Ground in-out type shield tunneling stability evaluation method

Abstract

The invention relates to a method for evaluating the tunneling stability of a ground access type shield tunnel. The method comprises the following steps: determining random variables influencing the tunneling stability of the ground access type shield tunnel; determining an appropriate probability distribution for each random variable; establishing an analysis model of the tunneling stability of the ground access type shield tunnel; a Monte Carlo simulation method is introduced for simulation, and a stability evaluation index influencing the tunneling stability of the ground access type shield tunnel is calculated; performing statistical analysis on the simulation result to obtain probability distribution of stability evaluation indexes; comparing and analyzing the probability distribution of the stability evaluation indexes with a construction design safety standard, and calculating the instability probability of the ground access type shield tunnel structure and the surrounding stratum thereof; and carrying out risk assessment on the tunneling stability of the ground access type shield tunnel based on the instability probability. According to the method, various uncertain factors and randomness are comprehensively considered, and the tunneling stability of the ground access type shield tunnel can be comprehensively evaluated.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel construction, and particularly relates to a method for evaluating the stability of a ground access shield tunnel during tunneling. Background Art

[0002] With the acceleration of the urbanization process and the continuous growth of traffic demand, the development and utilization of urban underground space have gradually become key problems. In cities with complex geological conditions and highly dense building environments, the shield method has become a widely used construction method. However, traditional shield tunnel construction requires the construction of large-scale and deep launching shafts and receiving shafts for the launching and receiving of the shield. In contrast, the ground access shield method, as an innovative technology, does not rely on working shafts. This technology enables the shield to directly start from the ground surface, successively pass through the zero-cover, ultra-shallow-cover, and shallow-cover stages, and then enter the predetermined tunneling route. After that, it experiences the reverse cover change process and finally returns to the ground to complete the reception. The ground access shield method has the advantages of reducing construction risks, reducing the amount of excavated soil, and saving construction time, and is particularly suitable for densely built areas in large cities with limited construction sites.

[0003] During the tunneling process of a ground access shield tunnel, it is necessary to experience cover changes, and at the same time, factors such as geological conditions, construction processes, and the surrounding environment are complex. Therefore, the stability of a ground access shield tunnel during tunneling is an engineering problem worthy of attention and urgent solution. Traditional methods for analyzing the stability of shield tunnel tunneling are mainly based on deterministic analysis models, and these methods generally assume that all input parameters are known and determined. However, this analysis method based on deterministic assumptions may underestimate risks in some cases, especially when the shield tunneling experiences significant cover changes and faces complex geological and construction environments, and it is difficult to fully consider the uncertainty and randomness factors in the system.

[0004] For example, geological conditions usually show obvious spatial variability. The physical and mechanical parameters of soil, such as compression modulus, cohesion, and internal friction angle, may have significant differences in values at different spatial positions. At the same time, factors such as the fluctuation of the groundwater level, the change of the cover thickness, and the upward (or downward) propulsion angle during the shield propulsion process are all highly random. However, traditional deterministic analysis methods will assume that soil parameters, groundwater level, cover thickness, etc. are all known and determined when dealing with this problem. Evaluating the risk of shield tunnel tunneling with these determined parameters will lead to a large deviation in the stability evaluation results, and this deviation may bring potential risks in actual engineering applications and affect the safety and reliability of shield tunnel projects. Summary of the Invention

[0005] To solve the above problems, the present invention provides a method for evaluating the stability of a ground access shield tunnel excavation, which comprehensively considers various uncertainty factors and their randomness, breaks through the limitations of traditional analysis methods in dealing with random factors, and can comprehensively evaluate the stability status and potential instability risks of the ground access shield tunnel excavation.

[0006] The present invention is realized through the following scheme. A method for evaluating the stability of a ground access shield tunnel excavation includes the steps:

[0007] S1. Determine the random variables affecting the stability of the ground access shield tunnel excavation;

[0008] S2. Determine a suitable probability distribution for each of the random variables;

[0009] S3. Establish an analysis model for the stability of the ground access shield tunnel excavation;

[0010] S4. Introduce the Monte Carlo simulation method, use the analysis model for simulation, and calculate the stability evaluation index for measuring the stability of the ground access shield tunnel excavation;

[0011] S5. Conduct statistical analysis on the simulation results of the analysis model to obtain the probability distribution of the stability evaluation index;

[0012] S6. Compare and analyze the probability distribution of the stability evaluation index with the construction design safety standard, and calculate the instability probability of the ground access shield tunnel structure and the surrounding strata;

[0013] S7. Conduct risk assessment on the stability of the ground access shield tunnel excavation based on the instability probability.

