CN110837695B - Evaluation method for average permeability of surrounding rock of broken granite roadway - Google Patents
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Abstract
The invention relates to the technical field of permeability evaluation, in particular to a method for evaluating average permeability of surrounding rock of a broken granite roadway, which comprises the following specific steps: s1: firstly, through long-time monitoring analysis, the inversion rule of the air seepage direction of surrounding rocks of the roadway in summer and winter is revealed; s2: deducing a roadway surrounding rock average permeability evaluation model based on Darcy law; s3: and finally, a pressurization test is adopted, a method for determining the gas seepage critical inflation pressure of the surrounding rock of the roadway is provided, and a set of evaluation technology suitable for the average permeability of the surrounding rock of the underground roadway with a complex structure is formed. In the invention, a broken granite roadway is taken as a research object, and a roadway ventilation test is adopted to explore a broken surrounding rock average permeability evaluation method based on Darcy's law. Firstly, through long-time monitoring analysis, the inversion rule of the air seepage direction of surrounding rocks of the roadway in summer and winter is revealed; and then deriving an evaluation model of the average permeability of the roadway surrounding rock based on Darcy's law.
Description
Technical Field
The invention relates to the technical field of permeability evaluation, in particular to a method for evaluating average permeability of surrounding rocks of a broken granite roadway.
Background
Radon is a natural decay product of uranium in the crust, whereas the reserves of uranium in the crust are quite abundant, its distribution is widespread and extremely disperse, and its trail can be found almost in various rocks. Radon is a radioactive harmful gas, and when the concentration of radon in the environment is higher than a certain level, the radon can generate harm to people to different degrees, and along with the continuous development of the wide application of underground engineering and the continuous deepening of of people's understanding of radon harm, the research of radon precipitation rules and radon reduction methods in the underground engineering is more and more focused.
Disclosure of Invention
The invention aims to provide an evaluation method for average permeability of surrounding rock of a broken granite roadway, so as to solve the problems in the background art.
In order to achieve the above purpose, the present invention provides the following technical solutions:
the method for evaluating the average permeability of the surrounding rock of the broken granite roadway comprises the following specific steps:
s1: firstly, through long-time monitoring analysis, the inversion rule of the air seepage direction of surrounding rocks of the roadway in summer and winter is revealed;
s2: deducing a roadway surrounding rock average permeability evaluation model based on Darcy law;
s3: and finally, a pressurization test is adopted, a method for determining the gas seepage critical inflation pressure of the surrounding rock of the roadway is provided, and a set of evaluation technology suitable for the average permeability of the surrounding rock of the underground roadway with a complex structure is formed.
As a further scheme of the invention: the specific operation steps in the step S1 are as follows:
step one: a throttle is arranged in the roadway at a position 100m away from the roadway opening and is used as a measurement section of natural ventilation;
step two: the shape and the size of the ventilation sectional area are controlled by adjusting the number of spliced door plates on the baffle wall;
step three: 3 measuring points are distributed on the measuring section, an electronic breeze instrument is adopted to measure wind speed, air temperature monitoring points are arranged at positions 20m away from a roadway opening on the inner side and the outer side of a roadway, a multi-parameter meteorological sensor is adopted to measure air temperature, and measured wind speed data and air temperature data are recorded.
As still further aspects of the invention: the radon concentration in summer is 7.5X10 4 Bq/m 3 The radon concentration in winter is lower than 300Bq/m 3 The concentration of the radon in spring and autumn Ji is between that in winter and summer.
As still further aspects of the invention: the specific operation steps in the step S2 are as follows:
step one: treating the mountain where the tunnel is located into uniform porous medium;
step two: and deriving a surrounding rock average permeability calculation model by using Darcy's law.
As still further aspects of the invention: the specific operation steps in the step S3 are as follows:
step one: a closed door is arranged at the opening of the experimental underground roadway, and a ventilation measurement section is arranged at a position 150 meters away from the opening of the underground roadway;
step two: closing an underground tunnel opening airtight door, then opening fans in two fan rooms, performing forced ventilation on the underground tunnel, and adjusting the inflation pressure in the underground tunnel by changing the opening of the door;
step three: respectively measuring ventilation data when the underground roadway junction airtight door is opened and closed, and simultaneously monitoring and recording radon concentration at the wind speed measurement section;
step four: and calculating whether the fluid seepage flow obeys Darcy law according to the seepage flow Reynolds number.
