CN105910531A - In-situ digital three-dimensional borehole wall strain gauge based on complete temperature compensation technology - Google Patents

Abstract

The invention provides an in-situ digital three-dimensional hole wall strain gauge based on a complete temperature compensation technology, which belongs to the field of rock mass stress measurement and monitoring. The strain gauge includes a glue-injected hollow cladding strain gauge framework, a high-precision self-compensating strain sensor, a double ground wire and a complete temperature compensation measurement circuit, and a local digital acquisition integrated circuit board. The strain gage is installed by glue injection design. The self-compensating high-precision strain sensor and complete temperature compensation circuit eliminate the influence of temperature in long-term monitoring; the double ground circuit compensates the leveling range of the digital circuit; the instantaneous acquisition technology of the digital circuit board eliminates the influence of resistance heating and realizes monitoring data long-term validity and relevance. The strain gauge has two acquisition modes: manual power-off continuous acquisition and automatic continuous acquisition, and can be installed once to realize short-term and long-term monitoring of three-dimensional strain of the borehole wall. A variety of wireless connection modes and wireless charging interfaces are reserved, which can realize real-time data transmission from the measuring point to the control room.

Description

In-situ digital three-dimensional hole wall strain gauge based on complete temperature compensation technology

technical field

The invention relates to the field of rock mass stress measurement and monitoring, in particular to an in-situ digital three-dimensional hole wall strain gauge based on a complete temperature compensation technology.

Background technique

In-situ stress is the natural stress existing in rock mass, and it is the most important factor determining the excavation, design and stability analysis of underground engineering. The hollow inclusion strain gauge method for ground stress measurement is a three-dimensional ground stress measurement method recommended by the International Society of Rock Mechanics, and is currently the only ground stress measurement method that can obtain the magnitude and direction of the underground three-dimensional principal stress at one time.

However, most of the current methods of measuring ground stress with hollow inclusion strain gauges use long wires to lead out the measurement signals, and the resistance of the wires during signal transmission seriously affects the measurement accuracy. Professor Cai Meifeng invented the double ground loop to improve the measurement accuracy of the hollow inclusion method; the Australian Environmental Systems and Services Company invented the in-situ digital hollow inclusion strain gauge, which eliminated the influence of long wire resistance, and used 4 to convert the analog signal into a digital signal. The core wire leads out the data. Whether it is the improvement of the double ground loop or the realization of in-situ digitization, it is also necessary to use wires to pass through the drilling rig to derive real-time signals during the measurement. The operation is cumbersome, and the measuring wire and the common drilling rig channel for measuring the cooling water interact with each other, which will cause the accident that the wire is stuck during drilling.

Bai Jinpeng, Peng Hua, etc. (2013) improved the hardware of hollow inclusions and introduced it into deep hole stress measurement. However, it is based on the traditional hollow inclusion strain gauge structure, which cannot eliminate the influence of ambient temperature. Professor Cai Meifeng proposed the concept of accurate measurement of ground stress, and invented an improved hollow inclusion strain gauge and complete temperature compensation technology, which can greatly improve the accuracy and reliability of ground stress measurement. However, the improved hollow inclusion strain gauge has not yet realized local digitization and wireless transmission in measurement.

The invention aims at improving the localized and non-extracted ground stress measurement of hollow inclusions, and inherits the concepts of complete temperature compensation technology and accurate ground stress measurement.

Stress disturbance monitoring in rock is an important content in mining, hydropower station construction, and tunnel construction informatization construction, but there is no equipment that can realize this function at present. The borehole stress gauge used in mining has the advantages of simple installation and easy operation, but it is developed from the application of coal mining and uses oil pressure monitoring, which cannot achieve long-term measurement, and the measured data is the internal pressure value of the jack, not the rock mass Internal stress value; the local digital hollow cladding strain gauge in Australia can theoretically monitor the disturbance stress, but it adopts the traditional bridge acquisition method and must ensure stable power supply throughout the monitoring process; Bai Jinpeng, Peng Hua, etc. The developed non-exportable probe has a standby time of 3 months and a working time of 20 hours, and the temperature changes in the long-term monitoring are larger. The compensation sheet method of the traditional probe structure cannot fully compensate for the influence of temperature, and the accuracy is poor. Therefore, the above two kinds of hollow inclusion equipment cannot carry out long-term stress monitoring in the complex environment of underground space.

