CN107290222B - Rock triaxial test equipment and method - Google Patents
Rock triaxial test equipment and method Download PDFInfo
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- CN107290222B CN107290222B CN201710610035.0A CN201710610035A CN107290222B CN 107290222 B CN107290222 B CN 107290222B CN 201710610035 A CN201710610035 A CN 201710610035A CN 107290222 B CN107290222 B CN 107290222B
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Abstract
The embodiment of the invention provides rock triaxial test equipment and a rock triaxial test method, wherein the equipment comprises a main frame and a pressure chamber; wherein the main frame is a square frame, and the center of the main frame is provided with a space for accommodating the pressure chamber; the pressure chamber comprises a cylinder body and a base, and the rest bases of the cylinder body are detachably fixed together through split type hoops to form a sealed inner cavity; an upper pressure head and a lower pressure head are arranged in the cylinder body, and the positions of the upper pressure head and the lower pressure head correspond to each other so as to apply axial pressure on the test piece; and the base is provided with a confining pressure inlet and a confining pressure outlet so as to apply radial pressure to the test piece; an axial extensometer and a radial extensometer are arranged in the cylinder body; an air outlet is arranged at the top of the cylinder body, and an air inlet is arranged on the lower pressure head; the test device also comprises a pressure chamber confining pressure servo loading mechanism for providing power required by the test for the pressure chamber.
Description
Technical Field
The invention relates to the technical field of test equipment, in particular to rock triaxial test equipment and a rock triaxial test method.
Background
A method for measuring the methane adsorption amount of coal MT/T752-1997, an engineering rock mass test method standard GB/T50266, a railway engineering rock test regulation TB101115 and a highway engineering rock test regulation JTGE41-2005 are the current test standards mainly related to coal rocks or rocks. The uniaxial and triaxial compression of the coal rock and the gas permeation and water seepage high-temperature coupling test are important test modes for testing the coal rock and the rock, and the method can accurately measure various indexes of the coal rock and the rock and is very important for the field of infrastructure construction. The existing rock testing equipment has various types, but all have design defects, so that the final measuring result is not accurate enough.
Disclosure of Invention
Aiming at the problem that the final test result is not accurate enough due to the fact that rock test equipment in the prior art is unreasonable in structure, the embodiment of the invention aims to provide the device and the method for testing the triaxial earth rock test equipment, which are reasonable in structure and accurate in test result.
In order to solve the above problems, an embodiment of the present invention provides a triaxial rock testing apparatus, including a main frame and a pressure chamber; wherein the main frame is a square frame, and the center of the main frame is provided with a space for accommodating the pressure chamber; the pressure chamber comprises a cylinder body and a base, and the rest bases of the cylinder body are detachably fixed together through split type hoops to form a sealed inner cavity; an upper pressure head and a lower pressure head are arranged in the cylinder body, and the positions of the upper pressure head and the lower pressure head correspond to each other so as to apply axial pressure on the test piece; and the base is provided with a confining pressure inlet and a confining pressure outlet so as to apply radial pressure to the test piece; an axial extensometer and a radial extensometer are arranged in the cylinder body; an air outlet is arranged at the top of the cylinder body, and an air inlet is arranged on the lower pressure head;
the test device also comprises a pressure chamber confining pressure servo loading mechanism for providing power required by the test for the pressure chamber. The pressure chamber confining pressure servo loading mechanism comprises a hydraulic oil tank, an oil pump, a piston, a pressure chamber and an air compressor; wherein the pressure chamber may be the pressure chamber as shown. The hydraulic oil tank is connected with the pressure chamber through an oil pump, and the air compressor is also connected with the pressure chamber. The hydraulic oil tank is used for storing hydraulic oil so as to input the hydraulic oil into the pressure chamber through the action of a piston of the oil pump to provide confining pressure; and after the test is finished, the pressure chamber is pressurized by an air compressor so as to return the hydraulic oil to the hydraulic oil tank.
The technical scheme of the invention has the following beneficial effects: the technical scheme provides rock triaxial test equipment and a rock triaxial test method, which can test rocks (particularly coal rocks) more accurately.
