A method and system for determining the support force of shield tunneling under riverbeds with elevation differences

Abstract

This invention belongs to the field of tunnel construction technology and discloses a method and system for determining the support force of a shield tunneling machine (TBM) under riverbed strata with elevation differences. This method combines wedge failure theory and the limit equilibrium method, establishing a model that treats the actively failing soil in front of the TBM excavation face as a prism plus a wedge. It analyzes the mechanical equilibrium of the TBM support force and the sliding soil under the limit equilibrium state, dividing the river crossing process into five stages and calculating the support force at the excavation face of each uneven stratum under the river, thereby determining the magnitude of the ultimate support force at the excavation face of the TBM under the riverbed. This invention simplifies the wedge theory calculation model, avoiding complex formulas and cumbersome calculation steps, and accurately calculates the ultimate support force at the bottom of the riverbed, the river slope, the bottom layer without a riverbed, and the boundaries between different strata. This makes the support force calculation more consistent with actual engineering conditions, laying the foundation for subsequent theoretical analysis and technological development.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of tunnel construction, and particularly relates to a method and system for determining support force for a shield tunneling through a high-difference stratum of a river. BACKGROUND

[0002] With the continuous acceleration of urbanization, the population size of cities is expanding, and the bearing pressure of ground transportation systems is increasing. Shield construction has shown significant advantages in solving urban traffic congestion problems due to its strong climate adaptability, high automation, remote intelligent monitoring, short construction period, low labor demand, and small disturbance to the surrounding environment during deep excavation, and has gradually become an important construction technology for modern urban underground space development.

[0003] In the complex geological environment of large cities, implementing metro construction involves the challenge of passing through existing buildings, municipal pipelines, railways, and rivers, etc. This poses higher technical requirements for the control and optimization of the support force of the excavation face of the shield construction. When the shield tunnel passes close to the river, the construction risk increases significantly. Due to the large variation in the thickness of the soil cover around the river, if the support force parameters of the excavation face are not adjusted in time during the shield tunneling process, it can easily lead to instability of the excavation face, ground deformation, and river collapse, etc. Therefore, for the construction conditions of the shield passing close to the river, how to effectively control the ground settlement and the stability of the excavation face is still an engineering difficulty that needs to be solved.

[0004] Through the above analysis, the main problems and defects of the prior art in the construction of the shield tunneling through the high-difference stratum of the river are:

[0005] (1) Insufficient dynamic adaptation of support force; traditional support force calculation is mostly based on the assumption of uniform stratum, which is difficult to adapt to the conditions of sudden changes in the thickness of the soil cover in the river area, leading to a lag of the support force parameters behind the geological changes. The lack of real-time geology-mechanical coupling feedback mechanism results in a long adjustment period of the support force (usually lagging behind the assembly of 2-3 rings of segments), which can easily cause local instability of the excavation face.

[0006] (2) Limitations of water and soil pressure calculation model; the existing theories (such as Terzaghi's loose pressure theory) do not consider the influence of dynamic hydraulic gradient of the river, and when the shield passes through the permeable layer of the riverbed, the calculation error of the water and soil pressure can reach 20-30%. The coupling effect of soil arching effect and seepage force in the high-difference stratum is not quantified, resulting in a deviation of the set value of the support force from the actual demand.

[0007] (3) Delayed risk warning; relying on manual monitoring data (such as a settlement point spacing > 20m), it is difficult to capture the micro-deformation at the bottom of the river (initial deformation < 5mm cannot be detected). The response threshold of the existing system is fixed and cannot adapt to the changes in the risk level of different sections of the river (such as the difference in differential settlement rate between the main river and the embankment is 3 times).

[0008] (4) Construction control discretization; shield parameters and support force are not coordinated, and each system is independently adjusted, resulting in superimposed stratum disturbance (such as additional settlement caused by mismatching of simultaneous grouting pressure and support force); lack of digital twin deduction ability during the crossing process, unable to predict the impact of support force adjustment on river slope structure.

[0009] (5) Lack of response to special conditions; no plan for extreme conditions such as river dredging and sudden water level drop (such as water level change >1m in a single day during the rainy season), and the support force safety factor is rigid (usually fixed at 1.5, without considering the influence of permeability coefficient change). When crossing sandy gravel river, the existing model does not take into account the support pressure attenuation effect caused by particle migration.

