Tunnel heat damage type identification method

Abstract

The invention relates to the technical field of disaster prevention and reduction of tunnel engineering, and provides a tunnel heat damage type identification method in order to improve heat damage identification accuracy, surface water heat abnormal phenomenon annotation and drilling water chemical characteristics are newly added in an exploration design stage, and heat convergence characteristics and potential heat damage sections are identified based on newly added data and traditional data. For a potential heat damage section, drilling rock temperature monitoring, drilling water chemical characteristic monitoring and drilling gas component and concentration monitoring are added in addition to traditional comprehensive advanced geological forecast so as to identify heat convergence characteristics; and based on data acquired in the exploration design stage and the construction stage, identifying a potential disaster-causing structure and a position thereof by applying a fractured rock mass heat conduction theory, and determining a heat damage type according to a heat convergence characteristic corresponding to the position of the disaster-causing structure. And through multi-means cooperative detection and multi-source data fusion, the heat damage identification accuracy is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of disaster prevention and reduction in tunnel engineering, and in particular to a method for identifying the type of heat damage in a tunnel. Background Art

[0002] Abnormal ground temperature often induces five types of heat damage: high rock temperature, harmful gases, high rock temperature + high water temperature, high rock temperature + harmful gases, and high rock temperature + harmful gases + high water temperature. The related disasters cause great losses and challenges to the safe construction of tunnels passing through areas with abnormal ground temperature.

[0003] Currently, tunnel heat damage prediction and assessment technologies primarily rely on surface borehole temperature measurement, geophysical exploration (such as surface magnetotellurics, tunnel face seismic wave analysis, and geological radar), and numerical simulation. However, existing technologies have significant limitations in accurately identifying heat-damaging structures and determining the type of heat damage. These limitations stem from a neglect of the regional geothermal geological background and a lack of monitoring and identification of heat accumulation characteristics, making it difficult to determine the specific tunnel sections experiencing heat damage, the extent of heat damage, and the type of heat damage.

[0004] Regarding the regional geothermal geological background, existing heat damage prediction methods often focus on local geothermal anomaly monitoring near the tunnel axis or simple model deduction, and fail to systematically integrate and analyze the macro-geothermal geological background of the tunnel project through the area, including key information such as regional crust-mantle heat generation (such as crust-mantle structure, plate activity, and magma activity), tectonic heat accumulation (such as deep faults, sedimentary base undulations, and low-speed melt bodies), and surface heat flow (such as water temperature, hot spring water chemical characteristics, and gas composition). The lack of an in-depth understanding of regional-scale heat generation, heat transfer, and heat storage geological elements has led to fundamental defects in the judgment of the possible sources of heat damage encountered by the tunnel and its potential scale and sustainability.

[0005] For the monitoring and identification of heat accumulation characteristics (such as heat degree, heat scale, water pressure, water volume, harmful gas components, etc.), existing technologies only focus on static temperature values ​​or temperature gradients, and it is difficult to dynamically capture and quantify the accumulation, migration process and intensity of heat in the structure. There is a general lack of targeted monitoring and effective identification methods for "heat accumulation", a key disaster-causing process. Summary of the Invention

[0006] In order to improve the accuracy of heat damage identification, the present application provides a method for identifying the type of heat damage in a tunnel.

[0007] The technical solution adopted by the present invention to solve the above problems is:

[0008] Tunnel heat damage type identification method, including:

[0009] Step 1: During the survey and design phase, investigate the heat generation and heat transfer structures in the tunnel site to determine the location and scale of surface and underground heat sources;

[0010] Step 2: Based on step 1, determine the borehole location and conduct drilling in the tunnel area to obtain geothermal flow and geothermal gradient. , and conduct borehole water chemical characteristics analysis and core analysis to obtain heat accumulation structure characteristics and heat generation characteristics; analyze the heat accumulation structure characteristics to obtain rock thermal conductivity , thermal conductivity of fracture fluid , crack rate , rock mass specific heat capacity c, rock mass density ρ; analyze the heat generation characteristics to obtain the deep heat source heating term q;

[0011] Step 3: Establish an unsteady-state heat conduction control model based on the heat transfer mode;

[0012] Step 4: Reconstruct the three-dimensional ground temperature field along the tunnel based on the data obtained in step 2 and the unsteady heat conduction control model;

[0013] Step 5: Preliminarily identify heat accumulation characteristics based on the 3D geothermal field and determine potential heat damage areas;