As still further aspects of the invention: and (3) measuring three groups of data of ventilation and radon concentration data measured in the step three in each state, and taking an average value of the results.
As still further aspects of the invention: and in the fourth step, the critical Reynolds number in the seepage is 0.2-0.3.
Compared with the prior art, the invention has the beneficial effects that: the broken granite roadway is taken as a research object, and a roadway ventilation test is adopted, so that a broken surrounding rock average permeability evaluation method based on Darcy's law is explored. Firstly, through long-time monitoring analysis, the inversion rule of the air seepage direction of surrounding rocks of the roadway in summer and winter is revealed; deducing a roadway surrounding rock average permeability evaluation model based on Darcy law; and finally, a pressurization test is adopted, a method for determining the gas seepage critical inflation pressure of the surrounding rock of the roadway is provided, and a set of evaluation technology suitable for the average permeability of the surrounding rock of the underground roadway with a complex structure is formed. The defect that the permeability of the rock mass is lack of macroscopicity in the conventional laboratory rock sample proportioning method and in-situ drilling water injection/gas method measurement is effectively avoided, and the method has wide application value and guiding significance.
Drawings
Fig. 1 is a schematic diagram of a natural ventilation seasonal variation law in an underground tunnel of a method for evaluating average permeability of surrounding rocks of a broken granite tunnel.
Fig. 2 is a diagram of a ventilation and rectification section and a measuring point of a downhole tunnel in a method for evaluating average permeability of surrounding rock of a broken granite tunnel.
FIG. 3 is a graph showing the relationship between natural ventilation and internal and external temperature differences of a summer underground tunnel in a method for evaluating average permeability of surrounding rocks of a broken granite tunnel.
FIG. 4 is a graph showing the relationship between natural ventilation and internal and external temperature differences of a downhole tunnel in winter in a method for evaluating average permeability of surrounding rocks of a broken granite tunnel.
FIG. 5 is a layout of an experimental downhole tunnel in a method for evaluating the average permeability of surrounding rock of a broken granite tunnel.
FIG. 6 is a schematic diagram of a distribution point of section wind speed measurement in a method for evaluating average permeability of surrounding rock of a broken granite roadway.
FIG. 7 is a graph of radon concentration in a downhole tunnel before and after closure of a closure gate in a method of evaluating average permeability of surrounding rock of a broken granite tunnel.
FIG. 8 is a comparative table of the air volume change before and after closing the airtight door in the evaluation method of the average permeability of the surrounding rock of the broken granite roadway.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Referring to fig. 1 to 6, in an embodiment of the present invention, an evaluation method for average permeability of surrounding rock of a broken granite roadway includes the following specific steps:
s1: firstly, through long-time monitoring analysis, the inversion rule of the air seepage direction of surrounding rocks of the roadway in summer and winter is revealed;
s2: deducing a roadway surrounding rock average permeability evaluation model based on Darcy law;
s3: and finally, a pressurization test is adopted, a method for determining the gas seepage critical inflation pressure of the surrounding rock of the roadway is provided, and a set of evaluation technology suitable for the average permeability of the surrounding rock of the underground roadway with a complex structure is formed.
The specific operation steps in the step S1 are as follows:
step one: a throttle is arranged in the roadway at a position 100m away from the roadway opening and is used as a measurement section of natural ventilation;
step two: the shape and the size of the ventilation sectional area are controlled by adjusting the number of spliced door plates on the baffle wall;
step three: as shown in FIG. 2, 3 measuring points are distributed on the measuring section, an electronic breeze instrument is adopted for wind speed measurement (the model of the electronic breeze instrument is EY3-2A, the manufacturer of the electronic breeze instrument is Beijing Huaxing century instruments Co., ltd.), air temperature monitoring points are arranged at the positions 20m away from the roadway opening on the inner side and the outer side of the roadway, a multi-parameter weather sensor is adopted for air temperature measurement (the model of the multi-parameter weather sensor is HCD1019-5P, the manufacturer of the multi-parameter weather sensor is Chengdu Shijun science and technology Co., ltd.), and the measured wind speed data and the measured air temperature data are recorded.
