Method for evaluating influence of surface loading effect on existing subway segments
By constructing similar models and conducting experiments, the influence of surface loads on tunnel segments was analyzed. By using the surrounding rock pressure coefficient and displacement zoning table, the safety evaluation problem of sudden surface loads on tunnel structures was solved, and effective safety analysis and protection measures were provided.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-22
- Publication Date
- 2026-03-27
AI Technical Summary
Existing technologies are insufficient to effectively assess the impact of sudden surface loading on existing subway tunnel segments, threatening the safety and stability of the tunnel structure.
A similar model was constructed, and the influence of surface load on the surrounding rock pressure and deformation mode of tunnel segments was statistically analyzed through experiments. The modified surrounding rock pressure acting on the tunnel segments was described by the surrounding rock pressure amplification factor β and the surrounding rock pressure transmission factor η. A four-level displacement influence zoning table was constructed based on rail transit specifications for evaluation.
The study analyzed the impact of surface load on shield tunnel segments under different load amounts, eccentricities, and tunnel burial depths, providing safety evaluation and structural protection measures to reduce potential safety hazards in tunnel structures.
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Figure CN121744448A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of subway segment hazard assessment, and in particular to a method for assessing the impact of surface surcharge on existing subway segments. Background Technology
[0002] As the main load-bearing unit of the tunnel structure, the stability and safety of shield tunnel segments are crucial to the entire project.
[0003] However, in recent years, many shield tunnel structural failure accidents have occurred in China due to sudden ground loading, indicating that sudden ground loading in the vicinity is an important factor threatening the safety of existing shield tunnel structures.
[0004] Ground loading can cause additional stress and deformation in tunnel lining segments, and may even lead to structural damage and failure. Therefore, studying the impact of sudden loading on tunnel lining segments is of great significance for ensuring the safe operation and long-term stability of underground engineering projects.
[0005] Therefore, there is an urgent need for a method to assess the impact of surface surcharge on existing subway segments. Summary of the Invention
[0006] To address the aforementioned issues, this application proposes a method for assessing the impact of surface surcharge on existing subway tunnel segments, comprising the following steps: S1. Construct a similar model based on tunnel segment ring information and collapsible loess information; S2. Conduct experiments based on similar models and collect experimental data. Based on the experimental data, obtain the influence law of surface load on the surrounding rock pressure and deformation mode of tunnel segments. S3, Using the surrounding rock pressure amplification factor β With the pressure transmission coefficient of the surrounding rock η Describes the calculation method for the corrected surrounding rock pressure acting on tunnel segments under surface loading conditions; S4. Based on the shield segment deformation control standard in the rail transit specification, a four-level displacement influence zoning table is constructed, and the impact on tunnel segments under surface loading conditions is evaluated based on experimental data.
[0007] Preferably, the similarity model includes a basic component unit, a loess simulation unit, and a loading monitoring unit; The basic component units include an indoor model test chamber and segment rings; The loess simulation unit includes artificially prepared collapsible loess; The loading monitoring unit includes a hydraulic servo actuator, a pressure plate, an earth pressure gauge, and a displacement gauge.
[0008] Preferably, the indoor model test chamber is made of transparent plexiglass and is supported by three detachable steel supports to maintain its stability. The tube segment ring consists of six tube segments, which are 3D printed from ABS material with an elastic modulus of E=0.86GPa. Each tube segment includes one top block, two adjacent blocks, and three standard blocks. The bolt connection between the tube segments is achieved by binding wire. Preferably, the preparation process of the artificially prepared collapsible loess includes: To obtain the test soil, two undisturbed soil samples were taken every 2 meters. By drilling undisturbed soil samples, disturbed soil samples were taken from several layers in the actual strata. The disturbed loess was spread out, dried, crushed, and sieved to obtain the test soil. Artificial collapsible loess was prepared by adding CaO particles, industrial salt, and gypsum powder to the test soil. Preferably, the hydraulic servo actuator is equipped with three-dimensional gapless joint supports at both ends. The three-dimensional gapless joint supports include several joints connected by flanges. The bearing plate is composed of two pieces of plexiglass and a connecting rod. The upper plexiglass is tightly fastened to the bottom of the actuator, and the lower plexiglass is placed on the soil surface. The displacement gauges are installed inside the middle ring of the tunnel to measure the vertical convergence displacement and the lateral convergence displacement respectively. The earth pressure gauge is installed outside the segment ring to monitor the earth pressure at the arch crown, arch bottom, left and right arch shoulders, left and right arch waists, and left and right arch feet.
