A method and system for determining the impact load of a shield cutter in a soft-over-hard composite stratum

Abstract

The application belongs to the technical field of tunnel construction, and discloses a method and system for determining the impact load of a shield cutter in a soft-over-hard composite stratum, which divides the rock into a plurality of concentric circular regions by using a cavity expansion model, determines the radii of the regions, and obtains the relationship between the damage state of the rock body at different positions and the distance position of the cutter center; the influence of the cross-sectional penetration is introduced, the damage state of the cutter cross section at the cutter center in the lower contact area of the cutter is determined based on the influence of the damage difference between the vertical crack zone and the dense core zone in the process of cutter rock breaking, and the damage distribution state of the lower hard rock side of the cutter in the vertical crack propagation process at the interface is determined; the expression of the stress change of the transition section is determined based on the CSM model, the influence of the damage of the lateral shear zone is combined, and the impact load prediction of the shield cutter when penetrating the soft-over-hard composite stratum is realized. The application first introduces the damage effect and the cavity expansion model theory, improves the compatibility of the prediction model with the actual situation, and reduces the abnormal damage rate of the cutter.

Description

Technical Field

[0001] This invention belongs to the field of tunnel construction technology, and in particular relates to a method and system for determining the impact load of shield tunnel cutterhead in composite strata with soft upper and hard lower layers. Background Technology

[0002] Currently, my country's large-diameter shield tunnels are in a stage of rapid construction and development. The commencement of numerous large-diameter shield tunnel projects crossing rivers and seas is driving shield tunneling technology towards ultra-large cross-sections, ultra-long distances, and complex geological conditions. As the cross-sectional size of shields increases, the geological conditions they face are evolving from homogeneous strata to complex strata with varying degrees of hardness.

[0003] The cutter stress in composite strata of large-diameter shield tunnels differs significantly from that in homogeneous hard rock. The most common composite strata are soft upper layers and hard lower layers, meaning the upper section of the tunnel cross-section consists of relatively low-strength strata such as soft soil, strongly weathered rock, fractured rock layers, and karst caves. These strata generally have low strength, poor self-stability, and high water content. The lower section consists of moderately or weakly weathered strata, which generally have high strength, good self-stability, and high quartz content, placing high demands on the cutter's rock-breaking ability and wear resistance. When large-diameter shield tunneling in composite strata, the cutter is subjected to impact at the soft-hard interface, significantly increasing the abnormal damage rate. Abnormal cutter damage caused by interface impact in composite strata has become a key challenge limiting the safe and efficient construction of large-diameter shield tunnels. While existing cutter stress prediction models both domestically and internationally are based on different rock-breaking mechanisms, they are mostly established based on assumptions and experimental data related to homogeneous strata conditions. However, the failure mechanism of rock masses in composite strata differs significantly from that in homogeneous strata. Therefore, a method is needed to determine the magnitude and distribution of the impact load on the cutterhead of a shield tunneling machine in composite strata. Existing domestic and international technologies for determining the impact load on the cutterhead in composite strata mostly employ the CSM model. However, because the cutterhead pressure distribution analyzed by the CSM model based on homogeneous hard rock is nearly linear, only monotonic normal force values ​​with different slopes can be obtained during the transition period. Directly using this assumption for analysis cannot reflect the impact problem at the interface. Furthermore, this assumption is invalid when the mechanical bonding between soft and hard rock masses is not tight and the mechanical parameters differ significantly.

[0004] Based on the above analysis, the existing technologies have the following problems and shortcomings: Firstly, when traditional CSM models are applied to composite strata, the prediction error exceeds 40%, making it difficult to accurately reflect the actual stress on the cutterhead. Secondly, existing composite strata load prediction methods do not consider the deterioration of the rock mass below the cutterhead, limiting their ability to predict and prevent abnormal cutterhead damage. This proposed solution, however, uses the CSM model as a basis and considers damage mechanics and spatial expansion models, combined with the impact of lateral shear zone failure, to derive an impact load prediction formula for the transition zone cutting. This formula can improve the prediction accuracy to over 85%, accurately addressing the shortcomings of existing technologies and providing more reliable cutterhead stress analysis support for shield tunneling in composite strata. Summary of the Invention

[0005] To overcome the problems existing in related technologies, the present invention discloses a method and system for determining the impact load of shield tunnel cutterheads in composite strata with soft upper and hard lower layers. The aim is to predict the magnitude and distribution of the impact load borne by the cutterheads when they cut the soft-hard interface of the composite strata. The technical solution is as follows: This invention is implemented as follows: a method for determining the impact load of shield tunnel cutterhead in composite strata with soft upper and hard lower layers, comprising the following steps: S1, using a cavity expansion model, the rock is divided into multiple concentric circular regions, the radius of each region is determined, and the relationship between the damage state of the rock mass at different locations and the distance from the center of the cutting edge is obtained; S2, Introducing the influence of cross-sectional penetration, based on the difference in damage between the vertical crack zone and the dense core zone during the rock breaking process of the cutter, the damage state of the cutter cross-section at the distance from the center of the cutter edge within the lower contact area of ​​the cutter is determined, and the damage distribution state of the lower hard rock side of the cutter during the vertical crack propagation process at the interface is obtained. S3, based on the CSM model, derives an expression for the stress change in the transition section and, combined with the influence of lateral shear zone failure, realizes the prediction of impact load when the shield cutter passes through a composite stratum of soft upper and hard lower.