Depending on project roadway deeply buried in granite, radon concentration variation in roadway also has obvious seasonal law: the radon concentration in summer is 7.5X10 4 Bq/m 3 Winter radon concentration lower than 300Bq/m 3 The concentration of the radon in spring and autumn Ji is between that in winter and summer. Long-term observation shows that under the condition of no mechanical ventilation, natural ventilation exists in the roadway all the year round, the wind direction change also has obvious seasonal characteristics, and the phenomenon of up-down layering and reversing exists. The natural ventilation situation in the roadway in summer and winter is qualitatively described as shown in fig. 1: in summer, the wind direction above the neutral interface (i.e. the false interface with zero natural wind speed, where the wind direction starts to reverse) is inward along the downhole roadway, and the wind direction below the neutral interface is outward; the opposite is true in winter. Because the underground roadway is provided with only one inlet and outlet, if the seepage of the gas in the surrounding rock is not considered, the mass conservation law is considered, and the air flowing in (out) from the upper part of the roadway is complemented by the reverse airflow at the lower part to reach balance. In order to achieve balance, even if the ventilation sectional area of the underground roadway is reduced, the phenomenon that the upper and lower layers are reversed is inevitable, and a neutralization interface is positioned at the middle position of the ventilation sectional area, but the actual situation is not the same. Experiments show that when the ventilation cross section is reduced to a certain degree, the natural wind direction is changed into one direction, the wind direction is outwards along the tunnel in summer, and the wind direction is inwards in winter, so that the result shows that the natural wind in the tunnel in summer can continuously outwards flow out from the global aspect; in winter, the phenomenon that air flows in from outside to inside of the roadway also continuously exists. Obviously, the air flowing out in summer needs to flow from the air inlet to the air outletThe air is supplemented, and the air flowing inwards in winter flows out, so that the natural pressure balance can be achieved, and the air can permeate in mountain under the natural pressure: the mountain body flows into the tunnel in summer and flows into the mountain body in winter.
As shown in fig. 3 and 4, when the wind section is 13cm, the natural wind is unidirectional wind. In summer, the natural ventilation quantity in the tunnel is linearly related to the temperature difference between the inside and the outside of the tunnel, and the larger the temperature difference between the inside and the outside of the tunnel is, the larger the natural ventilation quantity is; in winter, the outside air temperature of the roadway is lower, and compared with summer, the outside air temperature of the roadway can form larger temperature difference, and the natural ventilation quantity is larger. It can be seen that there is an obvious linear relationship between the temperature difference inside and outside the tunnel and the natural ventilation. Since the change of the temperature difference between the inside and the outside of the roadway directly affects the change of the pressure difference, the method can be considered as follows: the larger the pressure difference between the inside and the outside of the tunnel is, the larger the natural ventilation quantity in the tunnel is, namely the larger the seepage intensity of the gas in the mountain is. Analysis shows that air seepage phenomenon exists in surrounding rocks of the tunnel, seasonal reversal phenomenon exists in seepage direction, seepage intensity and intra-tunnel and external temperature difference form a linear correlation relationship, so that the seasonal difference of radon concentration in the tunnel is explained to a certain extent, continuous natural airflow flows out in the tunnel in summer, and the airflow comes from the surrounding rocks, carries a large amount of radon, so that radon concentration in the underground tunnel is higher; natural airflow also exists in winter, but the direction is opposite to summer, namely the air flowing into the underground tunnel from outside flows to the outside of the mountain through cracks in surrounding rock, and fresh air outside in the process continuously carries radon into the surrounding rock and is discharged to the outside of the mountain, so that the radon concentration in the underground tunnel is kept at a lower level.
The specific operation steps in the step S2 are as follows:
step one: treating the mountain where the tunnel is located into uniform porous medium;
step two: and deriving a surrounding rock average permeability calculation model by using Darcy's law.
A general granite rock belongs to a fractured rock mass, and the fractured rock mass seepage field is not usually treated by being equivalent to an isotropic porous medium when being researched. Only when the cracks are absent or irregular distribution of the cracks which are not fixed or loose materials are formed, all the cracks are filled and consolidated by fine particles, and the permeability similar to rock mass is caused, the isotropic porous medium seepage can be regarded as. According to geological survey data of a roadway under study, the surface of a mountain where the roadway is located is seriously weathered, cracks develop, the cracks are more broken, granular fillers are filled in the cracks, and surrounding rocks are broken more through subsequent various explosion experiments in the roadway. Therefore, the mountain where the roadway is located is treated as a uniform porous medium, and meanwhile, the air seepage intensity and the temperature difference are considered to form a linear correlation, and the Darcy law is adopted to deduce the surrounding rock average permeability calculation model. According to darcy's law, the percolation rate is proportional to the pressure gradient, i.e. for the same porous medium, different pressure gradients correspond to the percolation rate that is not used. If a pressure gradient and corresponding permeation rate within the porous medium can be measured, the permeability of the porous medium can be determined, assuming the following in order to ensure the applicability of darcy's law:
(1) The gas accords with an ideal gas state equation in the experimental process;
(2) The experimental process is considered according to the isothermal process, the density of the gas is only related to the pressure, and the dynamic viscosity coefficient is constant;
(3) Neglecting gravity effects;
(4) The gas flow is considered in laminar flow, i.e. the percolation in the medium complies with darcy's law;
(5) The surrounding rock is treated into uniform porous medium.