[0010] At the same time, the above technical defects will increase the probability of excavation face collapse by 3-5 times (actual data shows that the accident rate of river section accounts for 62% of the whole line), the qualified rate of riverbed settlement control is less than 75% (compared with the 92% standard rate of non-river section), and the emergency treatment cost is 4-6 times that of conventional section construction. The essence of these problems lies in the fact that the existing method fails to establish a closed-loop control system of "geological variation-support response-environmental disturbance" in river elevation stratum, so it is urgent to develop an adaptive support force decision-making technology based on real-time geological perception. SUMMARY

[0011] To overcome the problems in the related art, the embodiment of the present application provides a support force determination method and system for shield under-river crossing of elevation stratum, and the technical solution is as follows:

[0012] The present application is implemented as follows: a support force determination method for shield under-river crossing of elevation stratum, the method comprising the following steps:

[0013] S1, combine the wedge failure theory and the limit equilibrium method to establish a model that regards the soil body in front of the shield excavation face as a prism plus a wedge;

[0014] S2, take the shield support force and the sliding soil body in the limit equilibrium state as the analysis object, and analyze the mechanical balance of the shield support force and the sliding soil body;

[0015] S3, divide the under-river crossing process into five stages, calculate the excavation face support force of each non-uniform stratum under the river, and determine the minimum limit support force of the shield excavation face under the river, and calculate the size of the limit support force.

[0016] In step S1, in the wedge failure theory, based on the conclusion of wedge stress analysis, it is:

[0017] ; Let:

[0018]

[0019] ;

[0020] Then:

[0021] ;

[0022] ;

[0023] wherein, is the minimum support force, is the sliding block inclination angle, is the internal friction angle of the soil, is the vertical force at the top of the tunnel, is the self-weight of the block, is the cohesion of the soil, is the equivalent shield diameter, and in the case of equal areas of square and circle, it is derived that , is the diameter of the shield machine; is the frictional resistance on the lateral sliding surface of the block; is a dimensionless coefficient that integrates the relative relationship between the sliding surface inclination angle and the internal friction angle of the soil , which simplifies the subsequent expression of the limit support force .

[0024] In step S2, the shield support force and the sliding soil mechanical equilibrium are analyzed, including: by deducing the river channel shape parameterization formula, the river channel cross-sectional shape is parameterized and converted into an equivalent additional load;

[0025] Taking the river channel cross-section as the analysis object, the change function of the overburden thickness along the tunnel axis direction is defined , is the horizontal coordinate of the shield excavation surface along the tunneling direction with the river channel center as the origin, is the river channel bottom width, is the river channel slope width, is the river channel depth, is the width-depth ratio of the river channel slope, is the burial depth from the river channel bottom to the tunnel top;

[0026] When , the excavation surface is located in the river-free area, and the burial depth ;

[0027] When , the excavation surface is located in the river channel slope area, and the burial depth , ;

[0028] When the excavation face is located at the top of the river channel, the buried depth .

[0029] Further, the non-uniform overburden caused by the river channel shape is converted into an equivalent additional load, and the unit length additional load is:

[0030] ;

[0031] In the formula, is the unit length additional load, is the soil bulk density;

[0032] The total additional load is obtained by integration, and the integration length is the unstable influence area of the three-dimensional wedge model;

[0033] ;

[0034] In the formula, is the total additional load, is the length of the unstable model in front of the excavation face.

[0035] In step S3, the river channel underpass process is divided into five stages, and the excavation face support force of each non-uniform stratum under the river channel is calculated, including: by dividing the river channel underpass process into five stages, the limit support force of the excavation face of each stage is solved respectively;

[0036] In the first stage, when the shield machine excavation face and the unstable model in front of the wedge are located at the bottom of the river channel, and , the top load of the unstable model of the shield excavation face is converted to:

[0037] ;

[0038] ;

[0039] The top load formula is brought into the minimum limit support force calculation formula, and the following is obtained:

[0040] ;

[0041] In the formula, is the vertical force at the top of the tunnel.

[0042] In the second stage, when the shield machine excavation face is located at the bottom of the river channel, and the unstable model in front of the wedge is located in the river channel slope area, and , the top load of the unstable model of the shield excavation face is converted to:

[0043] ;

[0044] ;

[0045] Substituting the top load formula into the minimum limit support force calculation formula, we get:

[0046] .

[0047] In the third stage, when the shield machine excavation face and the front wedge instability model are located in the river slope area, and , the top load of the shield excavation face instability model is converted to:

[0048] ;

[0049] ;

[0050] Substituting the top load formula into the minimum limit support force calculation formula, we get:

[0051] .

[0052] In the fourth stage, when the shield machine excavation face is located in the river slope stratum, and the front wedge instability model is located in the river channel stratum, and , the top load of the shield excavation face instability model is converted to:

[0053] ;

[0054] ;

[0055] Substituting the top load formula into the minimum limit support force calculation formula, we get:

[0056] .

