Rock dry-wet cycle test device and test method thereof

Abstract

The invention discloses a rock dry-wet cycle test device and a test method thereof, and belongs to the technical field of rock strength testing, the rock dry-wet cycle test device comprises a loading system, a test cylinder, a measuring system, a water circulation device, a drying device, an acoustic emission system and a computer control system; the test cylinder is divided into an inner cylinder and an outer cylinder, the outer cylinder is connected with the water circulation system and the drying device, a sample is fixed by the inner cylinder, and dry-wet circulation conditions with lateral confinement are created. The computer system controls the lifting platform to lift by controlling the hydraulic device so as to load and unload the sample; the data acquisition module is connected with an axial pressure sensor and a displacement sensor to acquire axial force and displacement data in real time; the water circulation device and the drying device are controlled to automatically realize test operations such as water feeding, water discharging and drying in dry-wet circulation; damage identification in the dry-wet cycle process of the mudstone sample is achieved by controlling the acoustic emission system, and an acoustic emission detection result is stored to analyze the degradation effect of dry-wet cycle on the physical and mechanical properties of the mudstone sample.

Description

Technical Field

[0001] The invention belongs to the technical field of rock strength testing, and in particular relates to a rock dry-wet cycle testing device and a testing method thereof. Background Art

[0002] Since mudstone exhibits obvious characteristics such as water disintegration, mudification, and dehydration cracking under the action of dry-wet cycles, mudstone slopes experience significant deterioration in slope stability after experiencing various forms of dry-wet cycles (rainfall, groundwater level fluctuations, etc.) under natural conditions, which can easily lead to corresponding engineering problems. Experimental research on mudstone disintegration and mechanical degradation under dry-wet cycles has become relatively common. Many scholars have conducted relevant research, revealing the mudstone degradation mechanism and proposing indicators for quantitatively characterizing the degree of mudstone degradation to serve engineering practice. At present, the operating methods of this type of test have a common feature, that is, the mudstone samples are carried out under unconfined conditions when experiencing dry-wet cycles.

[0003] However, through the investigation and analysis of the instability events of high mudstone slopes in deep cuttings of highways, it can be found that mudstone slopes in heavy rainfall areas are in a state of dry-wet cycle for a long time, and the joints and fissures of mudstone slopes are very developed. With the collapse of mudstone on the slope surface, rainwater can more easily penetrate into the slope under the action of heavy rainfall, causing the mudstone inside the slope to deteriorate, which in turn leads to reduced slope stability and even instability. Due to the influence of gravity and other factors, the mudstone inside the slope is in a complex stress state during the dry-wet cycle process. The stress state has a great influence on the degree of degradation of the mudstone. The existing mudstone unconfined dry-wet cycle test device and its test method are difficult to meet the actual mechanical conditions of the mudstone inside the actual mudstone slope.

[0004] Therefore, based on the contradiction between the current test methods and the actual conditions, it is necessary to design a rock dry-wet cycle test device and its test method to make up for the shortcomings of the existing test methods. Summary of the invention

[0005] The present invention aims to provide a rock dry-wet cycle test device and a test method thereof, which solves the problem that the existing mudstone unconfined dry-wet cycle test device and a test method thereof are difficult to meet the real mechanical conditions of mudstone inside an actual mudstone slope.

[0006] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is as follows:

[0007] A rock dry-wet cycle test device is provided, which includes a loading system, a test cylinder, a measuring system, a water circulation device, a drying device, an acoustic emission system and a computer control system;

[0008] The loading system includes a loading frame base, a hydraulic device is arranged on the loading frame base, a lifting platform is arranged on the top of the hydraulic device, and a test platform is arranged on the lifting platform; a reaction frame is arranged on the top of the loading frame base, and a pressure rod is arranged on the reaction frame;

[0009] The test cylinder comprises a test inner cylinder and a test outer cylinder arranged on the test platform, a plurality of water-permeable holes are arranged on the cylinder wall of the test inner cylinder, a mudstone sample is arranged inside the test inner cylinder, a force transmission component for contacting with a pressure rod is arranged at the top opening of the test inner cylinder, and a sample base for contacting with the upper end surface of the test platform is arranged at the bottom of the test inner cylinder; the test outer cylinder is sleeved on the outside of the test inner cylinder, a cover plate with a plurality of evaporation holes is arranged on the top of the test outer cylinder, and a circular hole for the pressure rod to pass through is arranged at the center of the cover plate;

[0010] The measuring system includes an axial pressure sensor fixed on the pressure rod and a displacement sensor fixed on the reaction frame;

[0011] The water circulation device is used to transport water into the test outer cylinder;

[0012] The drying device includes an annular electric heating tube arranged on the inner wall of the test outer cylinder;

[0013] The acoustic emission system comprises an upper acoustic emission probe, a lower acoustic emission probe and an acoustic emission signal amplifier, wherein the upper acoustic emission probe and the lower acoustic emission probe are respectively arranged on the force transmission component and the sample base;

[0014] The computer control system includes a computer and a display electrically connected to each other, and the hydraulic device, axial pressure sensor, displacement sensor, water circulation device, annular electric heating pipe, upper acoustic emission probe, lower acoustic emission probe and acoustic emission signal amplifier are all electrically connected to the computer.

