A method for determining the external water pressure of a shield tunnel

Abstract

The present application relates to a method for determining the external water pressure of a shield tunnel, belonging to the technical field of shield tunnel construction. The method includes determining the static water level line in the longitudinal section of the shield tunnel and the surrounding rock classification of the entire surrounding rock of the shield tunnel; determining the positions of long-term observation holes in different surrounding rock classifications according to the static water level line and setting long-term observation holes; observing through the long-term observation holes to obtain the static water level line and the external water pressure water level line during the high water period in different surrounding rock classifications; calculating the reduction coefficients of the surrounding rock of different classifications according to the static water level line and the external water pressure water level line during the high water period; and calculating the external water pressure at different surrounding rock classification locations according to the reduction coefficients of the surrounding rock of different classifications. The present application has the effects of improving the accuracy of calculating the external water pressure value, enhancing the reliability of data, reducing the construction cost, and ensuring the safety of construction.

Description

Technical Field

[0001] The present application relates to the technical field of shield tunnel construction, and in particular to a method for determining the external water pressure of a shield tunnel. Background Art

[0002] When a shield tunnel passes under a tall mountain, it will bear a large external water pressure during the construction and operation processes. The magnitude of the external water pressure has a great influence on the waterproof design of the shield tunnel deeply buried in bedrock. At present, the maximum pressure that the water stop strip of the shield segment can withstand is generally 0.6 - 0.8 MPa. When the actual pressure exceeds this value, the service life of the water stop strip will be greatly reduced, and leakage is likely to occur within a relatively short operation period, bringing huge challenges to the design and later operation safety.

[0003] The external water pressure is the groundwater pressure acting on the outer surface of the shield tunnel lining. The water pressure acting on the outer surface of the lining generated by the groundwater seepage in the overlying rock (soil) mass is often not equal to the acting water head (hydrostatic pressure head He) from the groundwater level to the tunnel center line, and there is a reduction in the water head with a reduction coefficient β e . In the prior art, for the reduction coefficient β e it is stipulated that during the preliminary exploration stage, the reduction coefficient β of the external water pressure can be determined by looking up a table according to the permeability grade of the rock and soil mass. e .

[0004] There are several problems in determining the above-mentioned external water pressure reduction coefficient β e as follows:

[0005] 1. Most exploration and design units refer to and implement the water conservancy and hydropower industry to determine the reduction coefficient, and the basis is rather far-fetched, and there may even be a large deviation from the actual working conditions.

[0006] 2. Shield tunnels in the water conservancy and hydropower industry generally allow water drainage, and rarely use fully sealed linings. The shield tunnel is formed by segments and is a typical fully sealed lining. It is more convenient to set up a water drainage system for shield tunnels in the water conservancy and hydropower industry. When leakage occurs in the later stage, it is convenient to enter the tunnel for maintenance. However, it is more difficult to design a water drainage system for shield tunnels, and it is necessary to consider increasing the tunnel diameter, which will greatly increase the cost; when leakage occurs in the later stage, it is very difficult to enter the tunnel for maintenance.

[0007] 3. The exploration period in the exploration stage is very short, and the obtained hydrostatic pressure is often the short-term observation result, and even has not experienced the flood season. The reliability of the data is poor, and the hydrostatic pressure provided at this time is on the small side, which is relatively dangerous for the project. Summary of the Invention

[0008] To solve the problem that there is a large deviation between the existing method of determining the reduction coefficient βe of the external water pressure by looking up a table to calculate the external water pressure during the exploration period of a shield tunnel and the actual working conditions in the prior art, the present application provides a method for determining the external water pressure of a shield tunnel.

[0009] The method for determining the external water pressure of a shield tunnel provided by the present application adopts the following technical solution: A method for determining the external water pressure of a shield tunnel, the steps include:

[0010] Determine the static water level line in the longitudinal section of the shield tunnel and the surrounding rock classification of the entire shield tunnel surrounding rock;

[0011] Determine the positions of long-term observation holes in different surrounding rock classifications according to the static water level line and set long-term observation holes;

[0012] Observe through the long-term observation holes to obtain the static water level line and the external water pressure water level line during the high water period in different surrounding rock classifications;

[0013] Calculate the reduction coefficients of the surrounding rock of different classifications according to the static water level line during the high water period and the external water pressure water level line during the high water period;

[0014] Calculate the external water pressure at different surrounding rock classification locations according to the reduction coefficients of the surrounding rock of different classifications.

