A kind of karst area groundwater air pressure monitoring osmometer and installation and use method

Abstract

The application discloses a kind of for karst area groundwater air pressure monitoring osmometer and installation use method, including osmometer body, osmometer body includes tubular shell, water-permeable seat and steel string being arranged in tubular shell, the water-permeable seat is fixed in tubular shell by inner seal, water-permeable stone is arranged in the front end portion of water-permeable seat in the front end side of tubular shell, diaphragm is arranged in water-permeable seat close to water-permeable stone side and along the direction of rear end of tubular shell, the fixed end of steel string is connected on diaphragm, the free end of steel string is connected with a cable by extending to the axis rear end direction of tubular shell and passing out water-permeable seat, exciting and receiving coil are arranged on the outside of water-permeable seat and the outer periphery of steel string.The application not only can fully reflect the change information of karst groundwater air pressure, better explain the mutation process and reason of karst groundwater air pressure, but also can replace, recycle osmometer sensor at any time, greatly reduce monitoring cost.

Description

Technical Field

[0001] This invention belongs to the field of groundwater pollution prevention and control and automatic groundwater monitoring technology in karst areas, and particularly relates to a piezometer for monitoring groundwater gas pressure in karst areas and its installation and usage method. Background Technology

[0002] Karst collapse is a sudden disaster, and its monitoring and early warning remain a global challenge. Changes in karst groundwater dynamics are the primary triggering factor for karst collapse. Most of southwestern my country is characterized by typical karst topography, with well-developed karst fissures, conduits, and underground rivers. The foundation for groundwater pollution control technology in karst areas is extremely weak. The unique water-air pressure variations in karst areas threaten the stability of geological structures. Research on long-term effective groundwater pollution control technologies in karst areas is still in the exploratory stage. Pumping water in karst areas leads to a rapid drop in groundwater levels. When ventilation fissures around karst cavities cannot effectively exchange gases with the outside environment, negative pressure quickly forms. The high-frequency vibrations of this negative pressure endanger the stability of geological structures. Traditional methods for monitoring changes in karst groundwater dynamics through groundwater level monitoring have long monitoring cycles, and the understanding of karst collapse mechanisms using groundwater level monitoring data that connects to atmospheric pressure is insufficient. Monitoring groundwater-air pressure in karst areas requires high-precision installation of piezometer sensors, which must be installed in sealed observation holes to eliminate the influence of external atmospheric pressure on the observed values. Summary of the Invention

[0003] The purpose of this invention is to provide a piezometer for monitoring groundwater and gas pressure in karst areas and its installation and usage method. This piezometer achieves a new technology for real-time dynamic monitoring of groundwater and gas pressure changes in karst fissures, enabling real-time and comprehensive reflection of groundwater and gas pressure changes within karst conduits and fissures. It effectively explains the abrupt changes and causes of groundwater and gas pressure fluctuations in karst areas. Furthermore, the piezometer sensor can be easily replaced and recycled, significantly reducing monitoring costs. To achieve the above objectives, this invention adopts the following technical solution:

[0004] According to one aspect of the present invention, a piezometer for monitoring groundwater and gas pressure in karst areas is provided. The piezometer includes a piezometer body, which includes a tubular shell, a permeable seat body disposed within the tubular shell, and a steel wire. The permeable seat body is sealed and fixed within the tubular shell by an internal seal. A permeable stone is disposed within the front end of the permeable seat body on one side of the front end of the tubular shell. A diaphragm is disposed within the permeable seat body near the permeable stone and along the direction towards the rear end of the tubular shell. The fixed end of the steel wire is connected to the diaphragm. The free end of the steel wire extends out of the permeable seat body and extends towards the rear end of the axis of the tubular shell, connecting to a cable. Excitation and receiving coils are disposed outside the permeable seat body and on the outer periphery of the steel wire.

[0005] In a further preferred embodiment of the above scheme, a surge arrester is provided at the rear end of the permeable base, and the surge arrester is connected to the grounding terminal of the tubular shell by a wire. A semiconductor thermometer is provided inside the tubular shell near the surge arrester, and a thermometer lead is connected to the semiconductor thermometer. A ring magnet is sleeved on the outer wall of the excitation and receiving coil.

