An online monitoring method for radon gas in unstable surrounding rocks of deep underground engineering

Abstract

The present invention provides an on-line monitoring method for radon gas in unstable surrounding rocks of deep underground engineering, which comprises the following steps: arranging the positions of monitoring holes and installing on-line radon detectors; before the in-situ stress causes rock fracture, the radon detectors monitor the free radon concentration in the original rock fissures under steady-state conditions, and after statistical analysis, it is used as the background value; after the rock mass is subjected to external stress, once rock fractures occur to generate fissures or pores, the sealed radon escapes to become free radon, resulting in a slight change in the radon gas concentration at the monitoring point; the radon detectors capture the signal and output the radon gas concentration change curve at this moment, observe and analyze the law of sudden steep increase or long-term continuous abnormality of the curve, and judge whether the rock mass shows signs of fracture instability; setting a threshold for prompt warning; according to the curve and the warning situation, combined with the on-site observation phenomena of the underground engineering, analyzing the rock mass state near the monitoring point, realizing the prediction of dynamic disasters of the surrounding rocks in the preset area, and being applicable to the long-term stability on-line monitoring of the underground engineering site.

Description

Technical Field

[0001] The present invention relates to the technical field of stability safety detection of underground engineering, and particularly relates to an on-line monitoring method for radon gas in unstable surrounding rock of deep underground engineering. Background Art

[0002] At present, the construction of underground engineering is continuously developing in the direction of "deep burial, long tunnel line, and high stress". The geological environment of more and more underground engineering is extremely complex, and problems such as high ground stress, high ground temperature, and high water pressure are prominent. The risk of sudden geological disasters is extremely high and difficult to predict, posing a huge threat to construction and operation safety. The deformation and failure problems of deep underground engineering have attracted much attention, and the rapid identification of brittle failure of rocks and its critical information has become a research hotspot and difficulty.

[0003] After the excavation of deep rock mass, a free face is generated inside the rock mass, and the initial ground stress is suddenly released, and the stress will be redistributed in the surrounding rock. The result of the redistribution is the unloading of the rock mass stress. Under the action of the unloading stress, the shear stress in the rock mass will increase and concentrate, and with the continuous progress of unloading, the rock mass will undergo unloading fracture. At the same time, under the combined action of high ground stress, high ground temperature, high osmotic pressure and construction disturbance, the surrounding rock of the deep engineering rock mass is prone to be in the working state of large deformation and strong rheology of soft rock, which restricts the support effect. The dynamic disasters in deep engineering are becoming increasingly serious, and affected by multiple factors, it is easy to damage the tunnel lining support structure, triggering landslides and secondary geological disasters. And one of the effective ways to solve this problem is to predict dynamic disasters in time. It is extremely urgent to accurately predict the dynamic disasters of rocks, which has great significance for ensuring the construction and operation safety of underground space and effectively preventing and containing major safety accidents.

[0004] The existing monitoring means for the internal state and mechanical characteristics of rocks in underground engineering include: microseismic, acoustic emission, electromagnetic radiation, wave velocity, potential signal, borehole camera, borehole stress monitoring, etc. For different on-site conditions and requirements, there are respective application scenarios, and the main deficiencies are as follows: the observation surface of the borehole method is very narrow and the original rock is damaged; the microseismic, electromagnetic radiation method, etc. are affected by construction vibration and interference of on-site electrical equipment; the measurement of microseismic, acoustic emission, wave velocity, and potential signal is complex and the data processing is more professional; most methods are difficult to achieve long-term on-line observation due to reasons such as difficult layout, function not allowed, and high instrument price.

[0005] The elements of the three natural radioactive series, namely the uranium series, thorium series, and actinium series, widely exist in natural rocks. Radon is their decay daughter product and is the only natural radioactive inert gas in nature. The distribution of radon is relatively wide. The higher the acidity of magmatic rocks, the higher the radon content, and the content in sedimentary rocks varies within a large range. Radon gas has the ability to diffuse and migrate, and there is free radon and bound radon in rocks. The low porosity of the rock itself affects the escape of radon atoms from minerals and the diffusion of free radon from the medium into the environment, hindering the release of radon. During the loading and failure process of the rock, the fissures and surface area of the rock increase significantly, and many dense microfissures are generated near the fissures. The interconnected microfissure network inside the rock or mineral increases both the porosity and permeability of the rock. Along with the dislocation of the crystal lattice in the rock minerals, the bound radon (adsorbed and partially enclosed) is released. In addition, with the increase in the temperature and pressure of the deep rock mass, it ultimately leads to an increase in the radon emanation pulse.

