Construction method of large-diameter shield tunneling in soft soil with low impact through existing high-speed railway subgrade

Abstract

This invention patent belongs to the field of shield engineering construction in soft soil strata, specifically to a construction method for a large-diameter shield in soft soil strata with low impact through an existing high-speed railway subgrade. It solves the problems of extensive grouting, inability to accurately grout the scope, and high grouting costs in the existing technology, and realizes surface directional controlled deep hole grouting, economically solving the surface settlement problem caused by shield tunneling. First, determine the controlled stratum and conduct preliminary process tests, then determine the surface directional controlled deep hole grouting plan; then implement on-site deep hole grouting. After the grouting reinforcement is completed, the shield machine excavates to the reinforced area below the existing high-speed railway subgrade. Finally, the effect of the surface directional controlled deep hole grouting application is evaluated.

Description

Technical Field

[0001] The patent of this invention belongs to the field of shield engineering construction in soft soil strata, and specifically relates to a construction method for a large-diameter shield in soft soil strata with low impact crossing of an existing high-speed railway subgrade. Background Art

[0002] Shield machines are widely used in tunnel construction due to their safety, stability, and efficiency. With the rapid development of my country's high-speed railways, the number of large-diameter shield tunnels passing under existing high-speed railway subgrades is increasing. Most high-speed railway lines do not have underpasses, and shield tunneling is often carried out in the underlying strata. Underpasses can disturb the surrounding soil, inducing ground loss and soil consolidation settlement. High-speed railways generally use ballastless track, which has extremely high requirements for rail deformation. The soil disturbance caused by shield tunneling can reduce the bearing capacity of the upper pile foundation and increase track irregularities. If not properly controlled, this can seriously impact the stability and safety of high-speed railway operations.

[0003] Existing Chinese patents, such as patent application publication number CN 117845659 A, disclose a construction method for an earth pressure shield tunnel under a high-speed railway subgrade. The method includes: Step 1: Determine the track settlement standard for the construction area; Step 2: Determine the construction scope of the earth pressure shield tunnel under the high-speed railway subgrade; Step 3: Survey the geological conditions within the construction area; and Step 4: Grouting and reinforcement of sleeve valve pipes during the high-speed railway's window period. This method meets the requirement that shield tunneling must be conducted between midnight and 4 a.m. daily during railway operations, with shield tunneling suspended during the remaining hours. By utilizing a combination of technologies, including geological radar exploration, micro-motion detection, continuous simulation of equivalent grouting tests during the window period, and preemptive secondary grouting, a method for continuous tunneling under the high-speed railway subgrade has been developed, controlling the maximum track surface settlement within a range of -5 mm to 3 mm, thus ensuring the safe operation of the high-speed railway.

[0004] For example, the invention patent application with publication number CN 115559157 A discloses a method for controlling the vertical deformation of a high-speed railway subgrade during shield tunneling under a high-speed railway. The method includes: assembling a grouting system, arranging a monitoring system, and setting monitoring points; calculating the required elevation of the high-speed railway subgrade surface; burying grouting bags; linking the grouting system with the monitoring system; and controlling the grouting process. The method uses dynamic "sinking and lifting" control to gradually start the grouting equipment. After the shield machine has completely passed through the high-speed railway subgrade and the bag's expansion and lifting effect meets the expected requirements, the non-setting slurry in the bag is replaced with a setting slurry. Once the slurry in the bag solidifies, the active control process ends. Using capsule-type active control technology and a monitoring-grouting construction linkage mechanism, precise, targeted, and directional compensatory lifting grouting is achieved, realizing integrated measurement and control.

[0005] While all of the aforementioned patents utilize grouting technology to mitigate the impact of shield tunneling on high-speed rail operations, they are only applicable to earth pressure shield tunneling and require precise dynamic measurement and control during the tunneling process. These methods employ extensive grouting methods, while existing high-speed rail subgrade reinforcement methods often employ sleeve valve pipe grouting, backward grouting, and MJS reinforcement. These methods suffer from issues such as difficulty controlling the grouting range, lengthy grouting processes, and complex construction procedures. They are also unable to achieve precise grouting reinforcement and are costly. Summary of the Invention

[0006] The present invention provides a construction method for a large-diameter shield machine to cross an existing high-speed railway subgrade in a soft soil layer with low impact, which solves the problems of extensive grouting, inability to accurately grout the scope, and high grouting cost in the prior art, realizes directional controlled deep-hole grouting on the surface, and economically solves the problem of surface settlement caused by the shield machine going under.

[0007] The present invention is achieved through the following technical solutions:

[0008] A construction method for a large-diameter shield tunnel in soft soil with low impact through an existing high-speed railway subgrade comprises the following steps:

[0009] S1. Determine the controlling strata and conduct preliminary tests on the processability;

[0010] S1.1. Determine the controlling stratum for deep hole grouting;

[0011] According to the requirements of track flatness required for existing high-speed railway operations, the control value of vertical deformation at any point on the ground surface within the grouting range is determined. d 0, calculate the shallowest grouting depth in the formation h 0, select the shallowest grouting depth h Deep hole grouting is carried out in the soft soil layer below 0, and the thickness of the soft soil layer is z s ;

[0012] Then, the same stratum as the grouting reinforcement area is selected to conduct a preliminary test of the process to determine the grouting parameters;

[0013] S2. Determine the surface directional controlled deep hole grouting scheme;

[0014] S2.1. Determine the grouting orientation: Consider the on-site environmental conditions and determine whether to grout on one side or on both sides. The distance between the drill hole and the railway should be greater than the tunnel diameter. D 1.2 times;

[0015] S2.2. Determine the scope of surface directional controlled deep hole grouting;

[0016] Through theoretical calculation and numerical simulation, the effects of grouting reinforcement under different depths, lengths and widths were analyzed to determine the specific scope of this surface directional controlled deep hole grouting reinforcement.