[0006] In a further preferred embodiment of the above scheme, a protective pipe made of HDPE material is provided on the outside of the piezometer body. The protective pipe consists of a sand-collecting pipe with a plug at the bottom, a water-filtering pipe in the middle, and a fixed section that is impermeable at the top. Water-permeable holes are opened at different heights on the outer wall of the middle part of the protective pipe. Clean fine sand is filled in the protective pipe 100mm-200mm below the front end of the piezometer body, on the periphery, and 100mm-200mm above the rear end. Bentonite (53) and cement slurry mixture are sequentially filled on the washed fine sand. A water-stop strip is tied at the bottom of the fixed section of the protective pipe.

[0007] In a further preferred embodiment of the above scheme, the permeable base includes a first permeable base, a second permeable base, and a third permeable base arranged sequentially from the front end to the rear end of the tubular shell. The outer wall of the first permeable base is sealed to the inner wall of the front end of the tubular shell. A funnel-shaped recess for placing permeable stones is provided at the front end of the first permeable base. A diaphragm is provided on the side wall of the front section of the second permeable base. One edge of the diaphragm is connected to the edge of the side wall of the front section of the second permeable base, and the other side of the diaphragm is close to the rear end side wall of the first permeable base. An excitation and receiving coil is connected between the rear end of the second permeable base and the front end of the third permeable base. A surge arrester is provided on the rear end side wall of the third permeable base. The rear end of the third permeable base and the surge arrester are sealed and fixed by an inner seal provided inside the rear end of the tubular shell. A fixed end of a steel wire is connected to the central side wall of the diaphragm. The free end of the steel wire passes sequentially through the second permeable base, the excitation and receiving coil, the third permeable base, and the inner seal and is connected to a cable.

[0008] In a further preferred embodiment of the above scheme, a fixed terminal is provided in the center of the surface of the diaphragm, extending into one side of the second permeable seat, and a fixed vibration block for passing through the supporting steel wire is provided in the center of the interior of the third permeable seat. The fixed end of the steel wire is connected to the fixed terminal of the diaphragm, and the free end of the steel wire passes through the third permeable seat and is connected to the upper part near the rear end of the tubular shell.

[0009] In a further preferred embodiment of the above scheme, an annular groove is provided on the outer circumferential wall near the rear end of the first permeable seat, and a first O-type coil is provided in the annular groove.

[0010] In a further preferred embodiment of the above scheme, a plurality of equally spaced outwardly protruding annular protrusions are provided on the outer circumference of the second permeable seat, and a second O-type coil is provided between adjacent annular protrusions with the steel wire as the center line of symmetry.

[0011] According to another aspect of the present invention, the present invention provides a method for installing and using a piezometer for monitoring groundwater and gas pressure in karst areas, comprising the following steps: Step 1, drilling and well formation: In the underground karst fissure development zone, drilling and well formation for monitoring groundwater and gas pressure is carried out using mechanical drilling methods such as clear water drilling or low water pressure drilling.

[0012] Step 2: Lower the protective pipe. Place a protective pipe made of HDPE material inside the water and gas pressure monitoring well as the depth of the water and gas pressure monitoring well and the depth of the underground karst fissure development zone. Based on the depth of the underground karst fissure development zone, water-permeable holes are spaced apart on the protective pipe.

[0013] Step 3: Piezometer installation. Place a protective pipe with permeable holes into the water-gas pressure monitoring well. Backfill the protective pipe with clean fine sand up to 150mm below the front end where the piezometer body will be placed. Then place the piezometer body into the protective pipe. Then fill the protective pipe with clean fine sand around the piezometer body until it is 150mm above the piezometer body. After the piezometer body is installed and adjusted, backfill the top of the protective pipe with a mixture of impermeable bentonite and cement slurry.

[0014] Step 4: Connect the piezometer body to the signal. Connect the cable on the piezometer body to the automated data acquisition instrument set on the ground through the data transmission line. After turning on the AC power of the automated data acquisition instrument, the groundwater and gas pressure in the karst area can be monitored, thus completing the installation and signal connection of the piezometer body.

[0015] In a further preferred embodiment of the above scheme, a data processing terminal is connected to the signal output end of the automated data acquisition instrument. The automated data acquisition instrument and the data processing terminal communicate via a wireless antenna, RS232 / 485, or TCP / IP communication method. The piezometer body transmits the groundwater and gas pressure change data in the karst area to the automated data acquisition instrument. The automated data acquisition instrument compares the received data with the ground subsidence threshold value to determine whether the real-time data exceeds the subsidence threshold value. If it exceeds the threshold value, an early warning is automatically issued so that timely measures can be taken to prevent sudden changes in water and gas pressure in the karst area from endangering the stability of the stratum structure.