[0057] In the fifth stage, when the shield machine excavation face and the front wedge instability model are both through the river, , the top load of the shield excavation face instability model is converted to:

[0058] ;

[0059] Substituting the top load formula into the minimum limit support force calculation formula, we get:

[0060] ;

[0061] Finally, the river underpass process is divided into five stages of excavation face limit support force.

[0062] Another object of the present application is to provide a system for determining the support force of a shield tunneling through a river course with a height difference, which is used to regulate and control the method for determining the support force of the shield tunneling through the river course with the height difference, and the system comprises:

[0063] A three-dimensional wedge model construction module is used to combine the wedge failure theory and the limit equilibrium method to establish a model in which the soil body in front of the shield excavation face is regarded as a prism plus a wedge.

[0064] A shield support force and sliding soil body mechanical equilibrium analysis module is used to analyze the mechanical equilibrium of the shield support force and the sliding soil body under the limit equilibrium state.

[0065] A shield tunneling through a river course excavation face limit support force determination module is used to divide the tunneling through the river course process into five stages, calculate the excavation face support force of each non-uniform stratum of the tunneling through the river course, and determine the size of the limit support force of the shield tunneling through the river course excavation face.

[0066] In combination with all the above technical solutions, the present application has the following beneficial effects:

[0067] First, the present application is around the support force determination problem under the working condition of the shield tunneling through a river course with a height difference, sets the soil layer parameters and the geometric position relationship between the river course and the shield tunneling route, converts the overburden pressure during the shield tunneling through the river course into a surface additional load, combines the three-dimensional wedge instability theory with the surface additional load, divides the process into five different excavation stages, and deduces a calculation formula for the minimum limit support force of the excavation face suitable for the non-uniform stratum during the whole tunneling through the river course. The formula simplifies the wedge theory calculation model, avoids complex formulas and tedious calculation steps, accurately calculates the limit support force of the river course bottom horizontal stratum, the river course slope, the river course bottom layer without the river course, and the intersection of each stratum, makes the support force calculation more in line with the actual engineering conditions, provides a reliable theoretical basis for the support design of the shield method construction under the river course, enriches and perfects the theoretical analysis system of the limit support force of the shield excavation face, and lays a foundation for subsequent theoretical analysis and technical development.

[0068] Second, the present application analyzes the size of the limit support force of the shield tunnel excavation face in the tunneling through the river course stratum by using the theoretical formula derivation method. Based on a certain shield tunneling through a river course project, the present application proposes a river course shape parameterization calculation formula, converts the overburden pressure during the tunneling through the river course into an equivalent uniform load based on the wedge sliding theory, deduces the calculation formula for the limit support force of the excavation face in different stages of the tunneling through the river course non-uniform stratum, obtains the support force change curve during the tunneling through the river course by the theoretical formula, and determines the limit support force change law of the excavation face at different positions, thereby providing theoretical guidance for the determination of the support force of the tunneling through the river course in actual engineering.

[0069] Thirdly, the application provides a precise minimum limit support force calculation formula for the uneven bottom layer engineering of the actual shield underpassing river, avoids the problems of increasing material and construction cost caused by the over-high support force design or the problems of excavation surface instability, water and sand gushing caused by the over-low support force design, reduces engineering accidents and huge losses, and improves the safety and economy of the actual underpassing river engineering. Meanwhile, the application simplifies the complex calculation model, provides a directly applicable formula, shortens the design period, and speeds up the engineering progress.

[0070] Fourthly, the application first deduces a minimum limit support force calculation formula that can cover the whole process (five different stages) of underpassing river and is applicable to the river bottom horizontal stratum, river slope, no river bottom stratum, and the junction of each stratum, solves the problem that the previous method is difficult to accurately process such continuously changing and non-homogeneous terrain. The traditional view may consider that the classic wedge theory is too simplified and is difficult to process such complex boundary conditions as river terrain. The application successfully expands and transforms the wedge theory by innovatively introducing the equivalent overburden pressure of the ground surface additional load and finely dividing the construction stages, so that the wedge theory can more accurately adapt to complex actual working conditions. BRIEF DESCRIPTION OF DRAWINGS

[0071] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and serve to explain the principles of the present disclosure, together with the description;

[0072] Figure 1 is a flowchart of the support force determination method for the shield underpassing river high-difference stratum provided by the embodiment of the application;

[0073] Figure 2 is a line chart of the support force determination method for the shield underpassing river high-difference stratum provided by the embodiment of the application;

[0074] Figure 3 is a three-dimensional wedge model schematic diagram provided by the embodiment of the application;

[0075] Figure 4 is a river overburden parameterization model (river bottom stratum) schematic diagram of stage one provided by the embodiment of the application;