[0006] Existing radon measurement technologies and systems are divided into the instantaneous method and the cumulative method. The instantaneous method generally makes single-point instantaneous measurements of air and soil, requires manual operation and the use of hygroscopic agents to reduce air humidity, so it is not suitable for long-term multi-point monitoring; the cumulative method has high work efficiency, but both require manual sampling and analysis, and the process is cumbersome. Therefore, the existing radon and its daughter product measurement technologies are used in industry and scientific research, with complex method operations, high prices, and large volumes, and are not suitable for long-term on-line monitoring at the underground engineering site. Summary of the Invention

[0007] The object of the present invention is: aiming at the deficiencies in the above background technology, to provide a solution that is more suitable for long-term on-line monitoring of radon and its daughter products in rock masses at the underground engineering site.

[0008] To achieve the above object, the present invention provides an on-line monitoring method for radon gas in unstable surrounding rocks of deep underground engineering, including the following steps:

[0009] S1. At the weak area or broken dangerous area of the surrounding rock of the underground project, arrange the positions of the monitoring holes and install radon detectors.

[0010] S2. Before the in-situ stress causes the rock to break, the radon detector monitors the free radon concentration in the original rock fissures under steady-state conditions, and the average value is statistically obtained and recorded as the background value R n0 ;

[0011] S3. After the rock mass is affected by external stress, once the rock breaks to generate fissures or pores, the sealed radon escapes to become free radon, resulting in a weak change in the radon gas concentration at the monitoring point at time t, recorded as R nt ;

[0012] S4. The radon detector outputs the radon gas concentration change curve y=(k n0 ·R n0 +k nt ·Rnt ) By observing and analyzing the sudden steep increase or the law of long-term continuous anomalies in the curve, determine whether there are signs of rock mass rupture and instability; where k n0 is the background value correction coefficient, and k nt is the measurement value correction coefficient at time t;

[0013] Set a threshold for prompt warning;

[0014] S5. According to the curve and the warning situation, combined with the on-site observation phenomena of the underground project, analyze the rock mass state near the monitoring point to realize the prediction of dynamic disasters of the surrounding rock in the preset area.

[0015] Furthermore, when arranging the monitoring holes, the diameter M of the monitoring holes s is larger than the outer diameter of the pipeline, and the depth M of the monitoring holes d depends on the thickness of the rock layer to be monitored, and the inclination angle M of the monitoring holes a depends on the dip angle of the rock layer and the engineering requirements.

[0016] Furthermore, during the hole-forming process, if water gushing or mud phenomena occur in the hole, cancel the arrangement of this monitoring point; after hole-forming, clean the hole to remove the residues remaining inside the hole.

[0017] Furthermore, the radon detector is an ionization chamber detector, and the ionization chamber detector includes a detector cavity. Inside the detector cavity, there are a pulse signal collecting electrode and a pulse ionization chamber voltage electrode. A high voltage is applied to the pulse ionization chamber voltage electrode to form an electric field inside the detector cavity. The detector cavity is provided with an air inlet, and the air inlet is connected to an extraction pipe. The extraction pipe is provided with a micro air pump and a filter, and the extraction pipe is used to extract the radon gas released by the surrounding rock mass.

[0018] Furthermore, the extraction pipe includes an extraction hose and an extraction hard pipe;

[0019] The first end of the extraction hose is connected to the air inlet, and the second end of the extraction hose is connected to the extraction hard pipe;

[0020] The first end of the extraction hard pipe is connected to the extraction hose, and the second end of the extraction hard pipe is axially provided with a plurality of air inlet holes, and the second end of the extraction hard pipe is inserted into the rock wall hole.

[0021] Furthermore, the radon detector can also monitor the humidity, temperature, and air pressure parameters inside the detector cavity to comprehensively calculate the change in the final radon gas content of the rock;

[0022] According to the following formula, calculate the radon gas concentration:

[0023]

[0024] In the formula: Rn Rn concentration in rock, P is the porosity of the rock, q is the radium content in the rock, ρ is the rock density, k is the correlation coefficient,

[0025] k = f(H, T, Ap, A, Gp, t)

[0026] wherein, the correlation coefficient k is directly proportional to the rock temperature T, the fracture surface area A, and the ground pressure Gp, inversely proportional to the air pressure Ap and the humidity H, and related to the time t of the rock mass under load.

[0027] Furthermore, the rock porosity P is calculated by the following formula:

[0028] P = P0 – A(Gp) n

[0029] where P0 is the rock porosity under normal conditions, and A and n are experimental constants.