[0016] In a further preferred embodiment of the above scheme, a layer of clean fine sand (52) is placed between the impermeable bentonite and cement slurry mixture, and the height of the clean fine sand layer is 100 mm-300 mm.

[0017] In a further preferred embodiment of the above scheme, water-permeable holes are opened at different heights on the protective pipe and spaced 100mm apart. There are four water-permeable holes at the same horizontal height, which are arranged symmetrically at 90°. The diameter of the water-permeable holes is 8mm-15mm.

[0018] In summary, because the present invention adopts the above-described technical solution, the present invention has the following technical effects:

[0019] (1) By combining the piezometer and the protective pipe, the present invention realizes real-time dynamic monitoring of water and gas pressure in the cavity of karst area. It can not only reflect the changes in groundwater and gas pressure in the fissures of karst pipes, but also explain the sudden change process and cause of groundwater and gas pressure in karst. Furthermore, the piezometer sensor can be replaced and recycled at any time, which greatly reduces the monitoring cost.

[0020] (2) The piezometer for monitoring groundwater gas pressure in karst areas of the present invention is made of special steel for its main components. It has excellent performance and sufficient strength to be installed and used in a variety of harsh environments.

[0021] (3) The piezometer for monitoring groundwater and gas pressure in karst areas of the present invention can monitor the changes in water and gas pressure in the cavity of karst areas in real time by connecting to or having its own automated data acquisition instrument. When the water and gas pressure in karst areas fluctuates greatly, the data processing center (data processing terminal) will compare the received data with the critical data of ground collapse to determine whether the real-time data exceeds the critical value, so as to take timely measures to prevent sudden changes in water and gas pressure from endangering the stability of the stratum structure in karst areas.

[0022] (4) This invention can realize the monitoring of groundwater gas pressure in karst areas, which has important guiding significance for the formation mechanism of karst collapse and early warning and prevention. At the same time, it can accumulate experience in groundwater pollution prevention and control in karst areas and form a replicable and scalable groundwater pollution prevention and control management model. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of a piezometer for monitoring groundwater gas pressure in karst areas according to the present invention;

[0024] Figure 2 This is a front view structural diagram of the protective tube of the present invention;

[0025] Figure 3 This is a side view of the protective tube of the present invention;

[0026] Figure 4 This is a schematic diagram of the installation of a piezometer for monitoring groundwater gas pressure in karst areas according to the present invention;

[0027] Figure 5This is a schematic diagram of the system connection of a piezometer for monitoring groundwater gas pressure in karst areas according to the present invention.

[0028] In the attached diagram, 1 is a permeable stone, 1a is a funnel-shaped notch, 2 is a first permeable seat, 3 is a first O-type coil, 4 is a diaphragm, 5 is a steel wire, 6 is a second O-type coil, 7 is an excitation and receiving coil, 8 is a wire, 9 is a ring magnet, 10 is a surge arrester, 11 is a grounding terminal, 12 is a semiconductor thermometer, 13 is a thermometer lead, 14 is a tubular housing, 15 is an inner seal, 16 is a cable, 17 is a piezometer body, 20 is a second permeable seat, 21 is a third permeable seat, 22 is an annular groove, 23 is an annular protrusion, and 24 is a data transmission line. 24. Transmission line, 25. Ground, 26. Automated data acquisition instrument, 27. AC power supply, 28. Data processing terminal, 29. Comprehensive room, 31. Wireless antenna, 40. First fixed terminal, 41. Fixed vibration block, 50. Protective pipe, 51. Water permeable hole, 52. Fine sand, 53. Bentonite, 54. Cement slurry mixture, 100. Underground karst fissure development zone, H-Depth of water and gas pressure monitoring well; H1-Length of piezometer body, H2-Length of opening section, H3-Length of sealing section. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and preferred embodiments. However, it should be noted that many details listed in the specification are merely to provide the reader with a thorough understanding of one or more aspects of the present invention, and these aspects of the invention can be implemented even without these specific details.