[0014] A further improvement of the present invention is that the random variables determined in step S1 are selected from soil physical and mechanical parameters, tunnel burial depth parameters, shield attitude and excavation parameters, and segment structure parameters.

[0015] A further improvement of the present invention is that when performing step S2: based on the characteristics presented by each of the random variables, select an adapted probability distribution model, and determine the statistical parameters corresponding to the random variables based on the selected probability distribution model; wherein, the probability distribution model is selected from normal distribution, lognormal distribution, uniform distribution, and power-law distribution, and the statistical parameters are selected from some or all of the mean, standard deviation, maximum value, and minimum value.

[0016] A further improvement of the present invention is that the stability evaluation index calculated in step S4 includes segment stress, segment strain, segment floating amount, formation stress, and formation displacement.

[0017] A further improvement of the present invention lies in that: when performing step S6, the instability probability is calculated separately for each of the stability evaluation indicators, and then based on the importance degree of each of the stability evaluation indicators for the tunneling stability of the ground access shield tunnel and the corresponding instability probability, the comprehensive instability probability of the ground access shield tunnel structure and the surrounding strata is determined comprehensively; when performing step S7, the stability of the ground access shield tunnel tunneling is evaluated for risk based on the comprehensive instability probability.

[0018] A further improvement of the present invention lies in that when performing step S7: the stability risk levels are divided according to the level of the instability probability, and different risk control measures and suggestions are given based on different stability risk levels; the risk level to which the comprehensive instability probability belongs is judged, and the stability evaluation result is output, and the stability evaluation result includes the judged risk level, and the risk control measures and suggestions corresponding to the risk level.

[0019] A further improvement of the present invention lies in that the analysis model in step S3 is constructed by means of numerical simulation.

[0020] The present invention includes but is not limited to the following beneficial effects:

[0021] 1. The present invention uses the Monte Carlo random sampling simulation technology to comprehensively consider various uncertainties existing in the construction process. Compared with the traditional analysis method, it can effectively avoid the limitations in dealing with uncertainties, and can comprehensively evaluate the stability status and potential instability risks of the ground access shield tunnel tunneling, thus significantly improving the accuracy and reliability of the evaluation.

[0022] 2. By implementing a large number of random simulation calculations, the present invention can accurately obtain the probability distribution of the stability evaluation indicators of the ground access shield tunnel tunneling. This way breaks through the inherent limitations of simple deterministic analysis, effectively avoids potential safety hazards caused by a single analysis method, and provides a more accurate basis for risk assessment.

[0023] 3. By providing the instability probability and risk assessment results of the ground access shield tunnel structure and the surrounding strata, the present invention provides key data support for construction management personnel during the tunneling construction of the ground access shield tunnel. With these data, construction management personnel can make more scientific and effective decisions, thereby significantly improving the safety during the construction process, ensuring the project quality, and ensuring the smooth progress of the ground access shield tunnel construction project. Brief Description of the Drawings

[0024] Figure 1 The flowchart showing the evaluation method of the present invention is shown.

[0025] Figure 2The principle block diagram of the evaluation method of the present invention is shown.

[0026] Figure 3 The schematic diagram of the probability distribution of the random variable is shown.

[0027] Figure 4 The schematic diagram of the analysis model for the stability of the ground access shield tunnel driving is shown.

[0028] Figure 5 The schematic diagram of the probability distribution of the stability evaluation index is shown. Specific implementation manners

[0029] In order to solve the problem that the traditional analysis method has limitations when dealing with random factors, which in turn leads to large deviations in the stability evaluation results, the present invention provides a method for evaluating the stability of the ground access shield tunnel driving, comprehensively considering various uncertainty factors and their randomness, breaking through the limitations of the traditional analysis method when dealing with random factors, and being able to comprehensively evaluate the stability status and potential instability risks of the ground access shield tunnel driving.