[0017] S2.3. Determine the surface drilling location;

[0018] According to the grouting orientation obtained in step S2.1 and the grouting range obtained in step S2.2, determine the horizontal inclination angle and spacing of the grouting holes, the ground opening method, and the overlap method;

[0019] S3: Implement on-site deep hole grouting. After the grouting reinforcement is completed, the shield machine excavates to the reinforced area below the existing high-speed railway foundation;

[0020] S4. Evaluation of the effectiveness of surface directional controlled deep hole grouting.

[0021] Furthermore, in step S2.2, determining the surface directional controlled deep hole grouting range includes the following steps:

[0022] First, calculate the ground deformation caused by the shield tunneling without grouting reinforcement;

[0023] Define the length direction of the high-speed railway subgrade as the x direction, the tunnel centerline direction as the y direction, the stratum thickness direction as the z direction, and the settlement control value specified in the specification S ( x S ) is the control value of the settlement state in step S1.1 d 0;

[0024] According to the settlement control value specified in the specification S ( x S ), the settlement risk distance along the existing high-speed railway line is obtained; the reinforcement length formula for deep hole grouting technology in the stratum is:

[0025] x S = x S左 + x S右 ,

[0026] in, x S左 It means that the calculated settlement value is greater than or equal to the settlement control value S ( x S ) is the distance value to the left half of the tunnel center axis.

[0027] x S右 It means that the calculated settlement value is greater than or equal to the settlement control value S ( x S ) is the distance to the right half of the tunnel central axis;

[0028] Secondly, calculate the distance of deep hole grouting along the direction of large diameter shield tunneling to obtain the reinforcement width required by deep hole grouting technology y s ;

[0029] Again, depending on the depth h 0 below the thickness of the selected weak stratum z s , reinforcement length x S , reinforcement width y s , the volume of the grouting reinforcement area can be obtained V , and then calculate the total grouting volume of the construction in order to calculate the economic cost;

[0030] Finally, a numerical model was established to calculate the shield tunneling and verify the reliability and cost performance of the reinforcement of the control area stratum. h 0 below the selected weak strata and their thickness z s , to compare the reliability and cost-effectiveness of different reinforcement schemes, and obtain the optimal range of this surface directional controlled deep hole grouting reinforcement.

[0031] Furthermore, in step S1.1, when determining the control value of the vertical deformation of any point on the ground surface within the grouting range, d 0, the shallowest grouting depth h 0 is calculated by the following formula:

[0032]

[0033] in, d Z is the vertical deformation value of any point on the surface; q is the grouting volume per unit time; t is the grouting time; β It is the angle between the line connecting any point on the ground surface and the center of the slurry outlet and the vertical plane; h is the depth of the slurry outlet; a is the radius of the spherical pulp bubble formed at the pulp outlet.

[0034] Furthermore, in step S2.2,

[0035] First, calculate the ground deformation caused by the shield tunneling without grouting reinforcement. The calculation is as follows:

[0036]

[0037]

[0038]

[0039] in, S ( x ) is the distance from the tunnel center axis x Surface settlement value at distance; V L is the loss rate of soil, the loss rate of clay soil is 0.5%~2%, and the loss rate of sandy soil is less than 0.5%; D is the tunnel diameter; i is the width coefficient of the sedimentation tank; i 粘性 is the width coefficient of the settlement trough in cohesive soil; i 砂性 is the width coefficient of the settlement trough in sandy soil; H The depth of the tunnel.

[0040] Furthermore, in step S2.2, the reinforcement width y s The calculation process is as follows:

[0041]

[0042] in, y s The reinforcement width that requires deep hole grouting technology; α is the safety control coefficient, and in soft soil layer α ≥2; L It is the width of the existing high-speed railway subgrade.

[0043] Furthermore, in step S2.2, the calculation process of the total grouting volume is as follows:

[0044]

[0045] Among them, Σ Q is the total grouting volume; n The porosity (fracture degree) of the formation is 2% to 5% for fracture zones, 10% to 20% for fault fracture zones, and 30% to 40% for sand layers, filled caves, and karst development zones. α is the filling rate of stratum voids or cracks, which is taken as 70%~80%; β The slurry loss rate is 5%~20% for fracture zones and fault fracture zones, and 10%~20% for sand layers, filled caves and karst development zones.