[0030] According to one aspect of the invention, in combination Figure 1As shown, this invention provides a piezometer for monitoring groundwater and gas pressure in karst areas. The piezometer includes a piezometer body 17, which comprises a tubular shell 14, a permeable seat body disposed within the tubular shell 14, and a steel wire 5. The tubular shell 14 is made of stainless steel. The permeable seat body is sealed and fixed within the tubular shell 14 by an inner seal 15. A permeable stone 1 is disposed at the front end of the permeable seat body on one side of the front end of the tubular shell 14. The standard permeable stone of the piezometer body 17 is made of sintered stainless steel with 50μm pores and has good permeability. A diaphragm 4 is disposed within the permeable seat body near the permeable stone 1 and along the direction towards the rear end of the tubular shell 14. The fixed end of the steel wire 5 is connected to the diaphragm 4, and the free end of the steel wire 5 extends out of the permeable seat body and towards the rear end of the tubular shell 14. A cable 16 extends in the direction of the piezometer body. Excitation and receiving coils 7 are arranged on the outside of the permeable base and around the outer periphery of the steel wire 5. A ring magnet 9 is fitted on the outer wall of the excitation and receiving coils 7. The ring magnet 9 uses magnetic force to maintain the diaphragm 4 within a certain range. A surge arrester 10 is arranged at the rear end of the permeable base. The surge arrester 10 is connected to the grounding terminal 11 of the tubular housing 14 via a wire 8. A temperature-readable semiconductor thermometer 12 is arranged inside the tubular housing 14 near the surge arrester 10. A thermometer lead 13 is connected to the semiconductor thermometer 12. The semiconductor thermometer 12 provides different resistance values ​​as the temperature changes. The thermometer lead 13 is connected to the internal semiconductor thermometer 12. Because uneven temperature changes in the piezometer body 17 during use may produce erroneous readings, the piezometer body 17 needs to be allowed to reach equilibrium with the ambient temperature of the monitored point after 15-20 minutes. The semiconductor thermometer 12 mainly obtains the zero reading of the piezometer and corrects the piezometer reading.

[0031] In this invention, the permeable seat is made of sintered stainless steel with 50 μm pores to facilitate the discharge of air from the osmotic pressure gauge cavity; simultaneously, to prevent damage to the sensor diaphragm, the permeable seat isolates solid particles; combined with Figure 1As shown, the permeable seat body includes a first permeable seat 2, a second permeable seat 20, and a third permeable seat 21 arranged sequentially from the front end to the rear end of the tubular shell 14. The outer wall of the first permeable seat 2 is sealed to the inner wall of the front end of the tubular shell 14. A funnel-shaped notch 1a extending towards the rear end and used to place the permeable stone 1 is provided at the front end of the first permeable seat 2. A diaphragm 4 is provided on the side wall of the front end section of the second permeable seat 20, and one edge of the diaphragm 4 is connected to the front end section of the second permeable seat 20. The diaphragm 4 is connected to the edge of the sidewall, and the other side of the diaphragm 4 is close to the rear end sidewall of the first permeable base 2. An excitation and receiving coil 7 is connected between the rear end of the second permeable base 20 and the front end of the third permeable base 21. A surge arrester 10 is installed on the rear end sidewall of the third permeable base 21. More specifically, a three-electrode plasma surge arrester 10 is installed inside the third permeable base 21 to prevent peak voltage from entering the third permeable base 21 through the wires. The rear end of the third permeable base 21 and the surge arrester 10 are connected... An inner seal 15 is installed inside the rear end of the tubular housing 14 for sealing and fixing. The inner seal 15 is sealed with silicone. The fixed end of the steel wire 5 is connected to the central side wall of the diaphragm 4. The free end of the steel wire 5 passes through the second water-permeable seat 20, the excitation and receiving coil 7, the third water-permeable seat 21, and the inner seal 15 in sequence and is connected to the inductor cable 16. A fixed terminal 40 is provided in the center of the surface of the diaphragm 4, extending into one side of the second water-permeable seat 20. A fixed vibration block 41 for supporting the steel wire 5 is provided in the center of the interior of the third water-permeable seat 21. The fixed end of the steel wire 5 is connected to the fixed terminal 40 of the diaphragm 4. The free end of the steel wire 5 passes through the third water-permeable seat 21 and is connected near the rear end of the tubular housing 14. The steel wire 5 vibrates by the fixed vibration block 41 between the interior of the third water-permeable seat 21 and the free end of the steel wire 5. The steel wire 5 vibrates stably under the support of the fixed vibration block 41 and does not drift randomly, which increases the stability and accuracy of the detection. An annular groove 30 is provided on the outer circumference of the piezometer body 17 near the rear end of the first permeable seat 2. A first O-type coil 3 is disposed within the annular groove 30. The first O-type coil 3 and the first permeable seat 2 at the front end of the piezometer body 17 can be removed for troubleshooting. An ohmmeter is connected across the output terminal of the piezometer body 17 and the first O-type coil 3 to check the coil resistance. Under normal circumstances, the resistance of the first O-type coil 3 is 180Ω (±5%). Adding the resistance of the cable and the 22AWG wire, the resistance is approximately 15Ω per 100 feet. If the ohmmeter detects a very high or infinite resistance, the cable may be broken or open-circuited. If the resistance is very low, the wires inside the piezometer body 17 may be short-circuited. Multiple equally spaced outwardly protruding annular protrusions 23 are provided on the outer circumference of the second permeable seat 20. A second O-type coil 6 is disposed between adjacent annular protrusions 23 with the steel wire 5 as the symmetrical center line.