[0009] Preferably, the specific content of the influence law of surface load on the surrounding rock pressure and deformation mode of tunnel segments in S2 includes the mechanical response law of the superload on the existing subway segments, the mechanical response law of the load location on the existing subway segments, and the mechanical response law of the load burial depth on the existing subway segments. The mechanical response law of the superstructure load on the existing subway tunnel segments is as follows: As the value of the upper load P increases, the confining pressure at the measuring point increases, and the distribution of the confining pressure change at the measuring point shows a symmetrical pattern from left to right, with the same distribution law. As the upper load increases, the overall confining pressure at the measuring points continuously increases, and the distribution pattern remains the same. When the tunnel burial depth C=0.15m (6m), as the upper load P above the shield tunnel gradually increases, the vertical convergence displacement Sh and the lateral convergence displacement Sv of the shield tunnel both show an increasing trend. The change in the shield tunnel is minimal when there is no load directly above it. When the upper load P=40kPa, the vertical convergence displacement of the shield tunnel reaches the warning value of 10mm; When the upper load is P=20kPa, the lateral convergence displacement reaches the monitoring and early warning value of 5mm. At this time, it is necessary to pay attention to the structural status of the shield tunnel. When the upper load is P=75kPa, the vertical convergence displacement reaches the control value of 20mm; when the upper load is P=100kPa, the lateral convergence displacement reaches the warning value of 10mm. When the lateral convergence displacement or vertical displacement deformation of the tunnel segment exceeds 20mm, there is a safety hazard risk in the shield tunnel structure.
[0010] Preferably, the mechanical response characteristics of the surcharge location to existing subway tunnel segments include: With the load position as the control variable, the load eccentricity is defined as the horizontal distance from the center of the load to the center of the shield tunnel. When the ground load is directly above the tunnel, the eccentricity is 0D, where D is the diameter of the shield tunnel. The test load eccentricities are e=0D, e=0.5D, e=1D, and e=2D. The confining pressure at the tunnel arch crown, unloaded side arch waist and arch corners, and arch bottom generally shows a decreasing trend as the eccentricity increases; The decreasing trend of tunnel confining pressure on the eccentrically loaded side is smaller than that on the non-eccentric side; When e=0.5D, the confining pressure on the eccentric side of the tunnel increases slightly compared to when the surcharge e=0D. The increases in the arch shoulder, waist, and foot on the loaded side of the tunnel are 0.2, 0.08, and 0.25 kPa, respectively. After that, the confining pressure begins to decrease as e further increases. Using the eccentricity of the surcharge as the control variable, the horizontal distances of the ground surcharge center offset from the tunnel center are set to e=0D, e=0.5D, e=1D, and e=2D. Under the conditions of P=75kPa and burial depth C=6m: When the load is located directly above the shield tunnel, the vertical convergence displacement of the tunnel is 20mm, which exceeds the control value specified in the standard. When the eccentricity of the ground load is 1.2D, the vertical convergence displacement of the shield tunnel is 10mm. It is necessary to pay attention to the structural condition of the tunnel. As the eccentricity of the ground load increases, the vertical convergence displacement of the shield tunnel becomes smaller and smaller. When the eccentricity of the load is greater than 1.2D, the vertical convergence displacement of the shield tunnel is less than 10mm, which meets the specified value in the specification. Under the same upper load, when the burial depth C=14m, the vertical convergence displacement of the shield tunnel segments also shows the same pattern as the eccentricity of the load increases. When the load is located directly above the shield tunnel, the vertical convergence displacement of the tunnel is 15mm, which meets the warning value standard. When the eccentricity of the load is 1.5D, the vertical convergence displacement of the shield tunnel is 10mm. When the eccentricity of the load is greater than 1.5D, the vertical convergence displacement of the shield tunnel is less than 10mm, which meets the specified value in the code.
[0011] Preferably, the specific content of the mechanical response law of existing subway tunnel segments to the burial depth is as follows: As tunnel depth increases, the confining pressure under sudden surcharge decreases significantly, but the shape of the confining pressure remains similar. The effect of sudden surcharge on tunnel confining pressure decreases with increasing burial depth. This is because the additional vertical stress on the soil generated by local surcharge at the ground decreases sharply with increasing burial depth C. As the tunnel depth increases, the change in longitudinal deformation of the tunnel gradually decreases, and the tunnel is less affected by the ground load from above.