Contents of the invention

The technical problem to be solved by the present invention is to provide an in-situ digital three-dimensional hole wall strain gauge based on complete temperature compensation technology.

The strain gauge includes a glue-injected hollow cladding strain gauge skeleton, a high-precision self-compensating strain sensor, a double ground wire and a complete temperature compensation measurement circuit, and a local digital acquisition integrated circuit board; a high-precision self-compensating strain sensor, a double ground wire and a complete The temperature compensation measurement circuit and the local digital acquisition integrated circuit board are set in the skeleton of the glue-injected hollow-body strain gauge, and the strain gauge uses a double ground loop to connect the local digital integrated circuit board.

Among them, the skeleton of the glue-injected hollow inclusion strain gauge is cylindrical, the head is a guide head, and a circle of glue holes is set under the guide head, and the glue hole is connected with the internal glue outlet channel. The middle part is covered with an epoxy resin cylinder, and the outside of the epoxy resin cylinder is pasted with strain rosettes. A single-chip microcomputer acquisition instrument is installed in the tail of the glue-injected hollow inclusion strain gauge skeleton. The single-chip microcomputer acquisition instrument is connected to the battery. The glue-injected hollow inclusion strain gauge skeleton head The connection between the central part and the central part is sealed with a sealing rubber ring.

High-precision self-compensating strain sensor under long-term measurement status, the temperature coefficient of the sensor is 1.33[(μm/m)/℃] at 0℃-20℃, and 0.28[(μm/m)/℃] at 20℃-40℃ , 1.20[(μm/m)/℃] at 40°C-60°C, 1.60[(μm/m)/°C] at 60°C-80°C, the error rate of the complete temperature compensation measurement circuit is 2.43%; long-term During the measurement, the 0-point drift of the measurement system is 10 μm/year.

The strain gage reserves wireless transmission interfaces such as wifi, bluetooth, and very low frequency through-the-earth communication. Data acquisition and charging adopt wireless or wired methods. There are various wireless connection modes and wireless charging interfaces reserved, which can realize the transfer from the measuring point to the control room. data transmission in real time.

The strain gauge acquisition system adopts the bridge instantaneous acquisition technology, and the signal acquisition is completed at the instant when the bridge circuit is connected. There is no instantaneous on-resistance and the influence of heating of the resistance sheet, no long-term power supply is required, and the mining can be realized immediately after power-on, and the signal is the real resistance value of the resistance strain sheet itself. Four modes of continuous acquisition, interval acquisition, timing acquisition and standby mode are set, and the short-term and long-term monitoring of the three-dimensional strain of the borehole wall can be realized in one installation.

The ground stress measurement and stress monitoring using the strain gauge includes the following steps:

When measuring ground stress, drill holes in the roadway, tunnel or slope rock wall, install the strain gauge in the drill hole, and make the strain sensor part of the strain gauge and the hole wall tightly bonded by pushing the glue injection, and then the hole wall strain can be measured. The boreholes were removed, and the spatial stress inside the rock mass was estimated based on the elastic mechanics theory. Specific steps include:

1. Drill a large hole with a diameter of 130mm-150mm at the measuring point;

2. Concentrically drill a small hole with a diameter of 42mm at the bottom of the large hole, and the depth of the small hole is 40cm;

3. Use epoxy resin colloid to bond the probe in the small hole;

4. Use the same drill bit as drilling the large hole to release the core with a probe, and record the strain change of the hole wall during the release process;

5. The probe records the strain change of the core from the stress state of the original rock to the stress-free state. The elastic mechanics theory is used to establish the stress-strain relationship in the stress change process of the elastic body, and the elastic modulus and Poisson's ratio for calculation are obtained by laboratory tests. And other parameters, into the elastic mechanics infinite body hole formula can be regressed to get the stress value.

During stress monitoring, the strain gauge is a high-precision self-compensating strain sensor, and the temperature calibration is completed when the probe leaves the factory. The installation method is the same as the stress measurement, except that there is no need to drill a large concentric hole for release. The stress change of the rock mass can be obtained by measuring the strain change at different times and combining with the relevant theoretical analysis. The stress monitoring probe can carry out short-term measurement and long-term monitoring of stress in the non-release state. The reading mode can be selected from manual measurement and automatic collection and transmission. The specific steps are:

1. Drill a small hole with a diameter of 42mm, and the drilling depth reaches the position of the monitoring point;

2. Bond the probe and connect to the power supply (if the manual collection method is adopted, the power supply is not required);