[0014] Step 6: For potential heat damage sections, during the construction phase, track and monitor the unfavorable geological bodies, set up monitoring holes, and track and monitor the tunnel rock temperature, tunnel water and heat transfer, and tunnel gas through the monitoring holes; obtain the rock thermal conductivity based on the monitoring results , thermal conductivity of fracture fluid , crack rate , rock mass specific heat capacity c and rock mass density ρ;

[0015] Step 7: Based on the rock thermal conductivity obtained in step 6 , thermal conductivity of fracture fluid , crack rate , rock mass specific heat capacity c, rock mass density ρ, the deep heat source heating term q obtained in step 2 and the unsteady-state heat conduction control model to reconstruct the actual temperature field within the project range;

[0016] Step 8: Identify heat accumulation characteristics based on the real temperature field;

[0017] Step 9: Based on the data collected during the survey and design phase and the construction phase, apply the theory of heat conduction in fractured rock mass to identify potential disaster-causing structures and their locations, and obtain their heat accumulation characteristics;

[0018] Step 10: Determine the type of heat damage based on the disaster-causing structure and heat accumulation characteristics.

[0019] Furthermore, step 1 uses geological survey, geophysical exploration of the tunnel site and mapping of surface hydrothermal anomalies to explore the heat generation and heat transfer structures of the tunnel site.

[0020] Furthermore, the heat accumulation structural characteristics include: distance from the fault zone, fracture heat accumulation, rock RQD and rock thermal conductivity, and the heat generation characteristics include heat energy source, gas source and water source.

[0021] Furthermore, the sources of gas include mantle-derived gas, crust-derived gas, and gas generated by water-rock interaction in hydrothermal reservoirs. The judgment method is as follows:

[0022] Mantle-derived gases: The value ranges from -6.5 to -8‰, The ratio reaches 5 ~ 8Ra, The value ranges from -3 to 3‰;

[0023] Shell source gas: The ratio is lower than 0.1 Ra, The value is +10 ~ +20‰;

[0024] Gas generation from water-rock interaction in hydrothermal reservoirs The value is between -2 ~ +5‰ or -20 ~ -10‰, -28 ~-18‰;

[0025] Ra = Atmosphere ratio.

[0026] Furthermore, the deep heat source q includes the radioactive decay term and deep heat conduction term , .

[0027] Further, ,in, is the rock density; is the unit heat power generated by the radioactive decay of U, Th, and K; is the content of U, Th, and K; ,in, is the thermal conductivity of rock; To measure the geothermal gradient in the borehole; Estimate the thickness for the heat source.

[0028] Furthermore, the heat transfer method is heat conduction or heat convection.

[0029] Furthermore, when the heat transfer mode is heat conduction, the unsteady-state heat conduction control model is expressed as: When the heat transfer mode is convection, the unsteady heat conduction control model is expressed as: ;in, represents the gradient, is the equivalent thermal conductivity, q is the heating term of the deep heat source, is the geothermal gradient, ρ is the rock density, c is the rock specific heat capacity, , is the thermal conductivity of rock mass, is the thermal conductivity of the fracture fluid, is the crack rate, is the fracture convection velocity field.

[0030] Furthermore, the heat accumulation characteristics include: heat supply, heat section, heat phenomenon, heat degree, heat scale and heat level,

[0031] Heat supply indicates whether there is geothermal supply in the area, including heat source intensity, heat flux density and thermal conductivity characteristics;

[0032] Thermal section refers to a section with continuous thermal anomaly in space, including the spatial thermal scale and thermal anomaly distribution range;

[0033] Thermal phenomena refer to abnormal manifestations of temperature, water or gas;

[0034] The heat degree represents the intensity of the temperature in the heat damage area;

[0035] Thermal scale indicates the spatial distribution breadth of the heat concentration area;

[0036] The thermal grade characterizes the risk level of heat damage.

[0037] Furthermore, the monitoring holes are arranged as follows: radial monitoring holes are arranged at equal intervals in the excavated section, and the advanced geological drill holes are regarded as axial monitoring holes. The two side holes of the advanced geological drill holes are symmetrical with the central axis of the face and are at the same height as the radial temperature measuring holes. The center of the face is the central drill hole of the advanced geological drill hole, and the upper and lower advanced geological drill holes are symmetrical with the central drill hole.