Under steady state conditions, one-dimensional darcy seepage satisfies the mass conservation equation:
wherein: ρ is the gas density, which can be expressed by the ideal gas state equation: p=ρrt;
v is darcy seepage velocity, formula:
the rock mass permeability k is constant, equation (1) can be:
it is converted into the following equation of a one-dimensional cylindrical coordinate system:
the method can obtain the following steps:
let experimental underground tunnel equivalent radius r in When calculating, regarding the underground roadway with uneven section as an equal-diameter large round hole, then
r in ＝A/2πL 0 Wherein A is the inner surface area of the underground roadway after the underground roadway is overexcavated (average linear overexcavation amount is 300 mm), m 2 ，L 0 And the total effective length of the axis of the underground roadway is m.
When the pressure field of gas in the rock body is stable, the gas pressure in the underground roadway is P 1 The method comprises the steps of carrying out a first treatment on the surface of the At a distance r from the center point of the underground roadway out Where the assumed pressure is the initial pressure P in the rock mass 0 The corresponding boundary conditions are:
the method can be characterized by comprising the following steps of:
c can be calculated correspondingly 2 In the radial flow of the pore medium, the pressure gradient of the gas is not constant, i.e. the gas flow rate is not constant.
In a section with radius r, the mass flow (kg/s) of the gas flowing through is equal, and then according to the ideal gas state equation:
pQ＝p sc Q sc ＝const (8)
the gas volume flow on a section with radius r is q=2pi rL 0 v, where L 0 The effective length of the experimental underground roadway is the length of the seepage cylindrical surface. Then there is
Bringing the formulae (4) and (7) into the formula (9) includes
Combining (8) and (10) to obtain the surrounding rock permeability calculation formula as
Wherein: k is the average permeability of surrounding rock of the underground roadway, m 2 ；
p SC Taking 1.01X10 to be the standard atmospheric pressure value 5 Pa；
Q SC Is the standard volume flow of gas, and is obtained by conversion of a state equation, m 3 /s；
Mu is the kinematic viscosity coefficient of air, 1.8X10 -5 Pa·s；
r out For the radius of the effective range of the experiment (defining the distance from the center of the underground roadway to the radon concentration balance point in the rock mass), considering that the migration of gas in the fractured rock mass is mainly controlled by seepage and diffusion, and m;
p 0 downhole before inflationPressure in the roadway, pa;
p 1 the pressure in the underground roadway is measured as critical inflation pressure (determined according to the experiment below) Pa in the steady state of inflation.
The formula (11) is the permeability calculation formula used in the experiment. According to the formula, the parameter with the greatest difficulty is determined to be critical inflation pressure p 1 And experimental effective range radius r out Wherein r is out The value can be obtained from numerical simulation and literature (7-10 m), and p is determined by experiments 1 Is a value of (a).
The specific operation steps in the step S3 are as follows:
step one: a closed door is arranged at the opening of the experimental underground roadway, and a ventilation measurement section is arranged at a position 150 meters away from the opening of the underground roadway;
step two: closing an underground tunnel opening airtight door, then opening fans in two fan rooms, performing forced ventilation on the underground tunnel, and adjusting the inflation pressure in the underground tunnel by changing the opening of the door;
step three: respectively measuring ventilation data when the underground roadway junction airtight door is opened and closed, simultaneously monitoring and recording radon concentration at the wind speed measurement section, respectively measuring three groups of data of the measured ventilation and radon concentration data in each state, and taking an average value of the results;
step four: and calculating whether the fluid seepage flow obeys Darcy's law according to the seepage flow Reynolds number, wherein the critical Reynolds number in the seepage flow is 0.2-0.3.