[0015] Furthermore, the reaction frame includes a reaction beam and two metal columns respectively arranged on both sides of the upper end surface of the loading frame base. The two sides of the reaction beam are respectively slidably connected to the two metal columns. An upper nut and a lower nut are threadedly connected to each metal column, and the reaction beam is located between the upper nut and the lower nut; a pressure rod is arranged at the center position of the lower end surface of the reaction beam; and a displacement sensor is arranged on one of the metal columns.

[0016] Furthermore, a strip-shaped level bubble is provided on the upper end surface of the reaction beam.

[0017] Furthermore, a slot is provided on the upper end surface of the test platform, and the bottom of the test outer cylinder is fixedly arranged in the slot.

[0018] Furthermore, a layer of metal filter is arranged inside the test inner cylinder; the test inner cylinder is assembled from three arc-shaped valves, and two fixing rings are arranged vertically and spaced apart on the circumferential outer wall of the test inner cylinder.

[0019] Furthermore, an upper permeable stone and a lower permeable stone are respectively arranged on the top and bottom of the mudstone sample; the upper end surface of the upper permeable stone contacts the force transmission component, and the lower permeable stone contacts the upper end surface of the sample base.

[0020] Furthermore, the force transmission component includes a sample top cap arranged on the upper end surface of the upper permeable stone, the sample top cap is provided with a force transmission cap, and the force transmission cap is provided with a steel ball in contact with the bottom of the pressure rod; the upper acoustic emission probe is arranged on the sample top cap.

[0021] Furthermore, a water inlet and a water outlet are respectively arranged on one side of the top and the other side of the bottom of the test outer cylinder; the water circulation device includes a water storage bucket, a drainage bucket and a drainage pipe, a water pump electrically connected to the computer is arranged in the water storage bucket, a water outlet of the water pump is connected to a water inlet pipe, and a free end of the water inlet pipe is connected to the water inlet;

[0022] One end of the drain pipe is connected to the water outlet, and the other end of the drain pipe is located in the exhaust barrel and is provided with an electric valve electrically connected to the computer.

[0023] The present invention also provides a test method for a rock dry-wet cycle test device, which comprises:

[0024] Step 1, preparing a test mudstone sample;

[0025] Step 2, sample loading: Place an upper permeable stone and a lower permeable stone on the upper end surface and the lower end surface of the mudstone sample respectively, then put the mudstone sample, the upper permeable stone and the lower permeable stone into the test inner cylinder together, and make the surface of the mudstone sample closely contact with the inner side of the test inner cylinder, and then use two fixing rings to fix the test inner cylinder;

[0026] Step 3, install the force transmission components, acoustic emission system and test inner cylinder: fix the two lower acoustic emission probes on the sample base, then place the sample base on the test platform, adjust the center of the sample base to align with the center of the test platform, then place the test inner cylinder and the mudstone sample as a whole on the sample base, fix the two upper acoustic emission probes on the sample top cap, then place the sample top cap on the upper permeable stone, place the force transmission cap on the sample top cap, and place the steel ball on the loading cap;

[0027] Step 4, install the test outer cylinder: place the test outer cylinder on the test platform, fix the test outer cylinder using the card slot on the test platform, and place the test cover plate on the test outer cylinder;

[0028] Step 5. Install and debug the loading system: adjust the position of the lower nut to move the reaction beam downward until the lower end surface of the pressure rod contacts the steel ball, and level the reaction beam to keep the strip level bubble of the reaction beam horizontal; tighten the lower nut and the upper nut to fix the reaction beam in the position of the metal column;

[0029] Step 6, conducting a dry-wet cycle test under confined conditions of mudstone: a computer-controlled loading system, a water circulation device, a drying device, and an acoustic emission system are used to conduct multiple dry-wet cycle tests on the test mudstone sample;

[0030] Step 7, perform uniaxial compression test on mudstone: after completing the corresponding number of dry-wet cycles on the mudstone sample, control the hydraulic device through the computer to lower the lifting platform, remove the test outer cylinder and the test inner cylinder, place the sample base on the test platform, align the center of the sample base with the center of the test platform, place the mudstone sample on the sample base, and then place the sample top cap on the upper permeable stone on the top surface of the mudstone sample, place a force transmission cap on the sample top cap, place a steel ball on the loading cap, control the hydraulic device to raise the lifting platform, and the axial pressure sensor and displacement sensor monitor the axial stress and axial displacement during the test respectively. When the mudstone sample is damaged, the lifting platform stops rising. The basis for judging whether the mudstone sample is damaged is that the axial stress drops to 50% of the peak stress. During the whole test, the acoustic emission system scans the mudstone sample with acoustic signals.

