Deep-buried tunnel surrounding rock permeability coefficient testing method based on horizontal drilling water burst measurement

Abstract

The invention discloses a deep-buried tunnel surrounding rock permeability coefficient testing method based on horizontal drilling water burst measurement, which comprises the following steps: pressing a drilling sleeve into a horizontal drilling hole, connecting a measuring pipe to an outlet of the drilling sleeve at an orifice position, mounting a flow meter and a pressure meter, and recording the water yield and the water burst pressure of water burst. Then calculating pressure loss caused by flowing of gushing water in the drill hole casing according to a dynamic water pressure drop formula, then obtaining the gushing water pressure at the measurement position, and then calculating the permeability coefficient at the measurement position. According to the calculation method, the water pressure does not need to be measured through frequent plug lowering in the deep drill hole, and compared with plug lowering, the method is easy to operate and rapid in measurement. And meanwhile, the measurement failure caused by poor plugging of the lower plug is also avoided.

Description

Technical Field

[0001] The present invention relates to the field of hydrogeological exploration and evaluation, and is particularly applicable to a method for testing the permeability coefficient of surrounding rock of a deep-buried tunnel based on horizontal drilling water gushing measurement. Background Art

[0002] In the engineering geological survey of deep tunnels, the surrounding rock permeability coefficient is a key component in the evaluation of hydrogeological conditions. This coefficient is typically determined through water pressure testing, but this is complex, time-consuming, and labor-intensive. This is particularly challenging in deep boreholes, where plugging is difficult. Furthermore, testing is often impossible in fractured strata.

[0003] At present, horizontal drilling along the axis of the tunnel has become an important means of engineering geological survey for deep-buried tunnels, especially the use of horizontal drilling to expose fault fracture zones. During the implementation of horizontal drilling, water in the rock mass will continue to gush out from the orifice. By measuring the amount of water gushing and the water pressure of the horizontal borehole during the survey stage, and then calculating the permeability coefficient of the tunnel surrounding rock, the method is simple and fast, and is also applicable to strata in fault fracture zones. However, it is difficult to measure the water pressure on site, and the existing patents all use the method of segmented plugging with embolism to obtain the water pressure. In deep boreholes of deep-buried tunnels, it is time-consuming and laborious to frequently insert plugs to measure water pressure, and the measurement may fail due to poor plugging. The method for testing the permeability coefficient of surrounding rock of deep-buried tunnels of the present invention can solve the problem of time-consuming and labor-intensive frequent insertion of plugs to measure water pressure, and is simple and fast to operate, and has strong applicability. Summary of the Invention

[0004] The present invention aims to provide a method for testing the permeability coefficient of surrounding rock in deep-buried tunnels based on horizontal borehole water gushing measurement, which is used to solve the problem of frequent plugging and measuring water pressure, which is time-consuming and laborious. To achieve the above object, the present invention adopts the following technical solutions: The method for testing the permeability coefficient of surrounding rock of a deep-buried tunnel based on horizontal drilling water gushing measurement of the present invention comprises the following steps: S1, drilling a hole horizontally along the tunnel axis and pressing in a drilling casing; ensuring that a section of the hole wall is exposed between the end of the drilling casing and the bottom of the hole; S2, connecting a measuring tube to the drilling casing at the orifice, wherein a flow meter and a pressure gauge are installed on the measuring tube; S3, close the orifice to allow the horizontal borehole water to flow out of the measuring tube; use the flow meter to record the stable water flow Q ; S4, close the outlet of the measuring pipe and observe the pressure gauge. If the pressure is displayed, record the water pressure. P If there is no pressure, grout the area around the casing at the orifice. After the grout solidifies, observe the pressure gauge again and record the water inflow pressure. P ; S5, according to the water inflow Q Calculate the pressure loss Δ caused by friction between water flow and borehole casing P ; S6, according to the water inflow Q , water pressure P and pressure loss Δ P Determine the permeability coefficient K of the exposed hole wall section between the borehole casing and the hole bottom.

[0005] Furthermore, the exposed hole wall is set to 5 meters.

[0006] Furthermore, the step S5 specifically includes: S5.1, based on the measured water inflow from horizontal boreholes Q , calculate the water flow rate v and Reynolds number R e ; S5.2, based on the Reynolds coefficient, select an appropriate method to calculate the friction coefficient between the water flow and the borehole casing λ ; S5.3. Calculate the pressure loss Δ caused by friction between the water flow and the borehole casing using the horizontal pipeline pressure drop formula. P .

[0007] Furthermore, the permeability coefficient of the exposed hole wall section between the borehole casing and the hole bottom is ,in, ρ is the density of water, unit is 1000kg / m 3 ; g is the acceleration due to gravity, H is the length of the horizontal drilling test section, in meters; r is the radius of the horizontal drilling test section, in m.

