Water chemistry and multi-isotope tunnel spring source and circulation tracing methods

Abstract

The application discloses a water chemical and multi-isotope tunnel gushing water source and circulation tracing method, and belongs to the technical field of tunnel gushing water prevention and treatment, and is characterized by comprising the following steps: step A, performing constant water chemical index and isotope testing on water samples; step B, revealing the recharge elevation, recharge source, runoff path, time length, renewal capacity and water-rock interaction degree of the tunnel gushing water; step C, revealing the factors controlling the water chemical formation and evolution of the tunnel gushing water; step D, revealing the source and circulation process of strontium, lithium, nitrogen and sulfur in the tunnel gushing water; step E, calculating the mineral saturation coefficient of the tunnel gushing water, and using the same to evaluate the balance and reactivity between minerals and the tunnel gushing water, and verifying the source of ionic components in the tunnel gushing water; and step F, drawing a model conceptual diagram. The application can quantitatively analyze the source of ionic components in the tunnel gushing water under complex geological conditions in a large range, reveals the circulation mechanism, and improves the accuracy of the discrimination result.

Description

Technical Field

[0001] This invention relates to the field of tunnel water inrush prevention technology, and in particular to a method for tracing the source and circulation of tunnel water inrush based on water chemistry and multi-isotope methods. Background Technology

[0002] Tunnel inrush and water surge refers to the process during underground engineering excavation where the original geological structure is disrupted, breaking the mechanical balance between the soil and water within the strata, leading to water inrush into the excavated tunnel if timely protective measures are not taken. In recent years, the coverage area of ​​high-speed railways and highways in my country has expanded rapidly. During road construction, various undulating terrains and adverse geological conditions must be addressed, particularly in southwestern my country and plateau regions, where the proportion of tunnels is continuously increasing due to karst and mountainous terrain. Along with tunnel excavation, tunnel inrush and water surge frequently occur. Therefore, clearly understanding the sources and circulation mechanisms of groundwater in excavation areas is of great significance for the management and prevention of tunnel inrush and water surge.

[0003] When tracing tunnel inrush water, identifying the source of the water supply is a crucial part of the tracing process. Different types of water supply, such as rainfall, snowmelt, or river water, directly affect the flow rate, volume, and hydrochemical characteristics of the water. Secondly, it is essential to reveal the circulation mechanism of the inrush water after it is supplied and until it exits the tunnel. Differences in the lithology and depth of the path the water travels during this circulation will result in different temperatures and hydrochemical characteristics. Therefore, clearly defining the source of the water supply and the lithology and depth of its flow path can improve the effectiveness of inrush water management and prevention in excavated tunnels.

[0004] Currently, in the prevention and control of tunnel water inrush, the main methods used to trace the source and circulation mechanism of tunnel water inrush include traditional hydrochemical and single isotope analysis to analyze the hydrochemical characteristics of tunnel water inrush, or injecting isotope-containing water samples into boreholes and identifying the seepage path, location, and volume of water inrush through indoor models or field experiments. Using single isotopes to determine the source and circulation mechanism of tunnel water inrush has significant limitations and shortcomings when facing complex groundwater occurrence conditions and complex groundwater migration channels. It is also greatly affected by local geological lithological anomalies, which limits the accuracy of the determination results. While models or experiments using borehole injection of isotope-containing water samples have good tracing effects for localized tunnel water inrush over short distances, for tunnels with large excavation depths and spans, these methods are labor-intensive and economically inefficient, and cannot solve the problem of large-scale tunnel water inrush source and circulation mechanism identification. Furthermore, for tunnel water inrush problems under complex geological conditions, it is not a simple or quick way to identify the source and circulation mechanism of water inrush.

[0005] Chinese patent document CN111929742A, published on November 13, 2020, discloses a method for identifying high-temperature hot water in deep-buried tunnels in complex mountainous areas with geothermal anomalies. The method is characterized by the following steps: S1. Based on the geological structure distribution, stratigraphic lithology distribution and preliminary geothermal background characteristics of the area obtained from geothermal geology and hot spring surveys, and combined with topography and geomorphology, a preliminary judgment was made on the groundwater overflow zone. S2, based on ground geophysical exploration and airborne geophysical exploration, identifies geothermal anomaly blocks in the transportation corridor, reveals the planar and cross-sectional distribution characteristics of hard rock tunnel fault zones and dense joint zones, and further determines the groundwater overflow zone. S3 reveals the stratigraphic structure, groundwater, and fracture zone location through deep-hole exploration. Borehole stratified temperature measurement data reveals the geothermal temperature and its variation characteristics within the borehole. The stratigraphic position of the geothermal temperature is analyzed. Through comprehensive testing and geothermal steepness, the outburst characteristics of high-temperature hot water in the deep-buried tunnel are further determined. S4. Simultaneously, samples were taken from groundwater and surface water to analyze their hydrochemical components. The differences between high-temperature hot water and surface water and groundwater were analyzed and compared to make a comprehensive judgment on whether high-temperature hot water exists within the tunnel body.

[0006] The patent document discloses a method for identifying high-temperature hot water in deep-buried tunnels in complex mountainous areas with geothermal anomalies. This method characterizes the potential leakage range of high-temperature hot water in tunnels, providing data for the design and construction of tunnels with high-temperature hot water features. However, it cannot analyze the source and circulation mechanism of ionic components in tunnel water under complex geological conditions, affecting the accuracy of the identification results. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, this invention provides a method for tracing the source and circulation of tunnel water inflow based on hydrochemistry and multi-isotope methods. This invention can quantitatively analyze the source of ionic components in tunnel water inflow under complex geological conditions over a wide range, reveal the circulation mechanism, and improve the accuracy of the discrimination results.

