Drilling tangential strain measuring device and stress measuring method thereof

Abstract

The invention discloses a drilling tangential strain measuring device and a stress measuring method thereof, and the device comprises a base which is of a hollow cylindrical structure; the strain gauge fixing device comprises a pre-pressing piece arranged in the base and a plurality of sets of elastic supporting pieces connected with the pre-pressing piece in a sliding mode, one ends of the elastic supporting pieces are arranged in the sliding ways in a sliding mode, the other ends of the elastic supporting pieces extend out of the base, the elastic supporting pieces are pressed, the elastic supporting pieces retract towards the interior of the base, and the elastic supporting pieces are fixed to the base. The strain gauge is arranged at the other end of the elastic supporting piece; the limiting device comprises a limiting rod and an elastic limiting pin, one end of the limiting rod is connected with the pre-pressing piece, the elastic limiting pin is matched with the limiting rod, a plurality of limiting grooves are formed in the outer wall of the limiting rod, the elastic limiting pin is clamped in the limiting grooves to limit the pre-pressing piece, the other end of the limiting rod extends out of the base, and the elastic limiting pin is limited on the base; and the strain gauge is electrically connected with the strain gauge. According to the invention, the strain gauge does not need to be pasted on the inner wall of the drill hole during testing, and the strain gauge can adapt to drill holes with different sizes.

Description

Technical Field

[0001] The invention belongs to the technical field of rock mechanics testing, and in particular relates to a borehole tangential strain measuring device and a stress measuring method thereof. Background Art

[0002] Geostress measurement is a very important issue in major construction projects. Correctly determining the geostress of the rock mass is the basis for correctly and reasonably calculating the excavation load of underground projects. Therefore, geostress measurement is very important. There are two methods for on-site geostress testing: stress relief method and hydraulic fracturing method. Among them, the stress relief method is to drill a small hole (about tens of centimeters in size) along the axis of the borehole at the bottom of the borehole, put the measuring device into the small hole (there are many different types of devices), and then continue to drill the core down along the borehole to remove the stress of the surrounding rock at the bottom of the hole. The existing stress detection equipment suitable for the local wall stress relief method uses glue to stick the stress sheet to the sampling section, relieve the stress of the core in the sampling section, and test the geostress by recording the strain data changes of the strain sheet. However, it has the following defects: (1) It cannot directly carry out continuous sampling: the stress gauge needs to be re-pasted for different sampling sections, which is time-consuming and laborious; (2) The stress gauge is easily damaged: as a precision electronic component, the high-precision strain gauge is prone to mechanical damage during the process of repeated pasting and removal, especially when drilling oil, it is very easy to be damaged by the rock cuttings in the drilling fluid and the irregular hole wall; (3) The stress gauge is difficult to paste on the surface of the well wall under complex drilling conditions, and its success rate is low. Therefore, it is necessary to develop a borehole tangential strain measurement device that can fix the strain gauge more firmly and does not need to be removed when changing the test section. Summary of the invention

[0003] One object of the present invention is to address the deficiencies of the prior art and provide a borehole tangential strain measurement device, which does not require the strain gauge to be pasted on the inner wall of the borehole during testing and can be adapted for use in borehole testing of different sizes.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] A drilling tangential strain measuring device comprises a base, a strain gauge fixing device, a strain gauge, a limit device and a strain meter;

[0006] A base, which is a hollow cylindrical structure;

[0007] A strain gauge fixing device, comprising a pre-pressed part arranged in a base and a plurality of groups of elastic support parts slidably connected to the pre-pressed part, the pre-pressed part is in a truncated cone shape, and its diameter gradually increases as it approaches the limit device, a plurality of slideways extending along its length direction are arranged on the outer wall of the pre-pressed part, one end of the elastic support part is slidably arranged in the slideway, and the other end of the elastic support part extends out of the base, and the elastic support part is pressed, and the elastic support part retracts into the base, and the strain gauge is arranged on the other end of the elastic support part. During the test, the strain gauge is tightly attached to the inner wall of the borehole to be tested under the action of the elastic support part;

[0008] The limiting device includes a limiting rod connected to the pre-pressed part at one end and an elastic limiting pin matched with the limiting rod. A plurality of limiting grooves are arranged on the outer wall of the limiting rod. The elastic limiting pin is clamped in the limiting groove to limit the pre-pressed part. The other end of the limiting rod extends out of the base, and the elastic limiting pin is limited on the base.