[0008] Furthermore, steps S1 to S6 are repeated to calculate the permeability system of the next rock mass.

[0009] The advantage of the present invention lies in that a borehole casing is pressed into a horizontal borehole, a measuring tube is connected to the outlet of the borehole casing at the orifice, and a flow meter and pressure gauge are installed to record the water output and pressure of the gushing water. The pressure loss caused by the gushing water flowing in the borehole casing is then calculated according to the dynamic water pressure drop formula, and the gushing water pressure at the measurement location is then obtained, and the permeability coefficient at the measurement location is calculated. This calculation method does not require frequent plugging in deep boreholes to measure water pressure. Moreover, compared with plugging, the present invention is simple to operate and measures quickly. It also avoids measurement failures caused by poor plugging. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1This is a flow chart of the method for testing the permeability coefficient of surrounding rock of a deep-buried tunnel based on horizontal drilling water gushing measurement according to the present invention.

[0011] Figure 2 Schematic diagram of the implementation of the method for testing the permeability coefficient of surrounding rock of a deep-buried tunnel based on horizontal drilling water gushing measurement according to the present invention.

[0012] Figure 3 Schematic diagram of grouting around the drilling casing at the hole mouth in the method of the present invention.

[0013] Figure 4 This is a diagram of the arrangement of grouting nozzles in the method described in the present invention. DETAILED DESCRIPTION

[0014] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts are within the scope of protection of the present invention.

[0015] Example 1 like Figure 1 、 Figure 2 As shown, the method for testing the permeability coefficient of surrounding rock of a deep-buried tunnel based on horizontal drilling water gushing measurement of the present invention comprises the following steps: S1, implement horizontal drilling 2 along the tunnel axis. During the implementation of horizontal drilling 2, the drilling casing 3 is pressed into the hole. The drilling casing 3 can be used to maintain the stability of the hole wall and also has the effect of stopping water. The end of the casing is left at a certain distance from the bottom of the hole, which is the exposed hole wall 4, generally 5m.

[0016] S2. At the orifice, use a tee connector with one end connected to the borehole casing 3 and the other end connected to the measuring tube 5. The measuring tube 5 is equipped with a flow meter 6 and a pressure gauge 7.

[0017] S3. Use the orifice sealing device 8 to close the orifice, ie, close the other end of the tee connector; so that the horizontal borehole 2 flows out from the measuring tube 5, and after the water flow stabilizes, record the water flow measured by the flowmeter 6.

[0018] S4. Seal the measuring tube 5 with the tube seal 9 and observe the pressure gauge 7.

[0019] If the pressure gauge 7 shows pressure, wait until the gushing water pressure is stable and then record the gushing water pressure measured by the pressure gauge 7.

[0020] If the pressure gauge 7 shows no pressure, grouting is performed around the borehole casing at the orifice. After the grouting solidifies, the pressure gauge is observed again and the water gushing pressure measured by the pressure gauge 7 is recorded.

[0021] S5. The horizontal borehole water inflow measured in step S3 Q , first calculate the water flow rate v , the formula is as follows: ; Where, v is the water flow velocity (m / s), Q is the measured water inflow from the horizontal borehole (m 3 / s), D is the inner diameter of the drilling casing (m).

[0022] Then calculate the Reynolds number R e : ; Where, R e is the Reynolds number, η is the kinematic viscosity of water (about 1×10 -6 m 2 / s); The flow pattern of the gushing water is determined by the Reynolds coefficient, and the friction coefficient between the water flow and the borehole casing is calculated according to the flow pattern by selecting an appropriate method. λ .

[0023] In general, if the water flow is laminar ( R e <2000), calculate the friction coefficient according to the following formula: ; If the water is turbulent ( R e ≥4000), the friction coefficient is solved iteratively according to the following formula: ; Where, β The absolute roughness of the drilled casing. In the transition zone of 2000-4000, the flow state is unstable and can usually be calculated conservatively according to turbulence or determined through experiments.

[0024] After obtaining the friction coefficient, the pressure loss Δ caused by the friction between the water flow and the borehole casing 3 is calculated according to the horizontal pipeline pressure drop formula P : ; Where, Δ P is the pressure loss (Pa), L is the length of the borehole casing (m), ρ is the density of water (1000kg / m 3 ).

[0025] S6. The horizontal borehole water inflow measured in step S3 Q , the horizontal borehole water pressure measured in step S4 P , and the pressure loss Δ calculated in step S5 P , calculate the permeability coefficient K of the exposed hole wall section 4 between the borehole casing 3 and the hole bottom: ; Where, K is the permeability coefficient (m / s), P is the measured horizontal borehole water pressure (Pa), r is the radius of the horizontal drilling test section (m), H is the length of the horizontal drilling test section (m), g is the acceleration due to gravity (9.8m / s 2 ).