[0008] This invention is achieved through the following technical solution: The method based on water chemistry and multi-isotope tunneling water source and circulation tracing is characterized by including the following steps: Step A: Conduct field hydrogeological surveys and sample collection in the tunnel area, collect tunnel water inflow and surface water, and perform constant water chemical index and isotope tests on the water samples; Step B: Based on the hydrogen, oxygen and tritium isotope characteristics of the water sample, reveal the recharge elevation, recharge source, runoff path, duration, renewal capacity and degree of water-rock interaction of the tunnel water inflow. Step C: Analyze the water-rock interaction characteristics of tunnel water inflow during underground runoff or seepage based on Gibbs diagrams and ion ratio diagrams, and reveal the factors controlling the hydrochemical formation and evolution of tunnel water inflow. Step D: By analyzing the isotopic characteristics of strontium, lithium, nitrogen, oxygen, and sulfur in the water sample, and in combination with hydrogeological conditions, the source and cycle process of strontium, lithium, nitrogen, and sulfur in the tunnel water inflow were revealed. Step E: Calculate the mineral saturation coefficient of the tunnel water inflow using PHREEQC3.0 software to assess the balance and reactivity between minerals and tunnel water inflow, and to verify the source of ionic components in the tunnel water inflow. Step F: Analyze the sources and circulation process of water inflow in the existing excavated tunnel and draw a conceptual model diagram.

[0009] In step A, the water inflow in the tunnel includes underground hot water and underground cold water.

[0010] Step B specifically includes: Step B1: Calculate the recharge elevation of tunnel water inflow based on the elevation formula for hydrogen isotopes in water. Formula 1 In the formula, The elevation for water replenishment in the tunnel, in meters (m). The elevation for surface water sampling is in meters (m). For tunnel water inflow value,‰; Atmospheric precipitation value,‰; For the region The elevation decreasing gradient, % / m; Step B2: Determine the location of the watershed and the direction of surface water runoff in the tunnel site area. Use ArcGIS 10.8 software to delineate the range and location of the recharge area in the region to determine the source of tunnel water inflow. Step B3: Determine the age of tunnel water inflow based on the concentration of tritium isotopes in the water sample to reveal the origin and formation age of the groundwater; Step B4: Based on the principle of radioactive decay of tritium isotopes, the age of tunnel water inflow is quantitatively calculated using mathematical modeling, and the flow path, duration, regeneration capacity, and degree of water-rock interaction of tunnel water inflow are determined. Formula 2 In the formula, The age of the water inrush in the tunnel, in years; The decay constant of tritium; The half-life of tritium is 12.43 years. TU represents the initial tritium concentration input into the underground aquifer by atmospheric precipitation. TU represents the tritium concentration in the water sample.

[0011] Step B3 specifically refers to using tritium for qualitative age estimation. When the tritium isotope concentration is less than 1 TU, it is considered old water, replenished before 1953; when the tritium isotope concentration is between 1 and 3 TU, it is old water mixed with new water, 0-10 years ago; when the tritium isotope concentration is between 3 and 10 TU, it is new water, replenished within 0-10 years; when the tritium isotope concentration is between 10 and 20 TU, it indicates that nuclear explosion 3H is still present; when the tritium isotope concentration is >20 TU, it is determined to have been replenished in the 1960s.

[0012] Step D specifically includes: Step D1, using strontium isotope ratios 87 Sr / 86 Sr is the ordinate, Mg 2+ / Ca 2+ The values ​​are plotted on the x-axis, and the three end-members of silicate rock, limestone and dolomite are labeled. If the sample point is located between or near the three end-members, the contribution rate of different sources in the groundwater is quantitatively estimated by combining the three-end-member mixing model. Step D2: Use strontium isotopes to determine the hot and cold mixing relationship of geothermal water during its formation process and calculate the mixing ratio curve; Formula 3 In the formula, For end element A The mixing ratio; For end element A Sr concentration; For end element B Sr concentration; For end element A of 87 Sr / 86 Sr isotope ratio; For end element B of 87 Sr / 86 Sr isotope ratio; For use A and B Assumptions for calculating the predetermined mixing ratio of the two endmembers 87 Sr / 86 Sr isotope ratio; Surface water is selected as the cold water end-unit and deep geothermal water is selected as the hot water end-unit. The mixing curve is calculated and plotted. Based on the location of the geothermal water on the graph, the mixing ratio of cold water in the geothermal water is determined. Step D3: Estimate the temperature of the underground reservoir hot water; Formula 4 In the formula, The temperature of the underground reservoir hot water, in °C; The value is the lithium isotope value of the water sample, in‰; The geothermal temperature gradient in the tunnel site area is then used to calculate the circulation depth of the hot water. Formula 5 In the formula, The depth of the deep thermal reservoir is measured in meters (m). The temperature of the underground reservoir hot water, in °C; is the temperature of the temperate zone, in °C; G is the geothermal gradient, in °C / m. Depth of the normal temperature zone, in meters (m). Step D4: Calculate the relationship between lithium isotope fractionation values ​​and temperature in the temperature range of 25-250℃ to obtain the reservoir rock mass reacting with underground hot water. Value range to determine reservoir lithology; Formula 6 In the formula, for The degree of fractionation in solid-solution, ‰; Step D5: Quantitatively estimate the mixing ratio of nitrate sources in tunnel water using a Bayesian mixture model; Step D6: By judging the changes in sulfur and oxygen isotopes in the water, trace the source and migration path of sulfate pollutants.

[0013] In step D6, the sulfate pollutants in the water body include sulfide oxidation, atmospheric precipitation, fertilizers, sewage, and evaporite dissolution.

[0014] Step F specifically refers to analyzing the sources of tunnel water inrush in excavated tunnels by combining hydrogeological conditions, tectonic development, recharge elevation, recharge source, runoff path, duration, factors controlling the formation and evolution of water inrush in the tunnel, and mineral coefficients, and drawing corresponding model concept diagrams to intuitively reveal the source and circulation process of tunnel water inrush.

[0015] The factors controlling the hydrochemical formation and evolution of tunnel water inflow include the contribution ratio of different rocks, the mixing ratio of hot and cold water, reservoir temperature, reservoir lithology, and the degree of influence of human activities.

[0016] The PHREEQC mentioned in this invention refers to computer software used to calculate various low-temperature hydrogeochemical reactions.

[0017] The Gibbs diagram mentioned in this invention refers to the Gibbs diagram.

[0018] The ArcGIS 10.8 mentioned in this invention refers to a geographic information system.

[0019] The beneficial effects of this invention are mainly reflected in the following aspects: 1. Compared with the prior art, the present invention can quantitatively analyze the source of ionic components in tunnel water under complex geological conditions over a wide range, reveal the circulation mechanism, and improve the accuracy of the discrimination results.