[0030] Furthermore, in the setting of the threshold, first a initial threshold T1 is given, and then it is gradually corrected in combination with the observation of the on-site rock mass fracture, and finally a reasonable alarm threshold T2 is formed;

[0031] wherein, T2 is calculated by the following formula:

[0032] X overall sample data observed from the on-site rock mass fracture form a distribution f(x), then the objective is:

[0033]

[0034] where, f i (x) is the preset rock mass fracture data, g i is the fracture data distribution of the actual rock mass, T is the adjustment factor, and the corresponding iterative formula generated from the above formula is:

[0035]

[0036] According to the iterative result of the above formula, a reasonable alarm threshold T2 is formed as:

[0037]

[0038] Calculate the abnormal warning coefficient C. If the abnormal warning coefficient C exceeds the threshold T2, then a warning prompt for a single radon detector is issued, informing that the radon gas is abnormal within the monitoring range of the single radon detector;

[0039] C = J·(R nt -R n0 )

[0040] where J is the radon detector correction coefficient;

[0041] Set the total abnormal warning coefficient C of dangerous rock mass in the area Z When multiple instruments have abnormal radon emission values, the total abnormal warning coefficient C Z If the set threshold is exceeded, an early warning will be automatically issued at this moment t;

[0042] C z =J1·(R n1 -R n10 )+J2·(R n2 -R n20 )+......+J N ·(R nN -R nN0 )

[0043] Where: J1 is the correction coefficient of the first radon detector, J2 is the correction coefficient of the second radon detector, J N is the correction factor of the Nth radon detector, R n1 is the abnormal radon value in the first radon detector hole, R n10 is the radon background value in the first radon detector hole, R n2 is the abnormal radon value in the second radon detector hole, R n20 is the radon background value in the second radon detector hole, R nN is the abnormal radon value in the hole of the Nth radon detector, R nN0 It is the radon background value in the Nth radon detector hole.

[0044] Furthermore, the radon detector adopts remote online measurement and control to compare the measured radon concentration value with the background value, and analyze and study the rules.

[0045] Furthermore, the radon detector adopts proximal measurement and control, a Bluetooth module is arranged on the radon detector, and after the monitoring software is installed on the mobile phone, parameters of each radon detector can be set and data can be read at close range on site.

[0046] The above scheme of the present invention has the following beneficial effects:

[0047] The online monitoring method for unstable surrounding rock radon gas in deep underground engineering provided by the present invention has the advantages of simple installation and construction, and only requires conventional drilling installation and fixing without special treatment; the measurement is less affected by external interference, and is basically not affected by electromagnetic interference, potential difference, etc.; compared with methods such as borehole stress monitoring, the measurement area is larger, and the stability of rock mass within a certain range around the borehole can be monitored; compared with methods such as microseismic monitoring, the resulting curve is intuitive and clear, and no complex data processing and analysis is required, and no specialized technicians are required to perform tedious data analysis; transient measurement by methods such as borehole photography requires manual operation if long-term monitoring is to be carried out, while this method can monitor the change of weak horizontal radon concentration caused by rock mass rupture in underground engineering on site for a long time;

[0048] This method can identify multi-dimensional and rapid brittle fractures of surrounding rocks and their critical information, monitor various environmental influencing factors such as ground temperature, humidity, and air pressure, comprehensively measure and correct the influence on weak radon gas concentration, so as to achieve accurate measurement; it can realize matrix multi-point networking layout of monitoring points, flexibly monitor the depth and area of rock masses from multiple angles, and mutually verify to improve monitoring accuracy; the monitoring equipment can realize wireless and wired networking control, remotely or closely monitor the brittle fractures and their critical information of soft rock layers, fracture zones, and tectonic areas in underground engineering tunnels for a long time, and achieve timely and rapid detection and early warning of rock mass dynamic disasters;

[0049] The radon detector used in this method is an ionization chamber detector. Compared with conventional detectors such as semiconductors, it has the advantages of good moisture resistance, low background pollution, and high sensitivity. Moreover, the structure of the entire measurement system is simple, the cost is low, and it has better on-site applicability;

[0050] Other beneficial effects of the present invention will be described in detail in the subsequent specific implementation part. Brief Description of the Drawings

[0051] Figure 1 is the step flow chart of the present invention;

[0052] Figure 2 is the layout of the monitoring hole positions and the installation schematic diagram of the radon detector in the present invention;

[0053] Figure 3 is the structural schematic diagram of the radon detector in the present invention;

[0054] Figure 4 is the curve of radon gas change in a certain hole of the surrounding rock monitored in the embodiment of the present invention.

[0055]

Description of the Reference Numerals

[0056] 1. Radon detector; 2. Tunnel support and lining; 3. Radon escape channel; 4. Suction hose; 5. Suction hard pipe; 6. Air inlet; 7. Pulse signal collection electrode; 8. Pulse ionization chamber voltage electrode; 9. Detector cavity; 10. Micro suction pump; 11. Alpha ray; 12. Filter. Detailed Description of the Invention

[0057] The following specific examples illustrate the embodiments of the present disclosure. Those skilled in the art can easily understand the other advantages and effects of the present disclosure from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all of the embodiments. The present disclosure can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present disclosure. It should be noted that, without conflict, the following embodiments and the features in the embodiments can be combined with each other. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present disclosure without creative efforts belong to the scope of protection of the present disclosure.