[0026] The theoretical basis is as follows: The water inflow of a deep tunnel can be calculated according to the Goodman formula as follows: ; Where, h is the height from the groundwater level to the tunnel centerline (m).

[0027] According to the horizontal borehole water pressure measured in step S4 P , and the pressure loss Δ calculated in step S5 P , we can calculate h The value of is as follows: ; Will h Substituting the calculation formula into the Goodman formula and sorting it out, the calculation formula for the permeability coefficient K in step S6 of the present invention can be obtained.

[0028] After obtaining the permeability coefficient of the current section, the horizontal borehole 2 continues to drill. After drilling to a certain depth, steps S1 to S6 are repeated to calculate the permeability coefficient of the next section of rock mass.

[0029] Example 2 like Figure 3 As shown, when the pressure gauge on the measuring tube does not display pressure, grouting is required around the borehole casing at the orifice. The agitator 11 is located in the slurry pool 10, the grouting pump 12 is connected to the slurry pool 10 through a delivery pipe 13, and the grouting nozzle 14 is connected to the grouting pump 12 through a delivery pipe 13. The slurry in the slurry pool 10 is pumped to the grouting nozzle 14 by the grouting pump 12 and injected into the formation around the borehole casing 3. The grouting nozzles 14 are evenly distributed around the borehole casing 3, as shown in FIG. Figure 4 shown.

[0030] Example 3 During the investigation phase of a deep-buried tunnel project, horizontal drilling was carried out along the tunnel axis. According to the methods of Example 1 and Example 2, the water inflow of the horizontal drilling was measured to be 1.32m 3 / h, water gushing pressure 0.784MPa, horizontal drilling test section radius 61mm, test section length 4.8m, borehole casing inner diameter 106mm, borehole casing length 165m.

[0031] Water flow rate: ; Reynolds number: (turbulence); The friction coefficient is solved iteratively according to the following formula λ : ; ; Pressure loss: ; Permeability coefficient of the test section rock mass: ; The rock permeability is classified as moderately permeable.

Claims

1. A method for testing the permeability coefficient of surrounding rock of a deep buried tunnel based on horizontal drilling water inrush measurement, characterized in that: The following steps are involved: S1, drilling a hole horizontally along the tunnel axis and pressing in a drilling casing; ensuring that a section of the hole wall is exposed between the end of the drilling casing and the bottom of the hole; S2, connecting a measuring tube to the drilling casing at the orifice, wherein a flow meter and a pressure gauge are installed on the measuring tube; S3, close the orifice to allow the horizontal borehole water to flow out of the measuring tube; use the flow meter to record the stable water flow Q ; S4, close the outlet of the measuring pipe and observe the pressure gauge. If the pressure is displayed, record the water pressure. P If there is no pressure, grout the area around the casing at the orifice. After the grout solidifies, observe the pressure gauge again and record the water inflow pressure. P ; S5, according to the water inflow Q Calculate the pressure loss Δ caused by friction between water flow and borehole casing P ; S6, according to the water inflow Q , water pressure P and pressure loss Δ P Determine the permeability coefficient K of the exposed hole wall section between the borehole casing and the hole bottom.

2. The method for testing the permeability coefficient of surrounding rock of a deep-buried tunnel based on horizontal borehole water inrush measurement according to claim 1, characterized in that: The exposed hole wall is set to 5 meters.

3. The method for testing the permeability coefficient of surrounding rock of a deep-buried tunnel based on horizontal drilling water gushing measurement according to claim 1, characterized in that: The S5 step specifically includes: S5.1, based on the measured water inflow from horizontal boreholes Q , calculate the water flow rate v and Reynolds number R e ; S5.2, based on the Reynolds coefficient, select an appropriate method to calculate the friction coefficient between the water flow and the borehole casing λ ; S5.

3. Calculate the pressure loss Δ caused by friction between the water flow and the borehole casing using the horizontal pipeline pressure drop formula. P .

4. The method for testing the permeability coefficient of surrounding rock of a deep-buried tunnel based on horizontal borehole water inrush measurement according to claim 1, characterized in that: The permeability coefficient of the exposed hole wall section between the borehole casing and the hole bottom is ,in, ρ is the density of water, unit is 1000kg / m 3 ; g is the acceleration due to gravity, H is the length of the horizontal drilling test section, in meters; r is the radius of the horizontal drilling test section, in m.

5. The method for testing the permeability coefficient of surrounding rock of a deep-buried tunnel based on horizontal drilling water inflow measurement according to claim 1, characterized in that: Repeat steps S1 to S6 to calculate the permeability system of the next rock mass.

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