[0031] Further, step 6 comprises:

[0032] Step 6.1: Determine the overburden stress of the rock based on the depth of the rock sampling location and record it as σ z , the time required for the mudstone standard sample to change from dry state to saturated state under natural immersion conditions is measured in advance as t1, and the time required for the mudstone standard sample to change from saturated state to dry state under 60℃ oven conditions is measured as t2. The hydraulic device is controlled to raise the lifting platform, and the axial pressure sensor monitors the change of axial stress σ. When σ=σ z After the lifting platform stops rising, the acoustic emission system conducts a longitudinal wave velocity test on the mudstone sample every 5 minutes;

[0033] Step 6.2, the computer controls the water pump to pump the distilled water prepared in advance in the water storage bucket into the test outer cylinder along the water inlet pipe;

[0034] Step 6.3, after the immersion time reaches t1, the electric valve is controlled by the computer to open, and the water in the test outer cylinder is discharged into the drainage bucket along the drainage pipe. After the drainage is completed, the computer controls the electric valve of the drainage pipe to close, and then controls the annular electric heating tube to open, and the mudstone sample is dried at a temperature of 60°C. After the drying time reaches t2, the computer sends a command to close the switch of the annular electric heating tube, so that the mudstone sample is cooled at room temperature for 1 hour;

[0035] Step 6.4: Repeat steps 6.2 and 6.3 to conduct multiple dry-wet cycle tests on the test mudstone sample.

[0036] The beneficial effects of the present invention are as follows: 1. The present invention simulates the dry-wet cycle test of mudstone under lateral confinement conditions by designing a suitable test cylinder. The mudstone sample tends to expand laterally under the action of axial force, and cannot be deformed under the restriction of the test inner cylinder. It can be equivalent to the test inner cylinder applying confining pressure to the sample. Since rock masses in nature are under the ground stress field conditions dominated by gravity, the working conditions simulated by the present invention are more in line with actual conditions.

[0037] 2. The test tube of the present invention is exquisitely designed and easy to process. A large number of water-permeable holes are opened on the test inner tube, and a layer of 300-mesh metal filter is welded on the inner side. While ensuring water permeability, it not only prevents the loss of mudstone debris during the dry-wet cycle, but also reduces the stress concentration effect on the mudstone sample caused by the holes in the test inner tube. A large number of annular electric heating tubes are fixed on the inside of the test outer tube, which can accelerate the drying rate of the mudstone sample in the drying stage. At the same time, the evaporated water vapor can be discharged through the evaporation holes on the cover plate.

[0038] 3. The present invention is equipped with a computer control system and monitoring equipment such as axial pressure sensors, displacement sensors, and acoustic emission systems. Control instructions can be set in advance according to the test plan to automatically carry out dry-wet cycle tests under lateral confinement conditions, and mechanical tests of rocks after dry-wet cycles can also be carried out. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic structural diagram of the rock dry-wet cycle test device in the present invention.

[0040] Figure 2 for Figure 1 Schematic diagram of the structure in the AA direction.

[0041] Figure 3 for Figure 1 Schematic diagram of the structure in the BB direction.

[0042] Figure 4 for Figure 1 Schematic diagram of the structure in CC direction.

[0043] Among them, 1-metal column, 2-upper nut, 3-reaction beam, 4-lower nut, 5-axial pressure sensor, 6-cover plate, 7-upper acoustic emission probe, 8-test outer cylinder, 9-annular electric heating tube, 10-test inner cylinder, 11-water permeable hole, 12-lower acoustic emission probe, 13-drain pipe, 14-electric valve, 15-pressure rod, 16-computer, 17-evaporation hole, 18-steel ball, 19-force transmission cap, 20-acoustic emission signal amplifier, 21-sample top cap, 22-upper permeable stone, 23-fixing ring, 24-mudstone sample, 25-displacement sensor, 26-lower permeable stone, 27-water inlet pipe, 28-water pump, 29-sample base, 30-water storage bucket, 31-test platform, 32-lifting platform, 33-hydraulic device, 34-loading frame base, 35-drainage bucket, 36-metal filter, 37-strip level bubble. DETAILED DESCRIPTION

[0044] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0045] like Figure 1 to Figure 4 As shown, the present invention provides a rock dry-wet cycle test device, which includes a loading system, a test cylinder, a measuring system, a water circulation device, a drying device, an acoustic emission system and a computer 16 control system; the computer 16 control system includes a computer 16 and a display that are electrically connected to each other.

[0046] The loading system includes a loading frame base 34 , on which a hydraulic device 33 is arranged, on the top of which a lifting platform 32 is arranged, on which a test platform 31 is arranged; on the top of the loading frame base 34 , a reaction frame is arranged, on which a pressure rod 15 is arranged.