[0058] It should be noted that the following describes various aspects of embodiments within the scope of the appended claims. It should be apparent that the aspects described herein can be embodied in a wide variety of forms, and any specific structure and / or function described herein is illustrative only. Based on the present disclosure, those skilled in the art should understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of the aspects described herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using other structures and / or functionality in addition to one or more of the aspects described herein.

[0059] It should also be noted that the drawings provided in the following embodiments only illustrate the basic concept of the present disclosure schematically. The drawings only show the components related to the present disclosure, rather than being drawn according to the number, shape, and size of the components in actual implementation. The types, quantities, and proportions of the components in actual implementation can be arbitrarily changed, and the component layout type may also be more complex. Additionally, in the following description, specific details are provided to facilitate a thorough understanding of the examples. However, those skilled in the art will understand that the described aspects can be practiced without these specific details.

[0060] The present invention relates to an on-line monitoring method for radon gas in unstable surrounding rocks of deep underground engineering. Among them, the three natural radioactive series elements of the uranium series, thorium series, and actinium series are widely present in natural rocks. The half-lives of the parent elements are very long, and radon is their decay daughter, which are respectively 222 Rn, 220 Rn, and 219 Rn. The actinium series always coexists with the uranium series, but the amount of the parent nuclide 235 U in the actinium series is very small. Generally, 219The influence of Rn on measurement can be ignored. Under normal circumstances, radon is in a stable state and does not react with any element. It also widely exists in natural rocks. However, the radon content varies significantly in rocks of different lithologies. The higher the acidity of igneous rocks, the higher the radon content. The content range of sedimentary rocks is relatively large. Due to the influence of factors such as humidity, ground temperature, ground pressure, air temperature, air pressure, groundwater content, and geological structure, even in the same area, there are significant differences in the radon content of rocks. Radon has the property of escaping. The radon emission rate from rocks increases with the increase of the internal porosity and surface area coefficient of the rocks. Radon gas reveals the radon anomaly mechanism and the precursor characteristics mechanism of dynamic disasters such as rock burst, soft rock deformation, and overall instability.

[0061] The decay of radon gas and its daughters will release α rays 11. The decay process mainly releases radionuclides of α rays 11. For the uranium series, it is as shown in Equation (1), and for the thorium series, it is as shown in Equation (2). In practical applications, when measuring radon gas, it is mainly to measure the α particles generated by radon and its subsequent α decay daughters.

[0062]

[0063] Based on this, the online radon gas monitoring method for unstable surrounding rocks in deep underground engineering provided by the present invention includes the following steps:

[0064] S1, arranging the monitoring hole positions and installing the radon detector 1.

[0065] In this embodiment, in the weak area or broken dangerous area of the surrounding rock of the underground project, select the positions for arranging the monitoring holes. The hole positions are arranged at a certain interval by means of air drilling, etc. Or the air extraction pipe can be embedded in the engineering anchor rod hole positions as the monitoring points, and the monitoring is intensified in the key monitoring areas. As Figure 2 shown, arrange the monitoring hole positions at the position of the tunnel lining 2 and install the radon detector 1. The radon escape channel 3 has been marked schematically in the figure.

[0066] Among them, when arranging the monitoring holes, three issues are mainly considered: the diameter M of the monitoring hole s , the depth M of the monitoring hole d and the inclination angle M of the monitoring hole a . The diameter M of the monitoring hole s is slightly larger than the pipeline. The depth M of the monitoring hole d depends on the thickness of the rock layer to be monitored. The inclination angle M of the monitoring hole a depends on the dip angle of the rock layer and the requirements of the project. During the hole-forming process, if water gushing or mud phenomenon occurs in the hole, then cancel the arrangement of this monitoring point. After the hole is formed, clean the hole, and use the air compressor air pipe to clean it to remove the residues remaining in the hole.

[0067] The air extraction pipe includes an air extraction flexible pipe 4 and an air extraction rigid pipe 5. One section with multiple air inlet holes is inserted into the rock wall hole, and the other section is exposed and connected to the radon detector 1. The air inlet 6 of the radon detector 1 faces the hole position and is fixed on the tunnel support and lining 2. The air extraction flexible pipe 4 is used to connect the air extraction rigid pipe 5 well. Seal the exposed end of the air extraction rigid pipe 5 with a sealing rubber ring, or foaming glue, or cement, or other materials, and tightly block it to prevent external air from entering.

[0068] Based on the fact that the unloading and fracture range of rock mass is often large, after the monitoring is started, the abnormal values measured at the monitoring points are mutually verified. Since the air extraction rigid pipe 5 itself has multiple air inlet holes, even if a certain section of the monitoring hole may be blocked, it can still ensure the effective extraction of radon gas released from the surrounding rock mass.