[0020] 2. Compared with traditional hydrochemical and single isotope analysis methods, this invention provides more conclusions on the source and circulation process of tunnel water inflow, making it more suitable for the study of deep-buried and long-span tunnels under complex geological conditions. Furthermore, the combination of multiple isotopes can mutually verify the results, reducing the errors caused by traditional hydrochemical and single isotope analysis.

[0021] 3. Compared with methods derived from indoor models or field experiments, the operation of this invention is simpler and faster. It only requires collecting water samples on-site and sending them to the laboratory for analysis. The corresponding conclusions can be obtained by combining relevant software and formulas. Furthermore, compared with single-point or short-distance analysis of indoor models or field experiments, multi-isotope analysis can reveal the source and circulation process of water inflow within the entire tunnel or local area.

[0022] 4. This invention can not only reveal the source and circulation process of underground cold water flowing upwards, but also the source and circulation process of underground hot water flowing downwards. At the same time, it quantitatively analyzes the impact of human activities on tunnel water inflow. Therefore, it is applicable to a wider range of tunnel water inflow types.

[0023] 5. The final conclusion of this invention is to propose a conceptual diagram of the source model of water inrush in excavated tunnels, which visualizes the source and circulation process of water inrush in excavated tunnels, providing a new approach for the study of water inrush in tunnels under complex geological conditions and providing effective support for the prevention and control of water inrush in tunnels. Attached Figure Description

[0024] The present invention will now be further described in detail with reference to the accompanying drawings and specific embodiments: Figure 1 This is a flowchart of the present invention; Figure 2 The hydrogen and oxygen isotopes δD-δ of this invention 18 O-relationship diagram; Figure 3 This is a schematic diagram of the tunnel water inflow recharge area according to the present invention; Figure 4 The Mg of the present invention 2+ / Ca 2+ and 87 Sr / 86 Sr relationship diagram; Figure 5 For the 1 / Sr of the present invention and 87 Sr / 86 Sr relationship diagram; Figure 6This is a graph showing the relationship between TDS and mineral saturation coefficient according to the present invention; Figure 7 This is a schematic diagram illustrating the source of water inrush in the excavated tunnel of this invention. Detailed Implementation

[0025] Example 1 See Figure 1 Based on water chemistry and multi-isotope tunneling water source and circulation tracing methods, the method includes the following steps: Step A: Conduct field hydrogeological surveys and sample collection in the tunnel area, collect tunnel water inflow and surface water, and perform constant water chemical index and isotope tests on the water samples; Step B: Based on the hydrogen, oxygen and tritium isotope characteristics of the water sample, reveal the recharge elevation, recharge source, runoff path, duration, renewal capacity and degree of water-rock interaction of the tunnel water inflow. Step C: Analyze the water-rock interaction characteristics of tunnel water inflow during underground runoff or seepage based on Gibbs diagrams and ion ratio diagrams, and reveal the factors controlling the hydrochemical formation and evolution of tunnel water inflow. Step D: By analyzing the isotopic characteristics of strontium, lithium, nitrogen, oxygen, and sulfur in the water sample, and in combination with hydrogeological conditions, the source and cycle process of strontium, lithium, nitrogen, and sulfur in the tunnel water inflow were revealed. Step E: Calculate the mineral saturation coefficient of the tunnel water inflow using PHREEQC3.0 software to assess the balance and reactivity between minerals and tunnel water inflow, and to verify the source of ionic components in the tunnel water inflow. Step F: Analyze the sources and circulation process of water inflow in the existing excavated tunnel and draw a conceptual model diagram.

[0026] This embodiment is the most basic implementation method. Compared with the prior art, it can quantitatively analyze the source of ionic components in tunnel water under complex geological conditions over a wide range, reveal the circulation mechanism, and improve the accuracy of the discrimination results.

[0027] Example 2 See Figure 1 Based on water chemistry and multi-isotope tunneling water source and circulation tracing methods, the method includes the following steps: Step A: Conduct field hydrogeological surveys and sample collection in the tunnel area, collect tunnel water inflow and surface water, and perform constant water chemical index and isotope tests on the water samples; Step B: Based on the hydrogen, oxygen and tritium isotope characteristics of the water sample, reveal the recharge elevation, recharge source, runoff path, duration, renewal capacity and degree of water-rock interaction of the tunnel water inflow. Step C: Analyze the water-rock interaction characteristics of tunnel water inflow during underground runoff or seepage based on Gibbs diagrams and ion ratio diagrams, and reveal the factors controlling the hydrochemical formation and evolution of tunnel water inflow. Step D: By analyzing the isotopic characteristics of strontium, lithium, nitrogen, oxygen, and sulfur in the water sample, and in combination with hydrogeological conditions, the source and cycle process of strontium, lithium, nitrogen, and sulfur in the tunnel water inflow were revealed. Step E: Calculate the mineral saturation coefficient of the tunnel water inflow using PHREEQC3.0 software to assess the balance and reactivity between minerals and tunnel water inflow, and to verify the source of ionic components in the tunnel water inflow. Step F: Analyze the sources and circulation process of water inflow in the existing excavated tunnel and draw a conceptual model diagram.

[0028] In step A, the water inflow in the tunnel includes underground hot water and underground cold water.

[0029] Step B specifically includes: Step B1: Calculate the recharge elevation of tunnel water inflow based on the elevation formula for hydrogen isotopes in water. Formula 1 In the formula, The elevation for water replenishment in the tunnel, in meters (m). The elevation for surface water sampling is in meters (m). For tunnel water inflow value,‰; Atmospheric precipitation value,‰; For the region The elevation decreasing gradient, % / m; Step B2: Determine the location of the watershed and the direction of surface water runoff in the tunnel site area. Use ArcGIS 10.8 software to delineate the range and location of the recharge area in the region to determine the source of tunnel water inflow. Step B3: Determine the age of tunnel water inflow based on the concentration of tritium isotopes in the water sample to reveal the origin and formation age of the groundwater; Step B4: Based on the principle of radioactive decay of tritium isotopes, the age of tunnel water inflow is quantitatively calculated using mathematical modeling, and the flow path, duration, regeneration capacity, and degree of water-rock interaction of tunnel water inflow are determined. Formula 2 In the formula, The age of the water inrush in the tunnel, in years; The decay constant of tritium; The half-life of tritium is 12.43 years. TU represents the initial tritium concentration input into the underground aquifer by atmospheric precipitation. TU represents the tritium concentration in the water sample.