[0038] Compared with existing technologies, this invention offers the following advantages: It adds mapping of surface hydrothermal anomalies and borehole hydrochemical characteristics to the survey and design phase. Heat accumulation characteristics and potential heat damage zones are identified based on this new data alongside traditional data. For these potential heat damage zones, in addition to traditional comprehensive advanced geological forecasting, borehole rock temperature monitoring, borehole hydrochemical characteristics monitoring, and borehole gas composition and concentration monitoring are added to identify heat accumulation characteristics. Based on data collected during the survey and design phase and the construction phase, the theory of thermal conduction in fractured rock is applied to identify potential disaster-causing structures and their locations. The type of heat damage is determined based on the corresponding heat accumulation characteristics at the location of the disaster-causing structures. This collaborative multi-method exploration and the fusion of multi-source data improve the accuracy of heat damage identification. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a flow chart of the tunnel heat damage type identification method;

[0040] Figure 2 Schematic diagram of high ground temperature assessment in tunnel based on geothermal flow and geothermal gradient;

[0041] Figure 3 Schematic diagram of the location of disaster-causing structures for geophysical exploration and drilling during the survey and design phase;

[0042] Figure 4 This is a schematic diagram of rock, water and gas tracking monitoring during the tunnel construction phase;

[0043] Figure numbers: 1 is the geothermal measuring hole, 2 is the geothermal gradient, 3 is the geothermal flow, 4 is the surface hot spring, 5 is the tunnel line selection, 6 is the deep and large fault, 7 is the horizontal drilling hole in the cave wall, 8 is the advanced horizontal drilling hole, and 9 is the temperature testing point. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0045] Heat at the Earth's surface primarily comes from solar radiation. However, the impact of external climate factors, such as solar radiation, on surface temperatures is minimal and insufficient to cause widespread subsurface temperature anomalies. Heat within the Earth's interior primarily originates from heat deep within the crust and upper mantle. In some areas, heat is also released from the decay of radioactive elements U, Th, and K in the shallow crust, high-temperature magma pockets, residual heat from magma, and melt within the crust. This substantial heat source is a decisive factor influencing subsurface temperature anomalies and a focal point for widespread attention and prevention in tunnel engineering. This heat generation within the Earth's interior is accompanied by the production of large quantities of harmful gases, such as carbon dioxide, hydrogen sulfide, methane, and carbon monoxide. These heat and gases are transferred to the shallower parts of the Earth through rock fractures and groundwater seepage, forming zones of geothermal anomalies. These anomalies may even develop surface hydrothermal phenomena, such as hot springs, hydrothermal explosions, and fumaroles.

[0046] Based on this, the present invention provides a method for identifying the type of tunnel heat damage. During the tunnel site scale survey and design stage, the method focuses on the tunnel site area to conduct a more detailed geological-geothermal collaborative survey, targets and deduce potential high-temperature sections along the tunnel, and conducts preliminary identification of the tunnel's "heat supply, hot sections, thermal phenomena" and other heat accumulation characteristics; for potential high-temperature sections, during the construction stage, advance geological prediction of geothermal anomalies and tracking monitoring of multiphase thermal parameters such as borehole rock temperature, hydrochemical characteristics, gas types and concentrations are carried out to conduct advanced targeted identification of heat accumulation characteristics such as "heat degree, heat scale, heat grade" in the high geothermal sections of the tunnel, integrate the change indicators, change amounts and change rates of the advanced geological prediction and monitoring parameters, and apply the theory of heat conduction in fractured rock mass to identify potential disaster-causing structures and their locations, as well as their corresponding heat accumulation characteristics, thereby realizing the identification of potential heat damage types.

[0047] Specifically, such as Figure 1 Shown, including:

[0048] Step 1: During the survey and design phase, investigate the heat generation and heat transfer structures in the tunnel site to determine the location and scale of surface and underground heat sources.