[0046] Furthermore, in step S1, selecting the same stratum as the grouting reinforcement area for a preliminary test of processability to determine grouting parameters includes the following steps:

[0047] S1.2, Drilling positioning: Locate and position according to the design. Each drilling rig must be equipped with a ruler and angle measuring tools;

[0048] S1.3. Selection of grouting materials: Ordinary Portland cement single slurry and cement-water glass double slurry are used as grouting materials, and early strength HPC admixture is added to the single slurry ratio;

[0049] S1.4. Drilling and grouting casing material: Based on the information that the shield machine will pass through the existing high-speed railway line in the orthogonal direction and require reinforcement of the stratum, the depth of the pre-test drilling hole is set, and grouting holes are drilled using Φ146 mm casing, and casing material is poured;

[0050] After solidification, the casing material must be able to be crushed by hand, so that the casing material solid body can be squeezed open under the grouting pressure in the stratum. The weight ratio of the components of the casing material is water: Portland cement: sodium bentonite = 2.5:1:1.5;

[0051] S1.5, sleeve valve pipe installation: When the hole is completed, after withdrawing the drill rod, start installing the PVC sleeve valve pipe with an inner diameter of 66 mm and a wall thickness of 5 mm and a Φ20 mm PE pipe for injecting the shell material;

[0052] Before lowering the pipe, check in advance whether the inner wall of the pipe is smooth, whether there are any debris in the pipe, and whether the sealing of the sleeve valve pipe rubber position is intact and without any damage. When connecting the sleeve valve pipe, apply PVC glue to the interface and wrap it firmly with tape;

[0053] The drilling depth, angle, and sleeve valve pipe installation quality must be controlled by a dedicated person; the drilling rig should not be placed too far away so that when the hole is unqualified or there is an abnormality such as a collapsed hole, the hole can be repaired in time;

[0054] S1.6. Determine the grouting parameters: the mix ratio of ordinary cement single-liquid slurry is water: cement = 0.8~1.1:1, the mix ratio of cement-water glass two-liquid slurry is water: cement = 0.8:1~1.1, and the volume ratio of cement: water glass = 1:1; the grouting pressure is 2~3 MPa.

[0055] Furthermore, in step S3, the implementation of on-site deep hole grouting includes the following steps:

[0056] S3.1. Site Leveling: Before the equipment is brought into the site, the site must be leveled and paved, the working area must be marked and repeatedly compacted, and a mud box or sedimentation tank must be set up;

[0057] S3.2, Pile Position Stakeout: After the hole positions are laid out at fixed points, the construction axis is measured and laid out according to the design drawings and coordinate grid points. After the line is verified to be qualified, the hole positions to be drilled are re-measured; the hole positions are determined on the construction axis, and the pile numbers, hole numbers, and serial numbers are assigned. The ground elevation of each hole opening is measured based on the benchmark points.

[0058] S3.3 Drilling: Use a multi-functional drilling rig to drill holes on the ground at the marked hole location and the designed inclination angle. Use Φ146 casing to follow the drilling. The horizontal deviation of the hole location should be ≤ 2 cm. At the same time, the front end of the drill rig holder should be pressed against the ground to prevent fluctuations in the drilling inclination angle.

[0059] S3.4. Install the directional control grouting pipe: When the hole is completed, withdraw the drill rod and begin installing the 66 mm inner diameter, 5 mm wall thickness PVC sleeve valve pipe and the 20 mm PE pipe. Check them thoroughly before installing them. When connecting the sleeve valve pipe, apply PVC glue to the joint and wrap it securely with tape.

[0060] S3.5. Inject casing material: After the sleeve valve tube is lowered into the hole, inject casing material through a 20 mm PE tube until the mud returns through the borehole orifice;

[0061] S3.6 Grouting reinforcement construction: adopt backward segmented grouting, that is, grouting starts from the bottom of the grouting hole and proceeds upward. Each grouting section is 1.0 m long. After the first grouting section is completed, the grouting core pipe is withdrawn and the second grouting section is carried out until the entire grouting reinforcement section is completed.

[0062] S3.7. Sealing and clearing the site: After the grouting is completed, the sleeve valve pipe is no longer used, and cement mortar with a water-cement ratio of 0.6:1 is slowly injected into the hole to seal the grouting hole.

[0063] Furthermore, in step S4, the evaluation of the effect of the surface directional controlled deep hole grouting application includes the following steps:

[0064] S4.1. Evaluation of grouting effect: Comprehensively adopt the P - Q - t Evaluation is carried out using the change analysis method (, inspection hole coring method after grouting reinforcement is completed, and cross-hole CT method for in-situ testing of grouting positions);

[0065] S4.2. On-site monitoring feedback after the large-diameter shield tunnel passes under the Shanghai-Nanjing Intercity High-Speed ​​Railway: Real-time monitoring is carried out on site during the large-diameter shield tunnel passes under the Shanghai-Nanjing Intercity High-Speed ​​Railway.

[0066] Compared with the prior art, the present invention has the following beneficial effects:

[0067] 1. Unlike the currently popular extensive grouting method, the above-mentioned low-impact construction method for large-diameter shield tunneling through existing high-speed railway subgrades in soft soil layers achieves surface directional controlled deep-hole grouting through scientific calculations and theoretical derivation. This allows for precise grouting reinforcement of soft soil layers, ensuring both the reliability of ground reinforcement and the economic efficiency of construction costs. Through comprehensive evaluation using multiple methods, the low-impact construction method for large-diameter slurry shield tunneling through existing high-speed railway subgrades in soft soil layers has been achieved.