[0015] Optionally, the determining the static water level line in the longitudinal section of the shield tunnel and the surrounding rock classification of the entire shield tunnel surrounding rock specifically includes: adopting comprehensive exploration means including one or more of geological mapping, drilling, and geophysical exploration to determine the static water level line in the longitudinal section of the shield tunnel and the surrounding rock classification of the entire shield tunnel surrounding rock.

[0016] Optionally, the observing through the long-term observation holes to obtain the static water level line and the external water pressure water level line during the high water period specifically includes: the long-term observation holes include static water level long-term observation holes and external water level long-term observation holes. Observe the static water level during the high water period through the static water level long-term observation holes, and then fit the static water level lines during multiple high water periods; observe the external water pressure during the high water period through the external water level long-term observation holes, and then fit the external water pressure water level lines during multiple high water periods.

[0017] Optionally, the setting method of the static water level long-term observation holes and the external water level long-term observation holes specifically includes: setting static water level long-term observation holes and external water level long-term observation holes respectively at the positions of several typical surrounding rocks. The static water level long-term observation holes and the external water level long-term observation holes set at the position of the same typical surrounding rock are spaced at a set distance and are located in the same seepage field of the same hydrogeological unit.

[0018] Optionally, the setting method of the long-term static water level observation hole specifically includes: drilling a hole with a diameter of 100-110 mm and a depth reaching 1-3 m below the bottom of the shield tunnel. According to the requirements of hydrogeological tests, wash the hole, pump water and set a steel casing to avoid blockage in the hole caused by caving of the hole wall.

[0019] Optionally, the setting method of the long-term external water level observation hole specifically includes:

[0020] Drill a hole with a diameter of 400-600 mm and a depth reaching 10-11 m above the shield tunnel;

[0021] Use a drill bit with a diameter of 100-110 mm to drill to a depth of 1-3 m below the bottom of the shield tunnel to finish the hole;

[0022] Wash the hole and pump water according to the requirements of hydrogeological tests;

[0023] Configure a filter pipe and a riser pipe. The part above the flange is the riser pipe, and a conventional steel casing is used. The part below the flange is the filter pipe, and the pipe diameters are both 90-100 mm. The hole spacing of the filter holes of the filter pipe is 15-25 cm, and two adjacent rows are arranged in a staggered manner. The aperture of the filter holes of the filter pipe is 0.5-1.5 cm;

[0024] Pour cement slurry into the outside of the riser pipe from the top of the hole until the cement slurry overflows the hole opening.

[0025] Optionally, the setting method of the long-term external water level observation hole specifically includes:

[0026] Drill a hole with a diameter of 100-110 mm and a depth reaching 1-3 m below the bottom of the shield tunnel;

[0027] Wash the hole and pump water according to the requirements of hydrogeological tests.

[0028] Calculate the fine sand body according to the hole diameter and first put in 4 m long section of fine sand.

[0029] Put in two piezometers, and the two piezometers are arranged in a staggered manner;

[0030] Put in fine sand and wait for the fine sand to settle and stabilize;

[0031] Pour cement slurry from the bottom of the hole until the cement slurry overflows the hole opening, and pour all the hole sections above the sandy soil into concrete.

[0032] Optionally, calculating the reduction coefficient β of surrounding rocks of different grades according to the static water level line in the flood season and the external water pressure water level line in the flood season e , specifically includes: establishing a calculation formula for the external water pressure reduction coefficient β e :

[0033]

[0034] Among them, β e : coefficient of reduction of external water pressure;

[0035] H w : the pressure head of external water pressure actually acting on the outer surface of the lining structure after being affected by seepage, that is, the external water pressure head;

[0036] H e : the acting head from the groundwater level line to the center of the tunnel, that is, the hydrostatic pressure head;

[0037] Calculate the coefficient of reduction of external water pressure β according to the formula e .