[0006] In step S1, the analysis describes the failure evolution of the rock mass below the cutter from the perspective of damage mechanics. The determination of the damage range is based on the relevant assumptions and conclusions of the cavity expansion theory; the central vertical crack extends in a semi-circular pattern with a radius of [missing information]. r c When the rock is broken by a roller cutter, the damage and deterioration zone inside the rock mass is consistent with the range of vertical crack propagation. A mechanical model of rock breaking by a roller cutter based on damage influence in composite strata is constructed. A cavity expansion model was constructed, dividing the soft rock region below the hob into multiple concentric circular regions from the center point of the cutter ring's cutting edge; based on the differences in the failure mechanisms of each region, from the inside out, the regions are as follows: outer radius is... r d The dense core region, with a width of 2 w Keep it consistent; outer radius isr p The fractured zone; outer radius r c The cracked area has an outer radius of... r e The elastic zone is the outermost undisturbed zone, and the confining pressure of the rock mass at infinity is the outermost zone. σ 0; Damage and failure occur within the rock mass as the dense core expands. Based on the zoning of the damage mechanics and cavity expansion model, when the equivalent attenuation coefficient of the rock mass has a linear relationship with the average degree of damage and failure, and the damage changes linearly along the expansion direction, a damage factor is used to describe the damage state of the rock during this process, establishing the damage state at different locations in the soft rock mass. D S ( r Distance from the center of the blade r Relationship; In the formula, the superscript S represents soft rock. The absolute value symbol represents... r It is a non-negative number. In the formula... This represents the truncation function, when... x When >0, when x When <0, . The radius of the radial crack zone in the soft rock. The radius of the soft rock fracture zone is given.

[0007] Furthermore, the damage state at different locations of the soft rock mass was analyzed. D S ( r Distance from the center of the blade r The relationship is averaged to obtain the equivalent damage at different locations in the soft rock. ; From the relationship between material damage and damage state, the relationship between the equivalent attenuation coefficient and damage state of soft rock mass is obtained as follows: In the formula, The attenuation coefficient of the fractured rock mass is... The attenuation coefficient of the undisturbed intact rock mass. This is the equivalent attenuation coefficient for soft rock masses.

[0008] In step S2, the model is analyzed according to the plane strain problem: based on the analysis method of plane strain problem, the radial stress inside the soft rock mass is analyzed. With tangential stress According to the equilibrium equation and the relationship between stress and displacement Obtain the general solution In the formula, , These are the elastic modulus and Poisson's ratio of the material, respectively. For radial displacement, r s The distance between the center of the cutting edge in soft rock is denoted as C1 and C2, which are integral constants determined by the boundary conditions. Relationship 1: Based on stress boundary conditions , have to , ,in, For soft rock, the tensile strength of the rock. Represents the pressure of the surrounding rock at infinity; The surrounding rock pressure at infinity for soft rock; and Substituting the general solution Based on the elastic zone displacement boundary condition Obtain the radius of the elastic zone in soft rock. Radial crack zone radius The relation is: Relationship 2: Stress conditions in the radial crack zone , Substituting into the equilibrium equation, the stress in the radial crack zone is obtained. , Uniaxial compressive strength of soft rock; based on boundary stress continuity condition ,in, , These are the limiting approximation methods for the inner and outer radii of the interface between the radial crack zone and the fractured zone, respectively, to obtain the radius of the radial crack zone in soft rock. With the radius of the fracture zone The relation is: Relationship 3: Fractured zone based on Mohr-Coulomb strength criterion Perform calculations, where... Correlation coefficient ,and Related uniaxial compressive strength of rock , σ θ For tangential stress, The internal friction angle of the rock mass. c The material's cohesion; substituting the Mohr-Coulomb strength criterion into the equilibrium equation, when the rock inside the crushed zone generates vertical stress due to yielding and failure... p and horizontal stressq If the dense core region is equivalent to the roller penetration load being transmitted in the form of hydrostatic pressure, then... p = q = p 0, p 0 is the reference pressure; according to the stress boundary conditions , The radius of the fractured zone in soft rock was obtained. radius of dense core region The relation is: In the formula, For soft rock, the coefficient is related to the internal friction angle; This is the reference pressure for soft rock.