3. Set the collection interval and collection start time. (If collected manually, this step is not required);

4. Use field cores to conduct indoor tests to obtain the elastic modulus and Poisson's ratio of the rock at the measuring point;

5. According to the strain change during monitoring, the stress change value can be calculated. The current stress state can be obtained by adding the stress change value and the in-situ stress value to realize stress monitoring. (The specific formula is the same as that of ground stress measurement)

The rosette is a high-precision self-compensating strain sensor. The high-precision self-compensating strain sensors are arranged on the 1.5mm thick epoxy resin cylinder wall at a circumferential interval of 120°, and the epoxy resin cylinder wall is coated on the glue storage cavity to realize hollow Design, use the double ground loop connection method to connect the rear acquisition system.

The double ground wire and complete temperature compensation measurement circuit is the introduction of the complete temperature compensation technology invented by Academician Cai Meifeng, combined with the double ground wire connection method, which technically eliminates the error of the lead wire and the change of the strain value caused by the temperature change, and the complete temperature compensation circuit The error rate that can be eliminated is 2.43%, and the precision of strain measurement is improved.

The local digital acquisition circuit board adopts digital circuit integration technology to complete the digital conversion of signals in the equipment cavity, eliminates the measurement error of long wires in other measurement methods, realizes instantaneous acquisition and rolling acquisition of each channel, and at the same time can realize the storage of collected data, transmission. The local digital acquisition integrated circuit board provides two acquisition modes: manual power-off continuous acquisition and automatic continuous acquisition, and four operating modes of continuous work, regular work, micro-standby work and standby work. It can be installed at one time to realize the three-dimensional strain of the borehole wall Short-term and long-term monitoring.

The storage battery is powered by a 5V rechargeable lithium battery with a battery capacity of 6800mAh, and the working current of the collector is 0.02mA, which can realize one month of standby and seven days of static continuous collection.

The beneficial effects of above-mentioned technical scheme of the present invention are as follows:

The present invention adopts digital instantaneous mining technology, no power supply is required during standby, and eliminates the influence of lifting resistance and instantaneous current; it adopts complete temperature compensation technology and temperature self-compensation sensor, and realizes the maximum elimination of temperature influence under long-term measurement conditions; the double ground wire structure is The application in the digital circuit increases the acquisition range and measurement stability of the electronic circuit. The probe developed by the invention has been updated many times, and a large number of related experiments have been carried out indoors and on the spot. With the support of actual measurement data, the integration of in-situ stress measurement and stress monitoring and the long-term monitoring function of disturbance stress have been realized.

The invention effectively solves the problems of cumbersome and complicated installation of the wired strain acquisition instrument, low measurement accuracy, short working time and inability to monitor for a long time. Through the indoor simulated ground stress test bench test and the confining pressure rate calibration comparison test of the measured value and the calibration value of the device of the present invention, the comparison shows that the measurement error is 1% (1με/100με), and the measurement accuracy is 1με. The experimental device has carried out 3 measuring points in the underground iron mine in Gongchangling District, and a total of 5 on-site stress relief tests, of which 2# hole and 3# hole are tested in the same hole at the -220m level, 4# hole and 5# The hole is a test in the same hole at the -280m level, and the distribution law of the in-situ stress field in the measuring point area is obtained. Among them, the conventional hollow inclusion strain gauge and the present invention were tested twice at the same measuring point, and the present invention is much better than the conventional hollow inclusion strain gauge in terms of operability, data stability, and reliability. The device of the invention has broad application prospects in complex environments such as mines, tunnels and slopes.

Description of drawings

Fig. 1 is the structure diagram of the in-situ digitized three-dimensional hole wall strain gauge based on the complete temperature compensation technology of the present invention;

Figure 2 is a layout diagram of the high-precision self-compensating strain sensor;

Figure 3 is the calibration curve of the high-precision self-compensating strain sensor;

Fig. 4 is a schematic diagram 1 of the acquisition system window and instructions;

Fig. 5 is the acquisition system window and instruction schematic diagram II;

Fig. 6 is a schematic diagram of acquisition system window and instructions III;

Figure 7 is the fourth schematic diagram of the acquisition system window and instructions.

Among them: 1-guide head; 2-sealing rubber ring; 3-glue outlet hole; 4-glue outlet channel; 5-epoxy resin tube; 6-strain rosette; 7-single-chip microcomputer collector;

detailed description

In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will describe in detail with reference to the drawings and specific embodiments.