[0030] The following further illustrates the method for evaluating the stability of the ground access shield tunnel driving with specific embodiments in combination with the drawings.

[0031] Refer to Figures 1 to 2 As shown, a method for evaluating the stability of the ground access shield tunnel driving includes the steps:

[0032] Step S1, determining the random variables affecting the stability of the ground access shield tunnel driving. Specifically, according to the characteristics of the specific engineering project, one or more preliminary estimated values of the random variables that have a significant impact on the stability of the ground access shield tunnel driving are screened out. Generally, the more complex the construction environment, the more the number of random variables, but almost all are selected from the physical and mechanical parameters of the soil mass (such as soil cohesion, internal friction angle, depth of the groundwater level, etc.), tunnel burial depth parameters (reflected by the thickness of the overburden soil above the tunnel), shield attitude (such as the upward / downward propulsion angle of the shield, horizontal projection turning radius, etc.) and excavation parameters (such as synchronous grouting pressure, synchronous grouting volume, etc.), and segment structure parameters (such as segment structure size, number of segment blocks, etc.). The methods for obtaining the preliminary estimated values of the above random variables include: directly obtaining the actual data of the engineering site through on-site surveys; experimental tests, conducting professional experiments on soil samples, etc. to determine relevant parameters; consulting literature data, referring to the research results of past similar projects; and extracting key design parameters from the ground access shield construction design scheme.

[0033] Step S2: Determine a suitable probability distribution for each of these random variables. Specifically, based on the characteristics presented by each random variable, a suitable probability distribution model needs to be carefully selected. In the field of probability statistics, common distribution models include: the normal distribution, which is often used to describe data affected by multiple independent factors and having a central tendency; the log-normal distribution, applicable to data that can exhibit normal characteristics after logarithmic transformation; the uniform distribution, used to represent the situation where the probability of taking values within a certain interval is equal; the power-law distribution, which is reflected in many phenomena with self-similarity and scale-free characteristics. Determining the statistical parameters of each variable is a key step in constructing an accurate probability distribution. Different probability distribution models may involve different statistical parameters, but almost all are selected from some or all of the mean, standard deviation, maximum value, and minimum value. For the mean, it reflects the average level of the values taken by the random variable. For the standard deviation, it is used to measure the degree of dispersion of the data; for the maximum and minimum values, they define the boundaries of the value range of the random variable. By accurately determining the statistical parameters, it can effectively ensure that the selected probability distribution model accurately depicts the actual characteristics of the random variable. Refer to Figure 3 as shown, which shows the probability distribution diagram of a certain random variable.

[0034] Step S3: Establish an analysis model for the stability of the ground access shield tunnel during tunneling. Specifically, use finite element software such as ABAQUS, ANSYS, etc., or other numerical simulation tools to construct a two-dimensional or three-dimensional numerical model of the structure related to the stability analysis of the ground access shield tunnel during tunneling. It should be noted that during the model construction process, various factors need to be comprehensively considered, such as material nonlinear constitutive relations, boundary conditions, initial in-situ stress state, geometric characteristics of the ground access shield, changes in shield overburden, shield tunneling process, disturbance to the surrounding strata, and the interaction between the segment structure and the strata.

[0035] Step S4: Introduce the Monte Carlo simulation method and use this analysis model for simulation to calculate the stability evaluation index for measuring the tunneling stability of the ground-access shield tunnel. Specifically, adopt the Monte Carlo simulation method, perform random sampling operations respectively based on the probability distributions of each random variable, and then generate a large number (at least in the thousands or even more than ten thousands) of input values of different combinations of random variables. Then input each group of generated random variable input values into this analysis model, use this analysis model to conduct a large number (depending on the number of generated random variable input groups, for example, if there are 10,000 groups, then simulate 10,000 times) of simulations on the tunneling process of the ground-access shield tunnel, and calculate the stability evaluation index for measuring the stability of the ground-access shield tunnel. This stability evaluation index includes segment stress, segment strain, segment floating amount, formation stress, and formation displacement. To significantly improve the modeling efficiency, choose the method of using a finite element software script file to build the model. During the simulation process, the results obtained from each simulation need to be recorded in detail, and these recorded data will serve as important basic materials for subsequent statistical analysis.