[0068] 2. The above-mentioned construction method for low-impact large-diameter shield tunneling through existing high-speed railway subgrades in soft soil layers achieves surface directional controlled deep-hole grouting, enabling precise grouting reinforcement of soft soil layers. This method is highly reliable in reducing the impact of large-diameter slurry shield tunneling under existing high-speed railways.

[0069] 3. Aiming at the defects of possible errors in single method evaluation, a comprehensive evaluation method is adopted in the grouting process. P - Q - t Evaluation is carried out using the change analysis method, the inspection hole coring method after the grouting reinforcement is completed, and the cross-hole CT method for in-situ testing of the grouting position to ensure that the evaluation effect after grouting is true and accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 This is a flow chart of the construction method for low-impact crossing of an existing high-speed railway subgrade by a large-diameter shield tunnel in soft soil according to the present invention;

[0071] Figure 2 This is a schematic diagram of the longitudinal section of the surface directional controlled deep hole grouting reinforcement according to the present invention;

[0072] In the figure: 1. Shield tunnel, 2. Existing high-speed railway foundation, 3. Control area. DETAILED DESCRIPTION

[0073] In order to more clearly understand the features of the present invention, the present invention will be further described below with reference to the accompanying drawings and embodiments. The following description sets forth numerous specific details to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways than those described herein. Therefore, the specific embodiments disclosed below are not intended to limit the present invention.

[0074] Taking the tunnel passing vertically through the high-speed railway subgrade from the soft soil layer as an example, the length direction of the high-speed railway subgrade is defined as the x direction, the tunnel axis direction is defined as the y direction, and the thickness direction of the stratum is defined as the z direction. Figure 1 As shown, this embodiment discloses a construction method for a large-diameter shield tunnel in a soft soil layer with low impact through an existing high-speed railway subgrade, comprising the following steps:

[0075] Step S1: determine the control area stratum and conduct preliminary test of processability;

[0076] S1.1. Determine the controlling stratum for deep hole grouting;

[0077] Pre-grouting reinforcement of the ground before the shield tunneling may cause surface uplift. According to the requirements of track flatness required for existing high-speed railway operations, the control value of vertical deformation at any point on the ground within the grouting range is determined. d 0, and then calculate the shallowest depth of grouting in the formation h 0;

[0078] In this step, the control value d The value of 0 is determined based on practical experience. For example, high-speed rail operators specify a deformation value of less than 5 mm based on the geological conditions of a specific construction section (for example, soft soil that is sensitive to construction disturbance). The shield tunneling operator then determines whether 5 mm is acceptable based on past construction experience and data. (For example, in extremely shallow overburden situations, construction can easily cause surface deformation of 5 mm. In such cases, adopting this value would require increased investment in reinforcement and other technical support. If the cost is too high, detours or a new safety control value may be considered.) Once 5 mm is determined, it is multiplied by a safety factor (for example, 0.8), resulting in a control value of 5 * 0.8 = 4.

[0079] When determining the control value of vertical deformation at any point on the ground within the grouting range d 0, the shallowest grouting depth h 0 is calculated by the following formula:

[0080]

[0081] in, d Z is the vertical deformation value of any point on the surface; q is the grouting volume per unit time; t is the grouting time; β It is the angle between the line connecting any point on the ground surface and the center of the slurry outlet and the vertical plane; h is the depth of the slurry outlet; a is the radius of the spherical slurry bubble formed at the slurry outlet. In this embodiment, the radius of the spherical slurry bubble formed by grouting using a sleeve valve tube is about 0.5-2 m;

[0082] Choose the shallowest grouting depth h Deep hole grouting is carried out in the soft soil layer below 0, with a thickness of z s ;

[0083] S1.2, Drilling positioning: Locate and position according to the design. Each drilling rig must be equipped with a ruler and angle measuring tools;

[0084] S1.3. Selection of grouting materials: Ordinary Portland cement single slurry and cement-water glass double slurry are used as grouting materials. Early strength HPC admixtures can be added to the single slurry mix.

[0085] S1.4. Drilling and grouting casing material: Based on the information that the shield machine will pass through the existing high-speed railway line in the orthogonal direction and require reinforcement of the stratum, the depth of the pre-test drilling hole is set, and grouting holes are drilled using Φ146 mm casing, and casing material is poured;

[0086] After solidification, the casing material must be able to be crushed by hand, so that the casing material solid body can be squeezed open under the grouting pressure in the stratum. The weight ratio of the components of the casing material is water: Portland cement: sodium bentonite = 2.5:1:1.5;

[0087] S1.5, sleeve valve pipe installation: When the hole is completed, after withdrawing the drill rod, start installing the PVC sleeve valve pipe with an inner diameter of 66 mm and a wall thickness of 5 mm and a Φ20 mm PE pipe for injecting the shell material;

[0088] Before lowering the pipe, check in advance whether the inner wall of the pipe is smooth, whether there is any debris in the pipe, and whether the sealing of the sleeve valve pipe rubber position is intact and without any damage. When connecting the sleeve valve pipe, apply PVC glue to the interface and wrap it firmly with tape;

[0089] The drilling depth, angle, and sleeve valve pipe installation quality must be controlled by a dedicated person; the drilling rig should not be placed too far away so that when the hole is unqualified or there is an abnormality such as a collapsed hole, the hole can be repaired in time;

[0090] S1.6. Determine the grouting parameters: the mix ratio of ordinary cement single-liquid slurry is water: cement = 0.8~1.1:1, the mix ratio of cement-water glass two-liquid slurry is water: cement = 0.8:1~1.1, and the volume ratio of cement: water glass = 1:1; the grouting pressure is 2~3 MPa.