[0012] Preferably, the surrounding rock pressure amplification factor is used. β With the pressure transmission coefficient of the surrounding rock η The specific content describing the calculation method of the corrected surrounding rock pressure acting on tunnel segments under surface loading conditions is as follows: According to the traditional soil column method theory of surrounding rock pressure in ultra-shallow tunnels, the overlying soil layer of the tunnel is regarded as a vertical load acting on the lining: ; In the formula, q Vertical surrounding rock pressure at the top of the tunnel; γ : The unit weight of the rock mass; H The depth of the tunnel; Based on the error between the theoretical and measured values of the soil column method, a rock pressure amplification factor is introduced. β With the pressure transmission coefficient of the surrounding rock η ; ; In the formula: σ This refers to the pressure of the surrounding rock in the tunnel after loading. σ 0 This refers to the initial surrounding rock pressure of the tunnel. ; In the formula: △ σ This represents the increase in surrounding rock pressure in the tunnel after loading. P This refers to the surface loading volume; magnification factor β With transmission coefficient η Substituting the vertical surrounding rock pressure at the tunnel top, a corrected formula for the surrounding rock pressure in shallow-buried shield tunnels in collapsible loess strata is proposed. q m : .
[0013] Preferably, the contents of the fourth-level displacement-affected partition table are as follows: When the convergence displacement is greater than 20 mm, it is a Level I influence zone; When the convergence displacement is greater than 10 mm and less than 20 mm, it is a Level II influence zone; When the convergence displacement is greater than 5 mm and less than 10 mm, it is a Level III influence zone; When the convergence displacement is less than 5 mm, it is a Level IV influence zone; When the convergence displacement is in the Level IV influence zone, the safety is not affected; When the convergence displacement is in the Level I influence zone, tunnel monitoring should be closely strengthened to protect structural safety.
[0014] In summary, the method for evaluating the impact of surface surcharge on existing subway tunnel segments, as proposed in this invention, differs from traditional techniques. This invention uses a method of adding a certain proportion of CaO particles, industrial salt, and gypsum powder to loess to prepare loess with a certain degree of collapsibility, which is used to simulate the collapsible loess material in similar model tests. Furthermore, based on 3D printing and wire torsion testing methods, a construction technology for staggered joint assembly of shield tunnel segments is developed, realizing the construction of similar model tests.
[0015] Through similar model tests, the influence of surface load on the surrounding rock pressure and deformation mode of existing shield tunnel segments under different loads, different eccentricities and different tunnel burial depths was proposed.
[0016] The use of surrounding rock pressure amplification factor is proposed. β With the pressure transmission coefficient of the surrounding rock η A modified method for calculating the surrounding rock pressure acting on existing shield tunnel segments under surface loading conditions was described and its rationality was verified.
[0017] Based on the shield tunnel segment deformation control standard in the rail transit specifications, a four-level displacement influence zoning is proposed, and the evaluation of the impact on existing shield tunnel segments under surface loading conditions can be obtained by looking up tables.
[0018] The technical method of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description
[0019] Figure 1 This is a 3D representation of a similar model to the present invention; Figure 2 This is a comparison diagram of tunnel confining pressure caused by different load sizes according to the present invention; Figure 3 This is a diagram showing the variation of confining pressure in the tunnel lining according to the present invention. Figure 3 (a) shows the change in surrounding rock pressure at the crown and base of the arch. Figure 3 (b) is a diagram showing the changes in surrounding rock pressure on the left and right arch shoulders; Figure 4This is the displacement convergence value at a burial depth of 6m in this invention. Figure 4 (a) represents the vertical convergence displacement of the structure. Figure 4 (b) represents the lateral convergence displacement of the structure; Figure 5 This is the displacement convergence value when the burial depth is 14m. Figure 5 (a) represents the vertical convergence displacement of the structure. Figure 5 (b) represents the lateral convergence displacement of the structure; Figure 6 These are the measured values of surrounding rock pressure under eccentric loading according to the present invention. Figure 6 (a) is a diagram showing the changes in surrounding rock pressure at the crown and base of the arch. Figure 6 (b) is a diagram showing the changes in surrounding rock pressure on the left and right arch shoulders; Figure 7 This refers to the segment convergence displacement value when the eccentricity increases according to the present invention.
[0020] Figure Labels 1. Loading plate. Detailed Implementation
[0021] The technical method of the present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values of the components and steps described in these embodiments do not limit the scope of this application.
[0022] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the scope of this application and its application or use.
[0023] Techniques, systems, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, they should be considered part of the instruction manual.
[0024] In all the examples shown and discussed herein, any specific values should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.
[0025] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.