[0036] Step S5: Conduct statistical analysis on the simulation results of this analysis model to obtain the probability distribution of the stability evaluation index. Specifically, conduct statistical analysis respectively on the results of each stability evaluation index obtained from the simulation, calculate the probability distribution of each stability evaluation index, and draw a probability distribution graph (as Figure 5 shown, Figure 5 shows the probability distribution graph of a certain stability evaluation index) and a cumulative probability curve. For the convenience of subsequent analysis, at the same time, based on each probability distribution, statistical quantities such as the mean, median, standard deviation, and confidence interval of each stability evaluation index are also statistically calculated. By adopting the Monte Carlo simulation method to conduct a large number of random simulation calculations, the probability distribution of the stability evaluation index of the ground-access shield tunnel tunneling can be accurately obtained. This method breaks through the inherent limitations of simple deterministic analysis, effectively avoids potential safety hazards that may be brought about by a single analysis method, and provides a more accurate basis for risk assessment.

[0037] Step S6: Compare and analyze the probability distribution of the stability evaluation index with the construction design safety standard to calculate the instability probability of the ground access shield tunnel structure and the surrounding strata. Specifically, since the construction design safety standard is usually a determined value, when conducting the comparative analysis, statistical quantities such as the mean, median, and standard deviation of the stability evaluation index can be used for comparison. For example, when the entire probability distribution curve of the stability evaluation index is entirely on the left or right side of the standard value, it indicates that the instability probability is 0 or 100. When the probability distribution curve intersects with the standard value, a typical value such as the mean or median needs to be used to compare with the standard value, and the instability probability is determined according to the size of the difference. In the above manner, the instability probability is calculated for each stability evaluation index respectively, and then based on the importance (such as weight) of each stability evaluation index to the tunneling stability of the ground access shield tunnel and the corresponding instability probability, the comprehensive instability probability of the ground access shield tunnel structure and the surrounding strata is determined comprehensively.

[0038] Step S7: Conduct a risk assessment on the tunneling stability of the ground access shield tunnel based on the comprehensive instability probability. Preferably, the stability risk levels can be divided first according to the level of the instability probability, such as low risk, medium risk, and high risk. And different risk control measures and suggestions are given based on different stability risk levels, such as adjusting the propulsion parameters, changing the grouting pressure and grouting volume, and constructing the underlying reinforcement in advance. Then judge the risk level to which the comprehensive instability probability belongs and output the stability assessment result. The stability assessment result includes the judged risk level, the risk control measures and suggestions corresponding to the risk level. In order to be able to more clearly understand the potential risk of instability, the stability assessment result can further include the probability distribution diagram and cumulative probability curve of each stability evaluation index. These assessment results can be applied to the real-time monitoring during the construction process, timely adjust the construction parameters, and provide a basis for the design optimization of the ground access shield tunnel, thereby significantly improving the safety during the construction process, ensuring the project quality, and ensuring the smooth progress of the ground access shield tunnel construction project.

[0039] The following takes a specific engineering project evaluation example to further illustrate Figures 1 to 5 this method.

[0040] Engineering project background: A certain city needs to construct a tunnel using the ground access shield method. The shield tunneling length is 1140 m, and a earth pressure balance shield machine with a diameter D = 11.66 m is used for tunneling. The outer diameter of the shield tunnel structure is 11.36 m, the inner diameter is 10.36 m, the segment thickness is 500 mm, the center ring width is 1.5 m, and the segments are assembled in a staggered joint with universal segments. The geological exploration results show that the tunnel is mainly in ①1 fill soil, ②1 yellowish-brown to grayish-yellow silty clay, ③ tDriving in grey viscous silt, ③ grey silty clay with muddy texture, ④ grey muddy clay, ⑤1 grey clay, ⑤2 grey silty sand, and ⑤3 grey silty clay with silt interlayers, the shallow groundwater in the site belongs to the phreatic type. Due to the complex surrounding environment of the construction site, it is necessary to strictly control the impact of the ground access tunnel construction on the surrounding environment, so it is necessary to conduct a detailed assessment of its stability.

[0041] Step 1: Determine the random variables affecting the stability of the ground access shield tunnel driving.