[0091] Step S2: Determine the surface directional controlled deep hole grouting scheme:

[0092] S2.1. Determine the grouting orientation: Considering the on-site environmental conditions, there is another freight railway 50 m south of the high-speed railway to be reinforced by grouting in this embodiment. Based on experience, the solution of grouting on both sides of the road is not selected. Instead, a single-side grouting solution is selected. Single-side oblique deep hole grouting reinforcement is carried out on the north side of the existing high-speed railway. To ensure that the grouting drilling operation does not affect the daily operation of the existing high-speed railway, the distance between the drilling hole and the railway should be greater than the tunnel diameter. D 1.2 times;

[0093] S2.2. Determine the scope of surface directional controlled deep hole grouting;

[0094] Through theoretical calculation and numerical simulation, the effects of grouting reinforcement under different depths, lengths and widths were analyzed to determine the specific scope of this surface directional controlled deep hole grouting reinforcement.

[0095] First, calculate the ground deformation caused by the shield tunneling without grouting reinforcement. The specific calculation is as follows:

[0096]

[0097]

[0098]

[0099] in, S ( x ) is the distance from the tunnel center axis x Surface settlement value at distance; V L is the loss rate of soil, the loss rate of clay soil is 0.5%~2%, and the loss rate of sandy soil is less than 0.5%; D is the tunnel diameter; i is the width coefficient of the sedimentation tank; i 粘性 is the width coefficient of the settlement trough in cohesive soil; i 砂性 is the width coefficient of the settlement trough in sandy soil; H The depth of the tunnel;

[0100] Settlement control value specified in the specification S ( x S ) is the control value of the settlement state in step S1.1 d 0; According to the settlement control value specified in the specification S ( x S ) can be used to calculate the settlement risk distance along the existing high-speed railway line, that is, the length of the stratum that needs to be reinforced by deep hole grouting technology is x S = x S左 + x S右 ,

[0101] in x S左 It means that the calculated settlement value is greater than or equal to the settlement control value S ( x S ) is the distance value to the left half of the tunnel center axis. x S右 Similarly, x S右 It means that the calculated settlement value is greater than or equal to the settlement control value S ( x S ) is the distance to the right half of the tunnel central axis;

[0102] Secondly, calculate the distance required for deep hole grouting along the direction of the large-diameter shield tunneling, that is, the distance required for grouting perpendicular to the existing high-speed railway line. The specific calculation is as follows:

[0103]

[0104] in,y s The width that needs to be reinforced with deep hole grouting technology; α is the safety control coefficient, and in soft soil layer α ≥2; L is the width of the existing railway subgrade;

[0105] Again, depending on the depth h 0 below the thickness of the selected weak stratum z s , reinforcement length x S , reinforcement width y s , the volume of the grouting reinforcement area can be obtained V , and then calculate the total grouting volume of the construction in order to calculate the economic cost, as follows:

[0106]

[0107] Among them, Σ Q is the total grouting volume; n The porosity (fracture degree) of the formation is 2% to 5% for fracture zones, 10% to 20% for fault fracture zones, and 30% to 40% for sand layers, filled caves, and karst development zones. α is the filling rate of stratum voids or cracks, which is taken as 70%~80%; β is the slurry loss rate, which is 5% to 20% for fracture zones and fault fracture zones, and 10% to 20% for sand layers, filled caves, and karst development zones;

[0108] Finally, a numerical model was established using ABAQUS software to perform shield tunneling calculations to verify the reliability and cost-effectiveness of the reinforcement of the controlled strata. h 0 below the selected weak strata and their thickness z s , to compare the reliability and cost-effectiveness of different reinforcement schemes, and obtain the optimal range of this surface directional controlled deep hole grouting reinforcement.

[0109] In this embodiment, if Figure 2 As shown in the figure, in the stratum below the existing high-speed railway foundation 2, the optimal control area 3 is located above the shield tunnel 1 and two meters away from the tunnel top, in a cubic area with a length of 100 m, a width of 40 m, and a thickness of 10 m (i.e., the thickness of the 8-2 silty clay layer);

[0110] S2.3. Determine the horizontal inclination angle and spacing of the grouting holes, the ground opening method, and the overlap method based on the grouting orientation obtained in step S2.1 and the grouting range obtained in step S2.2;

[0111] The horizontal inclination angle of the grouting boreholes was determined to be 42°~83°. Multiple rows of holes were drilled on the ground, with overlapping holes arranged in a triangular plum blossom shape, with a horizontal spacing of 1.6 m, a vertical spacing of 1.6 m, and a diffusion radius of 1.0 m. Cement-water-glass two-liquid slurry was used in the peripheral holes, and ordinary cement single-liquid slurry was used in the middle holes.