[0009] In step S2, based on the geometry of each zone of the soft rock and the radius of the elastic zone in the soft rock... Radial crack zone radius Relationship, radial crack zone radius With the radius of the fracture zone Relationship, radius of the broken zone radius of dense core region The relationship determines the distribution and change of the damage range inside the soft rock during the roller cutter cutting process, and obtains the range of each damage area in the hard rock after the roller cutter has completely entered the hard rock through the interface. As the cutting tool gradually approaches the interface between the soft rock and hard rock in the soft rock, the damage and disturbance zone of the soft rock will come into contact with the hard rock due to the typical composite rock mass. Therefore, the damaged zone in the soft rock will be interrupted at the interface, and a dense core zone will be reformed in the hard rock when the cutter makes point contact with the hard rock. When the cutter fully penetrates the hard rock in the pressure zone, the lower damaged area expands to the level of the homogeneous rock mass. The size of the expansion range during this process is approximately equal to the length of the cutter. L The size of the contact zone entering hard rock Proportional to the damage distribution of hard rock during the propagation process, the relationship between the equivalent attenuation coefficient of soft rock and the damage state is used to obtain the damage distribution of hard rock during the propagation process. ; In the formula, the superscript H indicates hard rock. The length of the first half of the contact area of ​​the hob. The length of the contact zone into hard rock. For in position r The basic damage distribution function at the location, This is the hard rock damage distribution function after scaling transformation. At that time, through The location parameter r is scaled and then substituted into the hard rock foundation damage distribution function. In this context, it is used to describe the length L of the front half of the contact zone of the hob exceeding the length of the contact zone entering the hard rock. The distribution of hard rock damage varies with scale.

[0010] In step S2, based on the constructed rock-breaking force model of the roller cutter, the vertical crack zone in soft rock is determined according to the rock-breaking process of the roller cutter. With dense core region The impact of damage differences leads to the derivation of the distance from the center of the cutting edge within the lower contact area of ​​the hob. r Damage state of the hob section ,in r >0; In the formula, 、 The parameters for linear cutting tests with roller cutters in soft rock are determined, and their range depends on the properties of the rock mass and the degree of crack development; among them, soft rock... =0.3, =0.95, hard rock =0.35, =0.95, the penetration relationship of the hob section at a distance r from the center of the cutting edge. , Let the hob radius be... The penetration depth of the section where the hob is located at the center of the cutting edge. For position parameters, This indicates the location of the interface between soft and hard rocks.

[0011] In step S2, the damage state after the hob has fully entered the hard rock. D H ( x , r )and D S ( x , r ) consistent, among which When the vertical crack is close to the interface between soft and hard rock in the contact area of ​​the lower part of the cutter, it will be interrupted. After contacting the hard rock in the contact area, it will propagate again in the hard rock. The propagation law of the fracture damage zone satisfies the linear variation law of the damage distribution assumption of the hard rock. Combined with the damage state of the cutter section, the damage distribution state of the hard rock side of the lower part of the cutter during the vertical crack propagation process at the interface is obtained. In the formula, 、 The parameters for linear cutting tests of hard rock roller cutters are related to the properties of the rock mass and the degree of crack development. , .

[0012] In step S3, the dynamic change of the cutter force at the composite stratum interface is based on the CSM model used in homogeneous hard rock strata. By analyzing the influence of system deformation and composite rock mass damage on the pressure distribution and penetration of the cutter at the bottom, a predictive model for the impact load of the cutter in composite strata is constructed. The contact stress at the bottom of the CSM model is expressed as: in, φ θ is the contact angle between the cutter and the rock; C is a dimensionless coefficient. S The distance between the blades; σ c , σ t These are the rock mass compressive and tensile strengths, respectively. p s This represents the distributed contact stress at the bottom of the cutter ring; It is an integral variable used to describe the contact area from the beginning to the angular range; ψ This is the pressure distribution coefficient at the tool tip, ranging from -0.2 to 0.2, and varies with the tool tip width. T If the increase is due to the increase in size, 0.1 should be taken first. Integrating the load at the bottom of the hob, simplifying the expression... To obtain the stress changes in the soft rock section for: Similarly, the stress changes in the hard rock section can be obtained. for: The stress on the transition section is divided into two parts: the force of the soft rock section and the force of the intrusive hard rock section. By solving and summing the forces of the two parts separately, the stress variation formula of the transition section is obtained. ; In the formula, the superscript T represents the composite interface. , .

[0013] In step S3, the contact area length between the rock-breaking cycle and the cutter head is... L Consistently, as the cutter advances, the normal component provided by the shear zone continuously increases; when the shear zone fails, this component becomes zero. Limit force equilibrium analysis of the rock mass shear zone at the cutter's central section yields the following: In the formula, The angle between the bottom of the shear zone and the horizontal plane. θ c The cutting edge angle of the hobbing cutter. p l It is subjected to lateral force; According to the Mohr-Coulomb failure criterion ,Will Substitute to get ;right Find the partial derivative Substituting into the calculation, we get Bring back Lateral force Based on the contact geometry between the front half of the hob contact area and the shearing zone, the normal force component provided by the shearing zone is obtained. F Nl As the shear zone is destroyed F Nl The amplitude fluctuates; according to trigonometric function representation, the rock breaking period is consistent with the size of the cutter contact zone. To simplify the calculation of rock mass parameters, the position of the cutter centroid is used as the reference point. Based on the cavity expansion model, the stress change process of the transition section of the composite strata is analyzed from the perspective of damage mechanics, and the normal force component provided by the shear zone is calculated based on the failure effect of the lateral shear zone. The process will cause the transition section to be subjected to force. Normal force caused by lateral shear failure Summation to establish the final calculation formula + ; .