[0038] Optionally, the calculation method of the hydrostatic pressure head H e specifically includes: measuring the buried depth value of the static water level with a water level gauge, subtracting the buried depth value of the shield tunnel axis to obtain the hydrostatic pressure head H e ;

[0039] The calculation method of the external water pressure head H w specifically includes: measuring the buried depth value of the external water level with a water level gauge, subtracting the buried depth value of the shield tunnel axis to obtain the external water pressure head H w .

[0040] Optionally, calculating the external water pressure at different surrounding rock grades according to the reduction coefficients of different grades of surrounding rock specifically includes: determining the surrounding rock grade at the position where the external water pressure head needs to be calculated, obtaining the hydrostatic pressure head at the position where the external water pressure head needs to be calculated according to the static water level line, and calculating the external water pressure head at this position according to the following formula:

[0041] H w =H e ×β e

[0042] Among them, β e : coefficient of reduction of external water pressure;

[0043] H w : the pressure head of external water pressure actually acting on the outer surface of the lining structure after being affected by seepage, that is, the external water pressure head, m;

[0044] H e : the acting head from the groundwater level line to the center of the tunnel, that is, the hydrostatic pressure head.

[0045] In summary, the present application includes at least one of the following beneficial technical effects:

[0046] In this application, the reduction coefficient of external water pressure in different surrounding rock levels is calculated by setting long-term observation holes for static water levels and long-term observation holes for external water levels in different surrounding rock classifications, so as to obtain the accurate reduction coefficient of external water pressure corresponding to the surrounding rock level. Then, the external water level pressure value at the corresponding position is calculated through the reduction coefficient of external water pressure, which improves the accuracy of the calculation of the external water level pressure value, enhances the reliability of the data, reduces the construction cost, and ensures the safety of the construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 FIG. is a schematic diagram of the steps of a method for determining the external water pressure of a shield tunnel in an embodiment of the present application.

[0048] Figure 2 FIG. is a schematic diagram of the static water level line and the external water level pressure line during the high water period of a method for determining the external water pressure of a shield tunnel in an embodiment of the present application.

[0049] Figure 3 FIG. is a schematic diagram of the structure of the long-term external water level observation hole of a method for determining the external water pressure of a shield tunnel in the second embodiment of the present application.

[0050] Figure 4 FIG. is a schematic diagram of the structure of the long-term external water level observation hole of a method for determining the external water pressure of a shield tunnel in the first embodiment of the present application.

[0051] Figure 5 FIG. is a schematic diagram of the structure of the long-term static water level observation hole of a method for determining the external water pressure of a shield tunnel in an embodiment of the present application.

[0052] Wherein, 1. Shield tunnel; 2. The first long-term external water level observation hole; 21. Water pressure gauge; 22. Fine sand layer; 23. The first cement slurry layer; 24. Data signal line; 25. Sine reading instrument; 3. The second long-term external water level observation hole; 31. Standpipe; 32. Filter pipe; 33. Flange; 34. Expanded water stop tape; 35. The second cement slurry layer; 36. The first water level gauge; 4. Long-term static water level observation hole; 41. Steel casing; 42. The second water level gauge. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0053] The following specific embodiments illustrate the implementation manners of the present application. Those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in this specification.

[0054] Please refer to Figures 1-5It should be noted that the structures, ratios, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those familiar with this technology to understand and read, and are not used to limit the implementation conditions of this application. Therefore, they do not have any substantial technical significance. Any modification of the structure, change of the proportional relationship, or adjustment of the size, without affecting the effects that this application can produce and the purposes that can be achieved, should still fall within the scope covered by the technical content disclosed in this application. At the same time, the terms such as "upper", "lower", "left", "right", "middle", and "one" cited in this specification are only for the convenience of clear narration and are not used to limit the scope of implementation of this application. The change or adjustment of their relative relationship, without substantial change in the technical content, should also be regarded as the scope of implementation of this application.

[0055] The following will further elaborate on this application in conjunction with the attached Figures 1-5 drawings.