[0112] Step S3: Implement on-site deep hole grouting:

[0113] S3.1. Site Leveling: Before the equipment is brought into the site, the site must be leveled and paved, the working area must be marked and repeatedly compacted, and a mud box or sedimentation tank must be set up;

[0114] S3.2, Stake Position Stakeout: Complete the hole positions at fixed points, measure and lay out the construction axis according to the design drawings and coordinate grid points, and re-measure the planned hole positions after the line is verified to be qualified. Determine the hole positions on the construction axis, assign pile numbers, hole numbers, and sequence numbers, and measure the ground elevation of each hole opening based on the benchmark. Horizontal hole spacing is 1.6 m, with row spacing of 0.4 m between rows 1-28 (3.3 m between rows 1-15 and 16-28). Hole position deviation must not exceed 50 mm.

[0115] S3.3 Drilling: Use a multi-functional drilling rig to drill holes into the ground at the designated hole locations and the designed angle. Use Φ146 casing for follow-up drilling. The horizontal deviation of the hole location should be ≤ 2 cm. The front end of the drill rig holder should be pressed against the ground to prevent fluctuations in the drilling angle. Drill rigs and drilling areas should be numbered, with rig #1 corresponding to drilling area ①, rig #2 corresponding to drilling area ②, and so on. After drilling is completed, remove the drill and clean the hole.

[0116] Drilling sequence and skip hole principle:

[0117] ① In the first step, the holes on the four peripheral lines are drilled, namely: 1-1, 2-1, 3-1...27-1, 28-1, 29-1; 29-2, 29-3, 29-4...29-61, 29-62, 29-63; 28-63, 27-63, 26-63...3-63, 2-63, 1-63; 1-62, 1-61, 1-60...1-4, 1-3, 1-2, and the curtain is formed by double-liquid slurry sealing;

[0118] ② In the second step, drill the holes in single sequence: 3 rows, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27 rows, and then drill the holes in double sequence: 2 rows, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28 rows;

[0119] ③ Skip hole principle: Based on the skip row principle in step 2, each row of holes should be drilled at a distance of no less than 4.8 m. Taking the drilling area in zone ① as an example, drill 3-2 → 3-5 → 3-8 → 3-11... and so on;

[0120] S3.4. Install the directional controlled grouting pipe: When the hole is completed, withdraw the drill rod and begin installing a 66 mm inner diameter, 5 mm wall thickness PVC sleeve valve pipe and a 20 mm PE pipe (for the grouting shell material). Before installing, perform a thorough inspection. When connecting the sleeve valve pipe, apply PVC glue to the joint and secure it with tape.

[0121] S3.5. Inject casing material: After the sleeve valve tube is lowered into the hole, inject casing material through a 20 mm PE tube until the mud returns through the borehole orifice;

[0122] S3.6 Grouting reinforcement construction: adopt backward segmented grouting, that is, grouting starts from the bottom of the grouting hole and proceeds upward. Each grouting section is 1.0 m long. After the first grouting section is completed, the grouting core pipe is withdrawn and the second grouting section is carried out until the entire grouting reinforcement section is completed.

[0123] S3.7. Sealing and clearing the site: After grouting is completed, the sleeve valve pipe is no longer used, and cement mortar with a water-cement ratio of 0.6:1 is slowly injected into the hole to seal the grouting hole;

[0124] After the grouting reinforcement is completed and the shield machine excavates to the reinforcement area below the existing high-speed railway subgrade, targeted compensatory grouting will be carried out according to the changes in the ground surface and the existing subgrade;

[0125] S4. Evaluation of the effect of surface directional controlled deep hole grouting application:

[0126] S4.1. After the grouting reinforcement construction is completed for the tunnel under the high-speed railway project according to the above method and steps, the grouting effect is evaluated: the single method evaluation may have errors, and the comprehensive evaluation of the grouting process is adopted. P - Q - t Variation analysis method (grouting pressure P , grouting speed Q ,time t ), the inspection hole coring method after the grouting reinforcement is completed, and the cross-hole CT method for in-situ testing of the grouting position;

[0127] Record the grouting process at different time points P - Q - t The changes were evaluated, and some of the results are as follows:

[0128]

[0129] After grouting is completed, inspection holes are set up, with a number of 3% to 5% of the number of grouting holes and no less than 3. The strength of the inspection holes is evaluated by observation and core sampling. Some of the results are as follows:

[0130]

[0131] By using seismic wave CT geophysical exploration technology, the seismic wave velocity changes before and after grouting were compared and analyzed to judge the grouting effect.

[0132] The specific settings are as follows:

[0133]

[0134] In the detection area, the seismic wave velocity ranged from 1820 m / s to 2020 m / s before grouting and from 1820 m / s to 2300 m / s after grouting. Within the 30-42 m range in the borehole (28.5-40 m below the surface), the seismic wave velocity remained basically unchanged before and after grouting. Within the 42-55 m range in the borehole (40-52 m below the surface), the seismic wave velocity after grouting increased by 100-200 m / s compared with that before grouting. In other words, the vertical seismic wave velocity gradually increased with increasing burial depth, while the horizontal seismic wave velocity changed little.

[0135] S4.2. On-site monitoring feedback after the large-diameter shield machine passed under the high-speed railway: Real-time monitoring was carried out on site during the large-diameter shield machine's passage under the high-speed railway. 30 m after the shield machine left the railway, no settlement of the existing roadbed occurred, and some parts slightly uplifted, but within the control range. As the shield machine left, the surface gradually recovered.

Claims

1. A construction method for a large-diameter shield tunnel in soft soil to cross an existing high-speed railway subgrade with low impact, characterized in that: The following steps are involved: S1. Determine the controlling strata and conduct preliminary tests on the processability; S1.