[0030] Step B3 specifically refers to using tritium for qualitative age estimation. When the tritium isotope concentration is less than 1 TU, it is considered old water, replenished before 1953; when the tritium isotope concentration is between 1 and 3 TU, it is old water mixed with new water, 0-10 years ago; when the tritium isotope concentration is between 3 and 10 TU, it is new water, replenished within 0-10 years; when the tritium isotope concentration is between 10 and 20 TU, it indicates that nuclear explosion 3H is still present; when the tritium isotope concentration is >20 TU, it is determined to have been replenished in the 1960s.

[0031] This embodiment is a preferred implementation method. Compared with traditional hydrochemistry and single isotope analysis methods, it yields more conclusions by analyzing the source and circulation process of tunnel water inflow. It is more suitable for the study of deep-buried and long-span tunnels under complex geological conditions. Furthermore, the combination of multiple isotopes can mutually verify the results, reducing the errors caused by traditional hydrochemistry and single isotope analysis.

[0032] Example 3 See Figure 1 Based on water chemistry and multi-isotope tunneling water source and circulation tracing methods, the method includes the following steps: Step A: Conduct field hydrogeological surveys and sample collection in the tunnel area, collect tunnel water inflow and surface water, and perform constant water chemical index and isotope tests on the water samples; Step B: Based on the hydrogen, oxygen and tritium isotope characteristics of the water sample, reveal the recharge elevation, recharge source, runoff path, duration, renewal capacity and degree of water-rock interaction of the tunnel water inflow. Step C: Analyze the water-rock interaction characteristics of tunnel water inflow during underground runoff or seepage based on Gibbs diagrams and ion ratio diagrams, and reveal the factors controlling the hydrochemical formation and evolution of tunnel water inflow. Step D: By analyzing the isotopic characteristics of strontium, lithium, nitrogen, oxygen, and sulfur in the water sample, and in combination with hydrogeological conditions, the source and cycle process of strontium, lithium, nitrogen, and sulfur in the tunnel water inflow were revealed. Step E: Calculate the mineral saturation coefficient of the tunnel water inflow using PHREEQC3.0 software to assess the balance and reactivity between minerals and tunnel water inflow, and to verify the source of ionic components in the tunnel water inflow. Step F: Analyze the sources and circulation process of water inflow in the existing excavated tunnel and draw a conceptual model diagram.

[0033] In step A, the water inflow in the tunnel includes underground hot water and underground cold water.

[0034] Step B specifically includes: Step B1: Calculate the recharge elevation of tunnel water inflow based on the elevation formula for hydrogen isotopes in water. Formula 1 In the formula, The elevation for water replenishment in the tunnel, in meters (m). The elevation for surface water sampling is in meters (m). For tunnel water inflow value,‰; Atmospheric precipitation value,‰; For the region The elevation decreasing gradient, % / m; Step B2: Determine the location of the watershed and the direction of surface water runoff in the tunnel site area. Use ArcGIS 10.8 software to delineate the range and location of the recharge area in the region to determine the source of tunnel water inflow. Step B3: Determine the age of tunnel water inflow based on the concentration of tritium isotopes in the water sample to reveal the origin and formation age of the groundwater; Step B4: Based on the principle of radioactive decay of tritium isotopes, the age of tunnel water inflow is quantitatively calculated using mathematical modeling, and the flow path, duration, regeneration capacity, and degree of water-rock interaction of tunnel water inflow are determined. Formula 2 In the formula, The age of the water inrush in the tunnel, in years; The decay constant of tritium; The half-life of tritium is 12.43 years. TU represents the initial tritium concentration input into the underground aquifer by atmospheric precipitation. TU represents the tritium concentration in the water sample.

[0035] Step B3 specifically refers to using tritium for qualitative age estimation. When the tritium isotope concentration is less than 1 TU, it is considered old water, replenished before 1953; when the tritium isotope concentration is between 1 and 3 TU, it is old water mixed with new water, 0-10 years ago; when the tritium isotope concentration is between 3 and 10 TU, it is new water, replenished within 0-10 years; when the tritium isotope concentration is between 10 and 20 TU, it indicates that nuclear explosion 3H is still present; when the tritium isotope concentration is >20 TU, it is determined to have been replenished in the 1960s.

[0036] Step D specifically includes: Step D1, using strontium isotope ratios 87 Sr / 86 Sr is the ordinate, Mg 2+ / Ca 2+ The values ​​are plotted on the x-axis, and the three end-members of silicate rock, limestone and dolomite are labeled. If the sample point is located between or near the three end-members, the contribution rate of different sources in the groundwater is quantitatively estimated by combining the three-end-member mixing model. Step D2: Use strontium isotopes to determine the hot and cold mixing relationship of geothermal water during its formation process and calculate the mixing ratio curve; Formula 3 In the formula, For end element A The mixing ratio; For end element A Sr concentration; For end element B Sr concentration; For end element A of 87 Sr / 86 Sr isotope ratio; For end element B of 87 Sr / 86 Sr isotope ratio; For use A and B Assumptions for calculating the predetermined mixing ratio of the two endmembers 87 Sr / 86 Sr isotope ratio; Surface water is selected as the cold water end-unit and deep geothermal water is selected as the hot water end-unit. The mixing curve is calculated and plotted. Based on the location of the geothermal water on the graph, the mixing ratio of cold water in the geothermal water is determined. Step D3: Estimate the temperature of the underground reservoir hot water; Formula 4 In the formula, The temperature of the underground reservoir hot water, in °C; The value is the lithium isotope value of the water sample, in‰; The geothermal temperature gradient in the tunnel site area is then used to calculate the circulation depth of the hot water. Formula 5 In the formula, The depth of the deep thermal reservoir is measured in meters (m). The temperature of the underground reservoir hot water, in °C; is the temperature of the temperate zone, in °C; G is the geothermal gradient, in °C / m. Depth of the normal temperature zone, in meters (m). Step D4: Calculate the relationship between lithium isotope fractionation values ​​and temperature in the temperature range of 25-250℃ to obtain the reservoir rock mass reacting with underground hot water. Value range to determine reservoir lithology; Formula 6 In the formula, for The degree of fractionation in solid-solution, ‰; Step D5: Quantitatively estimate the mixing ratio of nitrate sources in tunnel water using a Bayesian mixture model; Step D6: By judging the changes in sulfur and oxygen isotopes in the water, trace the source and migration path of sulfate pollutants.