[0056] Example 1:

[0057] This example discloses a method for determining the external water pressure of a shield tunnel.

[0058] Referring to Figure 1 , a method for determining the external water pressure of a shield tunnel, the steps include:

[0059] S1. Determine the static water level line in the longitudinal section of the shield tunnel and the surrounding rock classification of the entire shield tunnel surrounding rock

[0060] Specifically, comprehensive exploration means including geological mapping, drilling, and geophysical exploration are adopted. According to the water levels measured at the detailed exploration holes during the detailed exploration period, the preliminary static water level line in the longitudinal section of the shield tunnel is determined. According to the detailed exploration results, the surrounding rock classification of the entire shield tunnel surrounding rock is determined, and the surrounding rock is classified into Class I surrounding rock, Class II surrounding rock, and Class III surrounding rock according to types.

[0061] S2. Determine the positions of long-term observation holes in different surrounding rock classifications according to the static water level line and set long-term observation holes

[0062] Specifically, long-term observation holes are set on Class I surrounding rock, Class II surrounding rock, and Class III surrounding rock. The long-term observation holes include static water level long-term observation holes and external water level long-term observation holes. Static water level long-term observation holes and external water level long-term observation holes are respectively set at the positions of Class I surrounding rock, Class II surrounding rock, and Class III surrounding rock. The static water level long-term observation holes and external water level long-term observation holes set at the positions of the same typical surrounding rock are spaced at a set distance and are located in the same seepage field of the same hydrogeological unit. The long-term observation holes should be arranged as close as possible to the highest point of the static water level in the surrounding rock section of this grade. Due to the mountain terrain and plant conditions, often the long-term observation holes can only be arranged at higher water level positions and cannot be arranged at the highest static water level position;

[0063] The setting method of the static water level long-term observation holes is:

[0064] Drill a hole with a diameter of 109 mm to a depth of 2 m below the bottom of the shield tunnel. According to the requirements of hydrogeological tests, wash the hole, pump water, and set up a steel casing to prevent blockage in the hole caused by spalling of the hole wall. Insert a casing water level gauge into the hole to form a long-term static water level observation hole 4 as shown in Figure 5 Figure 4. The long-term static water level observation hole 4 extends to 2 m below the bottom of the shield tunnel. A steel casing 41 is arranged inside the long-term static water level observation hole 4, and a second water level gauge 42 is arranged in the middle of the steel casing 41;

[0065] The setting method of the external water level long-term observation hole is as follows:

[0066] Drill a hole with a diameter of 400 - 600 mm to a depth of about 2 m above the top of the shield tunnel. The larger the diameter of this section, the more beneficial it is, but the longer the construction period and the higher the cost. It must be selected according to needs;

[0067] Then use a drill bit with a diameter of 109 mm to continue drilling to the end hole at 2 m below the bottom of the shield tunnel;

[0068] Wash the hole and pump water (or lift water) according to the requirements of hydrogeological tests;

[0069] Configure a filter pipe and a water-proof steel casing, connect them with a flange joint in the middle, set an expansion water-stop tape at the bottom of the flange, wind the expansion water-stop tape on the upper 2 m section. The diameter of the flange is slightly smaller than the upper hole diameter to ensure that it can be smoothly installed at the reduced diameter section. The pipe above the flange is a riser pipe, using a conventional steel casing, and the pipe below the flange is a filter pipe, both with a diameter of 98 mm. The hole pitch of the filter holes of the filter pipe is 20 cm, and the adjacent two rows are staggered, with a hole diameter of 1 cm;

[0070] Pour cement slurry from the top of the hole into the outside of the riser pipe until the cement slurry overflows the hole opening. Re-pouring is allowed;

[0071] When the hole depth is large and the center of the small-diameter hole at the reduced diameter section deviates significantly from the center of the large-diameter hole, the filter pipe below the flange may not be able to be installed into the lower hole section. At this time, the lower filter pipe can be cancelled. Since generally fewer fine particles seep out in the bedrock and will sink to the bottom sediment section, which has little impact on the water level measurement, a second type of external water level long-term observation hole 3 as shown in Figure 4 Figure 3 is formed. A riser pipe 31 is arranged in the middle of the second type of external water level long-term observation hole 3. The riser pipe 31 uses a steel casing. The lower end of the riser pipe 31 is connected with a filter pipe 33 through a flange 33. Expansion water-stop tapes 34 are covered on both the upper and lower sides of the flange 33. A second cement slurry layer is arranged in the gap between the riser pipe 31 and the hole wall, and a first water level gauge 36 is arranged in the middle of the riser pipe 31.

