a production unit (1) for producing a strain rosette (A) and a quick positioning unit (2) for pasting the strain rosette (A) on a core to be measured; the production unit (1) includes a shaping mold, the shaping mold includes an upper mold (11) and a lower mold (12), a pouring hole (111) is provided on the upper mold (11), a first arc surface (112) with the same radian as the contact surface of the core to be measured is formed on the upper surface of the lower mold (12), the lower surface of the upper mold (11) fits the upper surface of the lower mold (12), a longitudinal marking line (121) and a transverse marking line (122) are further provided on the upper surface of the lower mold (12), a plurality of the transverse marking lines (122) are arranged in parallel, and the longitudinal marking line (121) is arranged perpendicular to the transverse marking line (122); the quick positioning unit (2) includes a quick installation ring (21) and a high-pressure air source, the quick installation ring (21) includes a concentric inner ring (211) and an outer ring (212), the inner ring (211) and the outer ring (212) form a sealed ring cavity, three fitting holes (213) are provided on the inner ring (211), and the included angle between any two adjacent fitting holes (213) in the radial direction is 120°, and the ring cavity is communicated with the high-pressure air source.

2. The device for quickly and accurately orienting and pasting strain gauges on ASR method specimens according to claim 1, characterized in that: a convex part (214) protruding from the inner ring (211) in the radial direction towards the outer ring (212) is further formed on the outer side wall of the inner ring (211), the included angle between any two adjacent convex parts (214) in the radial direction of the inner ring (211) is 120°, a fitting channel (215) with the same shape as the fitting hole (213) is provided on the convex part (214), and the fitting hole (213) is located at the end of the fitting channel (215); a nozzle (216) is provided on the outer ring (212), the nozzle (216) is collinear with the fitting channel (215) and the fitting hole (213), and the nozzle (216) is communicated with the high-pressure air source.

3. The device for quickly and accurately orienting and pasting strain gauges on ASR method specimens according to claim 2, characterized in that: the quick positioning unit (2) further includes a mounting bracket (22), the mounting bracket (22) includes a chassis (221), a fixing structure (222) for fixing the core to be measured is provided on the chassis (221), a plurality of support columns (223) are further provided on the chassis (221), a clamping unit (224) is provided on the support columns (223), the clamping unit (224) is slidably arranged on the support columns (223) and can be fixed at any position on the support columns (223), and the clamping unit (224) is used for clamping the outer ring (212).

4. The device for quickly and accurately orienting and pasting strain gauges on ASR method specimens according to claim 3, characterized in that: The device for quickly and accurately orienting and pasting strain gauges on ASR method specimens further includes a lead wire frame (3), and the lead wire frame (3) is detachably arranged on the upper die (11), and the lead wire frame (3) is used to support the lead wires of the strain rosette (A).

5. The device for quickly and accurately orienting and pasting strain gauges on ASR method specimens according to claim 3, characterized in that: The device for quickly and accurately orienting and pasting strain gauges on ASR method specimens further includes a mold extractor (4), the front end shape of the mold extractor (4) is the same as the shape of the pouring hole (111), a convex head (41) is formed by the front end protrusion of the mold extractor (4), and the convex head (41) has a second arc surface (42) consistent with the radian of the core to be measured.

6. A test method, using the device for quickly and accurately orienting and pasting strain gauges on ASR method specimens according to any one of claims 1-5, characterized in that, it includes the following steps: S1. Fabricate the strain rosette (A): Before drilling the core, obtain the radian of the core contact surface according to the drilling equipment, and fabricate the strain rosette (A) according to the obtained radian. Each strain rosette (A) includes a pair of strain gauge groups (A0), and each strain gauge group (A0) includes a pair of strain gauges. The two strain gauges of one strain gauge group (A0) are fixed in an "I" shape, and the two strain gauges of the other strain gauge group (A0) are vertically fixed at positive 45° and negative 45°. Drop flexible glue into the pouring hole (111) to fix the positions of the strain gauges. After the flexible glue cures, take out the strain rosette (A); S2. Load the strain rosette (A): Place the fabricated strain rosette (A) into the fitting hole (213), keep the side of the strain rosette (A) with strain gauges facing the center of the inner ring (211), and apply glue to the side of the strain rosette (A) facing the center of the inner ring (211), and connect the annular cavity with a high-pressure gas source; S3. Paste the strain rosette (A): Drill the core to be measured from the rock mass, sleeved the quick installation ring (21) on the core to be measured, turn on and maintain the high-pressure gas source, and the strain rosette (A) is bonded to the side of the core to be measured under the action of the high-pressure gas source. After the bonding is completed, remove the quick installation ring (21); S4. Measure the inelastic strain of the core to be measured: Connect the lead wires of each strain rosette (A) to the leads of the strain gauge, keep the pore pressure and temperature of the core to be measured unchanged during the measurement, and the strain gauge continuously measures and records the inelastic strain value of the core to be measured; S5. Conduct a creep test, process the core to be measured to a length of 100 mm, and retain the strain rosette (A). Conduct a 48-hour creep test on the processed core under a constant uniaxial compression load, and obtain the inelastic strain recovery compliance in the shear and volume deformation modes; S6. Calculate the magnitude and direction of the in-situ stress in the area corresponding to the core through the inelastic strain recovery compliance and inelastic strain values obtained in the shear and volume deformation modes.

7. The test method according to claim 6, characterized in that: In step S1, an adhesive is attached to the upper surface of the lower die (12). The strain gauge group (A0) fixed in an "I" shape is composed of a first strain gauge (A1) and a second strain gauge (A2). The first strain gauge (A1) is horizontally attached to the upper surface of the lower die (12) along the horizontal marking line (122) through the adhesive, and the second strain gauge (A2) is vertically attached to the upper surface of the lower die (12) along the vertical marking line (121) through the adhesive, and the second strain gauge (A2) is perpendicular to the end of the first strain gauge (A1). The strain gauge group (A0) vertically pasted at +45° and -45° is composed of a third strain gauge (A3) and a fourth strain gauge (A4). The included angle between the third strain gauge (A3) and the vertical marking line (121) is -45°, and the included angle between the fourth strain gauge (A4) and the vertical marking line (121) is +45°. The third strain gauge (A3) and the fourth strain gauge (A4) are attached to the upper surface of the lower die (12) through the adhesive.

8. The test method according to claim 6, characterized in that: Drill a sample from the rock mass, and intercept the sample to form a core to be measured. The length of the core to be measured is not less than 20 cm, Treat, clean and air-dry the surface of the core to ensure that the strain rosette (A) group is fully bonded to the core.

9. The test method according to claim 6, characterized in that: In step S4, connect the lead wires of each strain gauge of the formed strain rosette (A) group to the male head of the Dupont terminal. The wiring of the strain gauge is connected by the female head of the Dupont terminal. Connect the male head and the female head together. Wrap the surface of the core with plastic wrap, then seal it with a plastic bag, and place the sealed core in a constant temperature water bath; Connect the strain gauge to an uninterruptible power supply to ensure that there is no power failure during the measurement of the inelastic strain compliance. The measurement period is 5 - 7 days.

10. The test method according to claim 6, characterized in that: In step S5, connect the axial and radial strain gauges in each strain rosette (A) to obtain the radial inelastic recovery strain and the axial inelastic recovery strain, and calculate the inelastic strain recovery compliance of the shear and volume deformation modes.

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