Drawings
FIG. 1 is a schematic side view of a main frame according to an embodiment of the present invention;
FIG. 2 is a schematic front view of the structure of FIG. 1;
FIG. 3 is a schematic sectional view of the pressure chamber;
FIG. 4 is a schematic view of a confining pressure servo loading mechanism of a pressure chamber;
FIG. 5 is a schematic structural diagram of a gas adsorption amount measuring apparatus;
FIGS. 6 and 7 are schematic views of high pressure displacement model tube configurations;
FIG. 8 is a schematic structural view of a ring pressure tracking and measuring mechanism;
FIG. 9 is a diagram showing the working state of the pressure chamber;
description of reference numerals:
1: a main frame;
2: a motor;
3: a pressure chamber;
31: a positioning pin hole;
32: hanging a lug;
33: a lifting guide rail;
34: a barrel;
35: an exhaust port;
36: an air inlet;
37: a confining pressure inlet and outlet;
38: a base;
39: a split type clamp;
301: an upper pressure head;
302: a lower pressure head;
303: an axial extensometer;
304: a radial extensometer;
4: a test piece;
5: a lifting mechanism;
6: a guide rail lifting mechanism;
71: a hydraulic oil tank;
72: an oil pump;
73: a piston;
74: a pressure chamber;
75: an air compressor;
81: a vacuum pump;
82: a pipeline calibration measuring tube;
83: a gas component detector;
84: a flow meter;
85: a high pressure gas cylinder;
86: a measuring tube is calibrated in the inflation tank;
87: a liquid bath;
88: an inflation tank;
89: a confining pressure booster;
90: a pressure sensor;
91: a pipeline volume calibration clamp;
92: a spoke-type force sensor;
93: a temperature sensor;
101: an exhaust hole;
102: an upper pressure head;
103: an axial extensometer;
104: a housing;
105: an inner shell;
106: a gas outlet pipe;
107: heat-shrinkable tubing;
108: a lower pressure head;
109: a drive-off gas inlet;
110: a drive-off gas outlet;
111: an interlayer pressure inlet;
201: an outlet gas reference tank;
202: an inlet gas reference tank;
203: a high pressure gas tank.
Detailed Description
In order to make the technical problems, technical solutions and advantages of the present invention more apparent, the following detailed description is given with reference to the accompanying drawings and specific embodiments.
The rock triaxial test equipment of the embodiment of the invention comprises: the main frame 1, the motor 2, the pressure chamber 3, the electro-hydraulic servo loading system, the functional device, the measurement control part, the computer control and data processing system form all parts and function description.
As shown in fig. 1 and 2, the main frame 1 is a square frame, and a space for accommodating the pressure chamber 3 is provided in the center; a lifting mechanism 5 and a rail lifting mechanism 32 are provided on one side of the main frame 1. As shown in fig. 2, the pressure chamber 3 comprises a cylinder 34 and a base 38, and the base 38 of the cylinder 34 is detachably fixed together by a split-type clamp 39 to form a sealed inner cavity; an upper pressure head 301 and a lower pressure head 302 are arranged in the cylinder 34, and the positions of the upper pressure head 301 and the lower pressure head 302 correspond to each other so as to apply axial pressure on the test piece 4; and the base 38 is provided with a confining pressure inlet and outlet 37 to apply radial pressure to the test piece 4; and an axial extensometer 303 and a radial extensometer 304 are arranged in the cylinder body 34. As shown in fig. 3, an exhaust port 35 is provided at the top of the barrel 34, and an intake port 36 is provided on the lower ram 302. As shown in fig. 3, a hanging lug 32 is provided on the top of the cylinder 34, and a positioning pin hole 31 is provided on the bottom of the base 38.
As shown in fig. 1, the lifting mechanism 5 includes a bracket, a lifting cylinder, and a piston rod; wherein the support lateral part is fixed on the side of main frame 1, and the lift cylinder is fixed on the support, lift cylinder bottom is equipped with the piston rod that extends the support, and the piston rod bottom is equipped with the buckle in order to drive pressure chamber 3 and remove with the hangers 32 detachable fixed connection at the barrel 34 top of pressure chamber 3.
A pressure chamber confining pressure servo loading mechanism as shown in fig. 4 is also included to provide the pressure chamber 3 with the power required for the test. The pressure chamber confining pressure servo loading mechanism shown in fig. 4 comprises a hydraulic oil tank 71, an oil pump 72, a piston 73, a pressure chamber 74 and an air compressor 75; wherein the pressure chamber 74 may be the pressure chamber 3 as shown in fig. 3. The hydraulic oil tank 71 is connected to the pressure chamber 74 via an oil pump 72, and the air compressor 74 is also connected to the pressure chamber 74. Wherein the hydraulic oil tank 71 is used for storing hydraulic oil to be input into the pressure chamber 74 by the action of the piston 73 of the oil pump 72 to provide confining pressure; and after the test is completed, the pressure chamber 74 is pressurized by the air compressor 75 to return the hydraulic oil to the hydraulic oil tank 71. Since the test piece 4 may be chipped during the test, a valve and a waste liquid pool for discharging muddy water may be provided in the bottom portion of the hydraulic oil tank 71.