[0014] Another objective of this invention is to provide a system for determining the cutterhead impact load of a shield tunneling machine in a composite stratum with soft upper layer and hard lower layer. This system is used to regulate the method for determining the cutterhead impact load in such a stratum. The system includes: The rock partitioning module is used to divide the rock into multiple concentric circular regions using a cavity expansion model, determine the radius of each partition, and obtain the relationship between the damage state of the rock mass at different locations and the distance from the center of the cutting edge. The damage state determination module is used to introduce the influence of the section penetration. Based on the influence of the damage difference between the vertical crack zone and the dense core zone during the cutter rock breaking process, it determines the damage state of the cutter section at the distance from the center of the cutter edge within the lower contact area of ​​the cutter, and obtains the damage distribution state of the lower hard rock side of the cutter during the vertical crack propagation process at the interface. The impact load prediction module derives the expression for the stress change in the transition section based on the CSM model, and combines the influence of lateral shear zone failure to realize the impact load prediction when the shield cutter passes through a composite stratum with soft upper and hard lower layers.

[0015] Combining all the above technical solutions, the beneficial effects of this invention are as follows: First, this invention addresses the problem of determining the impact load of shield tunneling in composite strata. It employs a cavity expansion model to divide the rock into multiple concentric circular regions, determining the radius of each region to obtain the relationship between the damage state at different locations of the rock mass and the distance from the cutter center. The influence of section penetration is introduced, considering the impact of the damage difference between the vertical crack zone and the dense core zone during the cutter's rock-breaking process. This yields the damage state of the cutter section at the cutter center within the lower contact area of ​​the cutter, and derives the damage distribution on the hard rock side of the cutter under the vertical crack propagation process at the interface. Combined with the CSM model formula, the stress formula for the transition section of the composite rock mass is obtained. Based on the above, the influence of lateral shear zone failure is introduced to obtain... + This invention makes the data more closely reflect reality. Existing domestic and international technologies for determining the impact load of shield tunnel cutterheads in composite strata mostly rely on the CSM model based on homogeneous hard rock formations. This invention, for the first time, introduces damage action and cavity expansion model theories to describe the failure evolution of the rock mass below the cutterhead from the perspective of damage mechanics. It achieves a function that the CSM model could not (accurately reflecting the actual stress on the cutterhead), filling the technological gap in determining the impact load of shield tunnel cutterheads in composite strata with soft upper layers and hard lower layers. This promotes technological upgrading in the industry, and its commercial value lies not only in direct economic benefits but also in enhancing my country's independent controllability in this field.

[0016] Secondly, the method for determining the impact load of the cutterhead in shield tunneling in composite strata with soft upper and hard lower formations, as described in this invention, uses a cavity expansion model to divide the rock into multiple concentric circular regions. The radius of each region is determined to obtain the relationship between the damage state at different locations of the rock mass and the distance from the cutterhead center. The influence of section penetration is introduced, considering the damage difference between the vertical crack zone and the dense core zone during the cutterhead rock-breaking process. This yields the damage state of the cutterhead section at the distance from the cutterhead center within the lower contact area of ​​the cutterhead, and derives the damage distribution state of the hard rock side of the cutterhead during the vertical crack propagation process at the interface. Based on the CSM model, this invention derives an expression for the stress change in the transition section. Combined with the influence of lateral shear zone failure, a formula for predicting the impact load when traversing composite strata can be derived, providing theoretical guidance for determining the impact load when large-diameter shield tunneling passes through composite strata in practical engineering.

[0017] To ensure compatibility with existing homogeneous rock mass stress theory models for cutterheads, this invention uses the CSM model employed in homogeneous hard rock strata to dynamically change the stress on cutterheads at composite strata interfaces. By analyzing the influence of system deformation and composite rock mass damage on the pressure distribution and penetration depth of the cutterhead, a predictive model for the impact load on cutterheads in composite strata is constructed. This improves the compatibility of the prediction model with actual conditions, reduces the impact impact on the cutterhead at the soft-hard interface, and lowers the abnormal damage rate of the cutterhead. This invention employs theoretical analysis and derivation to analyze the impact load on shield tunnel cutterheads in soft-upper-hard-lower composite strata. It can predict the magnitude and distribution of the impact load borne by the cutterhead when cutting through the soft-hard interface in soft-upper-hard-lower composite strata.

[0018] Third, the transformed version of this invention can provide precise theoretical guidance for determining the impact load when large-diameter shield tunnels traverse composite strata with soft upper layers and hard lower layers in actual engineering projects, reducing equipment maintenance and replacement costs and losses caused by cutter wear and damage, as well as construction delays. From a commercial perspective, it promotes the upgrading of cutter impact load prediction technology in composite strata in the field of tunnel construction, enhances my country's independent controllability in this field, and facilitates the application and promotion of related technologies and equipment in domestic and international projects, possessing broad market prospects.