[0026] This invention provides a method for evaluating the impact of surface surcharge on existing subway tunnel segments, comprising the following steps: S1. Construct a similar model based on tunnel segment ring information and collapsible loess information; like Figure 1 As shown, the similar model includes a basic component unit, a loess simulation unit, and a loading monitoring unit; The basic component units include an indoor model test chamber and segment rings; The loess simulation unit includes artificially prepared collapsible loess; The loading monitoring unit includes a hydraulic servo actuator, a pressure plate, an earth pressure gauge, and a displacement gauge.
[0027] The indoor model test chamber is made of transparent plexiglass and is supported by three detachable steel supports to maintain its stability. The tube segment ring consists of six tube segments, which are 3D printed from ABS material with an elastic modulus of E=0.86GPa. Each tube segment includes one top block, two adjacent blocks, and three standard blocks. The bolt connection between the tube segments is achieved by binding wire. The preparation process of the artificially prepared collapsible loess includes: To obtain the test soil, two undisturbed soil samples were taken every 2 meters. By drilling undisturbed soil samples, disturbed soil samples were taken from several layers in the actual strata. The disturbed loess was spread out, dried, crushed, and sieved to obtain the test soil. Artificial collapsible loess was prepared by adding CaO particles, industrial salt, and gypsum powder to the test soil. The hydraulic servo actuator is equipped with three-dimensional gapless joint supports at both ends. The three-dimensional gapless joint supports include several joints connected by flanges. The bearing plate is composed of two pieces of plexiglass and a connecting rod. The upper plexiglass is tightly fastened to the bottom of the actuator, and the lower plexiglass is placed on the soil surface. The displacement gauges are installed inside the middle ring of the tunnel to measure the vertical convergence displacement and the lateral convergence displacement respectively. The earth pressure gauge is installed outside the segment ring to monitor the earth pressure at the arch crown, arch bottom, left and right arch shoulders, left and right arch waists, and left and right arch feet.
[0028] S2. Conduct experiments based on similar models and collect experimental data. Based on the experimental data, obtain the influence law of surface load on the surrounding rock pressure and deformation mode of tunnel segments. The specific content of the influence law of surface load on the surrounding rock pressure and deformation mode of tunnel segments in S2 includes the mechanical response law of the superload on the existing subway segments, the mechanical response law of the load location on the existing subway segments, and the mechanical response law of the load burial depth on the existing subway segments. The mechanical response law of the superstructure load on the existing subway tunnel segments is as follows: like Figure 2 As shown, as the upper load P increases, the confining pressure at the measuring point increases continuously with the increase of the surcharge. The distribution of the confining pressure at the measuring point shows a symmetrical pattern from left to right, and the distribution law is the same. like Figure 3As shown, with the increase of the upper load, the overall confining pressure at each point is constantly increasing, and the distribution pattern is basically the same. like Figure 4 As shown, when the tunnel burial depth C=0.15m (6m), as the upper load P above the shield tunnel gradually increases, the vertical convergence displacement Sh and the lateral convergence displacement Sv of the shield tunnel both show an increasing trend. When there is no load directly above, the change in the shield tunnel is minimal, with the initial vertical convergence displacement of the shield segments being 4.4 mm and the initial lateral convergence displacement being 3.7 mm. When the upper load P=40kPa, the vertical convergence displacement of the shield tunnel reaches the warning value of 10mm; When the upper load is P=20kPa, the lateral convergence displacement reaches the monitoring and early warning value of 5mm. At this point, it is necessary to pay attention to the structural condition of the shield tunnel. When the upper load is P=75kPa, the vertical convergence displacement reaches the control value of 20mm; When the upper load is P=100kPa, the lateral convergence displacement reaches the warning value of 10mm. and Figure 5 When the tunnel depth C = 0.35m (14m), the initial vertical convergence displacement of the shield segment is 8.8mm and the initial lateral convergence displacement is 4.2mm.
[0029] When the upper load is P=25kPa, the vertical convergence displacement reaches the warning value of 10mm. When the upper load is P=35kPa, the lateral convergence displacement reaches the monitoring warning value of 5mm. When the upper load is P=100kPa, the vertical convergence displacement reaches the control value of 20mm. When the upper load is P=145kPa, the lateral convergence displacement reaches the warning value of 10mm.
[0030] When the lateral convergence displacement or vertical displacement deformation of the tunnel segment exceeds 20mm, there is a safety hazard risk in the shield tunnel structure. Appropriate prevention and control measures should be taken to avoid greater structural damage to the shield tunnel.