The device also comprises a gas adsorption quantity measuring mechanism as shown in figure 5, and is used for measuring the isothermal adsorption curve of the sample. As shown in fig. 5, the gas adsorption amount measuring mechanism includes: a pipeline calibration measuring tube 82, a gas composition detector 83, a flow meter 84, a high-pressure gas cylinder 85, an inflation tank calibration measuring tube 86, a liquid bath 87, an inflation tank 88, a confining pressure booster 89, a pressure sensor 90, a pipeline volume calibration clamp 91, a spoke type force sensor 92 and a temperature sensor 93. The confining pressure booster 89 is connected with the pressure chamber 3 through the pressure sensor 90 to boost the pressure chamber, and a temperature sensor 93 and a spoke type force sensor 92 are arranged in the pressure chamber 3. The pressure chamber 3 is connected with an inflation pipeline and an air discharge pipeline, and the inflation pipeline is provided with an inflation tank 88, an inflation tank calibration measuring tube 86 and a high-pressure gas bottle 85; and the air discharge pipeline is provided with a pipeline calibration measuring pipe 82, a gas composition detector 83 and a flowmeter 84; and a vacuum pump 81 connected with the inflation pipeline and the deflation pipeline in an openable and closable manner. As shown in fig. 5, the aeration tank is disposed in a bath 87, and the bath 87 may be a water bath or an oil bath. As shown in fig. 5, a pipe volume calibration jig 91 is further included.
The device also comprises a high-pressure displacement model pipe mechanism as shown in figures 6 and 7, and the high-pressure displacement model pipe is used for a high-pressure displacement test and an adsorption free expansion body deformation test. The high-pressure displacement model pipe is used for high-pressure displacement experiments and adsorption free expansion body change experiments, and in order to ensure that the volume of liquid around a test piece is not changed (the diameter and the length of the model pipe are not changed) when the pressure is changed, so that the precision of a measurement result is influenced, the model pipe of the embodiment of the invention adopts a double-layer structure, the pressure of an inner-layer pressure-resistant part is equal to that of an interlayer part, and the volume change quantity of the liquid in the model pipe (a measurement body change part) caused by pressure change is zero theoretically. The pressure in the model pipe is increased due to the expansion of the test piece, liquid in the model pipe needs to be pumped out by the metering pump in order to maintain the internal pressure unchanged, and the volume of the liquid pumped out by the metering pump is the variable of the free expansion body. The axial extensometer (applicable below 100 ℃) can measure the axial deformation, and the average radial deformation of the test piece can be calculated through the volume variable and the axial deformation. The model pipe and the heat conducting oil can expand along with the temperature, and the initial volume needs to be recorded or reset relative to the initial volume during the experiment of each temperature section. In order to reduce the excessive expansion caused by the temperature rise, the inner cylinder of the die tube, the supporting frame and the pressure heads at the two ends of the test piece can be made of invar steel, the linear expansion coefficient of the invar steel is only 1.8x10-6 on average at 0-200 ℃, and the invar steel is about 1/7 of common carbon steel (12.1-13.5x10-6), so that the measurement precision is higher. The high-precision metering pump provides steady voltage and volume change measurement for the test piece confining pressure.
As shown in fig. 5, the high-pressure displacement model pipe mechanism comprises a double-layer shell consisting of an outer shell 104 and an inner shell 105, and the double-layer shell is provided with an interlayer pressure inlet 111 for pressurizing an interlayer; as shown in fig. 5, a heat-shrinkable sleeve 107 for accommodating the test piece 4 is arranged in the double-layer shell; an upper ram 102 and a lower ram 108 are provided on the top and bottom of the heat shrink tubing 107, respectively. As shown in fig. 5, a gas outlet pipe 106 is arranged in the inner shell 105, the gas outlet pipe 106 is connected with a driving gas inlet 109, the driving gas inlet 109 is arranged at the bottom of the double-layer shell, one end of the gas outlet pipe 106 is connected with the driving gas inlet 109, and the other end extends to the top of the double-layer shell. As shown in fig. 5, the double-layered housing is provided with a vent hole 101 at the top and a purge gas outlet 110 at the bottom.
The ring pressure tracking and measuring mechanism comprises a high-precision differential pressure meter, a confining pressure servo loading device and a high-precision displacement sensor. The ring pressure tracking system can realize synchronous pressure rise of coal sample gas and confining pressure liquid in the heat shrinkage pipe of the reaction chamber, and displacement variation of the hole pressure servo loading device is measured through a high-precision displacement sensor so as to calculate the volume free expansion amount of coal sample adsorption. As shown in fig. 7, includes: the device comprises an oil storage tank 201, a high-pressure displacement model pipe 202, a confining pressure servo loading device 203 and a differential pressure gauge DP 2; a gas collector 204, a gas-liquid separator 205, a gas chromatograph 206; the confining pressure servo loading device 203 is connected with the high-pressure displacement model pipe 202, and the differential pressure gauge DP2 is connected with the high-pressure displacement model pipe 202; wherein the high pressure displacement model pipe 202 is connected with a gas-liquid separator 205 and a gas-liquid collector 204, and is also connected with a gas chromatograph 206 to analyze the gas components of the treatment process.