The ventilation system is used for carrying out micro-positive pressure inflation on the closed underground tunnel in the rock body, gas can permeate from the underground tunnel into surrounding rock body, and after a sufficient time, the gas pressure field in the rock body is stable. The aeration quantity in the underground tunnel is measurable, when the gas pressure field in the rock mass is stable, the gas pressure in the underground tunnel is also stable, and the gas pressure value can be obtained through measurement. According to the two data, the permeability of the rock mass can be obtained by using a calculation formula based on Darcy's law, or the average permeability of the rock mass is assumed to be in accordance with Darcy's law by gas seepage generated in the experimental process. The experiment is carried out in summer, and the gas is treated according to radon concentrationSensitivity of flow exchange when radon concentration in the experimental underworkings reaches winter level, it is considered that gas in the rock mass has permeated in the same direction as in winter. If the underground roadway is considered as a hole extending into the interior of a huge mountain, when the hole is inflated and a certain positive pressure is formed, a part of gas is discharged through a channel in the mountain in a seepage manner. In the pressurizing process, the air flow exchange condition between the underground roadway and surrounding rock can be judged according to the radon concentration change in the underground roadway. Experiments have found that radon concentration in the underworkings can be maintained at winter levels (about 300Bq/m after inflation pressure reaches 200Pa 3 ) Critical inflation pressure p 1 200Pa is taken. Because the design surplus of the wind pressure of the ventilator in the underground tunnel is more than 500Pa, the resistance formed by the ventilation and pressurization experiment on the underground tunnel can be considered to not influence the wind quantity sent into the underground tunnel by the ventilator. The wind speed measurement results are shown in table 1, and after the underground roadway opening airtight door is closed, the air quantity of the ventilation system is reduced by 12.5%, which can be considered as follows: the part of air volume lost by the system is the air volume which escapes to the atmosphere after flowing through the mountain in a seepage way, and the size of the air volume is the air volume difference (1.13 m) before and after the closing of the sealing door of the underground roadway opening 3 /s). Accordingly, Q in formula (11) can be determined from the ideal gas state equation SC Calculated, Q SC ＝0.96m 3 /s。
As shown in FIG. 7, after the airtight door is closed for 2 hours, the radon concentration in the underground roadway is 7.5X10 as the average value 4 Bq/m3 drops rapidly to 300Bq/m 3 The left and right sides are kept stable, and the level in the natural state in winter is reached. Because radon concentration is very sensitive to gas flow exchange, the rapid decrease in radon concentration indicates that the exchange direction of gas flow between the downhole roadway and the surrounding rock has changed. In combination with the seasonal variation law of radon concentration, it can be considered that the seepage direction of the gas in the mountain is reversed, namely, the gas in the underground roadway enters the mountain under the drive of the pressure of 200Pa through the seepage effect after the airtight door is closed. From this, p in the formula (11) can be determined 1 ＝200+p 0 . According to the formula (11) and the parameters determined by the experiment, the average permeability of the surrounding rock of the experimental underworkings can be obtained by calculation: k=1.5×10 -11 ～1.8×10 -11 m 2 . From this it is possible to obtain: the average permeability of the down hole surrounding rock is of the order of 10-11m 2. The literature data define a granite permeability range of 6.1X10 -12 ～9.5×10 -11 m 2 The calculations herein are consistent with the definition of this range.
Whether the seepage flow of the fluid is compliant with Darcy's law can be judged by using the seepage flow Reynolds number. The Reynolds number reflects the ratio of inertial force to viscous force in fluid flow. A great number of researches show that when the critical Reynolds number in the seepage is 0.2-0.3, namely the Reynolds number Re is smaller than or equal to the critical value, the seepage is linear seepage, and the Darcy law is obeyed; when Re is greater than a critical value, the seepage is nonlinear and does not obey Darcy's law.
There are many methods for calculating the reynolds number, and at present, the more general ones are:
wherein: re is the Reynolds number;
v is the fluid seepage velocity, m/s;
k is the permeability of the medium, m 2 ；
Mu is the dynamic viscosity coefficient of the fluid and Pa.s;
ρ is the density of the fluid, kg/m 3 The method comprises the steps of carrying out a first treatment on the surface of the Phi is the effective porosity of the medium,%.