[0072] S3. Obtain the static water level line and the external water pressure water level line during the high water period in different surrounding rock grades through observation of the long-term observation holes

[0073] Specifically, the water level observation time is more than one hydrological year. The static water level during the high water period is observed through long-term static water level observation holes, and then the static water level line during the high water period is fitted by multiple static water levels during the high water period; the external water pressure during the high water period is observed through long-term external water level observation holes, and then the external water level pressure water level line during the high water period is fitted by multiple external water pressures during the high water period, and the static water level line and external water level pressure water level line during the high water period as shown in Figure 2 are drawn.

[0074] S4. Calculate the reduction coefficients of surrounding rocks at different grades according to the static water level line during the high water period and the external water level pressure water level line during the high water period

[0075] Specifically, first, calculate the hydrostatic pressure head H e and the external water pressure head H w in Class I surrounding rock, Class II surrounding rock, and Class III surrounding rock. Measure the buried depth value of the static water level with a water level gauge, subtract the buried depth value of the shield tunnel axis to obtain the hydrostatic pressure head H e , measure the buried depth value of the external water level with a water level gauge, subtract the buried depth value of the shield tunnel axis to obtain the external water pressure head H w , so as to calculate the hydrostatic pressure head H e 1 and the external water pressure head H w 1 in Class I surrounding rock, the hydrostatic pressure head H e 2 and the external water pressure head H w 2 in Class II surrounding rock, and the hydrostatic pressure head H e 3 and the external water pressure head H w 3 in Class III surrounding rock;

[0076] Then, establish the calculation formula for the reduction coefficient β e of the external water pressure:

[0077]

[0078] where β e : reduction coefficient of external water pressure;

[0079] H w : the pressure head actually acting on the outer surface of the lining structure affected by seepage, that is, the external water pressure head, m;

[0080] H e : the acting head from the groundwater level line to the center of the tunnel, that is, the hydrostatic pressure head, m;

[0081] Finally, calculate according to the formula to obtain:

[0082] the reduction coefficient of external water pressure in Class I surrounding rock

[0083] the reduction coefficient of external water pressure in Class II surrounding rock

[0084] Reduction coefficient of external water pressure for Class III surrounding rock

[0085] S5. Calculate the external water pressure at different surrounding rock grades according to the reduction coefficients of surrounding rocks with different classifications

[0086] Specifically, determine the surrounding rock grade at the position where the external water pressure head needs to be calculated, obtain the hydrostatic pressure head at the position where the external water pressure head needs to be calculated according to the static water level line, and calculate the external water pressure head at this position according to the following formula:

[0087] H w = H e ×β e

[0088] where, β e : reduction coefficient of external water pressure;

[0089] H w : the pressure head actually acting on the outer surface of the lining structure after being affected by seepage, i.e., the external water pressure head, m;

[0090] H e : the acting head from the groundwater level line to the center of the tunnel, i.e., the hydrostatic pressure head, m;

[0091] When calculating the external water pressure head at a certain ɑ position in Class II surrounding rock, take the reduction coefficient β e 2 of Class I surrounding rock, obtain the hydrostatic pressure head H e ɑ at the ɑ position according to the static water level line, then the external water pressure head H w ɑ = H e ɑ × β e 2.