[0047] Specifically, the loading frame base 34 is composed of a rectangular metal base plate with a thickness of 150 mm and a metal shell. The bottom surface of the base is flat to ensure that it is in full contact with the bottom surface and the surface of the laboratory table to ensure the stability of the entire test equipment. The hydraulic device 33 is fixed on the bottom plate of the loading frame base 34, encapsulated in the metal shell of the loading frame base 34, and controlled by the computer 16; the lifting platform 32 is located on the telescopic end of the telescopic cylinder in the hydraulic device 33, and the lifting platform 32 can move up and down under the action of the hydraulic device 33. The upward movement of the lifting platform 32 is loading, and the downward movement is unloading; the test platform 31 is a circular steel plate with a thickness of 50 mm and a diameter of 200 mm, which is fixed on the upper part of the lifting platform 32.

[0048] like Figure 1 to Figure 3 As shown, the test cylinder includes a test inner cylinder 10 and a test outer cylinder 8 arranged on a test platform 31. A plurality of water-permeable holes 11 are arranged on the cylinder wall of the test inner cylinder 10, and the spacing between the plurality of water-permeable holes 11 is 2 mm to 3 mm. A mudstone sample 24 is arranged inside the test inner cylinder 10, a force transmission component for contacting with a pressure rod 15 is arranged at the top opening of the test inner cylinder 10, and a sample base 29 for contacting with the upper end surface of the test platform 31 is arranged at the bottom of the test inner cylinder 10; the test outer cylinder 8 is sleeved on the outside of the test inner cylinder 10, and a cover plate 6 with a plurality of evaporation holes 17 is arranged on the top of the test outer cylinder 8, and a circular hole for the pressure rod 15 to pass through is arranged at the center of the cover plate 6.

[0049] Specifically, the test inner cylinder 10 is made of inorganic non-metallic transparent materials that are resistant to high temperatures and corrosion. The inner diameter of the test inner cylinder 10 is 100 mm, the outer diameter is 120 mm, the height is 150 mm, and the thickness is 10 mm. A hole with a diameter of 5 mm is opened at the upper and lower parts, which are the water inlet and the water outlet, respectively. A layer of 300-mesh metal filter 36 is arranged inside the test inner cylinder 10 to prevent the loss of mudstone debris during the dry-wet cycle, and at the same time reduce the stress concentration effect on the mudstone sample 24 caused by the multiple water-permeable holes 11 in the test inner cylinder 10; the test inner cylinder 10 is assembled by three arc-shaped valves, and two fixing rings 23 are arranged vertically at intervals on the circumferential outer wall of the test inner cylinder 10. The inner diameter of the test inner cylinder 10 is 50 mm, the outer diameter is 70 mm, and the height is 110 mm; preferably, in order to make the contact between the valves more closely during assembly, one end of the assembly position is designed to be a groove and the other end is a protrusion. The inner diameter of the fixing ring 23 is 70 mm, and the outer diameter is 80 mm.

[0050] The cover plate 6 of the test outer cylinder 8 is a circular plate with a thickness of 5 mm and a diameter of 120 mm. It is made of high-temperature resistant and corrosion-resistant inorganic non-metallic transparent material. A circular hole with a diameter of 50 mm is opened with the center of the cover plate 6 as the center of the circle to allow the pressure rod 15 to pass through. Evaporation holes 17 are evenly drilled in the remaining parts. The aperture of the evaporation hole 17 is 1 mm, and the minimum distance between the two evaporation holes 17 is 10 mm, which is used to discharge the water vapor generated in the dry-wet cycle drying stage.

[0051] Preferably, a slot is provided on the test platform 31 for fixing the test outer cylinder 8 with an inner diameter of 100 mm and an outer diameter of 120 mm, so that the test outer cylinder 8 is in close contact with the test platform 31 and no water seepage occurs during the dry-wet cycle.

[0052] Specifically, Figure 1 and Figure 4As shown, as an implementation method of the reaction frame, the reaction frame includes a reaction beam 3 and two metal columns 1 respectively arranged on both sides of the upper end surface of the loading frame base 34, the two sides of the reaction beam 3 are slidingly connected to the two metal columns 1 respectively, each metal column 1 is threadedly connected with an upper nut 2 and a lower nut 4, and the reaction beam 3 is located between the upper nut 2 and the lower nut 4; a pressure rod 15 is arranged at the center position of the lower end surface of the reaction beam 3.