[0031] like Figure 6 As shown, the mechanical response of the surcharge location to existing subway tunnel segments includes: Using the load position as the control variable, the load eccentricity is defined as the horizontal distance from the center of the load to the center of the shield tunnel. When the ground load is directly above the tunnel, the eccentricity is 0D, where D is the diameter of the shield tunnel. The test load eccentricities are e=0D, e=0.5D, e=1D, and e=2D, with load size and tunnel depth of 7.5 kPa and 0.15 m, respectively. The corresponding actual work-sink load size and tunnel depth are 75 kPa and 6 m, respectively.
[0032] The confining pressure at the tunnel arch crown, unloaded side arch waist and arch corners, and arch bottom generally shows a decreasing trend as the eccentricity increases; The decreasing trend of tunnel confining pressure on the eccentrically loaded side is significantly smaller than that on the non-eccentric side; When e=0.5D, the confining pressure on the eccentric side of the tunnel increases slightly compared to when the surcharge e=0D. The increases in the arch shoulder, waist, and foot on the loaded side of the tunnel are 0.2, 0.08, and 0.25 kPa, respectively. After that, the confining pressure begins to decrease as e further increases. like Figure 7 As shown, with the eccentricity of the surcharge as the control variable, the horizontal distances of the ground surcharge center offset from the tunnel center are set to e=0D, e=0.5D, e=1D, and e=2D. This is under the condition of P=75kPa and burial depth C=6m. When the load is located directly above the shield tunnel, the vertical convergence displacement of the tunnel is 20mm, which exceeds the control value specified in the standard. When the eccentricity of the ground load is 1.2D, the vertical convergence displacement of the shield tunnel is 10mm, and attention needs to be paid to the structural condition of the tunnel. As the eccentricity of the ground load increases, the vertical convergence displacement of the shield tunnel becomes smaller and smaller. When the eccentricity of the load is greater than 1.2D, the vertical convergence displacement of the shield tunnel is less than 10mm, which meets the specified value in the specification. Under the same upper load, when the burial depth C=14m, the vertical convergence displacement of the shield tunnel segments also shows the same pattern as the eccentricity of the load increases. When the load is located directly above the shield tunnel, the vertical convergence displacement of the tunnel is 15mm, which meets the warning value standard. When the eccentricity of the load is 1.5D, the vertical convergence displacement of the shield tunnel is 10mm. When the eccentricity of the load is greater than 1.5D, the vertical convergence displacement of the shield tunnel is less than 10mm, which meets the specified value in the code.
[0033] The specific details of the mechanical response law of existing subway tunnel segments to surcharge depth are as follows: Using the burial depth as the control variable, two working conditions were established for actual tunnel depths of 6m and 14m. As the tunnel depth increased, the confining pressure under sudden burial load decreased significantly, but the shape of the confining pressure remained similar. Taking the change in confining pressure at the top of the tunnel as an example, when the tunnel depth increased from 6m to 14m, the confining pressure value decreased from 60kPa to 20kPa, a very large decrease, indicating that the effect of sudden burial load on the tunnel confining pressure diminishes with increasing burial depth. This is because the vertical additional stress on the soil generated by local burial load at the ground decreases sharply with increasing burial depth C. When the tunnel depth increased, the confining pressure under sudden burial load decreased significantly, but the shape of the confining pressure remained similar. The effect of sudden surcharge on tunnel confining pressure decreases with increasing burial depth. This is because the additional vertical stress on the soil generated by local surcharge at the ground decreases sharply with increasing burial depth C. When the superstructure load P = 75 kPa and the burial depth increases from 6 m to 14 m, the vertical convergence displacement of the tunnel gradually decreases with increasing burial depth, decreasing from 20 mm to 15 mm. This indicates that as the burial depth increases, the change in longitudinal deformation of the tunnel also gradually decreases, and the influence of the superstructure load on the tunnel also decreases. The main reason for this is that the additional stress acting on the tunnel due to the superstructure load decreases with the burial depth of the shield tunnel.
[0034] Ultimately, we can conclude that: (1) The confining pressure of the tunnel lining increases with the continuous increase of the load. When the load is applied directly above, the distribution of the confining pressure at the measuring point is roughly symmetrical from left to right, and the tunnel structure undergoes a "lateral elliptical" deformation. When the load is applied to the side, the shield tunnel undergoes an approximately "oblique elliptical" deformation. As the eccentricity gradually increases, the impact on the deformation of the shield tunnel becomes smaller.