[0069] In this embodiment, the radon detector 1 adopts the form of an ionization chamber detector, and the α-ray 11 is measured through the ionization chamber detector. The structure of the ionization detector is as Figure 3 shown. An electric field environment is formed by the pulse signal collection electrode 7 and the pulse ionization chamber voltage electrode 8. A high voltage is applied to the pulse ionization chamber voltage electrode 8 to form an electric field inside the detector cavity 9. Under the action of the micro air pump 10, air passes through the filter 12 to filter out larger particle dust and then enters the detector cavity 9. When the α-ray 11 generated by the decay of radon and its daughters moves inside the detector cavity 9, it gradually loses energy due to ionization collisions with gas molecules and is finally stopped. The result of the collision ionizes or excites the gas molecules, and a large number of electron-ion pairs are generated on the path where the particles pass. The electron ions drift in different directions under the action of the electric field. Due to electrostatic induction, the pulse signal collection electrode will sense charges and change with the drift of the electron-ion pairs. Thus, an ionization current is formed in the output circuit. The intensity of the current is determined by the number of collected electron-ion pairs, and the number of electron-ion pairs depends on the concentration of radon gas. Therefore, the radon gas concentration is judged according to the magnitude of the current.

[0070] It should be noted that in actual application, the micro air pump 10 starts at time intervals of "hours" or "days", and the air extraction time for each time is in the unit of "minutes". Free radon is collected from the rock drill hole through the air extraction pipe (air extraction rigid pipe 5 + air extraction flexible pipe 4). First, it passes through the filter 12 to filter out larger dust particles and then enters the detector cavity 9 for measurement.

[0071] In this embodiment, in addition to measuring the radon gas concentration, the radon detector 1 also monitors parameters such as humidity, temperature, and air pressure inside the detector cavity 9 to comprehensively calculate the change of the final radon gas content in the rock.

[0072] According to the following formula, calculate the radon gas concentration:

[0073]

[0074] In the formula: R nLet \(Rn\) be the radon concentration in the rock, \(P\) be the rock porosity, \(q\) be the radium content in the rock, \(\rho\) be the rock density, and \(k\) be a correlation coefficient (related to factors such as geothermal temperature, humidity, ground pressure, and air pressure).

[0075] \(k = f(H,T,Ap,A,Gp,t)\) (4)

[0076] Among them, the correlation coefficient \(k\) is directly proportional to the rock temperature \(T\), the fracture surface area \(A\), and the ground pressure \(Gp\), and inversely proportional to parameters such as the air pressure \(Ap\) and humidity \(H\). In addition, it also has a certain relationship with the time \(t\) during the loading process of the rock mass. Generally, in the early stage of rock mass fracture, due to the increase in ground stress, a large amount of radon in the original fractures is squeezed out, resulting in an abnormal increase in radon exhalation. As the ground stress continues to increase, the fractures are compacted and become fewer. As can be obtained from equations (5) and (6), the radon exhalation amount will have a small phased decrease.

[0077] \(P = P_0–A(Gp)\) n (5)

[0078] \(R\) nt \(=(R\) nt0 \(\cdot\mu)\cdot P\) (6)

[0079] Among them, \(P_0\) is the rock porosity under normal conditions, \(A\) and \(n\) are experimental constants, \(R\) nt is the free radon concentration in the rock pores at a certain moment, \(R\) nt0 is the total radon concentration generated by the rock, and \(\mu\) is the ratio of the free radon concentration in the rock pores to the total radon concentration generated by the rock. It can be understood that \(R\) nt is used to illustrate that the free radon concentration in the rock is affected by the rock porosity, that is, \(R\) nt \(\propto P\).

[0080] When the rock mass undergoes deformation and fracture, the cracks that appear cause the bound radon to escape under pressure, and the radon exhalation will increase. When the ground stress further expands, accompanied by the appearance of macroscopic fracture surfaces, the fracture surface area of the rock mass increases significantly, and the radon exhalation is more obvious. After the rock mass fracture deformation stabilizes, the radon anomaly tends to a stable state, and the correlation coefficient \(k\) also shows periodic and regular changes. At this time, the abnormal curve of the rock radon concentration presented will also change periodically with \(k\). This change is caused by external factors, rather than the actual rock fracture displacement. Attention should be paid when identifying curve anomalies.

[0081] S2. Before the ground stress causes the rock to fracture, the radon detector 1 monitors the free radon concentration in the original rock fissures under steady-state conditions, denoted as the background value \(R\) n0 .

[0082] S3. After the rock mass is affected by external stress, once the rock fractures to generate fissures or pores, the sealed radon escapes to become free radon, resulting in a slight change in the radon gas concentration at a certain moment at the measurement point, denoted as \(R\) nt .

[0083] According to formulas (4) to (6), the correlation coefficient k for a certain period can be generally obtained. Then, based on formula (3) and the fact that the radium content q in the rock is basically stable, the change trend of the rock porosity P can be qualitatively determined.