[0037] In step D6, the sulfate pollutants in the water body include sulfide oxidation, atmospheric precipitation, fertilizers, sewage, and evaporite dissolution.

[0038] Step F specifically refers to analyzing the sources of tunnel water inrush in excavated tunnels by combining hydrogeological conditions, tectonic development, recharge elevation, recharge source, runoff path, duration, factors controlling the formation and evolution of water inrush in the tunnel, and mineral coefficients, and drawing corresponding model concept diagrams to intuitively reveal the source and circulation process of tunnel water inrush.

[0039] The factors controlling the hydrochemical formation and evolution of tunnel water inflow include the contribution ratio of different rocks, the mixing ratio of hot and cold water, reservoir temperature, reservoir lithology, and the degree of influence of human activities.

[0040] This embodiment is the best implementation method. Compared with the methods obtained from indoor models or field experiments, its operation method is simpler and faster. It only requires collecting water samples on site and sending them to the laboratory for analysis. The corresponding conclusions can be obtained by combining relevant software and formulas. Moreover, compared with the single-point or short-distance analysis of indoor models or field experiments, multi-isotope analysis can reveal the source and circulation process of water inflow in the entire tunnel or local area.

[0041] It can reveal not only the source and circulation process of cold groundwater flowing upwards, but also the source and circulation process of hot groundwater flowing downwards. At the same time, it quantitatively analyzes the impact of human activities on tunnel water inflow. Therefore, it is applicable to a wider range of tunnel water inflow types.

[0042] The final conclusion is to propose a conceptual model of the source of water inrush in excavated tunnels, which visualizes the source and circulation process of water inrush in excavated tunnels, providing a new approach for the study of water inrush in tunnels under complex geological conditions and offering effective support for the prevention and control of water inrush in tunnels.

[0043] The invention will now be described in detail using a tunnel in a certain region as an example: S1: Conduct field hydrogeological surveys and sample collection in a tunnel area of ​​a certain region, systematically collect tunnel water inflow and surface water in the study area, and conduct constant water chemical index and isotope tests on water samples; A total of 12 samples of underground hot water, 15 samples of underground cold water, and 8 samples of surface water were collected before and after a tunnel in a certain region.

[0044] The indicators for on-site testing and experimentation of water samples include: Temperature, pH value, TDS, Na + K + Ca 2+Mg 2+ Cl － SO4 2－ HCO3 － NO3 － Sr, Li, and hydrogen and oxygen isotopes δD-δ 18 O, tritium isotope δ 3 H, strontium isotopes 87 Sr / 86 Sr, lithium isotope δ 7 Li, nitrogen and oxygen isotopes δ 15 N-NO3 － With δ 18 O-NO3 － and sulfur oxygen isotope δ 15 S-SO4 2－ With δ 15 O-SO4 2－ .

[0045] The geological conditions of a certain tunnel area in a certain region are complex. The burial conditions of the aquifer, its contact relationship with other aquifers, and the degree of rock fragmentation are all influenced by the geological structure. That is, the water-bearing capacity of the rock is related to its location in the geological structure and its burial depth. Generally speaking, the water-bearing capacity decreases from shallow to deep. Controlled by topography and geological structure, groundwater is mainly found in the fissures of gneiss and intrusive bedrock. In structurally favorable locations, there are also fracture waters in the fracture zones with relatively deep circulation.

[0046] S2: Plot the δD-δ of the sample 18 The relationship diagram of O, as follows Figure 2 As shown, almost all geothermal, cold groundwater, surface water, and groundwater samples were located near the global and southwestern regional precipitation lines, indicating that the main source of water recharge in the study area was atmospheric precipitation. Among them, geothermal sample No. 4 was located to the lower right of both precipitation lines, indicating a significant "oxygen drift" phenomenon. Considering its relatively high outcrop temperature of 84.7℃, it is speculated that the geothermal water underwent a relatively strong water-rock interaction during its migration due to the high-temperature environment, thus transferring oxygen from the surrounding rock. 18 O is dissolved and filtered into hot water.

[0047] Based on the elevation formula using hydrogen isotopes, the estimated recharge elevation of geothermal water is 2481-3518m, with an average of 2977m; the recharge elevation of cold groundwater is 2518-3231m, with an average of 2732m. Overall, the recharge elevation of geothermal water is generally higher than that of cold groundwater. Geothermal water has a deeper circulation depth and a longer flow path, thus its recharge source and range are wider, and its recharge elevation is higher. The recharge area near the tunnel region was delineated using ArcGIS 10.8 software. Figure 3As shown, the water in the tunnel mainly comes from atmospheric precipitation and snowmelt from the high mountains in the northwest, which infiltrates through faults, some secondary fault zones, and bedrock fissures to replenish the tunnel water.

[0048] Based on the tritium in the sample 3 The concentration of hydrogen isotopes can be used to determine the age of groundwater, thereby revealing its origin and formation period. The main test samples were cold groundwater. The tritium content of hot groundwater and geothermal water was 1.5-9.4±0.5TU, indicating that the cold groundwater in the tunnel area was relatively new, with a short flow path and time.

[0049] Based on the principle of radioactive decay of tritium isotopes, the age of groundwater was quantitatively calculated using a mathematical model. The calculated age of the underground cold water in the tunnel was 25.19-38.02 years, indicating that the recharge time of the underground cold water is relatively short, the path and time of its runoff below the surface are short, and its renewal capacity is strong. Therefore, the degree of water-rock interaction is relatively low.