1. Determine the controlling stratum for deep hole grouting; According to the requirements of track flatness required for existing high-speed railway operations, the control value of vertical deformation at any point on the ground surface within the grouting range is determined. δ 0, calculate the shallowest grouting depth in the formation h 0, select the shallowest grouting depth h Deep hole grouting is carried out in the soft soil layer below 0, and the thickness of the soft soil layer is z s ; Then, the same stratum as the grouting reinforcement area is selected to conduct a preliminary test of the process to determine the grouting parameters; S2. Determine the surface directional controlled deep hole grouting scheme; S2.

1. Determine the grouting orientation: Consider the on-site environmental conditions and determine whether to grout on one side or on both sides. The distance between the drill hole and the railway should be greater than the tunnel diameter. D 1.2 times; S2.

2. Determine the scope of surface directional controlled deep hole grouting; Through theoretical calculation and numerical simulation, the effects of grouting reinforcement under different depths, lengths and widths were analyzed to determine the specific scope of this surface directional controlled deep hole grouting reinforcement. Determining the scope of surface directional controlled deep hole grouting includes the following steps: First, calculate the ground deformation caused by the shield tunneling without grouting reinforcement; Define the length direction of the high-speed railway subgrade as the x direction, the tunnel centerline direction as the y direction, the stratum thickness direction as the z direction, and the settlement control value specified in the specification S ( x S ) is the control value of the settlement state in step S1.1 δ 0; According to the settlement control value specified in the specification S ( x S ), the settlement risk distance along the existing high-speed railway line is obtained; the reinforcement length formula for deep hole grouting technology in the stratum is: x S = x S左 + x S右 ， in, x S左 It means that the calculated settlement value is greater than or equal to the settlement control value S ( x S ) is the distance value to the left half of the tunnel center axis. x S右 It means that the calculated settlement value is greater than or equal to the settlement control value S ( x S ) is the distance to the right half of the tunnel central axis; Secondly, calculate the distance of deep hole grouting along the direction of large diameter shield tunneling to obtain the reinforcement width required by deep hole grouting technology y s ; Again, depending on the depth h 0 below the thickness of the selected weak stratum z s , reinforcement length x S , reinforcement width y s , the volume of the grouting reinforcement area can be obtained V , and then calculate the total grouting volume of the construction in order to calculate the economic cost; Finally, a numerical model was established to calculate the shield tunneling and verify the reliability and cost performance of the reinforcement of the control area stratum. h 0 below the selected weak strata and their thickness z s , to compare the reliability and cost-effectiveness of different reinforcement schemes and obtain the optimal range of this surface directional controlled deep hole grouting reinforcement; S2.

3. Determine the surface drilling location; According to the grouting orientation obtained in step S2.1 and the grouting range obtained in step S2.2, determine the horizontal inclination angle and spacing of the grouting holes, the ground opening method, and the overlap method; S3: Implement on-site deep hole grouting. After the grouting reinforcement is completed, the shield machine excavates to the reinforced area below the existing high-speed railway foundation; S4. Evaluation of the effectiveness of surface directional controlled deep hole grouting.

2. The method for low-impact crossing of an existing high-speed railway subgrade by a large-diameter shield in soft soil according to claim 1 is characterized in that: In step S1.1, when determining the control value of vertical deformation of any point on the ground surface within the grouting range δ 0, the shallowest grouting depth h 0 is calculated by the following formula: in, δ Z is the vertical deformation value of any point on the surface; q is the grouting volume per unit time; t is the grouting time; β It is the angle between the line connecting any point on the ground surface and the center of the slurry outlet and the vertical plane; h is the depth of the slurry outlet; a is the radius of the spherical pulp bubble formed at the pulp outlet.

3. The method for low-impact construction of a large-diameter shield tunnel through an existing high-speed railway subgrade in soft soil according to claim 1 is characterized in that: In step S2.2, First, calculate the ground deformation caused by the shield tunneling without grouting reinforcement. The calculation is as follows: in, S ( x ) is the distance from the tunnel center axis x Surface settlement value at distance; V L is the loss rate of soil, the loss rate of clay soil is 0.5%~2%, and the loss rate of sandy soil is less than 0.5%; D is the tunnel diameter; i is the width coefficient of the sedimentation tank; i 粘性 is the width coefficient of the settlement trough in cohesive soil; i 砂性 is the width coefficient of the settlement trough in sandy soil; H The depth of the tunnel.

4. The method for low-impact construction of a large-diameter shield tunnel through an existing high-speed railway subgrade in soft soil according to claim 3 is characterized in that: In step S2.2, the reinforcement width y s The calculation process is as follows: in, y s The reinforcement width that requires deep hole grouting technology; α is the safety control coefficient, and in soft soil layer α ≥2; L It is the width of the existing high-speed railway subgrade.

5. The method for low-impact large-diameter shield tunneling through an existing high-speed railway subgrade in soft soil according to claim 3 is characterized in that: In step S2.2, the calculation process of the total grouting volume is as follows: Among them, Σ Q is the total grouting volume; n The porosity (fracture degree) of the formation is 2% to 5% for fracture zones, 10% to 20% for fault fracture zones, and 30% to 40% for sand layers, filled caves, and karst development zones. α is the filling rate of stratum voids or cracks, which is taken as 70%~80%; β The slurry loss rate is 5%~20% for fracture zones and fault fracture zones, and 10%~20% for sand layers, filled caves and karst development zones.