[0084] S4. When the radon detector 1 measures, it outputs a radon gas change curve y=(k n0 ·R n0 +k nt ·R nt ) at a certain moment, where k n0 is the background value correction coefficient, and k nt is the measurement value correction coefficient at a certain moment. The abnormal situation is visually presented according to the formed radon gas concentration curve. If the curve suddenly increases steeply or shows continuous abnormalities for several days, such as the concentration increase exceeding 50% of the highest value, it can be warned that the rock mass may show signs of fracture instability, and timely on-site observation and disaster prediction are reminded.

[0085] Meanwhile, an early warning threshold can also be set. If the preset threshold is exceeded, a prompt warning can be given.

[0086] It should be noted that in actual setting, an initial value can be first given, and then gradually corrected in combination with the on-site rock mass fracture observation situation, and finally a more reasonable alarm threshold is formed.

[0087] In this embodiment, a multi-point online monitoring system is planned to be adopted. Multiple radon detectors 1 are arranged in an array at a certain interval according to the distribution of monitoring points to conduct real-time monitoring of the dynamic radon concentration in the unstable rock layer area in the underground project and monitor the state of the unstable rock mass from multiple angles. If the abnormal warning coefficient C obtained by formula (7) for the measured value of a certain instrument exceeds the set threshold, a single instrument early warning prompt is issued to inform the user that the radon gas is abnormal within the monitoring range of a certain instrument.

[0088] C = J·(R n -R n0 )(7)

[0089] where J is the radon detector correction coefficient, R n is the current radon concentration in the rock, and R n0 is the original radon gas background value in the hole.

[0090] The total abnormal warning coefficient C of the regional dangerous rock mass is obtained through formula (8) Z . When the radon emission values of multiple instruments are abnormal and exceed the set threshold, an early warning prompt is automatically issued.

[0091] C z = J1·(R n1 -R n10 ) + J2·(R n2 -Rn20 ) +...... + J N ·(R nN - R nN0 ) (8)

[0092] Where: J1 is the correction coefficient of the first radon detector, J2 is the correction coefficient of the second radon detector, J N is the correction coefficient of the Nth radon detector, R n1 is the abnormal radon value in the hole of the first radon detector, R n10 is the radon background value in the hole of the first radon detector, R n2 is the abnormal radon value in the hole of the second radon detector, R n20 is the radon background value in the hole of the second radon detector, R nN is the abnormal radon value in the hole of the Nth radon detector, R nN0 is the radon background value in the hole of the Nth radon detector.

[0093] S5. Observe the curve and, according to the warning value, combined with the observation phenomena of the underground project, comprehensively analyze the state of the rock mass near the monitoring point by multiple factors to realize the prediction of the dynamic disasters of the surrounding rock in a specific area.

[0094] Observation phenomena such as vertical and horizontal cracks and cracks appearing in the shotcrete; the bedding and joint cracks of the surrounding rock strata gradually becoming larger and opening; the sudden intensification or turbidity of water seepage and dripping on the rock wall, and the dripping position moving erratically; continuous falling of blocks and sand and gravel on the side wall or top of the project, as well as the dust flying without reason; abnormal phenomena such as the sudden appearance of dull thunder or crackling sounds without reason.

[0095] It should be noted that in this embodiment, two methods can be used for measurement and control: remote online measurement and control, through the special optical fiber network, RS-485 hub and the host computer or cloud communication of the project, the terminal will represent the multi-point monitoring data with charts, compare the measured radon concentration value with the background value, and analyze and study the law, and then predict the dynamic disasters of the rock mass rupture and deformation in the deep underground project; proximal measurement and control, a Bluetooth module is set on the radon detector, and after the mobile phone installs the monitoring software, the parameters can be set and the data can be read point-to-point at close range on site, and the radon gas evolution amount of the rock mass on site can be understood in real time, and the dynamic disasters of the rock mass deformation can be understood.

[0096] Case illustration: As Figure 4 shown, when the scheme provided by this embodiment is used for monitoring, assuming that the monitoring is started at intervals of "hours" as the time unit.

[0097] 1) Before 21:00, the rock radon gas concentration curve shows periodic fluctuations, which is inferred to be affected by environmental factors such as air pressure and humidity, and belongs to normal phenomena.

[0098] 2) After 21 o'clock, the curve continued to decline. It is inferred that this is mainly because under the action of pressure, the internal porosity of the rock mass becomes smaller, the cross-section of the radon exhalation channel of the rock becomes smaller, which is insufficient to drive the radon exhalation, and finally leads to the decline of the radon concentration.

[0099] 3) Then, after 25 o'clock, the curve suddenly increased steeply or showed continuous anomalies for several days. It is inferred that this is mainly because the rock mass enters the plastic deformation stage, the damage level of the rock mass is relatively high, the cracks generated gradually open and expand, and more secondary cracks are formed. Subsequently, macroscopic rock mass fractures occur, providing many continuous channels for the migration of radon gas, greatly increasing the radon emission area of the rock mass, and leading to a significant increase in the radon gas concentration; if the increase amplitude of the concentration exceeds 50% of the usual highest value, it can be used to warn that the rock mass may show signs of fracture and instability, and remind to go to the site for on-site observation and disaster prediction in time.