[0050] S3: Draw the Gibbs base map by projecting the measured sample data onto the map. Based on the analysis of the main hydrochemical components of global surface water, Gibbs classifies its hydrochemical formation and evolution mechanisms into three categories: evaporation-crystallization-dominated, rock weathering-dominated, and atmospheric precipitation-dominated. The Gibbs map consists of two sets of semi-logarithmic coordinate scatter plots, with the horizontal axis representing Cl. − / (Cl − +HCO3 − ) or Na + / (Na + Ca 2+ The ratio of ) is shown on the vertical axis, with the vertical axis representing the TDS value.

[0051] Cl in the tunnel water inflow sample in the example − / (Cl − +HCO3 − ) or Na + / (Na + Ca 2+ The ranges of the ratio and TDS values ​​are almost entirely within the rock weathering-dominated region, indicating that rock weathering is the dominant mechanism for the formation of groundwater chemical components in the study area.

[0052] Common forms of water-rock interaction include silicate weathering, evaporation of minerals, and carbonate dissolution. Generally, this can be achieved through the reaction of calcium... 2+ Mg 2+ Na + and HCO3 -The relevant ratios determine the main types of water-rock interaction. In the examples, the ranges of Ca / Na-Mg / Na and Ca / Na-HCO3 / Na ratios in the tunnel area water samples were calculated. The results show that tunnel water inflow and surface water are located in the transition zone between evaporite, silicate rock, and carbonate rock, indicating that the lithology of the study area is very complex. The dissolution of evaporite, silicate weathering, and carbonate mineral dissolution all affect the changes in the chemical composition of tunnel water inflow.

[0053] S4: Based on the results obtained from the Gibbs and ion ratios in S3 above, the sources and circulation processes of strontium, lithium, nitrogen, oxygen and sulfur in tunnel water can be further revealed by analyzing the isotopic characteristics of strontium, lithium, nitrogen and sulfur in the sample and combining them with hydrogeological conditions.

[0054] S4-1: Strontium comes from different sources, and its 87 Sr / 86 Sr and Mg 2+ / Ca 2+ The ratios also vary. (Using strontium isotope ratios...) 87 Sr / 86 Sr is the ordinate, Mg 2+ / Ca 2+ Use the values ​​as the x-axis to plot a ratio graph and label the three end members: silicate rock, limestone, and dolomite. Figure 4 Mg in the examples 2+ / Ca 2+ and 87 Sr / 86 The Sr relationship diagram shows that most of the tunnel water inflow is concentrated near the limestone dissolution end-member, and some sample points are close to the silicate rock and dolomite dissolution end-member, indicating that limestone is the main rock involved in the water-rock interaction during the tunnel water inflow process.

[0055] Based on a three-terminal-member mixing model, the contribution rates of different sources in groundwater between or near the three terminal members are quantitatively estimated: In the formula, f represents the contribution rate of different sources of water inflow in the tunnel; the average contribution rates of limestone, silicate rock and dolomite to water inflow in the tunnel are calculated to be approximately 78%, 20% and 2%, respectively.

[0056] For the geothermal water in the tunnel inflow, strontium isotopes are used to preliminarily determine the hot and cold mixing relationship during the formation process of the geothermal water, and the mixing ratio curve is calculated using the following formula: Surface water was selected as the cold water end-member, and deep geothermal water as the hot water end-member. The mixing curve was calculated and plotted, with 1 / Sr as the abscissa. 87 Sr / 86 Sr is the ordinate, such as Figure 5 As shown, some geothermal water is distributed between 10% and 20% of the nodes, indicating that the cold water mixing ratio in this part of the sample is relatively low, resulting in a higher hot water outflow temperature, which has a significant impact on tunnel construction. The remaining geothermal water sampling points are distributed far from the mixing line, indicating the existence of additional mixing end-members. Further calculation of the mixing ratio using other methods is needed.

[0057] S4-2: Based on the estimated mixing ratio of strontium isotopes in S4-1, the relationship between lithium isotopes and reservoir temperature was further used to estimate the temperature of the underground reservoir hot water. The estimated temperature range of the reservoir in the study area was 48-251℃, with an average temperature of 165℃. The large variation in the reservoir temperature range indicates that due to the large tunnel span, it crosses different structural regions, resulting in corresponding changes in the temperature of the hot water reservoir at different locations.

[0058] Based on the estimated reservoir temperature and the geothermal warming gradient in the tunnel site area, the estimated circulation depth ranges from 643 to 4404 m, with an average of 2814 m. This indicates that most of the underground hot water has undergone circulation at a relatively deep depth, along a long path, and over a long period of time, which is consistent with its high outcrop temperature, high reservoir temperature, and strong water-rock interaction.

[0059] The fractionation of lithium isotopes in hot water is affected by reservoir temperature. The estimated value of Δ in the groundwater is... 溶液-固体 The content varies from 7.27 to 15.34‰, therefore the δ of the rock mass reacting with underground hot water... 7 The Li value ranges from -5.90 to 5.05‰. The δ of the rock mass is estimated. 7 The Li value results and the δ¹⁴ ... 7 The Li values ​​are close to -5.03 to 10.16‰, indicating that the δ in hot water is... 7 Li originates from deep granite.

[0060] S4-3: In addition to the effects of atmospheric precipitation and water-rock interaction on the source and circulation of tunnel water inflow as shown in S2, S3, S4-1, and S4-2, human activities also have some influence on the source and circulation of tunnel water inflow. This can be primarily observed through nitrogen and oxygen isotope δ¹⁸O. 15 N-NO3 - With δ 18 O-NO3 -Identify different sources of nitrate in groundwater. The main sources of nitrate in aquatic ecosystems include atmospheric deposition, soil organic nitrogen, nitrate fertilizers, ammoniacal nitrogen fertilizers, domestic sewage, and livestock manure. A Bayesian mixture model was used to quantitatively estimate the mixed contribution ratio of nitrate sources in tunnel inflow. The model was run using the R package MixSIAR version 3.1.10. By considering the uncertainty of source values, MixSIAR improved the simpler linear mixture model, as shown in the following equation: Among them, X ij Let j be the isotopic value of sample i, where i = 1, 2, 3…, N and j = 1, 2, 3…, J; S jk Let k be the source value of isotope j, and its average value be μ. jk The standard deviation is ω 2 jk ;P k It is the proportional contribution of source k; C jk It is the fractionation factor of isotope j at source k, with a mean of λ. jk The standard deviation is τ 2 jk ;ε ij The mean is 0 and the standard deviation is σ. 2 j The residual.