[0053] The metal columns 1 are fixed on both sides of the bottom plate of the loading frame base 34, with a diameter of 80mm and a length of 1500mm. The spacing between the two metal columns 1 is 600mm. The reaction beam 3 is fixed on the two metal columns 1 by two upper nuts 2 and two lower nuts 4. The position of the reaction beam 3 can be adjusted by adjusting the position of the nuts on the metal columns 1. Specifically, a strip level bubble 37 is installed on the reaction beam 3. After adjusting the position of the reaction beam 3, the reaction beam 3 should be kept horizontal. The pressure rod 15 is installed at the center of the bottom surface of the reaction beam 3 by bolt connection. In the entire loading system, the centers of the lifting platform 32, the test platform 31 and the pressure rod 15 are located on the same vertical line.

[0054] Specifically, an upper permeable stone 22 and a lower permeable stone 26 are respectively disposed on the top and bottom of the mudstone sample 24 ; the upper end surface of the upper permeable stone 22 contacts the force transmission component, and the lower permeable stone 26 contacts the upper end surface of the sample base 29 .

[0055] The force transmission component includes a sample top cap 21 arranged on the upper end surface of the upper permeable stone 22, a force transmission cap 19 is arranged on the sample top cap 21, and a steel ball 18 in contact with the bottom of the pressure rod 15 is arranged on the force transmission cap 19; the upper acoustic emission probe 7 is arranged on the sample top cap 21.

[0056] The measuring system includes an axial pressure sensor 5 fixed on the pressure rod 15 and a displacement sensor 25 on one of the metal columns 1; specifically, the axial pressure sensor 5 is fixed inside the pressure rod 15, and collects the axial force data applied to the mudstone sample 24 in real time and transmits it to the computer 16 for storage; the displacement sensor 25 is fixed on the metal column 1 using a displacement sensor 25 bracket. When measuring the displacement, the pointer of the displacement sensor 25 should be kept vertical and stand on the test platform 31, so that the vertical displacement of the test platform 31 can be measured, that is, the axial displacement of the mudstone sample 24.

[0057] The water circulation device is used to transport water into the test outer cylinder 8; the water circulation device includes a water storage barrel 30, a drainage barrel 35 and a drainage pipe 13. A water pump 28 electrically connected to the computer 16 is provided in the water storage barrel 30, and a water inlet pipe 27 is connected to the water outlet end of the water pump 28, and the free end of the water inlet pipe 27 is connected to the water inlet; one end of the drainage pipe 13 is connected to the water outlet, and the other end of the drainage pipe 13 is located in the exhaust barrel and is provided with an electric valve 14 electrically connected to the computer 16.

[0058] Specifically, the water inlet pipe 27 is a high-temperature and corrosion-resistant plastic pipe with a diameter of 5 mm, one end of which is connected to the water inlet of the test outer tube 8, and the other end is connected to the water pump 28, which is placed in the water storage barrel 30. The water in the water storage barrel 30 can be injected into the test outer tube 8 along the water inlet pipe 27 by the water pump 28, and the pumping is stopped when the water level reaches the height of the water inlet; the drain pipe 13 is a high-temperature and corrosion-resistant plastic pipe with a diameter of 5 mm, one end of which is connected to the drain port of the test outer tube 8, and the other end is connected to the drain barrel 35. An electric water valve is arranged on the drain pipe 13. After the mudstone sample 24 is saturated, the valve of the drain pipe 13 is opened to allow the water in the test outer tube 8 to be discharged into the drain barrel 35 along the drain pipe 13, wherein the water pump 2828 and the electric valve 1414 of the drain pipe 13 can both be controlled by the computer 16.

[0059] The drying device includes an annular electric heating tube 9 arranged on the inner wall of the test outer cylinder 8; specifically, the annular electric heating tube 9 adopts a circular carbon fiber heating tube with an insulating surface. It is mainly used to increase the temperature in the test cylinder after drainage and accelerate the drying rate of the sample. Its dimensions are 100mm in diameter, 10mm in tube diameter, 220V in voltage, and 1200W in single power. The heating temperature can be controlled by a computer 16. The heating tube is fixed on the inner side of the test outer cylinder 8 with a vertical spacing of 20mm.

[0060] The acoustic emission system includes an upper acoustic emission probe 7, a lower acoustic emission probe 12 and an acoustic emission signal amplifier 20, and the upper acoustic emission probe 7 and the lower acoustic emission probe 12 are respectively arranged on the sample top cap 21 and the sample base 29. Specifically, the acoustic emission system is composed of two upper acoustic emission probes 7, two lower acoustic emission probes 12 and four acoustic emission signal amplifiers 20, and the acoustic emission probes are respectively connected to an acoustic emission signal amplifier 20, and the four acoustic emission signal amplifiers 20 are connected to the computer 16. The computer 16 controls the real-time longitudinal wave velocity test and acoustic signal collection of the mudstone sample 24 to obtain the degradation damage data of the mudstone sample 24 during the dry-wet cycle process and the uniaxial compression test.