[0049] During the survey and design phase, the crust-mantle structure, deep faults and other heat-generating and heat-transfer structures are explored through traditional macro-geological surveys and geophysical surveys of the tunnel site. The exploration of the crust-mantle structure mainly detects the thickness of the crust or shallow buried hidden heat reservoirs, such as magma chambers, melt bodies, hydrothermal reservoirs, etc., which can be explored using technologies such as three-dimensional magnetotelluric networks and infrared remote sensing. Deep faults are transmission channels for deep heat sources, which can carry out cross-layer material and energy migration; they can be detected based on controlled source audio frequency magnetotellurics (CSAMT), combined electromagnetic detection (EH4), transient electromagnetic method (TEM), high-density resistivity method (ERT), seismic tomography and other technologies. If there are geothermal anomalies such as hot springs and volcanoes near deep faults, they are advantageous heat conduction channels. Therefore, the present invention adds the mapping of surface hydrothermal anomalies to investigate the surface hydrothermal anomalies and scale near the tunnel site, which mainly refer to hydrothermal phenomena such as hot springs, hot springs, hydrothermal explosions, fumaroles, geothermal alteration zones, etc. Figure 2 As shown, 1 is the geothermal measuring hole, 2 is the geothermal gradient, 3 is the geothermal flow, 4 is the surface hot spring, 5 is the tunnel line selection, and 6 is the deep fault.

[0050] On the one hand, the data collected above can clarify the location and scale of surface and underground heat sources, providing a basis for the setting of heat source terms in the subsequent non-steady-state heat conduction control model; on the other hand, by identifying geothermal anomalies such as deep and large faults, it can be determined whether they are dominant heat conduction channels. Subsequent drilling needs to be carried out near the dominant heat conduction channels, and additional drilling needs to be carried out at the intersection of deep and large faults and tunnels to increase the amount of data collected.

[0051] Step 2: Based on step 1, conduct drilling in the tunnel site to obtain geothermal flow and geothermal gradient , and conduct borehole water chemical characteristics analysis and core analysis to obtain heat accumulation structure characteristics and heat generation characteristics; heat accumulation structure characteristics include distance from the fault zone, fracture heat accumulation, rock RQD, rock thermal conductivity, and the rock thermal conductivity can be obtained by analyzing the heat accumulation structure characteristics. , thermal conductivity of fracture fluid , crack rate , rock mass specific heat capacity c, rock mass density ρ; heat generation characteristics include heat energy source, gas source, and water source. The deep heat source heating item q is obtained by analyzing the heat generation characteristics.

[0052] Based on the location and scale of the surface and underground heat sources determined in step 1, the drilling locations are determined. Drilling is performed near the advantageous heat conduction channels of deep faults, and drilling is performed at the intersection of the predicted deep faults and tunnels. Figure 3As shown, traditional tunnel site drilling was carried out to obtain geothermal flow and geothermal gradient. The geothermal flow reflects the planar distribution of heat flux density, while the geothermal gradient reveals the vertical evolution of ground temperature. Combining the two reveals the three-dimensional characteristics of a regional geothermal field. Based on these two fundamental characteristics of a regional geothermal field, the spatial location of high-temperature anomalies can be preliminarily defined.

[0053] In addition, borehole hydrochemical analysis and core analysis were conducted to identify heat-collecting structures and thermal generation characteristics. The thermal generation characteristics indicate that the main source of heat energy is heat from deep in the crust and upper mantle. In some areas, there is even heat generated by the decay of radioactive elements U, Th, and K in the shallow crust, high-temperature magma pockets, residual heat from magma, and melts within the crust.

[0054] The sources of gas are mantle gas, crust gas, and thermally generated gas, excluding air, coal-bearing formation gas, oil reservoir gas, and natural gas. It mainly comes from deep magma degassing and mantle carbonate metamorphism degassing; crustal gas is mainly formed in the process of melt degassing, magma chamber evolution, metamorphism (organic matter pyrolysis, carbonate mineral metamorphism, carbonaceous rock contact thermal metamorphism, etc.) and radioactive decay; thermally generated gas is mainly generated by complex water-rock-gas multiphase reaction in the reservoir driven by heat, and the water-rock interaction forms through mineral dissolution, redox reaction and organic matter transformation. 、 After the thermally generated gases migrate to the surface, they are eventually released into the atmosphere in the form of soil micro-seepage, hot springs, fumaroles and hydrothermal explosions. Based on the above causes, the present invention provides the following gas sources for reference: mantle source The value is between -6.5~ -8‰, The ratio is 5 ~ 8Ra, mantle source The value is between -3 and 3‰, which is significantly different from the crustal carbonate rocks. and biogenic gases ( ); produced by decomposition of crustal carbonate rocks With higher value (-2 ~ +5‰), while organic matter pyrolysis of Significantly negative (-20 ~ -10‰) (Note: The CO2 from the shell is only for reference, and the differences between regions are large, so specific research is needed for specific regions), thermal cracking causes of The crustal He The ratio is generally lower than 0.1 Ra (Ra = atmospheric ratio), shell source Mainly derived from the thermochemical reduction of sulfate (TSR) and the decomposition of sulfides, The positive deviation is +10 ~ +20‰.