[0009] The strain gauge is electrically connected to the strain gauge and is used to collect strain data measured by the strain gauge.

[0010] Furthermore, an electronic compass is fixed on the end surface of the pre-pressed part, and the electronic compass is used to record the installation angle of the strain gauge.

[0011] Furthermore, one end of the base away from the limiting rod is an open end, and a guide member is provided at the open end of the base, and the guide member has an arc-shaped guide surface.

[0012] Furthermore, the elastic support rod includes a first support rod slidably connected in a slideway, a first spring connected to the first support rod at one end, and a second support rod connected to the other end of the first spring, and the strain gauge is fixed on the second support rod, wherein when testing the strain in the borehole to be tested, the first spring is in a compressed state.

[0013] Furthermore, it also includes a limit plate, which is sleeved outside the base and is a conical structure, and its diameter gradually decreases as it approaches the elastic support member, wherein the minimum diameter of the limit plate is smaller than the inner diameter of the drilled hole to be tested, and the maximum diameter of the limit plate is larger than the inner diameter of the drilled hole to be tested.

[0014] Furthermore, the elastic limiting pin includes a second spring limited in the side wall of the base and a limiting pin with one end connected to the second spring and the other end extending out of the base and clamped in the limiting groove.

[0015] Furthermore, it also includes a mounting rod, and when in use, the mounting rod is connected to the limiting rod through a connecting piece.

[0016] Another object of the present invention is to provide a method for measuring stress according to the above-mentioned drilling tangential strain measuring device, comprising the following steps:

[0017] Step 1, sending the drilling tangential strain measuring device to the test depth in the pre-drilled borehole to be tested, and then limiting the drilling tangential strain measuring device in the borehole to be tested;

[0018] Step 2: Push the limit rod to apply pressure to the pre-pressed part. During the pressure application process, the elastic support part slides in the slideway and makes the strain gauge close to the wall of the borehole to be tested;

[0019] Step 3: Stop pushing the limit rod, and the limit pin is locked in the corresponding limit groove on the limit rod, so that the preloaded part is limited and the strain gauge is locked. The installation angle of the strain gauge at this time is recorded, and the initial strain value of the strain gauge is recorded;

[0020] Step 4: Perform a stress release test, and record the strain value of each strain gauge 3 during the release process through the strain gauge;

[0021] Step 5: After the borehole to be tested is completely decased, the final strain value of the strain gauge after the decasing is obtained through the strain gauge. The strain change of each strain gauge before and after the decasing can be obtained by comparing the strain value before and after the decasing. The two-dimensional stress value on the cross section of the borehole to be tested is calculated based on the strain change, the installation angle of each strain gauge and the mechanical parameters of the rock.

[0022] Furthermore, it is characterized in that the mechanical parameters of the rock include the elastic modulus E and Poisson's ratio μ of the rock.

[0023] Furthermore, the two-dimensional stress value calculation method on the cross section of the borehole to be tested is:

[0024]

[0025] In the formula, ε i represents the strain value of the i-th strain gauge, k i represents the calibration coefficient of the i-th strain gauge, α i represents the installation angle corresponding to the i-th strain gauge, E represents the rock elastic modulus, μ represents the rock Poisson's ratio, σ x represents the stress value in the X direction, σ y Indicates the stress value in the Y direction.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention first fixes the drilling tangential strain measuring device on the borehole to be tested by a limiting plate, and then presses the strain gauge against the inner wall of the borehole to be tested by a preloaded part and an elastic support rod, and uses a limiting device to lock the preloaded part to lock the strain gauge, thereby eliminating the need to stick the strain gauge and eliminating the need to remove the strain gauge when changing the test borehole, thereby improving the efficiency and accuracy of the test; in addition, the elastic support rod can automatically adjust the length according to the inner diameter of the borehole to be tested, so the present invention can be adapted to boreholes of various sizes. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic structural diagram of a drilling tangential strain measurement device according to an embodiment of the present invention;