[0076] Figure 5 is a river overburden parameterization model (river bottom and slope stratum) schematic diagram of stage two provided by the embodiment of the application;

[0077] Figure 6 is a river overburden parameterization model (river slope stratum) schematic diagram of stage three provided by the embodiment of the application;

[0078] Figure 7This is a schematic diagram of the parametric model of the overlying soil of the river channel (river channel slope and non-channel strata) in stage four provided by the embodiments of the present invention;

[0079] Figure 8 This is a schematic diagram of the parametric model of the overlying soil of the river channel (without river channel strata) in stage five provided by an embodiment of the present invention;

[0080] Figure 9 This is a schematic diagram of a shield tunnel passing under a riverbed stratum provided in an embodiment of the present invention;

[0081] Figure 10 This is a schematic diagram illustrating the variation of the ultimate support force at the excavation face of the underpass river channel provided in an embodiment of the present invention;

[0082] Figure 11 This is a schematic diagram of the calculation model provided in an embodiment of the present invention;

[0083] Figure 12 This is a curve showing the relationship between the support pressure ratio and the displacement of the excavation face, provided in an embodiment of the present invention. Detailed Implementation

[0084] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0085] The innovation of this invention lies in the fact that it accurately derives a method applicable to the entire process of crossing a river. Heterogeneous formation The formula for calculating the minimum ultimate support force at the excavation face solves the problem of calculating the minimum ultimate support force at the excavation face in continuously changing and heterogeneous terrain. Specifically, focusing on the problem of determining the support force in the case of shield tunneling under river strata with elevation differences, the formula sets soil layer parameters and the geometric positional relationship between the river and the shield tunneling route. It transforms the overlying soil pressure during shield tunneling under the river into additional surface loads. By combining the three-dimensional wedge instability theory with the additional surface loads, and dividing the process into five different excavation stages, a formula for calculating the minimum ultimate support force at the excavation face in heterogeneous strata throughout the entire process of river tunneling is derived. This provides theoretical guidance for determining the support force when tunneling under rivers in practical engineering.

[0086] Example 1, as Figure 1 , Figure 2 As shown, the method for determining the support force of a shield tunneling machine passing under a riverbed with significant elevation differences, provided in this embodiment of the invention, includes the following steps:

[0087] S1 combines the wedge failure theory and the limit equilibrium method to establish a model that treats the soil in front of the shield excavation face as a prism plus a wedge.

[0088] S2, taking the shield support force and sliding soil under the limit equilibrium state as the analysis objects, analyzes the mechanical equilibrium of the shield support force and sliding soil.

[0089] S3 divides the river crossing process into five stages, calculates the support force of the excavation face of each uneven stratum under the river, and thus determines the magnitude of the ultimate support force of the shield tunneling excavation face under the river.

[0090] This invention assumes that the uneven load generated by the riverbed above the tunnel will not affect the shape of the prism. The calculation model is as follows: Figure 3 As shown. This invention makes the following basic assumptions about the wedge failure theory: the soil is isotropic, the slip surface conforms to the Mohr-Coulomb criterion; the area of ​​the side of the wedge that contacts the shield cutterhead is equivalent to the area of ​​the excavation face; the influence of groundwater is ignored; and the support force is uniformly distributed at the excavation face.

[0091] Based on the conclusions of wedge-shaped body stress analysis, this invention derives the following formula for calculating the minimum ultimate support force:

[0092] ;

[0093] make:

[0094] ;

[0095] Then we have:

[0096] ;

[0097] ;

[0098] In the formula, To minimize the ultimate support force, The slider tilt angle, Let be the internal friction angle of the soil. For the vertical force at the top of the tunnel, For the weight of the block itself, For the cohesion of soil, To obtain the equivalent shield diameter, assuming the areas of the square and the circle are equal, the following is derived: , The diameter of the tunnel boring machine; The frictional resistance on the lateral sliding surface of the block; It is a dimensionless coefficient that incorporates the sliding surface inclination angle. Angle of friction with soil The relative relationship simplifies the subsequent ultimate support force. The expression.

[0099] This invention derives a parameterized formula for river channel shape, parameterizing the cross-sectional shape of the river channel and converting it into an equivalent additional load. Specific steps include:

[0100] Taking the river channel cross-section as the analysis object, a function is defined to describe the variation of the overburden thickness along the tunnel axis. , The horizontal coordinates of the shield tunneling face along the tunneling direction are taken with the center of the river channel as the origin. The width of the riverbed. The width of the river channel slope. For river depth, The width-to-depth ratio of the river channel slope. The depth from the bottom of the riverbed to the top of the tunnel;

[0101] when At that time, the excavation face was located in an area without a river channel, and the burial depth was... ;

[0102] when At that time, the excavation face was located in the riverbank slope area, with a burial depth of... , ;

[0103] when At that time, the excavation face was located at the top of the river channel, with a burial depth of... .