[0055] Water source using multi-parameter water chemistry analysis (major ions, trace elements, stable isotopes ) and gas composition tests (Rn, CO2, H2S, etc.), establish a water-rock interaction model, trace the supply source and migration path of deep thermal reservoir fluids, and identify the contribution of mantle-derived volatile components.

[0056] The water-rock interaction model includes:

[0057] ① Geothermal temperature calibration and mixing effect identification: To determine whether there is low-temperature groundwater (such as well water) mixed in hot water springs, the main ion ratio bivariate graphical analysis method is used. First, select ion pairs with specific water chemical indicative significance for graphical analysis, including: Na vs. Cl, vs. Cl, Ca vs. , Mg vs. ; Analytical data points at Na-Cl and The distribution pattern and slope on the diagram. If different water sample points show the same slope, it means that there is no significant addition or removal of related ions between them, or the mixed water has similar related ion concentrations. and The distribution pattern and slope differences on the diagram. If different water sample point groups show significantly different slopes, it indicates the presence of significant cations ( ) added and / or anions ( ) dilution process. The difference in the size of the slope can be used to indicate the mixing ratio or dilution degree; the analysis results of the target water sample are compared with the characteristics of the potential mixed end member water. Combining the above-mentioned characteristics of the change in the ion ratio relationship (especially The presence of mixing of specific types of low-temperature groundwater and its impact on the hydrothermal chemical characteristics are inferred based on the change pattern of the ratio of the groundwater to the water and the chemical consistency with the potential end-member water.

[0058] ② Verification of material source and leaching process: In order to identify the material source of geothermal fluid (hot water) and the dominant water-rock interaction process, characteristic trace element (geothermal kit) and conservative element combination analysis methods were used, focusing on the typical geothermal trace element combination (geothermal kit), including Li, B, F and As. The enrichment of these elements in geothermal systems is mainly controlled by water-rock interaction and potential magma degassing; evaluate whether the geological background of the study area (such as the lack of igneous rocks and modern volcanic activity) supports a magma source; compare the absolute concentrations of target elements (such as Li, B, F, As) in hot water with those in typical high-temperature geothermal systems affected by magma by orders of magnitude, and significantly lower concentrations (such as 2-3 orders of magnitude lower) are key evidence to exclude the dominant contribution of magma degassing; systematically compare the concentrations of characteristic elements in hot water with other water bodies in the region (such as surface stream water, shallow groundwater / well water), and elements significantly higher than those in cold water (such as B, Cl), indicating that the hot water has undergone stronger water-rock interaction and leaching processes, and significantly lower than those in specific cold water (such as As). Combined with other evidence, it may indicate source differences or the influence of specific water-rock interactions (such as adsorption, precipitation); Cl and B are usually regarded as "conservative elements" in natural water-rock environments. This characteristic means that once dissolved in the fluid, these elements are not easily adsorbed or formed into secondary minerals. Their concentrations primarily reflect the extent of leaching of the source rock by the fluid and the characteristics of the initial source. The significant enrichment of B and Cl in the hot water (relative to the regional cold water) is interpreted as a clear geochemical signature of strong water-rock interaction and source rock leaching. Based on the above analysis (characteristic elemental composition, concentration differences with magmatic systems, elemental comparison with regional water bodies, and the enrichment of conserved elements), the primary source of the characteristic elements in geothermal fluids (dominated by water-rock interaction) and the fluid evolution processes implied are inferred.