[0032] In this invention, such as Figure 1As shown, the tubular housing 14 contains a sensitive stainless steel diaphragm 4, on which a vibrating steel string 5 (vibrating string) is connected. During use, changes in pressure on the diaphragm 4 cause the steel string 5 to move. This minute displacement of the steel string 5 can be measured by the tension and vibration frequency of the steel string 5, with the square of the vibration frequency proportional to the pressure on the diaphragm. The second permeable seat 20 has two spaced-apart second O-type coils 6, symmetrically placed close to the steel string. During use, a frequency-converted pulse signal is applied to the coils, causing the steel string 5 to vibrate at its natural frequency. When the excitation ends, the steel string 5 continues to vibrate, but the sinusoidal signal of its natural frequency gradually weakens on the coils and is transmitted to the automated data acquisition instrument 26, where it is demodulated and displayed, allowing for the reading of real-time monitoring data.

[0033] In this invention, a protective tube 50 made of HDPE material is provided on the outside of the piezometer body 17, such as... Figure 2 , Figure 3 and Figure 4 As shown, the protective pipe 50 consists of a bottom impermeable sand-collecting pipe with a plug, a middle water-filtering pipe, and an upper impermeable fixed section. Water-permeable holes 51 are opened at different heights on the outer wall of the middle section of the protective pipe 50. Clean fine sand 52 is filled inside the protective pipe 50, located 100mm-200mm below the front end, around the perimeter, and 100mm-200mm above the rear end. Bentonite 53 and a cement slurry mixture 54 are then sequentially filled on top of the washed sand 52. A water-stop strip is tied to the lower part of the fixed section of the protective pipe. The piezometer body is placed inside the special protective pipe, which is designed with openings and then backfilled and sealed with bentonite and an appropriate amount of sand alternately. This not only accurately and fully reflects the changes in water and gas pressure in karst fissures but also allows for easy replacement and recycling of the piezometer. When installing the piezometer body 17, cement mortar is slowly and evenly poured to the ground between the tubular shell 14 (the outer wall of the piezometer body 17) and the protective tube to isolate the internal and external environment of the protective tube 50, so as to truly and fully reflect the change information of water and gas pressure in the karst pipe fissures.

[0034] According to another aspect of the invention, such as Figure 4 , Figure 5 As shown, the present invention provides a method for installing and using a piezometer for monitoring groundwater gas pressure in karst areas, comprising the following steps:

[0035] Step 1, Drilling and Well Formation: In the underground karst fissure development zone 100, use a mechanical drilling method with a diameter of 127mm, either water drilling or low water pressure drilling, to drill and form one or more water and gas pressure monitoring wells.

[0036] Step 2: Lower the protective casing. Place a protective casing made of HDPE material as the protective casing 50 in each water and gas pressure monitoring well. After drilling with a 127mm diameter drill string, use a DN110mm HDPE pipe as the protective casing at the final borehole inner diameter. After borehole completion, insert the protective casing into the casing and then pull out the steel casing. The protective casing, made of DN110mm HDPE pipe, is lowered to the bottom of the well. The protective casing consists of three parts: a bottom section is a plugged, impermeable sand-collecting pipe; a middle section is a water filter pipe; and an upper, impermeable fixed section. A waterstop is tied to the lower part of the fixed section of the protective pipe. Cement mortar is slowly and evenly poured between the steel casing and the protective pipe to the ground surface to isolate the internal and external environments of the protective pipe, thus accurately and fully reflecting the changes in water and gas pressure in the karst conduit fissures. The depth of the water and gas pressure monitoring well is determined according to the type of karst aquifer to be exposed, its burial depth, and thickness. The borehole passes through the karst fissure development zone or karst conduit (due to core breakage or low core recovery rate, water inrush or leakage during drilling, drill bit loss, etc.) and records the depth H of the water and gas pressure monitoring well and the depth H2 of the underground karst fissure development zone 100. The protective pipe 50 is provided with permeable holes 51 at intervals, according to the length H1 of the piezometer body 17. The permeable holes 51 are opened at different heights on the outer wall of the middle section of the protective pipe 50 at height H2 (i.e., the length of the opening section is the same as the depth H2 of the lower karst fissure development zone 100). The permeable holes 51 are opened at different heights on the protective pipe 50 and are spaced 100mm apart. There are four permeable holes 51 at the same horizontal height, symmetrically arranged at 90°. The diameter of the permeable holes 51 is 8mm-15mm, preferably 10mm (e.g., ...). Figure 2 and Figure 3 As shown in the schematic diagram of the opening of the piezometer protective pipe, the groundwater gas pressure is connected to the piezometer body 17 through the permeable hole 51. In this invention, the protective pipe 50 consists of a sand settling pipe with a plug at the bottom, a filter pipe in the middle, and a fixed section that is also impermeable at the top.