As shown in fig. 9, the principle of the permeability to rock of the apparatus according to the embodiment of the present invention is:
1. placing a test piece 4 in the pressure chamber 3, sealing the upper pressure head 301 and the lower pressure head 302 with the test piece by using a protective sleeve, and wrapping the test piece 4 of the coal sample with a heat-shrinkable sleeve (or other materials) to isolate an air passage and an oil passage;
2. the sample 4, inlet gas reference tank 202, outlet gas reference tank 201 and tube are then placedVacuumizing the way and calibrating the volume; then vacuumizing the reactor to remove CO2Penetrating into the pores of the test piece 4 from the high-pressure steel cylinder 203 through the bottom of the triaxial penetration device, firstly introducing high-pressure gas into the gas inlet reference tank 202, closing the gas inlet valve, and reading the pressure difference value of the pressure difference meter CP 2; then the air inlet valve of the test piece is opened, CO2The sample 4 enters the gas outlet reference tank 201, and the permeability coefficient of the sample is calculated through the pressure difference and the volume of the gas inlet and outlet reference tank 201 after the pressure is balanced, wherein the specific calculation formula is as follows:
as shown in fig. 5, the experimental principle of coal rock adsorption is as follows:
1. the determination method comprises the following steps: and (3) loading the treated dry coal sample into a pressure chamber, adding a certain confining pressure, carrying out vacuum degassing, measuring the residual volume of an adsorption tank, filling a certain volume of methane into the pressure chamber, so that the pressure in the protective sleeve is balanced, part of gas is adsorbed, part of gas is still in the residual volume in a free state, knowing the volume of the filled gas, and deducting the free volume of the residual volume to obtain the adsorption volume.
2. Free space volume determination: setting and adjusting the temperature of the system to enable the temperature of the pressure chamber and the reference cylinder to reach required values, opening a helium tank to fill helium into the system, adjusting the pressure value of the reference cylinder to 2-30MPa, closing a valve of the reference cylinder, opening a connecting valve of the pressure chamber and the reference cylinder, and acquiring a group of data after pressure is balanced.
And repeating the steps twice to obtain the volume of the coal sample, and calculating the volume of the free space in the sample cylinder. The free space volume was measured 3 times repeatedly.
The volume calculation formula of the coal sample is as follows:
VSvolume of coal sample in cubic centimeters (cm)3)；p1Post-equilibrium pressure in megapascals (MPa); p is a radical of2Reference cylinder initial pressure, unitIs megapascal (MPa); p is a radical of3Sample cylinder initial pressure in megapascals (MPa); t is1The temperature after equilibrium is expressed in units of on (K); t is2Reference cylinder initial temperature in units of on (K); t is3The initial temperature of the sample cylinder is expressed by the unit of opening (K); vlThe total volume of the system is in cubic centimeters (cm)3)；V2Reference cylinder volume in cubic centimeters (cm)3)；V3The volume of the sample cylinder is in cubic centimeter (cm)3)；Z1The compression factor of the gas under equilibrium conditions; z2Reference cylinder initial gas compression factor; z3The compression factor of the initial gas of the sample cylinder.
And (5) solving the volume of the coal sample, and calculating the volume of the free space in the sample cylinder.
The calculation formula is shown as follows:
Vf＝V0-VS
in the formula, VfFree space volume in cubic centimeters (cm)3)；V0The total volume of the sample cylinder is in cubic centimeter (cm)3)；VSVolume of coal sample in cubic centimeters (cm)3)。
According to the equilibrium pressure and temperature of reference cylinder and pressure chamber, calculating adsorption quantity of different equilibrium pressure points, and its calculation formula is pV ═ nZRT
In the formula:
p is gas pressure in megapascals (MPa); v gas volume in cubic centimeters (cm)3) (ii) a n is the number of moles of gas, in moles (mol); z is the compressibility factor of the gas; r is a molar gas constant which is expressed in units of coke per mole (J/(mol. K)); t is the equilibrium temperature in units of on (K).
Respectively calculating the mole number n of the gas in the pressure chamber before the balance of each pressure point1And the number of moles n of gas in the pressure chamber after equilibrium2The number of moles n of the gas adsorbed in the coal sampleiComprises the following steps:
ni＝n1-n2
in the formula: n isiThe mole number of the gas is expressed in the unit of mole (mol); n is1Before balancingThe number of moles of gas in the sample cylinder is expressed in moles (mol); n is2The number of moles of gas in the sample cylinder after equilibration is in moles (mol).
Total volume (V) of adsorbed gas at each pressure pointi) See the following equation:
Vi＝ni×22.4×1000
adsorption amount (V) at each pressure pointAmount of adsorption) See the following equation:
Vamount of suction and delivery＝Vi/Gc
In the formula: vAmount of suction and deliveryThe absorption amount is in unit of cubic centimeter per gram (cm)3.g-1)；ViThe total volume of the adsorbed gas is in cubic centimeters (cm)3)；GcThe unit of the coal sample mass is gram (g).
3. Calculating VLAnd pL
According to Langmuir equation:
p/V＝p/VL+pL/VL
in the formula: p is gas pressure in megapascals (MPa); v is the absorption capacity under the pressure p and the unit is cubic centimeter per gram (cm)3.g-1)；VLThe maximum absorption capacity, also called Langmuir volume, is expressed in cubic centimeters per gram (cm)3.g-1)；pLLangmuir pressure in MegaPascals (MPa).