[0019] Fourth, existing domestic and international technologies for determining the impact load of shield tunnel cutterheads in composite strata are mostly based on the CSM model for homogeneous hard rock strata. However, this invention introduces damage mechanics and cavity expansion model theories on this basis for the first time, describing the failure evolution of the rock mass below the cutterhead from the perspective of damage mechanics. This improves the CSM model and fills the technical gap in the method for determining the impact load of shield tunnel cutterheads in composite strata with soft upper and hard lower layers.

[0020] Fifth, the problem of abnormal cutterhead damage caused by interfacial impact in composite strata has long limited the safe and efficient construction of large-diameter shield tunnels. Traditional models have large prediction errors in composite strata and do not consider the directionality of interfacial crack propagation. This invention solves this problem by achieving accurate prediction of cutterhead impact loads in such complex strata through an innovative method. There is a technical bias in the industry of establishing cutterhead stress prediction models based on homogeneous strata conditions, ignoring the significant differences between the failure mechanisms of composite strata and homogeneous strata. This invention breaks this bias and proposes a specific method for determining impact loads for composite strata with a soft upper layer and a hard lower layer. Attached Figure Description

[0021] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure; Figure 1 This is a flowchart of the method for determining the impact load of shield tunnel cutterhead in composite strata with soft upper and hard lower layers, provided in an embodiment of the present invention. Figure 2This is a schematic diagram of the method for determining the impact load of shield tunnel cutterhead in composite strata with soft upper and hard lower layers, provided in an embodiment of the present invention. Figure 3 This is a schematic diagram of the composite formation roller cutter rock breaking mechanical model provided in the embodiments of the present invention (Figure a is a schematic diagram of the x-axis normal phase plane; Figure b is a schematic diagram of the y-axis normal phase plane). Figure 4 This is a schematic diagram of the composite stratum rock-breaking cavity expansion model provided in the embodiments of the present invention (Figure a is a schematic diagram of model partitioning; Figure b is a schematic diagram of partitioning when the cutter is close to the interface). Figure 5 This is a stress variation diagram of the lower part of the composite formation cutter provided in an embodiment of the present invention; Figure 6 This is a comparison diagram of the normal force on the hob provided in an embodiment of the present invention. Detailed Implementation

[0022] 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.

[0023] The innovation of this invention lies in the fact that it introduces damage action and cavity expansion model theories on the basis of the CSM model for the first time. It describes the failure evolution of the rock mass below the cutter from the perspective of damage mechanics, and incorporates the influence of cross-sectional penetration when calculating the damage distribution. Based on the difference in damage between the vertical crack zone and the dense core zone during the cutter's rock-breaking process, it determines the damage state of the cutter cross-section at the distance from the cutter's center within the contact area below the cutter, and obtains the damage distribution state of the hard rock side below the cutter during the vertical crack propagation process at the interface. Furthermore, by combining the influence of the cutter's shear zone failure, it achieves a function that the CSM model could not realize (accurately reflecting the actual force magnitude and distribution law of the cutter).

[0024] Example 1, as Figure 1 As shown in the embodiment of the present invention, the method for determining the cutterhead impact load of a shield tunneling machine in a composite stratum with soft upper and hard lower formations includes the following steps: S1, using a cavity expansion model, the rock is divided into multiple concentric circular regions, the radius of each region is determined, and the relationship between the damage state of the rock mass at different locations and the distance from the center of the cutting edge is obtained; S2, Introducing the influence of cross-sectional penetration, based on the difference in damage between the vertical crack zone and the dense core zone during the rock breaking process of the cutter, the damage state of the cutter cross-section at the distance from the center of the cutter edge within the lower contact area of ​​the cutter is determined, and the damage distribution state of the lower hard rock side of the cutter during the vertical crack propagation process at the interface is obtained. S3, based on the CSM model, derives an expression for the stress change in the transition section and, combined with the influence of lateral shear zone failure, realizes the prediction of impact load when the shield cutter passes through a composite stratum of soft upper and hard lower.

[0025] Firstly, based on the cavity expansion model, the failure evolution of the rock mass under the cutter is described from the perspective of damage mechanics. The determination of the damage range is based on the relevant assumptions and conclusions of the cavity expansion theory. The establishment of the cavity expansion model, parameter calculation, and the formula for the damage distribution state of the rock side under the cutter are derived.

[0026] Considering the central vertical crack extends in a semi-circular pattern with a radius of curvature of [missing information]. r c When using a roller cutter to break rock, the damage and deterioration zone inside the rock mass should be consistent with the range of vertical crack propagation. A composite stratum roller cutter rock breaking mechanical model considering the damage effect should be constructed, such as... Figure 3 As shown.