[0037] Step 3: Installation of the piezometer body 17. In this invention, the piezometer body 17 is installed in an underground karst fissure development zone, including a surface part and an underground part. The underground part is the water-gas pressure piezometer sensing component, and the surface part is the power supply and automated data acquisition instrument connected to the piezometer. First, a protective pipe 50 with permeable holes 51 is placed in each water-gas pressure monitoring well. Clean fine sand 52 is used to backfill the protective pipe 50 to 150mm below the front end of the piezometer body 17. Then, the piezometer body 17 is placed into the protective pipe 50. Clean fine sand 52 is then placed inside the protective pipe 50 and around the piezometer body 17 until it is 150mm above the piezometer body 17. After the piezometer body 17 is installed and adjusted, impermeable bentonite 53 and cement slurry mixture 54 are used to backfill the top of the protective pipe 50. A sealing section with a length of H3 is formed to eliminate the influence of external atmospheric pressure on the observed value. When the fine sand 52 reaches 150mm or 100mm below the end of the piezometer body 17, the piezometer body 17 is placed in. Then, clean fine sand 52 is placed around the piezometer body 17, and the fine sand 52 is placed 150mm above the piezometer body 17, so that the 150mm below the front end and the 150mm above the rear end of the piezometer body 17 are completely surrounded by sand. Then, the top is backfilled with a mixture of impermeable bentonite 53 and cement slurry 54 to seal it. This not only ensures a stable installation between the piezometer body 17 and the protective tube 50, but also ensures that water entering from the protective tube 50 can quickly seep into the front end of the piezometer body 17 for detection through the sand, and is not affected by external forces on the piezometer body 17 during the detection process.

[0038] Step 4: Signal connection of the piezometer body 17. Connect the cable 16 on the piezometer body 17 to the input port of the multi-channel junction box 26a on the ground 25 via the data transmission line 24. In this invention, the sensing cable 16 of the piezometer can be directly buried in the soil or concrete as needed, and has good waterproof and electrical performance. The cable cores are all twisted pairs, individually shielded with tin foil, and the shielding rate is 100%. Connect the automated data acquisition instrument 26 to the output port of the multi-channel junction box 26a. After connecting the AC power supply 27 of the automated data acquisition instrument 26, the groundwater and gas pressure in the karst area can be monitored, thus completing the installation and signal connection of the piezometer body 17. In this invention, the automated data acquisition instrument 26 is placed in the comprehensive room 29. The signal output terminal of the data acquisition instrument 26 is connected to the data processing terminal 28, which is a portable computer. When the portable computer is used to process the monitored data, the automated data acquisition instrument 26 and the data processing terminal communicate via wireless antenna 31 or RS232 / 485 or TCP / IP communication. The piezometer body 17 transmits the monitored groundwater and gas pressure changes in the karst area to the automated data acquisition instrument 26. The automated data acquisition instrument 26 compares the received data with the ground subsidence threshold value to determine whether the real-time data exceeds the subsidence threshold value. If it exceeds the threshold value, it automatically issues an early warning so that timely measures can be taken to prevent sudden changes in the groundwater and gas pressure in the karst area from endangering the stability of the stratum structure. In this invention, the piezometer body 17 is installed at the bottom of the borehole, and the permeable stone 1 in the piezometer is submerged in the groundwater. When in use, the excitation and receiving coil 7 can receive frequency-converted pulse signals, causing the steel string to vibrate at its natural frequency. The received signal is converted into an electrical signal through the piezometer cable 16 and transmitted to the automated data acquisition instrument 26. The change in groundwater gas pressure causes the steel string 5 to vibrate, thereby causing the displacement of the lead diaphragm 4. The minute displacement of the diaphragm 4 is measured by the tension and vibration frequency of the vibrating string element. The sinusoidal signal is converted into an electrical signal through the piezometer cable 16 and transmitted to the automated data acquisition instrument 26.