[0061] The computer 16 control system realizes good human-computer interaction and automatic control of the test. By connecting with the hydraulic device 33, the loading system can be controlled to load the sample; by connecting with the data acquisition instrument of the axial pressure sensor 5 and the displacement sensor 25, the axial force and axial deformation data of the test can be collected in real time; by connecting with the water pump 28, the electric valve 14 and the annular electric heating tube 9 switch, the dry-wet cycle operation of the mudstone sample 24 can be performed according to different test schemes; by connecting with the acoustic emission signal amplifier 20, the upper acoustic emission probe 7 and the lower acoustic emission probe 12 can be controlled to perform real-time longitudinal wave velocity testing and acoustic signal collection on the mudstone sample 24, and the results are stored in the computer 16.

[0062] The present invention also provides a test method for a rock dry-wet cycle test device, which comprises:

[0063] Step 1, preparing the test mudstone sample 24: using a wire cutting machine to cut the blocky mudstone into standard samples of ф50 mm×100 mm along the direction perpendicular to the joints, using a balance to weigh the mass of the sample, and then placing the sample in a 60° C. oven for continuous drying for 48 hours, and after drying, using a balance to weigh the mass of the sample again, and placing the sample in a dry and closed environment to cool to room temperature to obtain the mudstone sample 24;

[0064] Step 2, sample loading: Place an upper permeable stone 22 and a lower permeable stone 26 on the upper end surface and the lower end surface of the mudstone sample 24, respectively, and then put the mudstone sample 24, the upper permeable stone 22 and the lower permeable stone 26 into the test inner cylinder 10 together, and make the surface of the mudstone sample 24 closely contact with the inner side of the test inner cylinder 10, and then use two fixing rings 23 to fix the test inner cylinder 10;

[0065] Step 3, install the force transmission components, the acoustic emission system and the test inner cylinder 10: fix the two lower acoustic emission probes 12 on the sample base 29, then place the sample base 29 on the test platform 31, adjust the center of the sample base 29 to align with the center of the test platform 31, then place the test inner cylinder 10 and the mudstone sample 24 as a whole on the sample base 29, fix the two upper acoustic emission probes 7 on the sample top cap 21, then place the sample top cap 21 on the upper permeable stone 22, place the force transmission cap 19 on the sample top cap 21, and place the steel ball 18 on the loading cap;

[0066] Step 4, installing the test outer cylinder 8: placing the test outer cylinder 8 on the test platform 31, fixing the test outer cylinder 8 by using the clamping groove on the test platform 31, and placing the test cover plate 6 on the test outer cylinder 8;

[0067] Step 5, install and debug the loading system: adjust the position of the lower nut 4 to move the reaction beam 3 downward until the lower end surface of the pressure rod 15 contacts the steel ball 18, and level the reaction beam 3 to keep the strip level bubble 37 of the reaction beam 3 horizontal; tighten the lower nut 4 and the upper nut 2 to fix the reaction beam 3 on the metal column 1;

[0068] Step 6, performing a dry-wet cycle test under confined conditions of mudstone: the computer 16 controls the loading system, the water circulation device, the drying device and the acoustic emission system to perform multiple dry-wet cycle tests on the test mudstone sample 24;

[0069] Step 7, perform uniaxial compression test on mudstone: after completing the corresponding number of dry-wet cycles on the mudstone sample 24, control the hydraulic device 33 through the computer 16 to lower the lifting platform 32, remove the test outer cylinder 8 and the test inner cylinder 10, place the sample base 29 on the test platform 31, align the center of the sample base 29 with the center of the test platform 31, place the mudstone sample 24 on the sample base 29, and then place the sample top cap 21 on the upper permeable stone 22 on the top surface of the mudstone sample 24, place the force transmission cap 19 on the sample top cap 21, place the steel ball 18 on the loading cap, control the hydraulic device 33 to raise the lifting platform 32 at a rate of 0.02 mm / min, and the axial pressure sensor 5 and the displacement sensor 25 respectively monitor the axial stress σ and the axial displacement ε during the test. When the mudstone sample 24 is damaged, the lifting platform 32 stops rising. The basis for judging whether the mudstone sample 24 is damaged is that the axial stress σ drops to the peak stress σ p During the whole test, the acoustic emission system scans the mudstone sample 24 for acoustic signals.