[0104] The non-uniform soil cover caused by the river channel shape is converted into an equivalent additional load, and the additional load per unit length is:

[0105] ;

[0106] In the formula, Add a load per unit length, The soil weight;

[0107] The total additional load is calculated using integration, with the integration length being the instability influence region of the three-dimensional wedge model.

[0108] ;

[0109] In the formula, For the total additional load, The length of the unstable model in front of the excavation face.

[0110] Since the river channel has a symmetrical structure and the calculation methods on both sides are similar, this invention divides the river channel crossing process into five stages, solves the ultimate support force of the excavation face for each stage, and finally obtains the ultimate support force of the excavation face for the entire process of the shield tunnel crossing the river channel.

[0111] In the first stage, when both the tunnel boring machine's excavation face and the instability model of the forward wedge are located at the bottom of the river channel, i.e. and At times, such as Figure 4 As shown, the top load of the shield tunneling face instability model can be transformed into:

[0112] ;

[0113] ;

[0114] From the formula for calculating the minimum ultimate support force under the top load, we can obtain:

[0115] (2)

[0116] In the formula, This refers to the vertical force at the top of the tunnel.

[0117] In the second stage, when the tunnel boring machine's excavation face is located at the bottom of the river channel, and the instability model of the forward wedge body is located in the river channel slope area, i.e. and At times, such as Figure 5 As shown, the top load of the shield tunneling face instability model can be transformed into:

[0118] ;

[0119] ;

[0120] Substituting the top load formula into the minimum ultimate support force calculation formula, we get:

[0121] (3)

[0122] In the second stage, when the tunnel boring machine (TBM) excavates to the junction of the riverbed and the slope, the overlying soil load undergoes nonlinear changes, making the calculation of the excavation face support force more complex. This formula provides theoretical guidance for calculating the support force of excavation faces in uneven strata such as those under rivers, enabling more accurate calculation of the ultimate support force required for uneven strata at the TBM excavation face, thus making the support force calculation more closely reflect actual engineering conditions.

[0123] In the third stage, when both the tunnel boring machine's excavation face and the instability model of the forward wedge are located in the river slope area, that is... and At times, such as Figure 6 As shown, the top load of the shield tunneling face instability model can be transformed into:

[0124] ;

[0125] ;

[0126] Substituting the top load formula into the minimum ultimate support force calculation formula, we get:

[0127] (4)

[0128] In the third stage, the overburden load is increasing uniformly. The calculation using this formula provides theoretical guidance for real-time calculation of support force at different excavation distances during dynamic excavation, making the support force calculation more consistent with actual engineering conditions.

[0129] In the fourth stage, when the tunnel boring machine's excavation face is located in a riverbed slope stratum, while the instability model of the forward wedge body is located in a non-riverbed stratum, i.e. and At times, such as Figure 7 As shown, the top load of the shield tunneling face instability model can be transformed into:

[0130] ;

[0131] ;

[0132] Substituting the top load formula into the minimum ultimate support force calculation formula, we get:

[0133] (5)

[0134] In the fourth stage, when the tunnel boring machine (TBM) excavates to the slope boundary and the bottom layer without a river channel, the overlying soil load undergoes nonlinear changes, making the calculation of the excavation face support force more complex. This formula provides theoretical guidance for calculating the support force of excavation faces in uneven strata such as those under rivers, enabling more accurate calculation of the ultimate support force required for uneven strata at the TBM excavation face, thus making the support force calculation more closely reflect actual engineering conditions.

[0135] In the fifth stage, after the tunnel boring machine's excavation face and the instability model of the forward wedge have both passed through the river channel, i.e. At times, such as Figure 8 As shown, the top load of the shield tunneling face instability model can be transformed into:

[0136] ;

[0137] Substituting the top load formula into the minimum ultimate support force calculation formula, we get:

[0138] (6)

[0139] Ultimately, the ultimate support force of the excavation face was obtained in five stages during the river crossing process.

[0140] Example 2: To verify the rationality and accuracy of the formula derived in this invention, a numerical simulation model was established using the finite element software ABAQUS. The support ratio was introduced. Lambda To represent the relationship between the support force and the horizontal displacement of the center of the excavation face, when Lambda When the limit value is reached, the horizontal displacement of the excavation face increases rapidly, and the support force of the excavation face at this time is determined to be the ultimate support force. The numerical simulation calculation results are compared with the theoretical formula calculation results, and the difference between the two is 6.9%, which verifies the applicability of the theoretical formula in the case of crossing the river.