[0092] Example 2:

[0093] The difference between this example and Example 1 is that the setting method of the long-term external water level observation hole in this example is as follows:

[0094] Drill a hole, with a general hole diameter of 109 mm and a hole depth of about 2 m below the bottom of the shield tunnel;

[0095] Wash the hole and pump water (or lift water) according to the requirements of hydrogeological tests;

[0096] Calculate the fine sand body according to the hole diameter, and first put in the fine sand for a section of 4 m in length;

[0097] Put in two piezometers, and the two piezometers are staggered by about 2.2 m;

[0098] Fine sand is added in sections of 6.2 m in length. At this point, the total length of the fine sand section filled into the hole bottom is 10.2 m. The bottom surface is at the bottom of the hole, and the top surface is 10.2 m above the bottom of the hole, that is, 2 m above the top of the shield tunnel.

[0099] Let it stand for a while until the fine sand settles and stabilizes;

[0100] Cement slurry is poured in from the bottom of the hole, gradually pulling it up while pouring until the cement slurry overflows the hole mouth, and the entire hole section above the sand is poured into concrete;

[0101] Formed as Figure 3 The first type of external water level long-term observation hole 2 shown in the figure has a hole depth of about 2m below the bottom of the shield tunnel. A fine sand layer 22 is set at the bottom of the hole. The thickness of the fine sand layer 22 is 10.2m. A first cement slurry layer 23 is set above the fine sand layer 22. Two water pressure gauges are set at different heights in the middle of the fine sand layer 22.

[0102] In this plan, the following matters need to be noted:

[0103] Placing two pressure gauges in each hole reduces the risk of a malfunctioning pressure gauge preventing readings. When both gauges are functioning properly, they can double-check each other, improving data accuracy.

[0104] Considering that the cement particles in the cement slurry will precipitate to a certain extent, the cement consolidation effect in the upper section of the hole may be poor. At this time, re-pouring can be carried out to ensure that the upper cement is poured completely and ensure that the bedrock fissure water in the non-fine sand section enters the hole.

[0105] When calculating the external water pressure level, use a sinusoidal readout to measure the data. According to the conversion formula provided by the sinusoidal readout, obtain the water level elevation, subtract the shield tunnel axis elevation, and obtain the external water pressure head.

[0106] In summary, this application calculates the external water pressure reduction coefficients in different surrounding rock layers by setting up long-term static water level observation holes and external water level observation holes at different surrounding rock levels, thereby obtaining accurate external water pressure reduction coefficients corresponding to the surrounding rock layers. The external water pressure reduction coefficients are then used to calculate the external water level pressure values at the corresponding locations. This improves the accuracy of the external water level pressure calculations, enhances data reliability, reduces construction costs, and ensures construction safety. Therefore, this application effectively overcomes the various shortcomings of the existing technology and has high industrial utilization value.

[0107] The above embodiments are only illustrative of the principles and effects of the present application and are not intended to limit the present application. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed in the present application should still be covered by the protection scope of the present application.

Claims

1. A method for determining the external water pressure of a shield tunnel, characterized in that the steps Including: Determine the static water level line in the longitudinal section of the shield tunnel and the surrounding rock classification of the entire shield tunnel surrounding rock. Specifically, adopt comprehensive exploration means including one or more of geological mapping, drilling, and geophysical exploration to determine the static water level line in the longitudinal section of the shield tunnel and the surrounding rock classification of the entire shield tunnel surrounding rock; Determine the positions of long-term observation holes in different surrounding rock classifications according to the static water level line and set long-term observation holes. Specifically, the long-term observation holes include static water level long-term observation holes and external water level long-term observation holes. Set static water level long-term observation holes and external water level long-term observation holes respectively at the positions of several typical surrounding rocks. The static water level long-term observation holes and external water level long-term observation holes set at the positions of the same typical surrounding rock are spaced at a set distance and are located in the same seepage field of the same hydrogeological unit; Obtain the static water level line and external water pressure water level line during the high water period in different surrounding rock classifications through long-term observation holes. Specifically, observe the static water level during the high water period through the static water level long-term observation holes, and then fit the static water level line during the high water period through the static water levels of multiple high water periods; observe the external water pressure during the high water period through the external water level long-term observation holes, and then fit the external water pressure water level line during the high water period through the external water pressures of multiple high water periods; Calculate the reduction coefficient of the surrounding rock of different classifications according to the static water level line during the high water period and the external water pressure water level line during the high water period; Calculate the external water pressure at different surrounding rock classification locations according to the reduction coefficient of the surrounding rock of different classifications.