[0059] ③ Isotope tracing of the recharge-evolution process: using groundwater hydrogen and oxygen stable isotopes ( , ) analysis method as a tracer to determine the origin, recharge characteristics and evolution of groundwater. and The data were plotted on a bivariate graph and the global atmospheric precipitation line (GMWL) and the local atmospheric precipitation line (LMWL) were marked. If a water sample data point fell on or near the GMWL / LMWL, it was determined to be of atmospheric precipitation origin. The data of different water samples were compared. and More negative isotope values ​​generally indicate higher recharge elevations and / or colder climate conditions. By comparing the isotope value sequences of different water bodies (such as river water, stream water, well water, hot water), their relative recharge elevations can be inferred; typical evaporation will lead to and Synchronous increase, the data points move along the evaporation line (slope is less than GMWL / LMWL). If no synchronous change is observed or the slope characteristics do not conform to the evaporation line, the evaporation effect can be excluded or regarded as a minor factor; Enriched The presence of substantial invariance (“oxygen drift”) is a hallmark of water-rock interaction (oxygen isotope exchange), a process often accompanied by significant changes in ion concentrations (e.g., hot water often exhibits a relative shift in ion concentration relative to surface water). enrichment, These hydrochemical evidences need to be analyzed in conjunction with isotope shift characteristics to confirm the existence and intensity of water-rock interaction; Enriched Basically unchanged can also indicate a small amount of rich The mixing of deep-source fluids (such as metamorphic water and magmatic water) with atmospheric precipitation requires a combination of regional geological background (whether there is a deep heat source, metamorphism) and other geochemical indicators (such as Isotope interpretations must be combined with water chemistry analysis results (major ions, trace elements), geological context information, and other potential tracers such as dissolved inorganic carbon isotopes ( ) combined to accurately distinguish “oxygen drift ( Enriched The main driving mechanisms of the "basically unchanged" phenomenon (water-rock interaction vs. deep mixing) and their impact on the chemical evolution of groundwater are discussed.

[0060] ④Integrated evidence chain of water-rock interaction model:

[0061] The final model construction relies on four-dimensional evidence cross-validation: 1) the cold water mixing ratio corrected by the silica-enthalpy model to explain the temperature scale deviation; 2) The slope of the ion ratio is abnormal, revealing the cation exchange and anion dilution caused by the mixing of cold water; 3) The enrichment degree of the conservative element B / Cl quantifies the leaching intensity; 4) The coordinated changes of unidirectional drift and water chemical parameters confirm the isotope exchange process. Drift unidirectionality, The mutual verification of three independent types of evidence for slope anomalies significantly reduced the multiplicity of solutions and ultimately identified water-rock interaction as the core mechanism of hydrothermal evolution.

[0062] Through the above analysis of heat generation characteristics, the deep heat source heating term q can be obtained. The deep heat source term q includes the radioactive decay term and deep heat conduction term : Radioactive decay mainly comes from the heat generated by the decay of radioactive elements such as U, Th, and K in the earth's crust. By drilling core samples and detecting the content of radioactive elements in rocks, we can analyze the heat generation characteristics and calculate the decay heat generation rate: ,in, is the rock density; is the unit heat power generated by the radioactive decay of U, Th, and K; are the contents of U (ppm), Th (ppm), and K (%). Deep heat conduction originates from the deep mantle or lower crust conducting heat flow from bottom to top. The heat generation characteristics are analyzed by fiber optic temperature sensors deployed in the borehole, and the actual borehole measurements are combined with the heat source thickness estimation to obtain: ,in, is the thermal conductivity of rock; To measure the geothermal gradient by drilling, we use the existing geothermal drilling holes in China. Estimate the thickness for the heat source.

[0063] Step 3: Establish a non-steady-state heat conduction control model based on the heat transfer method.

[0064] The heat transfer mode is divided into heat conduction and heat convection. Based on this, the present invention provides two unsteady-state heat conduction control models. When the heat transfer mode is heat conduction, the unsteady-state heat conduction control model is expressed as: When the heat transfer mode is convection, the unsteady heat conduction control model is expressed as: ;in, represents the gradient, is the equivalent thermal conductivity, q is the heating term of the deep heat source, is the geothermal gradient, ρ is the density, c is the heat capacity, , is the thermal conductivity of rock mass, is the thermal conductivity of the fracture fluid, is the crack rate, is the fracture convection velocity field.

[0065] Step 4: Reconstruct the three-dimensional geothermal field along the tunnel based on the data obtained in step 2 and the unsteady-state heat conduction control model.

[0066] Step 5: Preliminarily identify the heat accumulation characteristics based on the three-dimensional geothermal field and determine the potential heat damage areas.

[0067] Heat concentration characteristics include: heat supply, heat section, heat phenomenon, heat degree, heat scale and heat grade. The heat concentration characteristic elements and their descriptions are shown in the following table:

[0068] Step 6: For potential heat damage sections, during the construction phase, track and monitor the unfavorable geological bodies, set up monitoring holes, and track and monitor the tunnel rock temperature, tunnel water and heat transfer, and tunnel gas through the monitoring holes; obtain the rock thermal conductivity based on the monitoring results , thermal conductivity of fracture fluid , crack rate , rock mass specific heat capacity c, rock mass density ρ.