The invention provides an in-situ digitized three-dimensional hole wall strain gauge based on a complete temperature compensation technology.

The strain gauge includes a glue-injected hollow cladding strain gauge skeleton, a high-precision self-compensating strain sensor, a double ground wire and a complete temperature compensation measurement circuit, and a local digital acquisition integrated circuit board; a high-precision self-compensating strain sensor, a double ground wire and a complete The temperature compensation measurement circuit and the local digital acquisition integrated circuit board are set in the skeleton of the glue-injected hollow-body strain gauge, and the strain gauge uses a double ground loop to connect the local digital integrated circuit board.

As shown in Figure 1, the skeleton of the glue-injecting hollow-body strain gauge is cylindrical, and the head is a guide head 1. A circle of glue outlet holes 3 is set under the guide head 1, and the glue outlet holes 3 are connected with the internal glue outlet channel 4. The middle part of the framework of the glue-injected hollow-enclosed strain gauge is covered with an epoxy resin cylinder 5, and the outside of the epoxy-resin cylinder 5 is pasted with strain rosettes. A single-chip microcomputer acquisition instrument 7 and a single-chip microcomputer acquisition instrument 7 are installed in the tail of the glue-injected hollow-enclosed strain gauge framework. It is connected with the battery 8, and the joint between the head and the middle part of the skeleton of the glue-injected hollow inclusion strain gauge is sealed with a sealing rubber ring 2 .

As shown in Figure 2, the strain rosette 6 is a high-precision self-compensating strain sensor, and the high-precision self-compensating strain sensor is arranged on the wall of the epoxy resin cylinder 5 with a thickness of 1.5 mm at a circumferential interval of 120°.

As shown in Figure 3, under the long-term measurement state of the high-precision self-compensating strain sensor, the temperature coefficient of the sensor is 1.33[(μm/m)/℃] at 0℃-20℃, and 0.28[(μm) at 20℃-40℃ /m)/℃], 1.20[(μm/m)/℃] at 40℃-60℃, 1.60[(μm/m)/℃] at 60℃-80℃, fully temperature compensated measurement circuit to eliminate errors The rate is 2.43%; the zero point drift of the measurement system is 10μm/year in the long-term measurement.

As shown in Figure 4, Figure 5, Figure 6 and Figure 7, the local digital acquisition integrated circuit board provides two acquisition modes: manual power-off continuous acquisition and automatic continuous acquisition, continuous work, timing work, micro-standby work and standby work. This kind of working mode can realize the short-term and long-term monitoring of the three-dimensional strain of the borehole wall with one installation.

A specific example of applying the strain gauge is as follows.

The implementation methods of ground stress measurement are:

1. Drill a large hole with a diameter of 130mm-150mm at the measuring point and obtain the core. The drilling depth must be more than 3 times the diameter of the excavation space;

2. Concentrically drill a small hole with a diameter of 42mm at the bottom of the large hole, and the depth of the small hole is 40cm;

3. Prepare the curing colloid on site and pour it into the cavity of the probe. Installation is carried out with professional installation equipment for ground stress, and the installation speed, the orientation of the probe in the hole, and the advancing distance of colloid extrusion are controlled. After installation, use the handheld terminal to set the acquisition standby time and acquisition interval. The working indicator light in the observation hole is on, indicating that the probe is working normally;

4. After installation, the colloid solidifies for 24 hours (24 hours at 25°, if the temperature is lower than 10°, it takes 48 hours to solidify);

5. After the colloid is solidified, observe whether the working indicator light of the probe in the hole flickers within the set time interval. If the flickering interval indicates that the work is normal, the work can be started;

6. When releasing, ensure that the drilled hole is concentric with the original drill hole, and use the same kind of thin-walled drill bit as when drilling a large hole. When releasing, advance the drill bit to the empty bottom of the large hole, and start drilling after 30 minutes of water flow. Keep the pressure constant (about 1MPa) while drilling, and drill smoothly. Drill into the lifting depth of 50cm;

7. After lifting, take out the core, open the back cover of the probe, turn off the power, and terminate the collection. Observe the integrity of the core and mark it in situ. Use film to seal the core and prepare for indoor testing;

8. Conduct confining pressure rate calibration test and temperature calibration test to obtain elastic modulus, Poisson's ratio, and temperature coefficient of strain gauges in each channel, and perform data regression to obtain calculation strain values;