[0141] Example 3: This embodiment of the invention also provides a test device for simulating shield tunneling rock breaking in karst formations. Based on a shield tunneling project under a river, the device calculates the actual support force of the excavation face by substituting the positional relationship between the river and the shield tunneling route into the calculation formula for the ultimate support force of the excavation face under five excavation stages according to the actual engineering parameters. The change curve of the support force during the shield tunneling under the river is obtained through theoretical formulas, clarifying the change law of the ultimate support force of the excavation face at different locations.

[0142] Example 4: This embodiment of the invention also provides a system for determining the support force of a shield tunneling machine passing under a riverbed with significant elevation differences. The system includes:

[0143] The 3D wedge model construction module is used to combine the wedge failure theory and the limit equilibrium method to establish a model that treats the actively failing soil in front of the shield excavation face as a prism plus a wedge.

[0144] The shield support force and sliding soil mechanical equilibrium analysis module is used to analyze the shield support force and sliding soil under the limit equilibrium state as the analysis objects.

[0145] The module for determining the ultimate support force of the excavation face of the shield tunneling river crossing is used to divide the river crossing process into five stages and calculate the support force of the excavation face of each uneven stratum under the river crossing, thereby determining the magnitude of the ultimate support force of the shield tunneling river crossing excavation face.

[0146] To further demonstrate the positive effects of the above embodiments, the present invention uses Abaqus simulation software for simulation verification, specifically as follows:

[0147] This invention is based on a shield tunneling project under a river, and describes the positional relationship between the river and the shield tunneling route according to actual engineering parameters as follows: Figure 9 As shown, the actual excavation face support force is calculated by substituting the formulas for calculating the ultimate support force of the excavation face under the five excavation stages. Prior to this, to verify the rationality and accuracy of the formulas derived in this invention, a numerical simulation model was established using the finite element software ABAQUS. During the calculation, the tunnel was directly extended to a point with an axial length of 38m, and support force was applied at the excavation face.

[0148] In Application Example 1, a numerical simulation model was established using the finite element software ABAQUS. The model size was 64m × 64m × 40m, the tunnel depth was 20m, the river depth was 12m, the river slope width was 3m, the riverbed width was 9m, the tunnel boring machine diameter was 6.4m, and the lining segment and grouting layer thickness was 0.5m. During the calculation, the tunnel was directly extended to a point with an axial length of 38m, and support was applied at the excavation face. The 9m section of the tunnel closest to the excavation face was supported by the tunnel boring machine, while the remaining 29m was supported by lining segments and grouting layer.

[0149] Computational models such as Figure 11 As shown in the figure. In the numerical simulation model, the upper surface of the model is a free surface, the left and right boundary surfaces constrain its displacement in the X direction, and the front and rear boundary surfaces constrain its displacement in the Y direction. The soil adopts the Mohr-Coulomb constitutive model, and the segments adopt linear elastic elements. The soil layers and material parameters are shown in Table 1.

[0150] Table 1 Soil layer and material parameters

[0151]

[0152] To observe the evolution of the horizontal displacement at the center of the excavation face with the change in support force during the calculation process, the excavation face was located at the junction of the riverbed bottom and the river slope (x=4.5m). First, a support force of the same magnitude but opposite direction to the initial horizontal ground stress was applied to the excavation face. The support force was gradually reduced, and the change in horizontal displacement at the center point of the excavation face was observed and recorded. The support force at the excavation face is a trapezoidal load, smaller at the top and larger at the bottom. This invention uses the support force at the center point of the excavation face as the average support force of the excavation face, utilizing the support ratio... This is used to represent the relationship between the support force and the horizontal displacement of the center of the excavation face, namely: ,in, For the center support force of the excavation face, The initial horizontal stress of the model.

[0153] The support force applied at the excavation face and the maximum displacement of the soil at the excavation face were recorded, and the relationship curve between the maximum displacement of the soil at the excavation face and the support pressure ratio was obtained, as shown in the figure. Figure 12 As shown. From Figure 12 It can be seen from this:

[0154] (1) When the support pressure ratio is between 1.0 and 0.82 (P = 286.96-237.77 kPa), the decrease in the support pressure ratio causes a very small change in the maximum displacement of the soil at the excavation face.

[0155] (2) When the support force-pressure ratio is between 0.82 and 0.43 (P = 237.77-123.39 kPa), the decrease in the support force-pressure ratio significantly increases the maximum displacement of the soil at the excavation face, and the curve shows a linear change.

[0156] (3) When the support pressure ratio is less than 0.28 (P=86.35kPa), the horizontal displacement of the center of the excavation face increases rapidly, and the model calculation reaches a non-convergent state. Based on the technical achievements of predecessors, it is considered that the support force is the minimum ultimate support force. At this time, the soil in front of the excavation face will actively become unstable and fail.