[0069] Through traditional advanced geological prediction (geological radar GPR, seismic wave method TSP, induced polarization method IPM, cross-hole acoustic CT and optical television, etc.), the properties, scale and spatial distribution of the adverse geological body in front of the tunnel face are detected, and its potential as a superior heat conduction channel is analyzed.

[0070] Based on the unfavorable geological bodies determined in the previous steps, radial temperature measuring holes are arranged at equal intervals in the excavated section (where the thermal conductivity of the rock mass and fracture fluid in the unsteady heat conduction control model can be obtained). 、 , fracture ratio φ, rock mass specific heat capacity c, rock mass density ρ) and regard the advanced geological borehole as an axial temperature measurement hole, and obtain more accurate data through a specific advanced geological borehole distribution form. The two side holes of the advanced geological borehole are symmetrical with the middle axis of the tunnel face and are at the same height as the radial temperature measurement hole. The center of the tunnel face is the central borehole of the advanced geological borehole, and the upper and lower advanced geological boreholes are symmetrical with the central borehole. The layout form is as follows Figure 4 As shown in the figure, 7 is the horizontal borehole in the tunnel wall, 8 is the advance horizontal borehole, and 9 is the temperature test point. The temporal and spatial evolution of rock temperature during tunnel excavation is dynamically monitored using a distributed fiber optic temperature sensing array.

[0071] Simultaneously monitor groundwater in the tunnel's temperature measurement holes, tunnel faces, and advance geological boreholes, and perform hydrochemical and isotopic analyses on water samples (where the fracture convection velocity field can be obtained). ), to identify the mixing ratio of deep hot water storage and shallow cold water.

[0072] The types and concentrations of gases are monitored simultaneously in the temperature measuring holes, tunnel faces and advance geological boreholes of the tunnel, and the geochemical temperature scales of gases, such as the characteristic index of mantle-derived volatiles ( ratio, , pyrolysis gas abnormal indicators (H2S concentration, Rn activity, gas stable isotope fingerprint ( )).

[0073] Step 7: Based on the rock thermal conductivity obtained in step 6 , thermal conductivity of fracture fluid , crack rate , rock mass specific heat capacity c, rock mass density ρ, the deep heat source heating term q obtained in step 2, and the unsteady-state heat conduction control model are used to reconstruct the actual temperature field within the project range.

[0074] Step 8: Identify heat accumulation characteristics based on the real temperature field.

[0075] Step 9: Based on the data collected during the survey and design phase and the construction phase, apply the theory of heat conduction in fractured rock mass to identify potential disaster-causing structures and their locations, and obtain their heat accumulation characteristics.

[0076] Step 10: Determine the type of heat damage based on the disaster-causing structure and heat accumulation characteristics. The heat damage type determination table provided by the present invention is shown in the following table:

[0077] The present invention establishes a regional geothermal geological background analysis-tunnel site multi-stage targeted identification method system to identify tunnel heat damage-causing structures, forming a method system for multi-factor collaborative application, multi-means collaborative detection and multi-source heterogeneous data fusion, so as to achieve the purpose of improving the accuracy of heat damage type identification and thus realize timely early warning.

Claims

1. A method for identifying the type of tunnel heat damage, characterized in that: include: Step 1: During the survey and design phase, investigate the heat generation and heat transfer structures in the tunnel site to determine the location and scale of surface and underground heat sources; Step 2: Based on step 1, determine the borehole location and conduct drilling in the tunnel area to obtain geothermal flow and geothermal gradient. , and conduct borehole water chemical characteristics analysis and core analysis to obtain heat accumulation structure characteristics and heat generation characteristics; Analyze the heat accumulation structure characteristics to obtain the thermal conductivity of the rock mass , thermal conductivity of fracture fluid , crack rate , rock mass specific heat capacity c, rock mass density ρ; Analyze the heat generation characteristics to obtain the deep heat source heating term q; Step 3: Establish an unsteady-state heat conduction control model based on the heat transfer mode; Step 4: Reconstruct the three-dimensional ground temperature field along the tunnel based on the data obtained in step 2 and the unsteady heat conduction control model; Step 5: Preliminarily identify heat accumulation characteristics based on the 3D geothermal field and determine potential heat damage areas; Step 6: For potential heat damage sections, during the construction phase, track and monitor the unfavorable geological bodies, set up monitoring holes, and track and monitor the tunnel rock temperature, tunnel water and heat transfer, and tunnel gas through the monitoring holes; obtain the rock thermal conductivity based on the monitoring results , thermal conductivity of fracture fluid , crack rate , rock mass specific heat capacity c and rock mass density ρ; Step 7: Based on the rock thermal conductivity obtained in step 6 , thermal conductivity of fracture fluid , crack rate , rock mass specific heat capacity c, rock mass density ρ, the deep heat source heating term q obtained in step 2 and the unsteady-state heat conduction control model to reconstruct the actual temperature field within the project range; Step 8: Identify heat accumulation characteristics based on the real temperature field; Step 9: Based on the data collected during the survey and design phase and the construction phase, apply the theory of heat conduction in fractured rock mass to identify potential disaster-causing structures and their locations, and obtain their heat accumulation characteristics; Step 10: Determine the type of heat damage based on the disaster-causing structure and heat accumulation characteristics.