[0100] 4) When the radon gas rises to a certain concentration and remains at that level for a period of time and then shows a small decline, it is inferred that this is because after the rock mass is damaged, the originally sealed radon in the rock is gradually released, resulting in a decrease in the radon measurement value. The existing higher concentration mainly comes from the continuous decay of radium in the enlarged rock mass fracture surface. Of course, the curve may also show a large decline, which may be due to the occurrence of large cracks, resulting in connection with the external space of the underground project, and the radon gas in the monitoring hole is carried away by the underground fluid, resulting in a decrease in concentration.

[0101] In summary, this embodiment provides a simple, easy-to-implement, fast and reliable online monitoring method for radon gas in unstable surrounding rocks of deep underground projects. It has the advantage of simple installation and construction, only requiring conventional drilling for installation and fixation without special treatment; the measurement is less affected by external interference, and is basically not affected by electromagnetic interference, potential difference, etc.; compared with methods such as borehole stress monitoring, the measurement area is larger, and the stability of the rock mass in a certain range around the borehole can be monitored; compared with methods such as microseismic monitoring, the mapping curve is intuitive and clear, does not require complex data processing and analysis, and does not require specialized technicians to do cumbersome data analysis; compared with the transient measurement of methods such as borehole camera, if long-term monitoring is to be carried out, it must be manually operated, while this application can long-term monitor the change of weak-level radon concentration caused by rock mass fracture in underground projects on site.

[0102] This application can be a good supplement to existing measurement methods. Combined with other measurement methods, it can monitor the stability of the rock mass in underground projects from multiple angles.

[0103] The method provided by this application can identify multi-dimensional and rapid brittle fracture of surrounding rock and its critical information, can monitor various environmental influencing factors such as ground temperature, humidity, air pressure, etc., conduct comprehensive measurement, correct the influence on weak radon gas concentration, so as to achieve accurate measurement; it can realize matrix multi-point networking layout of monitoring points, flexibly monitor the depth and area of rock mass from multiple angles, and mutually verify to improve the monitoring accuracy; the monitoring equipment can realize wireless and wired networking control, remotely or closely monitor the brittle fracture and its critical information of soft rock strata, fracture zones, and tectonic areas in underground engineering tunnels for a long time, so as to detect and warn of rock mass dynamic disasters in a timely and rapid manner.

[0104] Existing radon measurement technologies and instrument systems generally require human assistance, such as parameter setting of the instantaneous method, replacement of desiccants, treatment before and after sampling by the activated carbon method, etc., and it is difficult to truly achieve long-term online monitoring. Moreover, they are generally used in industry and scientific research, with complex method operations, expensive equipment, and large volumes, and are not suitable for directly monitoring rock mass dynamic disasters at the site of underground engineering. The radon detector used in this embodiment is an ionization chamber detector, which has the advantages of better moisture resistance, low background pollution, and high sensitivity compared with conventional detectors such as semiconductors. In addition, the structure of the entire measurement system is simple, the cost is low, and it has better on-site applicability.

[0105] The above is the preferred implementation manner of the present invention. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle described in the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. An on-line monitoring method for radon gas in unstable surrounding rock of deep underground engineering, characterized in that, It includes the following steps: S1. At the weak area or dangerous fracture area of the surrounding rock of the underground project, arrange the monitoring hole positions and install radon detectors. S2. Before the in-situ stress causes rock fracture, the radon monitor measures the free radon concentration in the original rock fissures under steady-state conditions, and the average value is statistically calculated and recorded as the background value R n0 ; S3. After the rock mass is subjected to external stress, once cracks or pores are generated due to rock fracture, the sealed radon escapes to become free radon, resulting in a slight change in the radon gas concentration at the monitoring point at time t, denoted as R nt ; S4. The radon detector outputs the radon gas concentration change curve y=(k n0 ·R n0 +k nt ·R nt ) at time t, observes and analyzes the law of sudden steep increase or long-term continuous anomaly of the curve, and judges whether there are signs of rock mass rupture and instability; where k n0 is the background value correction coefficient, and k nt is the measured value correction coefficient at time t. Set a threshold for prompt warning. S5. According to the curve and warning situation, combined with the on-site observation phenomena of the underground project, analyze the rock mass state near the monitoring point to realize the prediction of dynamic disasters of the surrounding rock in the preset area.

2. The on-line radon gas monitoring method for unstable surrounding rock in deep underground engineering according to claim 1, characterized in that, Monitoring hole diameter M when arranging monitoring holes s Larger than the outer diameter of the pipeline, monitoring hole depth M d Depending on the thickness of the rock stratum to be monitored, monitoring hole inclination angle M a Depending on the dip angle of the rock stratum and engineering requirements.