[0061] The calculated contribution ratios of the mixed sources of nitrate are shown in Table 1 below: It can be seen that nitrate nitrogen fertilizer, atmospheric deposition, and soil organic nitrogen contribute significantly to nitrate levels in water. However, there is no large-scale human habitation, farming, or livestock raising near the tunnel area; therefore, the contribution of nitrate nitrogen fertilizer should be relatively low to be consistent with reality. This is because the three end-members of soil organic nitrogen, ammonia nitrogen fertilizer, domestic sewage, and livestock manure contribute significantly to nitrate levels in the delta-coated water. 18 O-NO3 - There is overlap in the values, therefore it is necessary to correct for the main sources of nitrates, that is, to reduce or eliminate the range of ammoniacal nitrogen fertilizer end-members. The corrected source proportions are shown in Table 2 below: The soil nitrogen source accounts for a large proportion of groundwater and surface water, with an average of 56%, followed by atmospheric deposition at 22%, nitrate nitrogen fertilizer at 10%, sewage and livestock manure at 9%, and ammonia nitrogen fertilizer at 3%. This indicates that the nitrate in groundwater and surface water mainly comes from soil nitrogen sources, and a small amount of nitrate nitrogen fertilizer, domestic sewage and livestock manure pollute the tunnel water inflow.

[0062] S4-4: By determining the sulfur and oxygen isotope δ in the water body 15 S-SO4 2-With δ 15 O-SO4 2- Changes in these conditions can be used to trace the sources and migration pathways of sulfate pollutants. The main sources of sulfate pollutants in water bodies include sulfide oxidation, atmospheric precipitation, fertilizers, wastewater, and evaporite dissolution.

[0063] The mixed contribution ratio of sulfate sources in groundwater was quantitatively assessed based on the Bayesian mixture model, as shown in Table 3 below: It can be seen that the proportions of mixed contributions are, in descending order: evaporites 61%, wastewater 13%, fertilizers 10%, atmospheric precipitation 10%, and sulfides 6%. Figure 7 As shown, evaporites provide the main sulfates in the geothermal water, while small amounts of sewage and fertilizers pollute the geothermal water. The conclusions are consistent with nitrogen and oxygen isotope analysis, confirming the rationality of the findings.

[0064] S5: Based on steps S3 and S4-1, the rock types and contribution rates involved in the water-rock interaction are obtained. PHREEQC3.0 is then used to calculate the saturation coefficient SI of the minerals in the sample to verify the accuracy of the results in step D1. The calculated minerals include aragonite, calcite, dolomite, anhydrite, gypsum, and rock salt. The saturation coefficient SI is the logarithm of the ratio of the ion activity product to the equilibrium constant, and its calculation formula is: In the formula, IPA is the activity product of ions in groundwater; K is the equilibrium constant.

[0065] Figure 6 This is a graph showing the relationship between the mineral saturation coefficient (SI) and total dissolved solids (TDS) in the examples. The graph shows that most water samples from the study area exhibit a relatively saturated state for aragonite, calcite, and dolomite, showing a tendency to precipitate during runoff. Anhydrite and gypsum show a slightly undersaturated state, transitioning between equilibrium and dissolution during runoff. Rock salt is undersaturated and shows a tendency to dissolve during runoff. Therefore, this indicates that groundwater and geothermal water interact with minerals such as aragonite, calcite, dolomite, anhydrite, and gypsum during runoff, confirming that the dissolution of evaporites and carbonate minerals affects the chemical composition of tunnel water inflow. These results are consistent with the regional hydrogeological conditions.

[0066] S6: Based on the specific conclusions drawn from S1, S2, S3 and S4 above, and combined with regional tectonics and hydrogeological conditions, a conceptual model diagram of the source of water inrush in a certain excavated tunnel in a certain region is proposed.

[0067] Figure 7This is a schematic diagram illustrating the source of water inrush in the excavated tunnel in the embodiment. As shown, atmospheric precipitation and snowmelt in the area with elevations of 2481-3518m infiltrate along fractures and flow along a slope driven by gravity. Due to the relatively young age of the groundwater, the flow path and time are short, and the water-rock interaction intensity is low. During the flow process, it mainly reacts with silicate and carbonate rocks, but the concentration of various ions in the groundwater is low. When it encounters the F51 deep fracture zone, the groundwater converges, therefore, the groundwater volume is the largest in F51 and its adjacent sections.

[0068] Due to plate subduction, mantle material upwelled in the tunnel area, forming a localized melt of granitic material in the crust. Meltwater from glaciers and precipitation seeped down along tectonic fractures under immense pressure. After being heated by the deep granitic localized melt, it rose along major faults, reaching a maximum temperature of 251℃ and a maximum circulation depth of 4404m. In the shallow gneiss fractured reservoir, it mixed with infiltrated surface cold water, with a mixing ratio between 10-20%. After mixing, the geothermal water continued to rise along the faults, undergoing intense water-rock interactions with the surrounding silicate, carbonate, and evaporites, increasing the sodium content of the geothermal water. + K + Ca 2+ and Mg 2+ The ion concentration continuously increases. The geothermal water that gushes out during tunnel construction is geothermal water mixed during its ascent; the temperature of the gushing water varies depending on the different mixing ratios of cold and warm water. Human activities around the tunnel excavation site, including wastewater from production and daily life, and agricultural activities, cause slight pollution to the tunnel water.

[0069] The above example of a tunnel in a certain region illustrates that the present invention can quantitatively analyze the source of ionic components in tunnel water under complex geological conditions over a large area, reveal the circulation mechanism, and improve the accuracy of the discrimination results.