[0028] Figure 2 for Figure 1 Left view of;

[0029] Figure 3 This is a diagram of the drilling coordinate system for stress calculation in an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present invention will be described clearly and completely below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0032] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0033] like Figure 1 and Figure 2As shown, an embodiment of the present invention discloses a drilling tangential strain measuring device, including a base 1, a strain gauge fixing device, a strain gauge 3, a limit device and a strain gauge. The base 1 is a hollow cylindrical structure with a cavity therein. One end of the base 1 is an open end, and the other end is provided with a first through hole for the limit device to pass through. The strain gauge fixing device includes a pre-pressed part 21 arranged in the cavity of the base 1 and a plurality of groups of elastic support members slidably connected to the pre-pressed part 21. In order to facilitate the positioning of the strain gauge 2 according to the inner diameter of the borehole to be tested, the pre-pressed part 2 is arranged in a truncated cone shape, and its diameter gradually increases as it approaches the limit device. A slideway 22 is arranged on the outer wall of the pre-pressed part 21 along its length direction. In this embodiment, three slideways 22 are arranged at equal intervals on the outer wall of the pre-pressed part 21, and correspondingly, three groups of elastic support members are slidably connected to the pre-pressed part 21. One end of each set of elastic support members is slidably disposed in the slideway 22, and the other end of the elastic support member extends out of the base 1. When the elastic support member is pressed, the elastic support member retracts into the base 1, and the strain gauge 3 is disposed on the other end of the elastic support member. The strain gauge 3 on each set of elastic support members is connected to the strain gauge through a cable, and the strain gauge is used to collect strain data measured by the strain gauge 3.

[0034] In this embodiment, the elastic support rod includes a first support rod 23 slidably connected in the slideway, a first spring 24 connected to the first support rod 23 at one end, and a second support rod 25 connected to the other end of the first spring 24. A second through hole is provided on the side wall of the base 1, and the second support rod 25 extends from the second through hole to the outside of the base 1, and the strain gauge 3 is provided on the second support rod 25. When testing the strain of the borehole to be tested, the first spring 24 is in a compressed state, and the strain gauge 3 is pressed against the inner wall of the borehole to be tested by the elastic action of the first spring 24. In order to record the installation angle of each strain gauge 3, an electronic compass 5 is installed on the end side of the preload. In addition, a guide member 11 is also provided at the open end of the base 1, and the guide member 11 has an arc-shaped guide surface. The arc-shaped guide surface of the guide member 11 can help to advance the device when the borehole tangential strain measurement device is placed in the borehole.

[0035] The limiting device includes a limiting rod 41 connected to the pre-pressed part 21 at one end and an elastic limiting pin matched with the limiting rod. A plurality of limiting grooves are arranged on the outer wall of the limiting rod 41, and the end of the elastic limiting pin is clamped in the limiting groove to limit the pre-pressed part 21. In this embodiment, a screw rod is used as the limiting rod, and the other end of the limiting rod 41 extends from the first through hole to the outside of the base 1. The elastic limiting pin includes a second spring 42 limited in the side wall of the base 1 and a limiting pin 43 connected to the second spring 42 at one end and extending from the base 1 and clamped in the limiting groove at the other end. Specifically, a clamping groove is arranged on the side wall of the base 1, and the second spring is limited in the clamping groove. After the limiting pin 43 is connected to the second spring 42, it extends from the side wall of the base 1 and is clamped in the limiting groove.

[0036] In order to facilitate the positioning of the borehole tangential strain measuring device, a conical limiting plate 6 is sleeved outside the base 1, and its diameter gradually decreases as it approaches the elastic support member, wherein the minimum diameter of the limiting plate 6 is smaller than the inner diameter of the borehole to be tested, and the maximum diameter of the limiting plate 6 is larger than the inner diameter of the borehole to be tested. During the test, the borehole tangential strain measuring device is fixed in the borehole to be tested by clamping the limiting plate 6 at the orifice of the borehole to be tested.