[0035] (2) When a sudden load occurs directly above the tunnel, the maximum confining pressure of the tunnel occurs below the center of the ground load, and the confining pressure gradually decreases as the value of e increases. Under eccentric loading, the tunnel structure deforms into an "oblique ellipse".
[0036] As the tunnel depth increases, the confining pressure under sudden loading decreases significantly, but the shape of the confining pressure remains similar. The confining pressure generally decreases with the increase of the eccentricity e. The decreasing trend of the confining pressure on the eccentric side is significantly smaller than that on the non-eccentric side. Furthermore, when the eccentricity e increases from 0 to 0.5D, a small area of the confining pressure on the loading side of the tunnel shows an increasing trend, followed by a decrease.
[0037] S3, Using the surrounding rock pressure amplification factor β With the pressure transmission coefficient of the surrounding rock η Describes the calculation method for the corrected surrounding rock pressure acting on tunnel segments under surface loading conditions; The theoretical calculation results of the surrounding rock pressure at the crown show that the relative errors between the calculated and measured values of the soil column method, Terzaghi method, Beer Bowman formula, Xie Jiaxiao method, and rock column theory method are 0.48%~11.9%, 11.0%~43.2%, 10.2%~42.5%, 26.7%~18.5%, and 10.2%~42.5%, respectively. Compared with other theoretical methods, the soil column method has smaller and more stable errors.
[0038] Using the surrounding rock pressure amplification factor β With the pressure transmission coefficient of the surrounding rock η The specific content describing the calculation method of the corrected surrounding rock pressure acting on tunnel segments under surface loading conditions is as follows: According to the traditional soil column method theory of surrounding rock pressure in ultra-shallow tunnels, the overlying soil layer of the tunnel is regarded as a vertical load acting on the lining: ; In the formula, q : The pressure of the surrounding rock at the top of the tunnel; γ : The unit weight of the rock mass; H The depth of the tunnel; Based on the error between the theoretical and measured values of the soil column method, a rock pressure amplification factor is introduced. β With the pressure transmission coefficient of the surrounding rock η ; ; In the formula: σ This refers to the pressure of the surrounding rock in the tunnel after loading. σ 0 This refers to the initial surrounding rock pressure of the tunnel. ; In the formula: △ σ This represents the increase in surrounding rock pressure in the tunnel after loading. P This refers to the surface loading volume; magnification factor β With transmission coefficient η Substituting the vertical surrounding rock pressure at the tunnel top, a corrected formula for the surrounding rock pressure in shallow-buried shield tunnels in collapsible loess strata is proposed: q m1 = γ H+Δ σ ; q m2 = βγH ; Due to the revised formula for vertical surrounding rock pressure at the tunnel top q m1 = γ H+Δ σ or q m2 = βγH The values are not completely equal, so the overall amplification factor of the surrounding rock pressure needs to be calculated simultaneously. β With transmission coefficient η The comprehensive impact on tunnel surrounding rock pressure, based on engineering design experience and the principle of ensuring safety margins, needs to be considered. q m1 and q m2 Taking the larger value as the design value, the final formula for correcting the surrounding rock pressure of ultra-shallow tunnels can be expressed as: .
[0039] When the corrected formula is applied to other operating conditions, the average relative error is 0.79% to 8.2%.
[0040] S4. Based on the shield segment deformation control standard in the rail transit specification, a four-level displacement influence zoning table is constructed, and the impact on tunnel segments under surface loading conditions is evaluated based on experimental data.
[0041] The fourth-level displacement affects the following entries in the partition table: When the convergence displacement is greater than 20 mm, it is a Level I influence zone; When the convergence displacement is greater than 10 mm and less than 20 mm, it is a Level II influence zone; When the convergence displacement is greater than 5 mm and less than 10 mm, it is a Level III influence zone; When the convergence displacement is less than 5 mm, it is a Level IV influence zone; When the convergence displacement is in the Level IV influence zone, the safety is not affected; When the convergence displacement is in the Level I influence zone, tunnel monitoring should be closely strengthened to protect structural safety.
[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical methods of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical methods of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical methods to deviate from the spirit and scope of the technical methods of the present invention.