If let A equal to 1/VLAnd B ═ pL/VLThe equation can be derived as a function of p/V and p:
p/V＝p/VL+pL/VLor p/V ═ Ap + B
According to the equation, the pressure and the suction amount data of each pressure balance point which are actually measured can be drawn into a scatter diagram which takes p as an abscissa and a p/V ratio as an ordinate, the regression line equation and the correlation coefficient (R) of the scatter diagrams are obtained by the least square method, the slope (A) and the intercept (B) of a line are obtained, and the Langmuir volume (V) is obtained according to the slope and the interceptL) And Langmuir pressure (p)L) Namely:
VL＝1/A
pLB/A or pL＝VLB
And drawing an isothermal adsorption curve according to the adsorption quantity V and the pressure p of each pressure point.
During the experiment, if the pressure of the reference cylinder is limited by the pressure of the gas cylinder and cannot meet the experiment requirement, the pressure of the reference cylinder can be compressed to a required value through the gas booster and then the experiment is carried out.
The pipeline connected to the pressure chamber is detached from the joint and connected with the gas inlet and outlet of the displacement pipe for CO2And (4) displacement experiment. At this time, a flow meter (10MPa,5sccm) was provided at the outlet end of the gas cylinder, and a gas composition detector and a flow meter (10MPa,5sccm) were provided at the outlet of the test piece.
The volume of the coal rock can expand after gas is adsorbed, the test piece can generate axial deformation and radial deformation under the condition that axial load is not added and confining pressure is kept unchanged during pressure, three radial deformation extensometers are installed at the upper, middle and lower positions of the test piece, deformation of the three extensometers is read through a computer control system, the average value is the radial deformation of the test piece, and the axial deformation is obtained by reading the data of the axial extensometers.
The pressure head part above the test piece is provided with a force sensor, the sensor part is connected with the equipment frame and keeps the position still, the counter force generated by the coal rock to the pressure head when expanding is transmitted to the force sensor, and the computer control system reads the data of the sensor and divides the data by the area of the test piece to obtain the axial stress generated by expansion.
The embodiments of the present invention can be summarized as follows:
1 pressure chamber lifting device
The pressure chamber lifting device is used for lifting a pressure chamber cylinder to the upper part when a test piece is disassembled and assembled so as to conveniently install the test piece, a clamping extensometer and the like, and comprises a hydraulic lifting oil cylinder, a support, a hoisting part and the like.
2 guide rail lifting device
The guide rail lifting device is used for enabling the pressure chamber trolley to fall onto the bottom loading plate during an experiment, and lifting the guide rail to be flush with the outer guide rail during entering and exiting. Mainly comprises a fixed guide rail, a movable trolley, a lifting guide rail, a cylinder bracket, a manual reversing valve and the like.
3 gas adsorption capacity testing device
The isothermal adsorption curve for measuring a sample mainly comprises a pipeline volume calibration clamp, a vacuum pump, a pipeline calibration measuring tube, an inflation tank calibration measuring tube, a gas booster, a high-pressure gas cylinder, a constant-temperature oil bath, a temperature control instrument, a pressure sensor, a pipeline and a valve.
4-pressure chamber confining pressure servo loading system
The loading, unloading and load-holding device is used for loading, unloading and load-holding confining pressure of a pressure chamber, has a servo motor ball screw structure, is small in confining pressure fluctuation amount and reliable in loading temperature, and comprises an electric servo supercharger, a confining pressure oil inlet and return device, a pipeline, a valve and the like.
When confining pressure oil enters, the stop valve is opened, the servo confining pressure actuator pumps the pressurizing oil in the oil tank into the high-pressure oil cavity, then the stop valve is closed, and the servo actuator injects the pressurizing oil into the pressure chamber. During the oil extraction, servo actuator unloads earlier, opens the air compressor machine valve, and the compressed air gas gets into the pressure chamber through the pressure chamber air inlet and extrudes pressure oil from the confined pressure oil drain hole with pressure oil, and pressure oil flows back to the oil tank and deposits, filters, injects into the pressure chamber through the actuator when the experiment needs next time.
5 Displacement model tube Unit section
The device consists of a high-pressure-resistant displacement model pipe, a constant temperature system, a reference cylinder and the like. Simulating high temperature, high pressure (confining pressure) and sealed environment of the stratum.
The high-pressure displacement model pipe is used for high-pressure displacement experiments and adsorption free expansion body change experiments, and in order to ensure that the liquid volume around a test piece is not changed when the pressure is changed (the diameter and the length of the model pipe are not changed), thereby influencing the precision of a measurement result, the model pipe adopts a double-layer structure, the pressure of an inner-layer pressure-resistant part is equal to that of an interlayer part, and the liquid volume change quantity in the model pipe (a measurement body change part) caused by the pressure change is zero theoretically. The pressure in the model pipe is increased due to the expansion of the test piece, liquid in the model pipe needs to be pumped out by the metering pump in order to maintain the internal pressure unchanged, and the volume of the liquid pumped out by the metering pump is the variable of the free expansion body. The axial extensometer (applicable below 100 ℃) can measure the axial deformation, and the average radial deformation of the test piece can be calculated through the volume variable and the axial deformation.