[0027] As a further implementation, a cavity expansion model is constructed, dividing the soft rock region below the hob into multiple concentric circular regions from the center point of the cutter ring's cutting edge. Based on the differences in the failure mechanisms of each region, from the inside out, the regions are arranged as follows: outer radius... r d The dense core region, whose width is (2 w Keep it consistent; outer radius is r p The fractured zone; outer radius r c The cracked area has an outer radius of... r e The elastic zone is the outermost undisturbed zone, and the confining pressure of the rock mass at infinity is the outermost zone. σ 0, such as Figure 4 As shown in Figure (a).

[0028] As a further implementation, damage and failure occur within the rock mass as the dense core expands. Based on the zoning of the damage mechanics and cavity expansion model, it is assumed that the equivalent attenuation coefficient of the rock mass has a linear relationship with the average degree of damage and failure, and that the damage changes linearly along the expansion direction. Therefore, a damage factor of some form can be used to describe the damage state of the rock during this process, establishing the damage state at different locations within the soft rock mass. D S ( r Distance from the center of the blade r relation.

[0029] (1) In the formula, the superscript S represents soft rock, H represents hard rock, and T represents the composite interface. The absolute value symbol represents...r It is a non-negative number. In the formula... This represents the truncation function, when... x When >0, when x When <0, . The radius of the radial crack zone in the soft rock. The radius of the soft rock fracture zone is given.

[0030] The equivalent damage at different locations of the soft rock is obtained by averaging using equation (1). See equation (2); from the relationship between material damage and damage state (the more severe the damage, the stronger the attenuation), the relationship between the equivalent attenuation coefficient of soft rock mass and damage state is obtained (3), as shown in equation (2). Figure 4 As shown in Figure (a).

[0031] (2) (3) In the formula, The attenuation coefficient of the fractured rock mass is... The attenuation coefficient of the undisturbed intact rock mass. This is the equivalent attenuation coefficient for soft rock masses.

[0032] The model is analyzed as a plane strain problem: Based on the analysis method of plane strain problems, the radial stress inside soft rock masses is analyzed. With tangential stress Based on the equilibrium equation (4) and the stress-displacement relationship (5), its general solution is obtained as equation (6).

[0033] (4) (5) (6) In the formula, , These are the elastic modulus and Poisson's ratio of the material, respectively. For radial displacement, r s The distance between the center of the cutting edge in soft rock is denoted as C1 and C2, which are integral constants determined by the boundary conditions. According to stress boundary conditions , achievable , .in This refers to the tensile strength of soft rock. Represents the pressure of the surrounding rock at infinity; The surrounding rock pressure at infinity for soft rock; and Substituting into equation (6), based on the displacement boundary conditions of the elastic zone Obtain the radius of the elastic zone in soft rock. Radial crack zone radius Relation (7).

[0034] (7) Stress conditions in the radial crack zone , Substitute into equation (4) to obtain the stress in the radial crack zone. , Uniaxial compressive strength of soft rock; based on boundary stress continuity condition ,in, , These are the limiting approximation methods for the inner and outer radii of the interface between the radial crack zone and the fractured zone, respectively, to obtain the radius of the radial crack zone in soft rock. With the radius of the broken zone Relation (8).

[0035] (8) In the formula, For soft rock, the coefficient is related to the internal friction angle; This is the reference pressure for soft rock.

[0036] As a further implementation method, the fractured zone is based on the Mohr-Coulomb strength criterion. Perform calculations, where... Correlation coefficient ,and Related uniaxial compressive strength of rock , σ θ For tangential stress, The internal friction angle of the rock mass. c Substituting equation (9) into equation (4) to represent the cohesion of the material, we assume that the rock inside the crushed zone generates vertical stress due to yielding and failure. p and horizontal stress q The dense core region can be approximated as transmitting the roller penetration load in the form of hydrostatic pressure, i.e. p = q = p 0( p 0 is the reference pressure) based on its stress boundary conditions , The radius of the fractured zone in soft rock can be obtained. radius of dense core region Relation (10).

[0037] (9) (10) As a further implementation method, based on Figure 4 The geometric shape of each soft rock zone in Figure (a) and Equations (7), (8) and (10) can determine the distribution and change of the damage range inside the soft rock during the cutting process of the roller cutter. After the roller cutter passes through the interface and completely enters the hard rock, the range of each damage area in the hard rock can be obtained by analogy based on the analysis of Equations (1) to (10).

[0038] When the cutting tool is in soft rock and gradually approaches the hard rock at the interface, such as Figure 4 As shown in Figure (b), the damage disturbance zone of the soft rock will contact the hard rock due to the typical composite rock mass. Therefore, the damaged zone in the soft rock will be interrupted at the interface, and a dense core zone will be reformed in the hard rock when the cutter makes point contact with the hard rock.

[0039] As a further implementation, assuming that the cutter fully penetrates the hard rock in the pressure zone, the lower damage zone expands to the level of the homogeneous rock mass, and the size of its expansion range is 2 times the length of the cutter. L The size of the contact zone entering hard rock Proportional, combined with equation (3), the damage distribution of hard rock during the propagation process can be obtained. See equation (11).