[0042] According to the characteristics of the specific engineering project, the selected random variables are soil cohesion c, internal friction angle φ, groundwater depth hw, overburden thickness C of the tunnel, upward (or downward) propulsion angle θ of the shield, synchronous grouting pressure P, and synchronous grouting volume V.

[0043] Step 2: Determine the appropriate probability distribution for each random variable.

[0044] Soil cohesion c: Lognormal distribution, mean 12 kPa, standard deviation 4 kPa;

[0045] Soil internal friction angle φ: Normal distribution, mean 25°, standard deviation 5°;

[0046] Groundwater depth hw: Uniform distribution, range 2 - 4 m;

[0047] Overburden thickness C of the tunnel: Uniform distribution, range 2 - 17 m;

[0048] Upward (or downward) propulsion angle θ of the shield: Normal distribution, mean 15° (or -15°), standard deviation 5.5°;

[0049] Synchronous grouting pressure P: Normal distribution, mean 300 kPa, standard deviation 50 kPa;

[0050] Synchronous grouting volume V: Normal distribution, mean 9.09 m³, standard deviation 1.2 m³.

[0051] Step 3: Establish an analysis model for the stability of the ground access shield tunnel driving.

[0052] Use the finite element software ABAQUS to establish a three-dimensional numerical model of the ground access shield tunnel. The modified Cambridge model that can reflect the rheological properties of soft soil is selected for soft clay, the Mohr-Coulomb constitutive model is selected for sandy soil, and the linear elastic constitutive model is selected for the segment structure and grouting layer. The model considers boundary conditions, initial in-situ stress state, geometric characteristics of the ground access shield, changes in shield overburden, shield driving process, disturbance to the surrounding strata, and interaction between the segment structure and the strata. The specific model diagram is as Figure 4As shown in the figure, it includes: (a) a three-dimensional model of the soil mass shown in the figure, and the part outlined in red in the figure corresponds to the area of the tunnel to be excavated. The diameter D of the tunnel to be excavated is 11.66 m; (b) a segment and grouting model shown in the figure, where the red part in the figure represents the grouting layer, and the green part represents the lining structure. The inner diameter of this lining structure is 10.36 m; and (c) a three-dimensional model of the segment structure shown in the figure, where the red part in the figure represents the crown block K, the blue part represents the adjacent block L, and the green part represents the standard block B.

[0053] Step 4: Introduce the Monte Carlo simulation method for simulation and calculate the stability evaluation index.

[0054] The number of simulations n = 10000, and random variables of different combinations of c, hw, C, θ, P, and V are generated by random sampling to form input value samples: c ~ LogNormal(12, 4); hw ~ U(2, 4); C ~ U(2, 17); θ ~ N(±15, 5.5); P ~ N(300, 50); V ~ N(9.09, 1.2).

[0055] Step 5: Conduct statistical analysis on the simulation results of the analysis model.

[0056] Collect the results of the stability evaluation index calculated in each simulation, and calculate and draw the probability density distribution diagrams of segment strain, segment floating amount, and ground surface uplift (or settlement), etc.

[0057] Step 6: Calculate the instability probability of instability based on the probability of the stability evaluation index.

[0058] Risk level setting:

[0059] High risk: instability probability > 30%;

[0060] Medium risk: instability probability 10% - 30%;

[0061] Low risk: instability probability < 10%.

[0062] Set the alarm value of the axial strain ε of the segment axial to be 0.5%, the alarm value of the bending strain ε of the segment b to be 1.0%, the alarm value of the segment floating amount u1 to be 10 mm, and the alarm value of the ground surface uplift (or settlement) u2 to be 20 mm. Based on the simulation results of the ground access shield tunnel excavation using the Monte Carlo algorithm, it is found that the instability probability of ε axial > 0.5% is 23%; the instability probability of ε bThe probability of instability greater than 1.0% is 19%; the probability of instability with u1 > 10 mm is 26%; the probability of instability with u2 > 20 mm is 25%. Since all the probabilities of instability are within the medium-risk range, the comprehensive probability of instability during the tunneling of the ground access shield tunnel should also be within the medium-risk range. It should be noted that if the probabilities of instability corresponding to each stability evaluation index do not all fall within the same risk level range, the comprehensive probability of instability during the tunneling of the ground access shield tunnel can be determined by comprehensively considering the weights of each stability evaluation index and their corresponding probabilities of instability, and then the risk level to which it belongs can be determined based on this comprehensive probability of instability.