6. The method for low-impact construction of a large-diameter shield tunnel through an existing high-speed railway subgrade in soft soil according to claim 1 is characterized in that: In step S1, the same stratum as the grouting reinforcement area is selected for a preliminary test of processability to determine grouting parameters, including the following steps: S1.2, Drilling positioning: Locate and position according to the design. Each drilling rig must be equipped with a ruler and angle measuring tools; S1.

3. Selection of grouting materials: Ordinary Portland cement single slurry and cement-water glass double slurry are used as grouting materials, and early strength HPC admixture is added to the single slurry ratio; S1.

4. Drilling and grouting casing material: Based on the information that the shield machine will pass through the existing high-speed railway line in the orthogonal direction and require reinforcement of the stratum, the depth of the pre-test drilling hole is set, and grouting holes are drilled using Φ146 mm casing, and casing material is poured; After solidification, the casing material must be able to be crushed by hand, so that the casing material solid body can be squeezed open under the grouting pressure in the stratum. The weight ratio of the components of the casing material is water: Portland cement: sodium bentonite = 2.5:1:1.5; S1.5, sleeve valve pipe installation: When the hole is completed, after withdrawing the drill rod, start installing the PVC sleeve valve pipe with an inner diameter of 66 mm and a wall thickness of 5 mm and a Φ20 mm PE pipe for injecting the shell material; Before lowering the pipe, check in advance whether the inner wall of the pipe is smooth, whether there are any debris in the pipe, and whether the sealing of the sleeve valve pipe rubber position is intact and without any damage. When connecting the sleeve valve pipe, apply PVC glue to the interface and wrap it firmly with tape; The drilling depth, angle, and sleeve valve pipe installation quality must be controlled by a dedicated person; the drilling rig should not be placed too far away so that when the hole is unqualified or there is an abnormal hole collapse, it can be repaired in time; S1.

6. Determine the grouting parameters: the mix ratio of ordinary cement single-liquid slurry is water: cement = 0.8~1.1:1, the mix ratio of cement-water glass two-liquid slurry is water: cement = 0.8:1~1.1, and the volume ratio of cement: water glass = 1:1; the grouting pressure is 2~3 MPa.

7. The method for low-impact crossing of an existing high-speed railway subgrade through a large-diameter shield in soft soil according to any one of claims 1 to 6, characterized in that: In step S3, the implementation of on-site deep hole grouting includes the following steps: S3.

1. Site Leveling: Before the equipment is brought into the site, the site must be leveled and paved, the working area must be marked and repeatedly compacted, and a mud box or sedimentation tank must be set up; S3.2, Pile Position Stakeout: After the hole positions are laid out at fixed points, the construction axis is measured and laid out according to the design drawings and coordinate grid points. After the line is verified to be qualified, the hole positions to be drilled are re-measured; the hole positions are determined on the construction axis, and the pile numbers, hole numbers, and serial numbers are assigned. The ground elevation of each hole opening is measured based on the benchmark points. S3.3 Drilling: Use a multi-functional drilling rig to drill holes on the ground at the marked hole location and the designed inclination angle. Use Φ146 casing to follow the drilling. The horizontal deviation of the hole location should be ≤ 2 cm. At the same time, the front end of the drill rig holder should be pressed against the ground to prevent fluctuations in the drilling inclination angle. S3.

4. Install the directional control grouting pipe: When the hole is completed, withdraw the drill rod and begin installing the 66 mm inner diameter, 5 mm wall thickness PVC sleeve valve pipe and 20 mm PE pipe. Check them thoroughly before installing them. When connecting the sleeve valve pipe, apply PVC glue to the joint and wrap it securely with tape. S3.

5. Inject casing material: After the sleeve valve tube is lowered into the hole, inject casing material through a 20 mm PE tube until the mud returns through the borehole orifice; S3.6 Grouting reinforcement construction: adopt backward segmented grouting, that is, grouting starts from the bottom of the grouting hole and proceeds upward. Each grouting section is 1.0 m long. After the first grouting section is completed, the grouting core pipe is withdrawn and the second grouting section is carried out until the entire grouting reinforcement section is completed. S3.

7. Sealing and clearing the site: After the grouting is completed, the sleeve valve pipe is no longer used, and cement mortar with a water-cement ratio of 0.6:1 is slowly injected into the hole to seal the grouting hole.

8. The method for low-impact large-diameter shield tunneling through an existing high-speed railway subgrade in soft soil according to claim 7 is characterized in that: In step S4, the evaluation of the effect of the surface directional controlled deep hole grouting application includes the following steps: S4.

1. Evaluation of grouting effect: Comprehensively adopt the P - Q - t Evaluation was conducted using the change analysis method, the inspection hole coring method after grouting reinforcement was completed, and the cross-hole CT method for in-situ testing of the grouting position; S4.

2. On-site monitoring feedback after the large-diameter shield tunnel passes under the Shanghai-Nanjing Intercity High-Speed ​​Railway: Real-time monitoring is carried out on site during the large-diameter shield tunnel passes under the Shanghai-Nanjing Intercity High-Speed ​​Railway.

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