9. Using elastic mechanics theory to carry out stress inversion and least squares regression to get the stress value.

The specific implementation of stress monitoring is as follows:

1. Drill a small hole with a diameter of 42mm, and the drilling depth reaches the position of the monitoring point;

2. Prepare the colloid, install the probe, and the installation steps are the same as those in the ground stress measurement;

3. Connect the probe power supply to the field circuit to ensure long-term power supply. After a power outage, the working time of the battery is more than 1 week. If the manual collection method is adopted, it does not need to be connected to the power supply;

4. Set the collection interval and collection start time. The collected data is connected to the orifice terminal by Bluetooth or cable, and connected to the underground ring network through optical fiber (this step is not required for manual collection).

5. Use field cores to conduct indoor tests to obtain the elastic modulus and Poisson's ratio of the rock at the measuring point;

6. Cooperate with the ground stress measurement to obtain the current ground stress value at the site measuring point;

7. According to the strain change during monitoring, the stress change value is also obtained by using the calculation formula of the hole deformation in an infinite body in the theory of elasticity. The current stress state can be obtained by adding the stress change value and the in-situ stress value to realize stress monitoring.

The above description is a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, these improvements and modifications It should also be regarded as the protection scope of the present invention.

Claims (6)

1. an original position digitized type three-dimensional hole wall strain gauge based on complete technique for temperature compensation, It is characterized in that: include that the strain of glue injection type hollow inclusion strain gauge skeleton, high-accuracy self-compensation passes Sensor, double earth wire and temperature-compensating measuring circuit and local digitization completely gather surface-mounted integrated circuit； High-accuracy self-compensation strain transducer, double earth wire and complete temperature-compensating measuring circuit and local number Wordization gathers surface-mounted integrated circuit and is arranged in glue injection type hollow inclusion strain gauge skeleton, this strain gauge Double earth wire loop is used to carry out local digitization surface-mounted integrated circuit connection.

Original position digitized based on complete technique for temperature compensation the most according to claim 1 Type three-dimensional hole wall strain gauge, it is characterised in that: described glue injection type hollow inclusion strain gauge skeleton is Cylindric, head is guide head (1), and guide head (1) lower section arranges a circle plastic hole (3), Plastic hole (3) is connected with internal plastic emitting passage (4), glue injection type hollow inclusion strain gauge skeleton Middle part outsourcing epoxy resin cylinder (5), epoxy resin cylinder (5) is outside posts strain rosette (6), Arranging single-chip microcomputer Acquisition Instrument (7) in glue injection type hollow inclusion strain gauge skeleton afterbody, single-chip microcomputer is adopted Collection instrument (7) be connected with accumulator (8), glue injection type hollow inclusion strain gauge skeleton head with in Junction, portion uses O-ring seal (2) to seal.

Original position digitized based on complete technique for temperature compensation the most according to claim 1 Type three-dimensional hole wall strain gauge, it is characterised in that: it is self-complementary that described strain rosette (6) is high accuracy Repaying strain transducer, circumferentially spaced-apart 120 ° of high-accuracy self-compensation strain transducer is arranged in On epoxy resin cylinder (5) wall that 1.5mm is thick.

Original position digitized based on complete technique for temperature compensation the most according to claim 1 Type three-dimensional hole wall strain gauge, it is characterised in that: described high-accuracy self-compensation strain transducer is being grown Under phase measuring state, be 1.33 during sensor temperature coefficient 0 DEG C-20 DEG C [(μm/m)/DEG C], 20 DEG C Be 0.28 when-40 DEG C [(μm/m)/DEG C], be 1.20 when 40 DEG C-60 DEG C [(μm/m)/DEG C], 60 DEG C Be 1.60 when-80 DEG C [(μm/m)/DEG C], complete temperature-compensating measuring circuit eliminates error rate and is 2.43%；Measuring system 0 point drift in long-term measurement is 10 μm/year.

Original position digitized based on complete technique for temperature compensation the most according to claim 1 Type three-dimensional hole wall strain gauge, it is characterised in that: this strain gauge reserves wifi, bluetooth, very low frequency Saturating ground communication wireless transmission interface, data acquisition and charging use wirelessly or non-wirelessly mode.

Original position digitized based on complete technique for temperature compensation the most according to claim 1 Type three-dimensional hole wall strain gauge, it is characterised in that: this strain gauge acquisition system uses that electric bridge is instantaneous adopts Collection technology, signals collecting completed in bridge circuit connection moment.