[0037] The drilling tangential strain measuring device also includes a mounting rod 7. Before the drilling tangential strain measuring device is sent into the borehole, the mounting rod 7 and the limiting rod 41 are fixedly connected by a mounting pin, and the drilling tangential strain measuring device is sent into the borehole to a specified depth of the borehole to be tested by the mounting rod 7. When testing the drilling stress, the mounting pin is removed to separate the mounting rod 7 from the limiting rod 41.

[0038] The stress in the process of stress relief of drilling is tested by using the drilling tangential strain measuring device of this embodiment, including the following steps:

[0039] Step 1, the limiting rod 41 is fixedly connected to the mounting rod 7, and the drilling tangential strain measuring device is sent to the test depth in the pre-drilled small borehole 8 to be tested through the mounting rod 7, and the drilling tangential strain measuring device is limited in the small borehole 8 to be tested through the limiting plate 6 on the base 1;

[0040] Step 2, connecting the cable 30 on each strain gauge 3 to the strain gauge;

[0041] Step 3, push the installation rod 7 to apply pressure to the preloaded part 21, and the preloaded part 21 is pressed to move forward into the borehole. At the same time, the elastic support member slidably connected to the preloaded part 21 slides in the opposite direction in the slideway 22 until the strain gauge 3 located at the end side of the elastic support member is pressed against the inner wall of the small borehole 8 to be tested. In the process of pushing the installation rod 7, it can be determined whether to continue to apply preload by reading the preload strain value of the strain gauge; when there is no need to continue to apply pressure, the strain gauge 3 is positioned, the installation rod 7 is stopped from being pushed, and the limit rod 41 also stops moving forward. The limit pin 43 located on the base 1 limits the limit rod 41, so that the strain gauge 3 is locked on the inner wall of the small borehole 8 to be tested;

[0042] Step 4: After the strain gauge 3 is locked, remove the mounting pin, withdraw the mounting rod 7, record the mounting angle of each strain gauge 3 at this time through the electronic compass 5, and record the initial strain value of each strain gauge 3 through the strain gauge;

[0043] Step 5: Perform a stress release test, and record the strain value of each strain gauge 3 during the release process through the strain gauge;

[0044] Step 6: After the test small borehole 8 equipped with the borehole tangential strain measuring device is completely uncored, the final strain value after uncoring is obtained through the strain gauge and the strain gauge 3. The strain change of each strain gauge 3 before and after uncoring can be obtained by comparing the strain value before and after uncoring. Combined with the elastic modulus E and Poisson's ratio μ of the rock obtained in advance, the strain change obtained after uncoring each strain gauge 3, the installation angle of each strain gauge, and the elastic modulus E and Poisson's ratio μ of the rock are substituted into the following formula to calculate the two-dimensional stress value on the cross section of the borehole, where the borehole coordinate system is as follows: Figure 3 As shown:

[0045]

[0046] In the formula, ε i represents the strain value of the i-th strain gauge, k i represents the calibration coefficient of the i-th strain gauge, α i represents the installation angle corresponding to the i-th strain gauge, E represents the rock elastic modulus, μ represents the rock Poisson's ratio, σ x represents the stress value in the X direction, σ y Indicates the stress value in the Y direction.

[0047] The above are only preferred embodiments of the present invention, and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the contents of the specification of the present invention should be included in the protection scope of the present invention.

Claims

1. A drilling tangential strain measurement device, characterized in that: It includes a base, a strain gauge fixing device, a strain gauge, a limit device and a strain gauge; A base, which is a hollow cylindrical structure; A strain gauge fixing device, comprising a pre-pressed part arranged in a base and a plurality of groups of elastic support parts slidably connected to the pre-pressed part, the pre-pressed part is in a truncated cone shape, and its diameter gradually increases as it approaches the limit device, a plurality of slideways extending along its length direction are arranged on the outer wall of the pre-pressed part, one end of the elastic support part is slidably arranged in the slideway, and the other end of the elastic support part extends out of the base, and the elastic support part is pressed, and the elastic support part retracts into the base, and the strain gauge is arranged on the other end of the elastic support part. During the test, the strain gauge is tightly attached to the inner wall of the borehole to be tested under the action of the elastic support part; The limiting device includes a limiting rod connected to the pre-pressed part at one end and an elastic limiting pin matched with the limiting rod. A plurality of limiting grooves are arranged on the outer wall of the limiting rod. The elastic limiting pin is clamped in the limiting groove to limit the pre-pressed part. The other end of the limiting rod extends out of the base, and the elastic limiting pin is limited on the base. The strain gauge is electrically connected to the strain gauge and is used to collect strain data measured by the strain gauge.