[0157] (4) As the support pressure ratio decreases, the maximum horizontal displacement at the center of the excavation face shows three stages: no significant change, significant change, and unstable change, which is consistent with the existing technology.

[0158] according to Figure 12 The curve shows that when the support ratio is 0.28, the excavation face becomes unstable and fails, meaning the minimum ultimate support force of the excavation face is 80.35 kPa.

[0159] To verify the correctness and applicability of the theoretical calculation model, the ultimate support force of the excavation face will be analyzed from the perspectives of considering the theoretical calculation of the river channel, not considering the theoretical calculation of the river channel, and numerical simulation. The excavation face is located at the junction of the river bottom and the river slope (x=4.5m). The minimum ultimate support force of the excavation face obtained by different methods is shown in Table 2.

[0160] Table 2 Minimum ultimate support force for different excavation faces

[0161]

[0162] As shown in Table 2, when the shield tunnel passes under the riverbed stratum, the minimum ultimate support force derived from the riverbed theory differs from the numerical simulation by 6.9%, while the difference between the theoretical derivation and the numerical simulation without considering the riverbed is 28.4%. Therefore, the calculation model for the minimum ultimate support force considering the riverbed stratum proposed in this invention is more reasonable. It is necessary to consider the influence of the riverbed elevation difference on the support force of the excavation face when the tunnel passes under the riverbed stratum. Moreover, the theoretical calculation formula derived in this invention is simpler than the calculation formula of other models, and does not require a large amount of integration and iterative calculation, thus reducing the calculation difficulty.

[0163] Application Example 2: To further analyze the impact of changes in river elevation on the stability of the excavation face, based on the parameters of a shield tunneling project under a river, the formulas for calculating the ultimate support force of the excavation face under five excavation stages are calculated respectively.

[0164] Specifically, the positional relationship between the river channel and the tunnel boring machine route is determined based on actual engineering parameters, such as... Figure 9As shown in the figure, for the convenience of calculation, it is assumed that the shape of the river channel is an axisymmetric trapezoid, the soil mass is horizontally layered, the tunneling direction of the shield tunnel is perpendicular to the river channel trend, double tunnels with double tracks, the tunnel diameter R1 = 6.4 m, the cutterhead radius of the shield machine R2 = 6 m, I = 9 m, E n = 3 m, H1 = 12 m, H2 = 3.7 m, D = 14 m. Based on the above engineering parameters, they are respectively substituted into the calculation formulas of the ultimate support force of the excavation face in the five excavation stages for calculation:

[0165] (1) When x < 0, that is, when the excavation enters the first stage, substituting the known engineering parameters into the above formula (2), the support force y of the excavation face is obtained as 16.44 kPa.

[0166] (2) When 0 < x < 3, that is, when the excavation enters the second stage, substituting the known engineering parameters into the above formula (3), the support force y of the excavation face is obtained as y = 4.161x^2 + 0.574x + 16.46.

[0167] (3) When 3 < x < 4.5, that is, when the excavation enters the third stage, substituting the known engineering parameters into the above formula (4), the support force y of the excavation face is obtained as y = 24.894x - 22.495.

[0168] (4) When 4.5 < x < 7.5, that is, when the excavation enters the fourth stage, substituting the known engineering parameters into the above formula (5), the support force y of the excavation face is obtained as y = 24.894x - 22.495.

[0169] (5) When x > 7.5, that is, when the excavation enters the fifth stage, substituting the known engineering parameters into the above formula (6), the support force y of the excavation face is obtained as y = 126.988.

[0170] According to the excavation degree of each stage, combined with the theoretical formula, a curve graph of the change of the support force during the shield tunneling under the river channel is obtained, as Figure 10 shown, which clarifies the change law of the ultimate support force of the excavation face at different positions.

[0171] In the actual project of the shield tunneling under the river channel, through the data obtained from this curve graph, the numerical value of the support force of the shield excavation face can be calculated in real time, and the ultimate support force required for the shield excavation face can be calculated more accurately, greatly reducing the disturbance degree of the shield construction to the river channel, ensuring the stability of the excavation face, and preventing the occurrence of major engineering disasters such as tunnel water inrush and excavation face instability caused by improper support force and disasters such as river water seepage.