Claims
1. A method for evaluating the impact of surface surcharge on existing subway tunnel segments, characterized in that, Includes the following steps: S1. Construct a similar model based on tunnel segment ring information and collapsible loess information; S2. Conduct experiments based on similar models and collect experimental data. Based on the experimental data, obtain the influence law of surface load on the surrounding rock pressure and deformation mode of tunnel segments. S3, Using the surrounding rock pressure amplification factor β With the pressure transmission coefficient of the surrounding rock η Describes the calculation method for the corrected surrounding rock pressure acting on tunnel segments under surface loading conditions; S4. Based on the shield segment deformation control standard in the rail transit specification, a four-level displacement influence zoning table is constructed, and the impact on tunnel segments under surface loading conditions is evaluated based on experimental data.
2. The method for evaluating the impact of surface surcharge on existing subway segments according to claim 1, characterized in that, The similarity model includes a basic component unit, a loess simulation unit, and a loading monitoring unit; The basic component units include an indoor model test chamber and segment rings; The loess simulation unit includes artificially prepared collapsible loess; The loading monitoring unit includes a hydraulic servo actuator, a pressure plate, an earth pressure gauge, and a displacement gauge.
3. The method for evaluating the impact of surface surcharge on existing subway segments according to claim 2, characterized in that, The indoor model test chamber is made of transparent plexiglass and is supported by three detachable steel supports to maintain its stability. The tube segment ring consists of six tube segments, which are 3D printed from ABS material with an elastic modulus of E=0.86GPa. Each tube segment includes one top block, two adjacent blocks, and three standard blocks. The bolt connections between the tube segments are made by binding wire.
4. The method for evaluating the impact of surface surcharge on existing subway segments according to claim 2, characterized in that, The preparation process of the artificially prepared collapsible loess includes: To obtain the test soil, two undisturbed soil samples were taken every 2 meters. By drilling undisturbed soil samples, disturbed soil samples were taken from several layers in the actual strata. The disturbed loess was spread out, dried, crushed, and sieved to obtain the test soil. Artificial collapsible loess was prepared by adding CaO particles, industrial salt, and gypsum powder to the test soil.
5. The method for evaluating the impact of surface surcharge on existing subway segments according to claim 2, characterized in that, The hydraulic servo actuator is equipped with three-dimensional gapless joint supports at both ends. The three-dimensional gapless joint supports include several joints connected by flanges. The bearing plate is composed of two pieces of plexiglass and a connecting rod. The upper plexiglass is tightly fastened to the bottom of the actuator, and the lower plexiglass is placed on the soil surface. The displacement gauges are installed inside the middle ring of the tunnel to measure the vertical convergence displacement and the lateral convergence displacement respectively. The earth pressure gauge is installed outside the segment ring to monitor the earth pressure at the arch crown, arch bottom, left and right arch shoulders, left and right arch waists, and left and right arch feet.
6. The method for evaluating the impact of surface surcharge on existing subway segments according to claim 1, characterized in that, The specific content of the influence law of surface load on the surrounding rock pressure and deformation mode of tunnel segments in S2 includes the mechanical response law of the superload on the existing subway segments, the mechanical response law of the load location on the existing subway segments, and the mechanical response law of the burial depth on the existing subway segments. The mechanical response law of the superstructure load on the existing subway tunnel segments is as follows: As the value of the upper load P increases, the confining pressure at the measuring point increases, and the distribution of the confining pressure change at the measuring point shows a symmetrical pattern from left to right, with the same distribution law. As the upper load increases, the overall confining pressure at the measuring points continuously increases, and the distribution pattern remains the same. When the tunnel burial depth C=0.15m, as the upper load P above the shield tunnel gradually increases, the vertical convergence displacement Sh and the lateral convergence displacement Sv of the shield tunnel both show an increasing trend. The change in the shield tunnel is minimal when there is no load directly above it. When the upper load P=40kPa, the vertical convergence displacement of the shield tunnel reaches the warning value of 10mm; When the upper load is P=20kPa, the lateral convergence displacement reaches the monitoring and early warning value of 5mm. At this time, it is necessary to pay attention to the structural status of the shield tunnel. When the upper load is P=75kPa, the vertical convergence displacement reaches the control value of 20mm; when the upper load is P=100kPa, the lateral convergence displacement reaches the warning value of 10mm. When the lateral convergence displacement or vertical displacement deformation of the tunnel segment exceeds 20mm, there is a safety hazard risk in the shield tunnel structure.