[0040] (11) In the formula, the superscript H indicates hard rock. The length of the first half of the contact area of ​​the hob. The length of the contact zone into hard rock. For in position r The basic damage distribution function at the location, This is the hard rock damage distribution function after scaling transformation. At that time, through The location parameter r is scaled and then substituted into the hard rock foundation damage distribution function. In this context, it is used to describe the length L of the front half of the contact zone of the hob exceeding the length of the contact zone entering the hard rock. The distribution of hard rock damage varies with scale.

[0041] Based on the above assumptions, the damage state at each point in the lower composite rock mass during the roller cutter cutting process can be completely determined.

[0042] Based on the constructed rock-breaking force model of the roller cutter, cross-sections are analyzed along the direction of the roller cutter's advance. The analysis considers the relationship between the cross-section and the center of the cutting edge. r Increase the penetration depth of the hobbing cutter Reduce, corresponding contact force P Follow They descended together.

[0043] Vertical crack zone considered in the rock-breaking process of a roller cutter in soft rock. D With dense core region D The impact of damage differences can be used to deduce the distance from the center of the cutting edge within the lower contact area of ​​the hob. r place ( r >0) Damage state of the hob cross section D S ( x , r ): (12) In the formula, D 、D The parameters for the linear cutting test using a roller cutter are determined, and their range depends on the properties of the rock mass and the degree of crack development. Among these, soft rock... D =0.3, D =0.95, hard rock D =0.35, D =0.95, the penetration relationship of the hob section at a distance r from the center of the cutting edge. , Where is the radius of the hob. The penetration depth of the section where the hob is located at the center of the cutting edge. For position parameters, This indicates the location of the interface between soft and hard rocks.

[0044] After the hobbing cutter fully penetrates the hard rock ( Its damage state D H ( x , r This is consistent with equation (12). When the contact zone at the lower part of the cutter is close to the interface between soft and hard rock, the vertical crack will be interrupted, such as... Figure 3 As shown in Figure (b). After contacting hard rock in the contact zone, the crack propagates again within the hard rock. The propagation law of its fracture damage zone satisfies the linear variation law assumed by equation (11). Combining equation (12), the damage distribution state of the lower part of the cutter on the hard rock side during the vertical crack propagation process at the interface is established as follows: (13) In the formula, 、 The parameters for linear cutting tests of hard rock roller cutters are related to the properties of the rock mass and the degree of crack development. , .

[0045] As a further implementation, considering compatibility with existing homogeneous rock mass stress theory models for cutterheads, this application uses the CSM model employed in homogeneous hard rock strata to predict the dynamic changes in cutterhead stress at the composite stratum interface. By considering the influence of system deformation and composite rock mass damage on the pressure distribution and penetration depth of the cutterhead, a predictive model for the impact load on cutterheads in composite strata is constructed. The contact stress at the bottom of the CSM model is expressed as: (14) (15) (16) (17) in, φ θ is the contact angle between the cutter and the rock; C is a dimensionless coefficient. S The distance between the blades; σ c , σ t These are the rock mass compressive and tensile strengths, respectively. p s This represents the distributed contact stress at the bottom of the cutter ring; It is an integral variable used to describe the contact area from the beginning to the angular range. ψ This is the pressure distribution coefficient at the tool tip, ranging from -0.2 to 0.2, and varies with the tool tip width. T It increases with increasing size, and is generally taken as 0.1.

[0046] Based on the above analysis, the stress variation in the soft rock section is obtained by integrating the load at the bottom of the cutter. As shown in equation (18), the stress variation of the hard rock section can be obtained similarly. As shown in equation (19).

[0047] (18) (19) Considering equation (13), the force on the transition section is divided into two parts: the force of the soft rock section and the force of the intrusive hard rock section. By solving and summing the forces of the two parts separately, the force variation equation of the transition section is obtained. As shown in equation (20).

[0048] (20) In the formula, the superscript T represents the composite interface. ; .

[0049] The force changes in the transition section obtained in this aspect The invention incorporates the influence of penetration depth and considers the impact of damage differences between the vertical crack zone and the dense core zone during the rock breaking process of the roller cutter. Furthermore, it sums the force of the roller cutter penetrating the hard rock section with the force of the soft rock section, resulting in a more realistic outcome. This enhances the approximation between the formula calculation results and actual conditions, reduces calculation errors, and avoids economic losses and safety issues caused by inaccurate calculations, thus enabling this application to better serve practical engineering projects.

[0050] Secondly, the calculation of the fluctuation of the force amplitude of the roller cutter in cutting and breaking rock mainly considers the impact of the failure of the lateral shear zone.

[0051] Assuming the contact zone length between the rock-breaking cycle and the cutter head... L Consistently, as the cutter advances, the normal component provided by the shear zone continuously increases. When the load-bearing shear zone fails, this component becomes zero. Limit force equilibrium analysis of the rock mass shear zone at the cutter's central section yields the following: (twenty one) In the formula, The angle between the bottom of the shear zone and the horizontal plane. θ c The cutting edge angle of the hobbing cutter. p l It is subjected to lateral force.