3. The on-line radon gas monitoring method for unstable surrounding rock in deep underground engineering according to claim 1, characterized in that, During the hole-forming process, if water gushing or mud phenomena occur in the hole, cancel the arrangement of this monitoring point; after hole-forming, clean the hole to remove the residues remaining in the hole.

4. The on-line radon gas monitoring method for unstable surrounding rocks in deep underground engineering according to claim 1, characterized in that The radon detector is an ionization chamber detector. The ionization chamber detector includes a detector cavity. A pulse signal collecting electrode and a pulse ionization chamber voltage electrode are arranged in the detector cavity. A high voltage is applied to the pulse ionization chamber voltage electrode to form an electric field inside the detector cavity. The detector cavity is provided with an air inlet, and the air inlet is communicated with an air extraction pipe. The air extraction pipe is provided with a micro air pump and a filter. The air extraction pipe is used to extract the radon gas released by the surrounding rock mass.

5. The on-line radon gas monitoring method for unstable surrounding rocks in deep underground engineering according to claim 4, characterized in that, The air extraction pipe includes an air extraction hose and an air extraction hard pipe. The first end of the air extraction hose is communicated with the air inlet, and the second end of the air extraction hose is communicated with the air extraction hard pipe. The first end of the air extraction hard pipe is communicated with the air extraction hose. A plurality of air inlet holes are axially opened at the second end of the air extraction hard pipe, and the second end of the air extraction hard pipe is inserted into the rock wall hole.

6. The on-line radon gas monitoring method for unstable surrounding rock in deep underground engineering according to claim 4, characterized in that The radon detector can also monitor the humidity, temperature, and air pressure parameters in the detector cavity to comprehensively calculate the change of the final radon gas content in the rock. Calculate the radon gas concentration according to the following formula: Where: R n is the radon concentration in the rock, P is the rock porosity, q is the radium content in the rock, ρ is the rock density, and k is the correlation coefficient, k = f(H, T, Ap, A, Gp, t) Among them, the correlation coefficient k is proportional to the rock temperature T, the fracture surface area A, and the ground pressure Gp, inversely proportional to the air pressure Ap and humidity H, and related to the time t of the rock mass under load.

7. The on-line radon gas monitoring method for unstable surrounding rocks in deep underground engineering according to claim 6, characterized in that, The rock porosity P is calculated by the following formula: P = P0 – A(Gp) n Among them, P0 is the rock porosity under normal conditions, and A and n are experimental constants.

8. A method for on-line monitoring of radon gas in unstable surrounding rock of deep underground engineering according to claim 6, characterized in that In the setting of the threshold, first give an initial threshold T1, and then gradually correct it in combination with the on-site rock mass fracture observation situation to finally form a reasonable alarm threshold T2. Among them, T2 is calculated by the following formula: Let the X overall sample data of the on-site rock mass fracture observation form a distribution f(x), then the goal is: Among them, f i (x) is the preset rock mass fracture data, and g i is the fracture data distribution of the actual rock mass. T is the adjustment factor. The corresponding iterative formula generated by the above formula is: According to the iterative result of the above formula, form a reasonable alarm threshold T2 as: Calculate the abnormal warning coefficient C. If the abnormal warning coefficient C exceeds the threshold T2, issue a warning prompt for a single radon detector to inform that the radon gas is abnormal within the monitoring range of this radon detector. C = J·(R nt - R n0 ) Among them, J is the radon detector correction coefficient. Set the total abnormal warning coefficient C of the dangerous rock mass in the area Z When multiple instruments have abnormal radon emission values, the total abnormal warning coefficient C Z If the set threshold is exceeded, an early warning will be automatically issued at this moment t; C z = J1·(R n1 - R n10 ) + J2·(R n2 - R n20 ) +...... + J N ·(R nN - R nN0 ) Among them: J1 is the correction coefficient of the first radon detector, J2 is the correction coefficient of the second radon detector, and J N is the correction coefficient of the Nth radon detector, R n1 is the abnormal radon value in the hole of the first radon detector, R n10 is the radon background value in the hole of the first radon detector, R n2 is the abnormal radon value in the hole of the second radon detector, R n20 is the radon background value in the hole of the second radon detector, R nN is the abnormal radon value in the hole of the Nth radon detector, R nN0 is the radon background value in the hole of the Nth radon detector.

9. The on-line radon gas monitoring method for unstable surrounding rock in deep underground engineering according to claim 1, wherein The radon detector adopts remote online measurement and control, compares the measured radon concentration value with the background value, and analyzes the research law.

10. A method for on-line monitoring of radon gas in unstable surrounding rocks of deep underground engineering according to claim 1, characterized in that, The radon detector adopts proximal measurement and control. A Bluetooth module is set on the radon detector. After the mobile phone installs the monitoring software, the parameters of each radon detector can be set and data can be read at close range on-site.

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