2. A method for determining the external water pressure of a shield tunnel according to claim 1, wherein: The setting method of the static water level long-term observation hole specifically includes: drilling a hole with a diameter of 109 mm and a depth reaching 2 m below the bottom of the shield tunnel. Perform hole washing, pumping, and set a steel casing according to the requirements of hydrogeological tests to avoid blockage in the hole caused by caving of the hole wall.

3. A method for determining the external water pressure of a shield tunnel according to claim 1, wherein: The setting method of the external water level long-term observation hole specifically includes: Drilling a hole with a diameter of 400 - 600 mm and a depth reaching 10 - 11 m above the top of the shield tunnel; Using a drill bit with a diameter of 100 - 110 mm to drill to a depth of 1 - 3 m below the bottom of the shield tunnel to finish the hole; Performing hole washing and pumping according to the requirements of hydrogeological tests; Configuring a filter pipe and a riser pipe. The part above the flange is the riser pipe, using a conventional steel casing. The part below the flange is the filter pipe, with a diameter of 90 - 100 mm for both. The hole spacing of the filter holes of the filter pipe is 15 - 25 cm, and adjacent two rows are arranged in a staggered manner. The aperture of the filter holes of the filter pipe is 0.5 - 1.5 cm; Pouring cement slurry from the top of the hole into the outside of the riser pipe until the cement slurry overflows the hole mouth.

4. A method for determining the external water pressure of a shield tunnel according to claim 1, wherein: The setting method of the external water level long-term observation hole specifically includes: Drilling a hole with a diameter of 100 - 110 mm and a depth reaching 1 - 3 m below the bottom of the shield tunnel; Performing hole washing and pumping according to the requirements of hydrogeological tests; Calculating the fine sand body according to the hole diameter and first putting in a 4 m long section of fine sand; Putting in two piezometers, and the two piezometers are arranged in a staggered manner; Putting in fine sand and waiting for the fine sand to settle and stabilize; The cement slurry is poured from the bottom of the hole until the cement slurry overflows the orifice, and the section of the hole above the sandy soil is all cast with concrete.

5. A method for determining the external water pressure of a shield tunnel according to claim 1, characterized in that: Calculating the reduction coefficient β of surrounding rocks of different grades according to the static water level line during the high water period and the external water pressure water level line during the high water period e , specifically including: establishing a calculation formula for the external water pressure reduction coefficient β e : Among them, β e : Reduction coefficient of external water pressure; H w : The pressure head actually acting on the outer surface of the lining structure affected by seepage, i.e., the external water pressure head, in m; H e : The acting head from the groundwater level line to the tunnel center, i.e., the hydrostatic pressure head, m; Calculate the reduction coefficient β of external water pressure according to the formula e .

6. A method for determining the external water pressure of a shield tunnel according to claim 5, characterized in that: The hydrostatic pressure head H e is calculated as follows: Measure the buried depth value of the static water level with a water level gauge, and subtract the buried depth value of the shield tunnel axis to obtain the hydrostatic pressure head H e ; The external water pressure head H w is calculated as follows: measure the buried depth value of the external water level with a water level gauge, and subtract the buried depth value of the shield tunnel axis to obtain the external water pressure head H w .

7. A method for determining the external water pressure of a shield tunnel according to claim 6, characterized in that: The external water pressure at different surrounding rock grades is calculated according to the reduction coefficients of surrounding rocks of different grades, which specifically includes: determining the surrounding rock grade at the position where the external water pressure head needs to be calculated, obtaining the hydrostatic pressure head at the position where the external water pressure head needs to be calculated according to the static water level line, and calculating the external water pressure head at this position according to the following formula: H w = H e × β e Among them, β e : reduction coefficient of external water pressure; H w : The pressure head actually acting on the outer surface of the lining structure affected by seepage, i.e., the external water pressure head, m; H e : The acting head from the groundwater level line to the tunnel center, i.e., the hydrostatic pressure head, m.

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