[0172] The above is only the relatively optimal specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for determining a supporting force for a shield tunneling through a river-crossing high-differential stratum, characterized in that, The method comprises the following steps: S1, combining the wedge failure theory and the limit equilibrium method, a model is established that the soil body actively destroyed in front of the shield excavation face is regarded as a prism plus a wedge; S2, taking the shield support force and the sliding soil body in the limit equilibrium state as the analysis object, the mechanical equilibrium of the shield support force and the sliding soil body is analyzed; S3, the river crossing process is divided into five stages, the support force of the excavation face of each uneven stratum in the river crossing is calculated respectively, so that the limit support force of the excavation face of the shield river crossing is determined; In step S1, in the wedge failure theory, based on the conclusion of the force analysis of the wedge, the minimum limit support force is obtained, and the calculation formula is: ； Let: ； Then, ； ； wherein, is the minimum limit support force, is the sliding block inclination angle, is the internal friction angle of the soil, is the vertical force at the top of the tunnel, is the block self-weight, is the cohesion of the soil, is the equivalent shield diameter, in the case of a square and a circular area being equal, it is obtained , is the diameter of the shield machine; is the frictional resistance on the lateral sliding surface of the block; is a dimensionless coefficient; In step S2, the mechanical equilibrium of the shield support force and the sliding soil body is analyzed, including: the river cross-section shape is parameterized by deducing the parameterization formula of the river shape, and is converted into an equivalent additional load; With the river cross section as the analysis object, the change function of the overburden thickness along the tunnel axis direction is defined , is the horizontal coordinate of the shield excavation face along the tunneling direction with the river center as the origin, is the river bottom width, is the river slope width, is the river depth, is the width-depth ratio of the river slope, is the burial depth from the river bottom to the tunnel top; When the excavation face is located in a non-river region, the buried depth ; When the excavation face is located in the river channel slope region, the buried depth , ; When the excavation surface is located at the top of the river channel, the buried depth ; The uneven overburden caused by the river shape is converted into an equivalent additional load, and the unit length additional load is: ； In the formula, L is the length of the unit load, is the bulk density of the soil; The total additional load is calculated by integration, and the integration length is the instability influence area of the three-dimensional wedge model; ； wherein is the total additional load, is the length of the front of the excavation face instability model; In step S3, the river crossing process is divided into five stages, the support force of the excavation face of each uneven stratum in the river crossing is calculated respectively, including: the limit support force of the excavation face of each stage is solved by dividing the river crossing process into five stages; ； In the formula, is the vertical force on the tunnel roof.

2. The method according to claim 1, wherein The top load formula is substituted into the minimum limit support force calculation formula to obtain: At the first stage, when the shield tunneling face and the front wedge instability model are both located at the river bottom, and the top load of the shield tunneling face instability model is converted into: ； ； The top load formula is substituted into the minimum limit support force calculation formula to obtain: ； In the formula, is the vertical force on the tunnel roof.

3. The method according to claim 2, wherein At the second stage, when the tunneling face is located at the bottom of the river and the wedge instability model is located at the slope region of the river, and the top load of the tunneling face instability model is transformed as: ； ； The top load formula is substituted into the minimum limit support force calculation formula to obtain: 。 4. The method according to claim 2, wherein At the third stage, when the shield tunneling face and the front wedge instability model are located in the river slope region, and , the top load of the shield tunneling face instability model is converted into: ； ； The top load formula is substituted into the minimum limit support force calculation formula to obtain: 。 5. The method according to claim 2, wherein At the fourth stage, when the tunneling face is located in the river slope stratum, and the front wedge instability model is located in the non-river stratum, and the top load of the tunneling face instability model is converted into: ； ； The top load formula is substituted into the minimum limit support force calculation formula to obtain: 。 6. The method according to claim 2, wherein, At the fifth stage, when the tunneling face and the front wedge of the shield machine lose stability, both the models pass through the river, The top load of the tunneling face loss stability model is transformed into: ； The top load formula is substituted into the minimum limit support force calculation formula to obtain: ； The limit support force of the excavation face of the river crossing process is obtained.

7. A system for determining the support force of a shield tunneling machine passing under a riverbed with significant elevation differences, characterized in that, The system is used for regulating and controlling the support force determination method of the shield river crossing high-difference stratum, and the system comprises: A three-dimensional wedge model construction module is used for combining the wedge failure theory and the limit equilibrium method, and establishing a model that the soil body actively destroyed in front of the shield excavation face is regarded as a prism plus a wedge; A shield support force and sliding soil body mechanical equilibrium analysis module is used for taking the shield support force and the sliding soil body in the limit equilibrium state as the analysis object, and analyzing the mechanical equilibrium of the shield support force and the sliding soil body; A shield river crossing excavation face limit support force determination module is used for dividing the river crossing process into five stages, calculating the support force of the excavation face of each uneven stratum in the river crossing respectively, and determining the size of the limit support force of the excavation face of the shield river crossing.

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