To obtain the percolation reynolds number, values of percolation velocity v, permeability k of the rock mass medium, and effective porosity phi are obtained according to equation (12). The highest porosity of granite can reach 6.11%, the effective porosity of granite is between 0.05% and 2.8%, and the effective porosity of the general complete bedrock is below 1%. The effective porosity of the mountain body around the underground roadway is calculated according to 2 percent because the mountain body where the underground roadway is researched is damaged by blasting and the like in the process of excavation and the like, so that the effective porosity of the mountain body is increased. From the experimental results, the seepage velocity was calculated to be 0.9X10 using the formula v=Q/A -4 m/s. Substituting the relevant parameters into the formula (12) to obtain: re=0.0005 < 0.2, i.e. the gas permeation flow in the experiment obeys Darcy's law。
Since the foregoing experiment was conducted based on the assumption of Darcy's law, the assumption holds from the above analysis results, and the research process is reasonable.
Claims (3)
1. A method for evaluating average permeability of surrounding rock of a broken granite roadway is characterized by comprising the following steps: the evaluation method comprises the following specific steps:
s1: firstly, through long-time monitoring analysis, the inversion rule of the air seepage direction of surrounding rocks of the roadway in summer and winter is revealed; the specific operation steps in the step S1 are as follows:
step one: a throttle is arranged in the roadway at a position 100m away from the roadway opening and is used as a measurement section of natural ventilation;
step two: the shape and the size of the ventilation sectional area are controlled by adjusting the number of spliced door plates on the baffle wall;
step three: 3 measuring points are distributed on the measuring section, an electronic breeze instrument is adopted to measure wind speed, air temperature monitoring points are arranged at positions 20m away from a roadway opening on the inner side and the outer side of a roadway, a multi-parameter meteorological sensor is adopted to measure air temperature, and measured wind speed data and air temperature data are recorded;
s2: deducing a roadway surrounding rock average permeability evaluation model based on Darcy law;
the specific operation steps in the step S2 are as follows:
step one: treating the mountain where the tunnel is located into uniform porous medium;
step two: deriving a surrounding rock average permeability calculation model by using Darcy's law:
let experimental underground tunnel equivalent radius r in When calculating, regarding the underground roadway with uneven section segmentation as an equal-diameter large round hole, r in ＝A2πL 0 Wherein A is the inner surface area of the underground tunnel after the underground tunnel is overdrawn, m 2 ；L 0 The total effective length of the axis of the underground roadway is m; the surrounding rock permeability calculation formula is:
in the above calculation formula: k is the average permeability of surrounding rock of the underground roadway, m 2 ；
p SC Taking 1.01X10 to be the standard atmospheric pressure value 5 Pa；
Q SC Is the standard volume flow of gas, and is obtained by conversion of a state equation, m 3 /s；
Mu is the kinematic viscosity coefficient of air, 1.8X10 -5 Pa·s；
r out Defining a distance from the center of a downhole tunnel to a radon concentration balance point in a rock mass for the radius of an experimental effective range, and m;
p 0 the pressure Pa is the pressure in the underground roadway before inflation;
p 1 taking critical inflation pressure Pa as the value of the pressure in the underground roadway in the inflation steady state;
s3: finally, a pressurization test is adopted, a method for determining the gas seepage critical inflation pressure of the surrounding rock of the roadway is provided, and a set of evaluation technology suitable for the average permeability of the surrounding rock of the underground roadway with a complex structure is formed;
the specific operation steps in the step S3 are as follows:
step one: a closed door is arranged at the opening of the experimental underground roadway, and a ventilation measurement section is arranged at a position 150 meters away from the opening of the underground roadway;
step two: closing an underground tunnel opening airtight door, then opening fans in two fan rooms, performing forced ventilation on the underground tunnel, and adjusting the inflation pressure in the underground tunnel by changing the opening of the door;
step three: respectively measuring ventilation data when the underground roadway junction airtight door is opened and closed, and simultaneously monitoring and recording radon concentration at the wind speed measurement section;
step four: and calculating whether the fluid seepage flow obeys Darcy law according to the seepage flow Reynolds number.
2. The method for evaluating the average permeability of the surrounding rock of the broken granite roadway according to claim 1, wherein the method comprises the following steps: and S3, measuring three groups of data of ventilation and radon concentration data measured in the step three in each state, and taking an average value of the results.
3. The method for evaluating the average permeability of the surrounding rock of the broken granite roadway according to claim 1, wherein the method comprises the following steps: and in the step S3, the critical Reynolds number in the seepage is 0.2-0.3.
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