2. The drilling tangential strain measuring device according to claim 1, characterized in that: An electronic compass is fixed on the end surface of the pre-pressed part, and the electronic compass is used to record the installation angle of the strain gauge.

3. The drilling tangential strain measuring device according to claim 1, characterized in that: One end of the base away from the limiting rod is an open end, and a guide member is arranged at the open end of the base, and the guide member has an arc-shaped guide surface.

4. The drilling tangential strain measuring device according to claim 1, characterized in that: The elastic support rod includes a first support rod slidably connected in a slideway, a first spring connected to the first support rod at one end, and a second support rod connected to the other end of the first spring, and the strain gauge is fixed on the second support rod, wherein when testing the strain in the borehole to be tested, the first spring is in a compressed state.

5. The drilling tangential strain measuring device according to claim 1, characterized in that: It also includes a limit plate, which is sleeved outside the base and is a conical structure, and its diameter gradually decreases as it approaches the elastic support member, wherein the minimum diameter of the limit plate is smaller than the inner diameter of the drilled hole to be tested, and the maximum diameter of the limit plate is larger than the inner diameter of the drilled hole to be tested.

6. The drilling tangential strain measuring device according to claim 1, characterized in that: The elastic limiting pin comprises a second spring limited in the side wall of the base and a limiting pin whose one end is connected to the second spring and the other end extends out of the base and is clamped in the limiting groove.

7. The drilling tangential strain measuring device according to claim 1, characterized in that: It also includes a mounting rod, which is connected to the limiting rod through a connecting piece when in use.

8. A method for measuring stress according to the drilling tangential strain measuring device according to any one of claims 1 to 7, characterized in that: The steps include: Step 1, sending the drilling tangential strain measuring device to the test depth in the pre-drilled borehole to be tested, and then limiting the drilling tangential strain measuring device in the borehole to be tested; Step 2: Push the limit rod to apply pressure to the pre-pressed part. During the pressure application process, the elastic support part slides in the slideway and makes the strain gauge close to the wall of the borehole to be tested; Step 3: Stop pushing the limit rod, and the limit pin is locked in the corresponding limit groove on the limit rod, so that the preloaded part is limited and the strain gauge is locked. The installation angle of the strain gauge at this time is recorded, and the initial strain value of the strain gauge is recorded; Step 4: Perform a stress release test, and record the strain value of each strain gauge 3 during the release process through the strain gauge; Step 5: After the borehole to be tested is completely decased, the final strain value of the strain gauge after the decasing is obtained through the strain gauge. The strain change of each strain gauge before and after the decasing can be obtained by comparing the strain value before and after the decasing. The two-dimensional stress value on the cross section of the borehole to be tested is calculated based on the strain change, the installation angle of each strain gauge and the mechanical parameters of the rock.

9. The method for measuring stress using a drilling tangential strain measuring device according to claim 8, characterized in that: The mechanical parameters of rock include the elastic modulus E and Poisson's ratio μ of rock.

10. The method for measuring stress using a drilling tangential strain measuring device according to claim 9, characterized in that: The calculation method of the two-dimensional stress value on the cross section of the drill hole to be tested is: In the formula, ε i represents the strain value of the i-th strain gauge, k i represents the calibration coefficient of the i-th strain gauge, α i represents the installation angle corresponding to the i-th strain gauge, E represents the rock elastic modulus, μ represents the rock Poisson's ratio, σ x represents the stress value in the X direction, σ y Indicates the stress value in the Y direction.

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