The model pipe and the heat conducting oil can expand along with the temperature, and the initial volume needs to be recorded or reset relative to the initial volume during the experiment of each temperature section. In order to reduce the excessive expansion caused by the temperature rise, the inner cylinder of the die tube, the supporting frame and the pressure heads at the two ends of the test piece can be made of invar steel, the linear expansion coefficient of the invar steel is only 1.8x10-6 on average at 0-200 ℃, and the invar steel is about 1/7 of common carbon steel (12.1-13.5x10-6), so that the measurement precision is higher.
The high-precision metering pump provides steady voltage and volume change measurement for the test piece confining pressure.
Unit part of 6 ring pressure tracking and measuring device
The high-precision pressure difference meter is composed of a high-precision pressure difference meter, a confining pressure servo loading device, a high-precision metering pump and the like. The ring pressure tracking system can realize synchronous pressure rise of coal sample gas and confining pressure liquid in the heat shrinkage pipe of the reaction chamber, and the volume of the heat conduction oil discharged due to the fact that the confining pressure is kept unchanged is measured through the high-precision metering pump, so that the volume free expansion amount of the coal sample adsorption is obtained.
In the experimental process, the ring pressure (the pressure of heat conducting oil in the interlayer) P1 needs to be slightly greater than the gas pressure P0 and adjusted by increasing or decreasing the gas pressure at any time, a confining pressure servo loading device applies load to the ring pressure to ensure that a differential pressure gauge DP2 is within a certain value, generally set at 0.1MPa, so as to ensure that the gas cannot leak into the heat conducting oil around the test piece in the displacement process, and the differential pressure gauge and the servo loading device are in servo closed-loop control.
The metering pump ensures that the pressure P2 around the test piece is consistent with the interlayer pressure P1, the change of the confining pressure flow is displayed in real time, the set value of the differential pressure gauge DP1 is 0, and the control is in closed-loop control with the metering pump stroke servo. The metering pump rotates ISCO-100DM, and the highest pressure resistance can reach 10000Psi (68.966 MPa).
Measurement control section
The measurement control system consists of a first all-digital multi-channel closed-loop controller, a hydraulic sensor, a load sensor, a displacement sensor and a deformation sensor;
(1) full digital multi-channel closed-loop controller
By adopting an advanced self-adaptive fuzzy PID control algorithm, the online precise closed-loop control of the control quantity of system parameters can be realized, and the functions of constant-speed loading and unloading, constant force, constant displacement and the like can be realized. Meanwhile, a control interface of the system parameters of the user is provided, and the user can set the system control parameters to adapt to different control environments, so that the method has good flexibility.
The control system is provided with 2 independent electro-hydraulic servo valve control channels, various control rates and control functions can be switched mutually in the test process, each actuator can simultaneously or respectively control the servo valve to work in a closed-loop mode according to test requirements, the synchronous or asynchronous control of the whole loading system is guaranteed, and the stability of the test system is greatly improved.
The data acquisition system has 9 paths of high-precision 24-bit A/D conversion pressure, displacement and deformation acquisition channels, and can achieve the indication accuracy: within + -0.1%. The sampling speed of the data reaches 10KHz, and the current sensor signal can be rapidly acquired, so that the closed-loop control module can better perform real-time closed-loop control.
The full-digital multi-channel closed-loop measurement and control instrument can be upgraded according to requirements of users. When the instrument breaks down, the maintenance can be conveniently carried out in time.
(2) A sensor:
the sensor has great influence on the precision of the testing machine, and through years of practice, the displacement adopts a magnetic displacement sensor, which is characterized in that: the displacement sensor has the advantages of high precision, high stability, high reliability, extremely strong anti-interference capability and low power consumption, and is the best displacement test sensor at present.