2. The method for identifying the type of tunnel heat damage according to claim 1, characterized in that: Step 1: Use geological survey, geophysical exploration of the tunnel site, and mapping of surface hydrothermal anomalies to explore the heat generation and heat transfer structures in the tunnel site.

3. The method for identifying tunnel heat damage types according to claim 1, characterized in that: The heat accumulation structural characteristics include: distance from the fault zone, fault heat accumulation, rock RQD and rock thermal conductivity; the heat generation characteristics include heat energy source, gas source and water source.

4. The method for identifying the type of tunnel heat damage according to claim 3, characterized in that: The sources of gas include mantle-derived gas, crust-derived gas, and gas generated by water-rock interaction in hydrothermal reservoirs. The identification method is as follows: Mantle-derived gases: The value ranges from -6.5 to -8‰, The ratio reaches 5 ~ 8Ra, The value ranges from -3 to 3‰; Shell source gas: The ratio is lower than 0.1 Ra, The value is +10 ~ +20‰; Gas generation by water-rock interaction in hydrothermal reservoirs: The value is between -2 ~ +5‰ or -20 ~ -10‰, -28 ~ -18‰; Ra = Atmosphere ratio.

5. The method for identifying the type of tunnel heat damage according to claim 3, characterized in that: The deep heat source q includes the radioactive decay term and deep heat conduction term , .

6. The method for identifying the type of tunnel heat damage according to claim 5, characterized in that: ,in, is the rock density; is the unit heat power generated by the radioactive decay of U, Th, and K; is the content of U, Th, and K; ,in, is the thermal conductivity of rock; To measure the geothermal gradient in the borehole; Estimate the thickness for the heat source.

7. The method for identifying tunnel heat damage types according to claim 1, characterized in that: The heat transfer method is heat conduction or heat convection.

8. The method for identifying the type of tunnel heat damage according to claim 7, characterized in that: When the heat transfer mode is heat conduction, the unsteady heat conduction control model is expressed as: When the heat transfer mode is convection, the unsteady heat conduction control model is expressed as: ;in, represents the gradient, is the equivalent thermal conductivity, q is the heating term of the deep heat source, is the geothermal gradient, ρ is the rock density, c is the rock specific heat capacity, , is the thermal conductivity of rock mass, is the thermal conductivity of the fracture fluid, is the crack rate, is the fracture convection velocity field.

9. The method for identifying the type of tunnel heat damage according to claim 1, characterized in that: Heat accumulation characteristics include: heat supply, heat section, heat phenomenon, heat degree, heat scale and heat level. Heat supply indicates whether there is geothermal supply in the area, including heat source intensity, heat flux density and thermal conductivity characteristics; Thermal section refers to a section with continuous thermal anomaly in space, including the spatial thermal scale and thermal anomaly distribution range; Thermal phenomena refer to abnormal manifestations of temperature, water or gas; The heat degree represents the intensity of the temperature in the heat damage area; Thermal scale indicates the spatial distribution breadth of the heat concentration area; The thermal grade characterizes the risk level of heat damage.

10. The method for identifying the type of tunnel heat damage according to any one of claims 1 to 9, characterized in that: The monitoring holes are arranged as follows: radial monitoring holes are arranged at equal intervals in the excavated section, and the advanced geological drill holes are regarded as axial monitoring holes. The two side holes of the advanced geological drill holes are symmetrical with the central axis of the tunnel face and are at the same height as the radial temperature measuring holes. The center of the tunnel face is the central drill hole of the advanced geological drill hole, and the upper and lower advanced geological drill holes are symmetrical with the central drill hole.

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