[0039] In another embodiment of the present invention, a layer of clean fine sand 52 is provided between the impermeable bentonite 53 and the cement slurry mixture 54. The height of the clean fine sand 52 is 100 mm-300 mm, and the specific height of the clean fine sand 52 can be selected as 150 mm.

[0040] This invention achieves real-time dynamic monitoring of water and gas pressure in karst cavities by combining a vibrating wire piezometer with a protective pipe, and issues early warnings based on the monitoring results. The piezometer can monitor changes in water and gas pressure in karst cavities online. When the water and gas pressure in the karst area fluctuates significantly, the data processing center compares the received data with the critical data for ground subsidence to determine whether the real-time data exceeds the critical value, so as to take timely measures to prevent sudden changes in water and gas pressure from endangering the stability of the karst geological structure.

[0041] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A piezometer for monitoring groundwater air pressure in karst areas, characterized by: The water vapor pressure monitoring osmometer comprises an osmometer body (17), the osmometer body (17) comprises a tubular shell (14), a water-permeable seat and a steel string (5) arranged in the tubular shell (14), the water-permeable seat is fixedly sealed in the tubular shell (14) by an inner seal (15), a water-permeable stone (1) is arranged in the front end of the water-permeable seat on the front end side of the tubular shell (14), a diaphragm (4) is arranged in the water-permeable seat close to the water-permeable stone (1) and in the direction of the rear end of the tubular shell (14), the fixed end of the steel string (5) is connected to the diaphragm (4), the free end of the steel string (5) extends out of the water-permeable seat and is connected to a cable (16) in the direction of the axis rear end of the tubular shell (14), an excitation and receiving coil (7) is arranged outside the water-permeable seat and around the outer periphery of the steel string (5); A lightning arrester (10) is arranged in the rear end of the water-permeable seat, the lightning arrester (10) is connected to a grounding terminal (11) of the tubular shell (14) by a lead wire (8), a semiconductor thermometer (12) is arranged in the tubular shell (14) close to the lightning arrester (10), a thermometer lead wire (13) is connected to the semiconductor thermometer (12), and an annular magnet (9) is sleeved on the outer wall of the excitation and receiving coil (7); The water-permeable seat comprises a first water-permeable seat (2), a second water-permeable seat (20) and a third water-permeable seat (21) arranged in the tubular shell (14) in sequence from the front end to the rear end, the outer wall of the first water-permeable seat (2) is sealingly connected to the inner wall of the front end of the tubular shell (14), a bucket-shaped notch (1a) for placing the water-permeable stone (1) is arranged on the front end of the first water-permeable seat (2), a diaphragm (4) is arranged on the front end cross-section side wall of the second water-permeable seat (20), one edge of the diaphragm (4) is connected to the edge of the front end cross-section side wall of the second water-permeable seat (20), the other edge of the diaphragm (4) is close to the rear end side wall of the first water-permeable seat (2), the excitation and receiving coil (7) is connected between the rear end of the second water-permeable seat (20) and the front end of the third water-permeable seat (21), the lightning arrester (10) is arranged on the rear end side wall of the third water-permeable seat (21), the rear end of the third water-permeable seat (21) and the lightning arrester (10) are sealingly fixed by the inner seal (15) arranged in the rear end of the tubular shell (14), the fixed end of the steel string (5) is connected to the central side wall of the diaphragm (4), the free end of the steel string (5) sequentially passes through the second water-permeable seat (20), the excitation and receiving coil (7), the third water-permeable seat (21) and the inner seal (15) and is connected to the cable (16).

2. The piezometer for monitoring groundwater air pressure in karst area according to claim 1, characterized in that: A protection pipe (50) made of HDPE material is arranged outside the osmometer body (17), which is composed of a lower part of a sand pipe with a plug and impermeable to water, a middle part of a filter pipe, and an upper part of an impermeable fixed section. Water-permeable holes (51) are arranged on the outer wall of the middle part of the protection pipe (50) at different heights. The inside of the protection pipe (50) is filled with clean fine sand (52) below the front end of the osmometer body (17) by 100-200 mm, around the periphery, and above the rear end by 100-200 mm. The clean fine sand (52) is further filled with bentonite (53) and cement slurry mixture (54) in sequence above the sand washing. A water stop belt is tied to the lower part of the fixed section of the protection pipe (50).