The radial load sensor is adopted for axial pressure bearing, and the confining pressure is measured by adopting a hydraulic sensor.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (5)
1. The rock triaxial test equipment is characterized by comprising a main frame and a pressure chamber; wherein the main frame is a square frame, and the center of the main frame is provided with a space for accommodating the pressure chamber; the pressure chamber comprises a cylinder body and a base, wherein the cylinder body and the base are detachably fixed together through a split type hoop to form a sealed inner cavity; an upper pressure head and a lower pressure head are arranged in the cylinder body, and the positions of the upper pressure head and the lower pressure head correspond to each other so as to apply axial pressure on the test piece; and the base is provided with a confining pressure inlet and a confining pressure outlet so as to apply radial pressure to the test piece; an axial extensometer and a radial extensometer are arranged in the cylinder body; an air outlet is arranged at the top of the cylinder body, and an air inlet is arranged on the lower pressure head;
the test device also comprises a pressure chamber confining pressure servo loading mechanism for providing power required by the test for the pressure chamber; the pressure chamber confining pressure servo loading mechanism comprises a hydraulic oil tank, an oil pump, a piston, a pressure chamber and an air compressor; the hydraulic oil tank is connected with the pressure chamber through an oil pump, and the air compressor is also connected with the pressure chamber; the hydraulic oil tank is used for storing hydraulic oil so as to input the hydraulic oil into the pressure chamber through the action of a piston of the oil pump to provide confining pressure; after the test is finished, pressurizing the pressure chamber by an air compressor so as to return the hydraulic oil to the hydraulic oil tank;
still include the gas adsorption capacity measuring mechanism who is used for measuring the isothermal adsorption curve of sample, this gas adsorption capacity measuring mechanism includes: the device comprises a pipeline calibration measuring pipe, a gas composition detector, a flowmeter, a high-pressure gas cylinder, an inflation tank calibration measuring pipe, a liquid bath, an inflation tank, a confining pressure supercharger, a pressure sensor, a pipeline volume calibration clamp, a spoke type force sensor and a temperature sensor; the confining pressure supercharger is connected with the pressure chamber through a pressure sensor to supercharge the pressure chamber, and a temperature sensor and a spoke type force sensor are arranged in the pressure chamber; the pressure chamber is connected with an inflation pipeline and an air discharge pipeline, and an inflation tank, an inflation tank calibration measuring tube and a high-pressure gas cylinder are arranged on the inflation pipeline; and the gas discharge pipeline is provided with a pipeline calibration measuring pipe, a gas composition detector and a flowmeter; the device also comprises a vacuum pump which is connected with the inflatable pipeline and the air discharging pipeline in an openable and closable manner.
2. The triaxial rock testing apparatus of claim 1, wherein a lifting mechanism and a rail lifting mechanism are provided at one side of the main frame; the lifting mechanism comprises a bracket, a lifting oil cylinder and a piston rod; wherein the support lateral part is fixed on the side of main frame, and the lift cylinder is fixed on the support, lift cylinder bottom is equipped with the piston rod that extends the support, and the piston rod bottom is equipped with the buckle in order to drive the pressure chamber removal with the hangers detachable fixed connection at the barrel top of pressure chamber.
3. The triaxial rock testing apparatus of claim 1, further comprising a high pressure displacement model tube mechanism for performing a high pressure displacement test and an adsorption free expansion body deformation test; the high-pressure displacement model pipe mechanism comprises a double-layer shell consisting of an outer shell and an inner shell, and the double-layer shell is provided with an interlayer pressure inlet for pressurizing an interlayer; a heat-shrinkable sleeve for accommodating a test piece is arranged in the double-layer shell; an upper pressure head and a lower pressure head are respectively arranged at the top and the bottom of the heat-shrinkable sleeve; a gas outlet pipe is arranged in the inner shell and connected with a driving-away gas inlet, the driving-away gas inlet is arranged at the bottom of the double-layer shell, one end of the gas outlet pipe is connected with the driving-away gas inlet, and the other end of the gas outlet pipe extends to the top of the double-layer shell; the top of the double-layer shell is provided with an exhaust hole, and the bottom of the double-layer shell is provided with a driving gas outlet.
4. The triaxial rock testing apparatus of claim 1, further comprising a ring pressure tracking and measuring mechanism for synchronously pressurizing the coal sample gas and the confining pressure liquid in the reaction chamber heat shrinkage tube to measure the displacement variation of the pore pressure servo loading device through a displacement sensor so as to calculate the volume free expansion amount absorbed by the coal sample, wherein the ring pressure tracking and measuring mechanism comprises: the device comprises an oil storage tank, a high-pressure displacement model pipe, a confining pressure servo loading device and a differential pressure gauge; a gas collector, a gas-liquid separator and a gas chromatograph; the confining pressure servo loading device is connected with the high-pressure displacement model pipe, and the differential pressure gauge is connected with the high-pressure displacement model pipe; the high-pressure displacement model pipe is connected with the gas-liquid separator and the gas-liquid collector and is also connected with the gas chromatograph to analyze the gas components in the treatment process.