[0063] After determining the risk level, corresponding recommended measures can be given. For this medium-risk level, the recommended measures may include: implementing ground reinforcement measures and surface weight measures in the ultra-shallow overburden section, strictly controlling the grouting pressure and grouting volume during the shield tunneling process, and adjusting the grouting parameters in a timely manner according to the response of the strata and segments. If the final risk level is low risk, no measures need to be taken. If it is high risk, appropriate improvement measure suggestions will be provided according to the degree of high risk.

[0064] Step 7: Output the stability evaluation results.

[0065] The present invention uses the Monte Carlo random sampling simulation technology to comprehensively consider various uncertain factors existing in the construction process. Compared with the traditional analysis method, it can effectively avoid the limitations in dealing with uncertain factors, can comprehensively evaluate the stability status and potential instability risks of the ground access shield tunnel tunneling, thereby significantly improving the accuracy and reliability of the evaluation.

[0066] The present invention has been described in detail above in combination with the embodiments with the accompanying drawings. Those of ordinary skill in the art can make various variations to the present invention according to the above description. Therefore, some details in the embodiments should not constitute a limitation to the present invention, and the protection scope of the present invention will be defined by the scope of the appended claims.

Claims

1. A method for evaluating the stability of a ground-access shield tunnel during tunneling, characterized in that, Including the steps: S1. Determine the random variables affecting the tunneling stability of a ground access shield tunnel; S2. Determine a suitable probability distribution for each of the said random variables; S3. Establish an analysis model for the tunneling stability of a ground access shield tunnel; S4. Introduce the Monte Carlo simulation method, use the said analysis model for simulation, and calculate the stability evaluation index for measuring the tunneling stability of a ground access shield tunnel; S5. Conduct a statistical analysis of the simulation results of the said analysis model to obtain the probability distribution of the stability evaluation index; S6. Compare and analyze the probability distribution of the said stability evaluation index with the construction design safety standard, and calculate the instability probability of the ground access shield tunnel structure and the surrounding strata; S7. Conduct a risk assessment of the tunneling stability of a ground access shield tunnel based on the said instability probability.

2. The ground access type shield tunnel excavation stability evaluation method according to claim 1, characterized in that: The said random variables determined in step S1 are selected from soil physical and mechanical parameters, tunnel burial depth parameters, shield attitude and excavation parameters, and segment structure parameters.

3. The method for evaluating the stability of a ground-access shield tunnel boring as claimed in claim 1, wherein When implementing step S2: Based on the characteristics presented by each of the said random variables, select an appropriate probability distribution model, and determine the statistical parameters corresponding to the said random variables based on the selected probability distribution model; wherein, the probability distribution model is selected from normal distribution, lognormal distribution, uniform distribution, and power-law distribution, and the statistical parameters are selected from some or all of the mean value, standard deviation, maximum value, and minimum value.

4. The method for evaluating the stability of a ground access shield tunnel boring according to claim 1, characterized in that, The said stability evaluation index calculated in step S4 includes segment stress, segment strain, segment floating amount, formation stress, and formation displacement.

5. The method for evaluating the tunneling stability of a ground access shield tunnel according to claim 4, wherein: When implementing step S6, calculate the instability probability for each of the said stability evaluation indexes respectively, and then comprehensively determine the comprehensive instability probability of the ground access shield tunnel structure and the surrounding strata based on the importance of each of the said stability evaluation indexes to the tunneling stability of a ground access shield tunnel and the corresponding instability probability; When implementing step S7, conduct a risk assessment of the tunneling stability of a ground access shield tunnel based on the said comprehensive instability probability.

6. The method for evaluating the stability of a ground access shield tunnel boring as claimed in claim 5, wherein When implementing step S7: Divide the stability risk levels according to the high or low of the instability probability, and give different risk control measures and suggestions based on different stability risk levels; Judge the risk level to which the said comprehensive instability probability belongs, and output the stability evaluation result, and the said stability evaluation result includes the judged risk level, and the risk control measures and suggestions corresponding to the risk level.

7. The method for evaluating the stability of a ground-access shield tunnel boring according to claim 1, characterized in that The said analysis model in step S3 is constructed by means of numerical simulation.

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