3. The piezometer for monitoring groundwater air pressure in karst area according to claim 1, characterized in that: A fixed terminal (40) is arranged in the center of the surface of the diaphragm (4) and extends into one side of the second water-permeable seat (20). A fixed vibration block (41) is arranged in the inner center of the third water-permeable seat (21) for penetrating the steel string (5). The fixed end of the steel string (5) is connected to the fixed terminal (40) of the diaphragm (4), and the free end of the steel string (5) penetrates out of the third water-permeable seat (21) and is connected to the upper part near the rear end of the tubular shell (14). An annular groove (30) is arranged on the circumferential outer wall near the rear end of the first water-permeable seat (2), and a first O-shaped coil (3) is arranged in the annular groove (30).

4. The piezometer for monitoring groundwater air pressure in karst area according to claim 3, characterized in that: A plurality of annular protrusions (23) are arranged on the circumferential outer wall of the second water-permeable seat (20) and protrude outward at equal intervals. A second O-shaped coil (6) is arranged between adjacent annular protrusions (23) with the steel string (5) as the center line.

5. The installation and use method of the piezometer for monitoring the groundwater gas pressure in karst areas according to any one of claims 1 to 4, characterized in that: The method comprises the following steps: Step 1: Drilling a well: in the underground karst fissure development zone, use the mechanical drilling method of fresh water drilling or low water pressure drilling to drill a water gas pressure monitoring well; Step 2: Lowering the protection pipe, placing the protection pipe made of HDPE material as the protection pipe (50) in the water gas pressure monitoring well; recording the depth of the water gas pressure monitoring well and the depth of the underground karst fissure development zone (100), and according to the depth of the underground karst fissure development zone (100), the water-permeable holes (51) are arranged on the protection pipe (50) at intervals; Step 3: Osmometer body (17) installation, placing the protection pipe (50) with water-permeable holes (51) in the water gas pressure monitoring well, and backfilling clean fine sand (52) in the protection pipe (50) to 150 mm below the front end part for placing the osmometer body (17), then placing the osmometer body (17) in the protection pipe (50), and then placing clean fine sand (52) around the osmometer body (17) in the protection pipe (50) until 150 mm above the osmometer body (17), after the installation and debugging of the osmometer body (17) are completed, backfilling the impermeable bentonite (53) and cement slurry mixture (54) to the top of the protection pipe (50) in sequence; Step 4, osmometer body (17) signal connection, the cable (16) on the osmometer body (17) is connected to the automatic data acquisition instrument (26) arranged on the ground (25) through the data transmission line (24), the monitoring of the karst area groundwater pressure can be carried out by turning on the alternating current power supply (27) of the automatic data acquisition instrument (26), thereby completing the installation and signal connection of the osmometer body (17).

6. The installation and use method of a karst area groundwater air pressure monitoring osmometer according to claim 5, characterized in that: A data processing terminal (28) is connected to the signal output end of the automatic data acquisition instrument (26), the automatic data acquisition instrument (26) and the data processing terminal are communicated through a wireless antenna (31) or an RS232 / 485 or TCP / IP communication mode, the osmometer body (17) transmits the karst area groundwater pressure change data to the automatic data acquisition instrument (26), the automatic data acquisition instrument (26) compares the received data with the ground collapse critical value, judges whether the real-time data exceeds the collapse critical value, and if the critical value is exceeded, automatically issues a warning to take timely measures to prevent the karst area water pressure from suddenly changing and endangering the stability of the stratum structure.

7. The installation and use method of the karst groundwater air pressure monitoring osmometer according to claim 5, characterized in that: A layer of clean fine sand (52) is arranged between the impermeable bentonite (53) and the cement slurry mixture (54), and the height of the layer of clean fine sand (52) is 100 mm-300 mm.

8. The installation and use method of the karst groundwater air pressure monitoring osmometer according to claim 5, characterized in that: Water-permeable holes (51) are arranged at different heights on the protection pipe (50) and are spaced apart by 100 mm, the water-permeable holes (51) at the same horizontal height are four and are symmetrically arranged at 90°, and the diameter of the water-permeable holes (51) is 8 mm-15 mm.

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