5. A triaxial rock testing method using the triaxial rock testing apparatus according to any one of claims 1 to 4, comprising:
the coal rock sample gas permeability test step comprises the following steps: placing the coal rock test piece in a pressure chamber, sealing the upper and lower pressure heads and the test piece with a protective sleeve, wrapping the coal sample test piece with a heat-shrinkable sleeve to isolate gas and oil paths, vacuumizing the test piece, the inlet gas reference tank, the reference tank and the pipeline after discharge, calibrating the volume, vacuumizing, and vacuumizing the CO2The high-pressure gas firstly enters the gas inlet reference tank, the gas inlet valve is closed, the pressure difference value of the pressure difference meter is read, the gas inlet valve of the test piece is opened, and CO is permeated into pores of the coal rock from the high-pressure steel cylinder through the bottom of the triaxial permeating device2The sample enters a gas outlet reference tank through the test piece, and the permeability coefficient of the test piece is calculated through the pressure difference and the volume of the gas inlet and outlet reference tanks after the pressure is balanced;
the coal rock test piece performance test step:
adsorption volume test substep: loading the treated dry coal sample into a pressure chamber, adding a certain confining pressure, carrying out vacuum degassing, and measuring the residual volume of an adsorption tank; filling a certain volume of methane into the pressure chamber, so that the pressure in the protective sleeve reaches balance, part of gas is adsorbed, and part of gas is still in the rest volume in a free state; knowing the volume of the gas to be charged, and deducting the free volume of the residual volume to obtain the adsorption volume;
free space volume test substep: setting and adjusting the temperature of the system to enable the temperature of the pressure chamber and the reference cylinder to reach required values; opening a helium bottle to fill helium into the system, adjusting the pressure value of the reference cylinder to 2-30MPa, and closing a valve of the reference cylinder; opening a pressure chamber and a reference cylinder connecting valve, and acquiring a group of data after pressure is balanced;
repeating the steps twice to obtain the volume of the coal sample, and calculating the volume of the free space in the sample cylinder; the free space volume needs to be measured 3 times repeatedly;
the volume calculation formula of the coal sample is as follows:
VSvolume of coal sample in cubic centimeters (cm)3)；p1Post-equilibrium pressure in megapascals (MPa); p is a radical of2Reference cylinder initial pressure in megapascals (MPa); p is a radical of3Sample cylinder initial pressure in megapascals (MPa); t is1The temperature after equilibrium is expressed in units of on (K); t is2Reference cylinder initial temperature in units of on (K); t is3The initial temperature of the sample cylinder is expressed by the unit of opening (K); vlThe total volume of the system is in cubic centimeters (cm)3)；V2Reference cylinder volume in cubic centimeters (cm)3)；V3The volume of the sample cylinder is in cubic centimeter (cm)3)；Z1The compression factor of the gas under equilibrium conditions; z2Reference cylinder initial gas compression factor; z3The compression factor of the initial gas of the sample cylinder;
solving the volume of the coal sample, and calculating the volume of a free space in a sample cylinder; the calculation formula is shown as follows:
Vf＝V0-VS
in the formula, VfFree space volume in cubic centimeters (cm)3)；V0The total volume of the sample cylinder is in cubic centimeter (cm)3)；VSVolume of coal sample in cubic centimeters (cm)3)；
According to the equilibrium pressure and temperature of the reference cylinder and the pressure chamber, the adsorption quantity of different equilibrium pressure points is calculated, and the calculation formula is
pV＝nZRT
In the formula:
p is gas pressure in megapascals (MPa); v gas volume in cubic centimeters (cm)3) (ii) a n is the number of moles of gas, in moles (mol); z is the compressibility factor of the gas; r is a molar gas constant which is expressed in units of coke per mole (J/(mol. K)); t is the equilibrium temperature in units of Kelvin (K);
respectively calculating the mole number n of the gas in the pressure chamber before the balance of each pressure point1And after balancingNumber of moles n of gas in pressure chamber2The number of moles n of the gas adsorbed in the coal sampleiComprises the following steps:
ni＝n1-n2
in the formula: n isiThe mole number of the gas is expressed in the unit of mole (mol); n is1The number of moles of gas in the sample cylinder before the balance is expressed as mole (mol); n is2The number of moles of gas in the sample cylinder after the balance is expressed as mole (mol);
total volume (V) of adsorbed gas at each pressure pointi) See the following equation:
Vi＝ni×22.4×1000
adsorption amount V of each pressure pointAmount of adsorptionSee the following equation:
Vamount of suction and delivery＝Vi/Gc
In the formula: vAmount of suction and deliveryThe absorption amount is in unit of cubic centimeter per gram (cm)3.g-1)；ViThe total volume of the adsorbed gas is in cubic centimeters (cm)3)；GcCoal sample mass in grams (g);
calculating V according to Langmuir equationLAnd pL：
p/V＝p/VL+pL/VL
In the formula: p is gas pressure in megapascals (MPa); v is the absorption capacity under the pressure p and the unit is cubic centimeter per gram (cm)3.g-1)；VLThe maximum absorption capacity, also called Langmuir volume, is expressed in cubic centimeters per gram (cm)3.g-1)；pLLangmuir pressure in MegaPascals (MPa);
if let A equal to 1/VLAnd B ═ pL/VLThe equation can be derived as a function of p/V and p:
p/V＝p/VL+pL/VLor p/V ═ Ap + B
According to the equation, the pressure and the suction amount data of each pressure balance point measured actually can be drawn into a scatter diagram with p as the abscissa and the p/V ratio as the ordinate, and the regression line of the scatter diagrams can be obtained by the least square methodEquation and correlation coefficient (R), calculating slope (A) and intercept (B) of straight line, and calculating Langmuir volume (V) according to slope and interceptL) And Langmuir pressure (p)L) Namely:
VL＝1/A
pLB/A or pL＝VLB
And drawing an isothermal adsorption curve according to the adsorption quantity V and the pressure p of each pressure point.
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