7. The method for evaluating the impact of surface surcharge on existing subway segments according to claim 6, characterized in that, The mechanical response of the loading location to existing subway tunnel segments includes: With the load position as the control variable, the load eccentricity is defined as the horizontal distance from the center of the load to the center of the shield tunnel. When the ground load is directly above the tunnel, the eccentricity is 0D, where D is the diameter of the shield tunnel. The test load eccentricities are e=0D, e=0.5D, e=1D, and e=2D. The confining pressure at the tunnel arch crown, unloaded side arch waist and arch corners, and arch bottom generally shows a decreasing trend as the eccentricity increases; The decreasing trend of tunnel confining pressure on the eccentrically loaded side is smaller than that on the non-eccentric side; When e=0.5D, the confining pressure on the eccentric side of the tunnel increases slightly compared to when the surcharge e=0D. The increases in the arch shoulder, waist, and foot on the loaded side of the tunnel are 0.2, 0.08, and 0.25 kPa, respectively. After that, the confining pressure begins to decrease as e further increases. Using the eccentricity of the surcharge as the control variable, the horizontal distances of the ground surcharge center offset from the tunnel center are set to e=0D, e=0.5D, e=1D, and e=2D, under the conditions of P=75kPa and burial depth C=6m: When the load is located directly above the shield tunnel, the vertical convergence displacement of the tunnel is 20mm, which exceeds the control value specified in the standard. When the eccentricity of the ground load is 1.2D, the vertical convergence displacement of the shield tunnel is 10mm. It is necessary to pay attention to the structural condition of the tunnel. As the eccentricity of the ground load increases, the vertical convergence displacement of the shield tunnel becomes smaller and smaller. When the eccentricity of the load is greater than 1.2D, the vertical convergence displacement of the shield tunnel is less than 10mm, which meets the specified value in the specification. Under the same upper load, when the burial depth C=14m, the vertical convergence displacement of the shield tunnel segments also shows the same pattern as the eccentricity of the load increases. When the load is located directly above the shield tunnel, the vertical convergence displacement of the tunnel is 15mm, which meets the warning value standard. When the eccentricity of the load is 1.5D, the vertical convergence displacement of the shield tunnel is 10mm. When the eccentricity of the load is greater than 1.5D, the vertical convergence displacement of the shield tunnel is less than 10mm, which meets the specified value in the code.
8. The method for evaluating the impact of surface surcharge on existing subway segments according to claim 6, characterized in that, The specific content of the mechanical response law of existing subway tunnel segments to surcharge depth is as follows: As tunnel depth increases, the confining pressure under sudden surcharge decreases significantly, but the shape of the confining pressure remains similar. The effect of sudden surcharge on tunnel confining pressure decreases with increasing burial depth; The vertical additional stress on the soil caused by local surcharge on the ground decreases sharply as the burial depth C increases; As the tunnel depth increases, the change in longitudinal deformation of the tunnel gradually decreases, and the tunnel is less affected by the ground load from above.
9. A method for evaluating the impact of surface surcharge on existing subway segments according to claim 6, characterized in that, Using the surrounding rock pressure amplification factor β With the pressure transmission coefficient of the surrounding rock η The specific content describing the calculation method of the corrected surrounding rock pressure acting on tunnel segments under surface loading conditions is as follows: According to the traditional soil column method theory of surrounding rock pressure in ultra-shallow tunnels, the overlying soil layer of the tunnel is regarded as a vertical load acting on the lining: ； In the formula, q Vertical surrounding rock pressure at the top of the tunnel; γ : The unit weight of the rock mass; H The depth of the tunnel; Based on the error between the theoretical and measured values of the soil column method, a rock pressure amplification factor is introduced. β With the pressure transmission coefficient of the surrounding rock η ; ； In the formula: σ This refers to the pressure of the surrounding rock in the tunnel after loading. σ 0 represents the initial surrounding rock pressure of the tunnel; ； In the formula: △ σ This represents the increase in surrounding rock pressure in the tunnel after loading. P This refers to the surface loading volume; magnification factor β With transmission coefficient η Substituting the vertical surrounding rock pressure at the tunnel top, a corrected formula for the surrounding rock pressure in shallow-buried shield tunnels in collapsible loess strata is proposed. q m : 。 10. The method for evaluating the impact of surface surcharge on existing subway segments according to claim 1, characterized in that, The fourth-level displacement affects the following entries in the partition table: When the convergence displacement is greater than 20 mm, it is a Level I influence zone; When the convergence displacement is greater than 10 mm and less than 20 mm, it is a Level II influence zone; When the convergence displacement is greater than 5 mm and less than 10 mm, it is a Level III influence zone; When the convergence displacement is less than 5 mm, it is a Level IV influence zone; When the convergence displacement is in the Level IV influence zone, the safety is not affected; When the convergence displacement is in the Level I influence zone, tunnel monitoring should be closely strengthened to protect structural safety.