[0070] Further, step 6 comprises:

[0071] Step 6.1: Determine the overburden stress of the rock based on the depth of the rock sampling location and record it as σ z , the time required for the mudstone standard sample to change from a dry state to a saturated state under natural immersion conditions is measured in advance as t1, and the time required for the mudstone standard sample to change from a saturated state to a dry state under 60°C oven conditions is measured as t2, the hydraulic device 33 is controlled to raise the lifting platform 32, and the axial pressure sensor 5 monitors the change of the axial stress σ. When σ=σ z After that, the lifting platform 32 stops rising, and the acoustic emission system performs a longitudinal wave velocity test on the mudstone sample 24 every 5 minutes;

[0072] Step 6.2, the computer 16 controls the water pump 28 to pump the distilled water prepared in advance in the water storage barrel 30 into the test outer cylinder 8 along the water inlet pipe 27, and the amount of water pumped is 500 ml;

[0073] Step 6.3, after the immersion time reaches t1, the electric valve 14 is controlled to open by the computer 16, and the water in the test outer cylinder 8 is discharged into the drainage bucket 35 along the drainage pipe 13, and the drainage time is 2 minutes; after the drainage is completed, the computer 16 controls the electric valve 14 of the drainage pipe 13 to close, and then controls the annular electric heating tube 9 to open, and the mudstone sample 24 is dried at a temperature of 60°C. After the drying time reaches t2, the computer 16 sends an instruction to close the switch of the annular electric heating tube 9, so that the mudstone sample 24 is cooled at room temperature for 1 hour;

[0074] Step 6.4: Repeat steps 6.2 and 6.3 to carry out multiple dry-wet cycle tests on the test mudstone sample 24.

[0075] In summary, the present invention simulates the dry-wet cycle test of mudstone under lateral confinement conditions by designing a suitable test cylinder. The mudstone sample 24 tends to expand laterally under the action of axial force, and cannot be deformed under the restriction of the test inner cylinder 10. It can be equivalent to the test inner cylinder 10 applying confining pressure to the sample. Since rock masses in nature are under the conditions of a geostress field dominated by gravity, the working conditions simulated by the present invention are more in line with actual conditions.

Claims

1. A rock dry-wet cycle test device, characterized in that: It includes a loading system, a test cylinder, a measuring system, a water circulation device, a drying device, an acoustic emission system and a computer control system; The loading system comprises a loading frame base, a hydraulic device is arranged on the loading frame base, a lifting platform is arranged on the top of the hydraulic device, and a test platform is arranged on the lifting platform; a reaction frame is arranged on the top of the loading frame base, and a pressure rod is arranged on the reaction frame; The test cylinder comprises a test inner cylinder and a test outer cylinder arranged on the test platform, a plurality of water-permeable holes are arranged on the cylinder wall of the test inner cylinder, a mudstone sample is arranged inside the test inner cylinder, a force transmission component for contacting the pressure rod is arranged at the top opening of the test inner cylinder, and a sample base for contacting the upper end surface of the test platform is arranged at the bottom of the test inner cylinder; the test outer cylinder is sleeved on the outside of the test inner cylinder, a cover plate with a plurality of evaporation holes is arranged on the top of the test outer cylinder, and a circular hole for the pressure rod to pass through is arranged at the center position of the cover plate; The measuring system comprises an axial pressure sensor fixed on the pressure rod and a displacement sensor fixed on the reaction frame; The water circulation device is used to transport water into the test outer cylinder; The drying device comprises an annular electric heating tube arranged on the inner wall of the test outer cylinder; The acoustic emission system comprises an upper acoustic emission probe, a lower acoustic emission probe and an acoustic emission signal amplifier, wherein the upper acoustic emission probe and the lower acoustic emission probe are respectively arranged on the force transmission component and the sample base; The computer control system includes a computer and a display electrically connected to each other, and the hydraulic device, axial pressure sensor, displacement sensor, water circulation device, annular electric heating pipe, upper acoustic emission probe, lower acoustic emission probe and acoustic emission signal amplifier are all electrically connected to the computer.

2. The rock dry-wet cycle test device according to claim 1, characterized in that: The reaction frame includes a reaction beam and two metal columns respectively arranged on both sides of the upper end surface of the loading frame base, the two sides of the reaction beam are respectively slidably connected to the two metal columns, each of the metal columns is threadedly connected with an upper nut and a lower nut, and the reaction beam is located between the upper nut and the lower nut; the pressure rod is arranged at the center position of the lower end surface of the reaction beam; the displacement sensor is arranged on one of the metal columns.

3. The rock dry-wet cycle test device according to claim 2, characterized in that: The upper end surface of the reaction beam is provided with a strip-shaped level bubble.

4. The rock dry-wet cycle test device according to claim 3, characterized in that: The upper end surface of the test platform is provided with a slot, and the bottom of the test outer cylinder is fixedly arranged in the slot.

5. The rock dry-wet cycle test device according to claim 4, characterized in that: A layer of metal filter is arranged inside the test inner cylinder; the test inner cylinder is assembled from three arc-shaped valves, and two fixing rings are arranged vertically and spaced apart on the circumferential outer wall of the test inner cylinder.

6. The rock dry-wet cycle test device according to claim 5, characterized in that: An upper permeable stone and a lower permeable stone are respectively arranged on the top and the bottom of the mudstone sample; the upper end surface of the upper permeable stone contacts the force transmission component, and the lower permeable stone contacts the upper end surface of the sample base.