Claims

1. A method for tracing the source and circulation of tunnel water inflow based on water chemistry and multiple isotopes, characterized in that, Includes the following steps: Step A: Conduct field hydrogeological surveys and sample collection in the tunnel area, collect tunnel water inflow and surface water, and perform constant water chemical index and isotope tests on the water samples; Step B: Based on the hydrogen, oxygen and tritium isotope characteristics of the water sample, reveal the recharge elevation, recharge source, runoff path, duration, renewal capacity and degree of water-rock interaction of the tunnel water inflow. Step C: Analyze the water-rock interaction characteristics of tunnel water inflow during underground runoff or seepage based on Gibbs diagrams and ion ratio diagrams, and reveal the factors controlling the hydrochemical formation and evolution of tunnel water inflow. Step D: By analyzing the isotopic characteristics of strontium, lithium, nitrogen, oxygen, and sulfur in the water sample, and in combination with hydrogeological conditions, the source and cycle process of strontium, lithium, nitrogen, and sulfur in the tunnel water inflow were revealed. Step E: Calculate the mineral saturation coefficient of the tunnel water inflow using PHREEQC3.0 software to assess the balance and reactivity between minerals and tunnel water inflow, and to verify the source of ionic components in the tunnel water inflow. Step F: Analyze the sources and circulation process of water inflow in the tunnel based on the existing excavated tunnel, and draw a conceptual model diagram; Step B specifically includes: Step B1: Calculate the recharge elevation of tunnel water inflow based on the elevation formula for hydrogen isotopes in water. Formula 1 In the formula, The elevation for water replenishment in the tunnel, in meters (m). The elevation for surface water sampling is in meters (m). For tunnel water inflow value,‰; Atmospheric precipitation value,‰; For the region The elevation decreasing gradient, % / m; Step B2: Determine the location of the watershed and the direction of surface water runoff in the tunnel site area. Use ArcGIS 10.8 software to delineate the range and location of the recharge area in the region to determine the source of tunnel water inflow. Step B3: Determine the age of tunnel water inflow based on the concentration of tritium isotopes in the water sample to reveal the origin and formation age of the groundwater; Step B4: Based on the principle of radioactive decay of tritium isotopes, the age of tunnel water inflow is quantitatively calculated using mathematical modeling, and the flow path, duration, regeneration capacity, and degree of water-rock interaction of tunnel water inflow are determined. Formula 2 In the formula, The age of the water inrush in the tunnel, in years; The decay constant of tritium; The half-life of tritium is 12.43 years. TU represents the initial tritium concentration input into the underground aquifer by atmospheric precipitation. The tritium concentration in the water sample is expressed in TU. Step D specifically includes: Step D1, using strontium isotope ratios 87 Sr / 86 Sr is the ordinate, Mg 2+ / Ca 2+ The values ​​are plotted on the x-axis, and the three end-members of silicate rock, limestone and dolomite are labeled. If the sample point is located between or near the three end-members, the contribution rate of different sources in the groundwater is quantitatively estimated by combining the three-end-member mixing model. Step D2: Use strontium isotopes to determine the hot and cold mixing relationship of geothermal water during its formation process and calculate the mixing ratio curve; Formula 3 In the formula, For end element A The mixing ratio; For end element A Sr concentration; For end element B Sr concentration; For end element A of 87 Sr / 86 Sr isotope ratio; For end element B of 87 Sr / 86 Sr isotope ratio; For use A and B Assumptions for calculating the predetermined mixing ratio of the two endmembers 87 Sr / 86 Sr isotope ratio; Surface water is selected as the cold water end-unit and deep geothermal water is selected as the hot water end-unit. The mixing curve is calculated and plotted. Based on the location of the geothermal water on the graph, the mixing ratio of cold water in the geothermal water is determined. Step D3: Estimate the temperature of the underground reservoir hot water; Formula 4 In the formula, The temperature of the underground reservoir hot water, in °C; The value is the lithium isotope value of the water sample, in‰; The geothermal temperature gradient in the tunnel site area is then used to calculate the circulation depth of the hot water. Formula 5 In the formula, The depth of the deep thermal reservoir is measured in meters (m). The temperature of the underground reservoir hot water, in °C; is the temperature of the temperate zone, in °C; G is the geothermal gradient, in °C / m. Depth of the normal temperature zone, in meters (m). Step D4: Calculate the relationship between lithium isotope fractionation values ​​and temperature in the temperature range of 25-250℃ to obtain the reservoir rock mass reacting with underground hot water. Value range to determine reservoir lithology; Formula 6 In the formula, for The degree of fractionation in solid-solution, ‰; Step D5: Quantitatively estimate the mixing ratio of nitrate sources in tunnel water using a Bayesian mixture model; Step D6: By judging the changes in sulfur and oxygen isotopes in the water, trace the source and migration path of sulfate pollutants.

2. The method for tracing the source and circulation of tunnel water inflow based on water chemistry and multiple isotopes according to claim 1, characterized in that: In step A, the water inflow in the tunnel includes underground hot water and underground cold water.

3. The method for tracing the source and circulation of tunnel water inflow based on water chemistry and multiple isotopes according to claim 1, characterized in that: Step B3 specifically refers to using tritium for qualitative age estimation. When the tritium isotope concentration is less than 1 TU, it is considered old water, replenished before 1953; when the tritium isotope concentration is between 1 and 3 TU, it is old water mixed with new water, 0-10 years ago; when the tritium isotope concentration is between 3 and 10 TU, it is new water, replenished within 0-10 years; when the tritium isotope concentration is between 10 and 20 TU, it indicates that nuclear explosion 3H is still present; when the tritium isotope concentration is >20 TU, it is determined to have been replenished in the 1960s.

4. The method for tracing the source and circulation of tunnel water inflow based on water chemistry and multiple isotopes according to claim 1, characterized in that: In step D6, the sulfate pollutants in the water body include sulfide oxidation, atmospheric precipitation, fertilizers, sewage, and evaporite dissolution.

5. The method for tracing the source and circulation of tunnel water inflow based on water chemistry and multiple isotopes according to claim 1, characterized in that: Step F specifically refers to analyzing the sources of tunnel water inrush in excavated tunnels by combining hydrogeological conditions, tectonic development, recharge elevation, recharge source, runoff path, duration, factors controlling the formation and evolution of water inrush in the tunnel, and mineral coefficients, and drawing corresponding model concept diagrams to intuitively reveal the source and circulation process of tunnel water inrush.

6. The method for tracing the source and circulation of tunnel water inflow based on water chemistry and multiple isotopes according to claim 5, characterized in that: The factors controlling the hydrochemical formation and evolution of tunnel water inflow include the contribution ratio of different rocks, the mixing ratio of hot and cold water, reservoir temperature, reservoir lithology, and the degree of influence of human activities.

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