7. The rock dry-wet cycle test device according to claim 6, characterized in that: The force transmission component comprises a sample top cap arranged on the upper end surface of the upper permeable stone, the sample top cap is provided with a force transmission cap, and the force transmission cap is provided with a steel ball in contact with the bottom of the pressure rod; the upper acoustic emission probe is arranged on the sample top cap.

8. The rock dry-wet cycle test device according to claim 7, characterized in that: A water inlet and a water outlet are respectively arranged on one side of the top and the other side of the bottom of the test outer cylinder; the water circulation device comprises a water storage bucket, a drainage bucket and a drainage pipe, a water pump electrically connected to the computer is arranged in the water storage bucket, a water outlet of the water pump is connected to a water inlet pipe, and a free end of the water inlet pipe is connected to the water inlet; One end of the drain pipe is communicated with the water outlet, and the other end of the drain pipe is located in the exhaust barrel and is provided with an electric valve electrically connected to the computer.

9. A test method for the rock dry-wet cycle test device according to claim 8, characterized in that: include: Step 1, preparing a test mudstone sample; Step 2, sample loading: Place an upper permeable stone and a lower permeable stone on the upper end surface and the lower end surface of the mudstone sample respectively, then put the mudstone sample, the upper permeable stone and the lower permeable stone into the test inner cylinder together, and make the surface of the mudstone sample closely contact with the inner side of the test inner cylinder, and then use two fixing rings to fix the test inner cylinder; Step 3, install the force transmission components, acoustic emission system and test inner cylinder: fix the two lower acoustic emission probes on the sample base, then place the sample base on the test platform, adjust the center of the sample base to align with the center of the test platform, then place the test inner cylinder and the mudstone sample as a whole on the sample base, fix the two upper acoustic emission probes on the sample top cap, then place the sample top cap on the upper permeable stone, place the force transmission cap on the sample top cap, and place the steel ball on the loading cap; Step 4, install the test outer cylinder: place the test outer cylinder on the test platform, fix the test outer cylinder using the card slot on the test platform, and place the test cover plate on the test outer cylinder; Step 5. Install and debug the loading system: adjust the position of the lower nut to move the reaction beam downward until the lower end surface of the pressure rod contacts the steel ball, and level the reaction beam to keep the strip level bubble of the reaction beam horizontal; tighten the lower nut and the upper nut to fix the reaction beam in the position of the metal column; Step 6, conducting a dry-wet cycle test under confined conditions of mudstone: a computer-controlled loading system, a water circulation device, a drying device, and an acoustic emission system are used to conduct multiple dry-wet cycle tests on the test mudstone sample; Step 7, perform uniaxial compression test on mudstone: after completing the corresponding number of dry-wet cycles on the mudstone sample, control the hydraulic device through the computer to lower the lifting platform, remove the test outer cylinder and the test inner cylinder, place the sample base on the test platform, align the center of the sample base with the center of the test platform, place the mudstone sample on the sample base, and then place the sample top cap on the upper permeable stone on the top surface of the mudstone sample, place a force transmission cap on the sample top cap, place a steel ball on the loading cap, control the hydraulic device to raise the lifting platform, and the axial pressure sensor and displacement sensor monitor the axial stress and axial displacement during the test respectively. When the mudstone sample is damaged, the lifting platform stops rising. The basis for judging whether the mudstone sample is damaged is that the axial stress drops to 50% of the peak stress. During the whole test, the acoustic emission system scans the mudstone sample with acoustic signals.

10. The test method of the rock dry-wet cycle test device according to claim 9, characterized in that: The step 6 comprises: Step 6.1: Determine the overburden stress of the rock based on the depth of the rock sampling location and record it as σ z , the time required for the mudstone standard sample to change from dry state to saturated state under natural immersion conditions is measured in advance as t1, and the time required for the mudstone standard sample to change from saturated state to dry state under 60℃ oven conditions is measured as t2. The hydraulic device is controlled to raise the lifting platform, and the axial pressure sensor monitors the change of axial stress σ. When σ=σ z After the lifting platform stops rising, the acoustic emission system conducts a longitudinal wave velocity test on the mudstone sample every 5 minutes; Step 6.2, the computer controls the water pump to pump the distilled water prepared in advance in the water storage bucket into the test outer cylinder along the water inlet pipe; Step 6.3, after the immersion time reaches t1, the electric valve is controlled by the computer to open, and the water in the test outer cylinder is discharged into the drainage bucket along the drainage pipe. After the drainage is completed, the computer controls the electric valve of the drainage pipe to close, and then controls the annular electric heating tube to open, and the mudstone sample is dried at a temperature of 60°C. After the drying time reaches t2, the computer sends a command to close the switch of the annular electric heating tube, so that the mudstone sample is cooled at room temperature for 1 hour; Step 6.4: Repeat steps 6.2 and 6.3 to conduct multiple dry-wet cycle tests on the test mudstone sample.

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