[0052] According to the Mohr-Coulomb violation criterion (Equation (22)), substituting Equation (21) into the equation, we get Equation (23).

[0053] (twenty two) (twenty three) As a further implementation, we take the partial derivative of equation (23). Substituting the values ​​into the calculation yields the following results: (See equation (24)), substituting it into equation (23) yields the lateral force. p l As shown in equation (25). Based on the contact geometry between the front half of the hob contact area and the shearing area, the normal force component provided by the shearing area is obtained. F Nl As the shear zone is destroyed F Nl The amplitude fluctuates up and down, and is generally characterized by trigonometric functions. The rock breaking cycle is consistent with the size of the cutter contact area. In order to simplify the calculation of rock mass parameters, the position of the cutter centroid is used to determine the result, which is Equation (26).

[0054] (twenty four) (25) (26) In summary, the derivation process involves two aspects: firstly, analyzing the stress changes in the transition zone of the composite strata from the perspective of damage mechanics based on the cavity expansion model; and secondly, considering the impact of lateral shear zone failure and calculating the normal force components provided by the shear zone. The process. The result of this invention is a final result obtained by summing the formulas derived from the above two aspects, taking into account their respective effects.

[0055] Based on the derivation results of the first two aspects, the stress on the transition section will be determined. Normal force caused by lateral shear failure Summation is performed by adding equations (20) and (26) to establish the final calculation formula. + .

[0056] (27) Compared to the traditional CSM cutterhead stress model (near-linear pressure distribution) in homogeneous rock strata, this final formula better reflects the nonlinear pressure distribution characteristics of the cutterhead, making the pressure distribution calculation closer to actual engineering conditions and enhancing the safety of construction under complex geological conditions. Simultaneously, it provides a reliable theoretical basis for calculating the stress state in shield tunneling, enriches and improves the theoretical analysis system for predicting shield impact loads, and lays the foundation for subsequent theoretical analysis and technological development.

[0057] Example 2: To verify the rationality and accuracy of the formula derived in this invention, the stress at the lower part of the composite stratum cutter was predicted by the formula as a function of the moving distance. During the process of the cutter moving from soft rock to hard rock, the vertical angle β of the resultant force of the cutter first increases and then decreases due to the change in the force distribution at the interface, which is consistent with the actual situation. The predicted results were compared and analyzed with the force changes at the interface of the composite stratum obtained by the linear cutting test. After introducing the failure effect of the lateral shear zone, the theoretical model of the calculation is more closely matched with the experimental results.

[0058] Example 3: The shield tunnel cutterhead impact load determination system for composite strata with soft upper and hard lower formations provided in this embodiment of the invention includes: The rock partitioning module is used to divide the rock into multiple concentric circular regions using a cavity expansion model, determine the radius of each partition, and obtain the relationship between the damage state of the rock mass at different locations and the distance from the center of the cutting edge. The damage state determination module is used to introduce the influence of cross-sectional penetration. Based on the influence of the damage difference between the vertical crack zone and the dense core zone during the cutter rock breaking process, it determines the damage state of the cutter cross-section at the distance from the center of the cutter edge within the lower contact area of ​​the cutter and the damage distribution state of the lower hard rock side of the cutter during the vertical crack propagation process at the interface. The impact load prediction module is used to determine the expression of stress change in the transition section based on the CSM model, and to predict the impact load when the shield cutter passes through the composite strata of soft upper and hard lower.

[0059] To further demonstrate the positive effects of the above embodiments, the present invention conducts the following experiments based on the above technical solutions.

[0060] The rationality and accuracy of the formula derived in this invention are verified by comparing and analyzing the predicted results with the stress changes at the interface of the composite strata obtained from the linear cutting test.

[0061] The dimensions of the cuboid rock blocks used for cutting were set to 420mm × 250mm × 250mm (length × width × height). Standard cylinders with a diameter of 50mm and a height of 100mm and standard cylinders with a diameter of 50mm and a height of 25mm were prepared from the same batch of rock blocks used for the physical parameter determination.

[0062] Semi-cylindrical soft and hard rock samples, each 50 mm in diameter and 25 mm in height, were prepared. The bonding interface of the rock masses was polished to ensure it was smooth, dry, and free of grease. Approximately 50 g of epoxy resin and epoxy resin hardener were thoroughly mixed in a 100:3 ratio and then evenly applied to the joint surfaces of the soft and hard rock samples. After bonding and assembling the rock masses, the two samples were clamped together. After 24 hours of fixation to ensure a strong and complete bond between the samples, cutting tests were conducted using the rock samples.

[0063] During the experiment, the interface normal of the composite rock sample was perpendicular to the direction of the applied force. Other samples besides the composite rock sample underwent uniaxial compression and Brazilian splitting tests. The uniaxial compressive strength, tensile strength, and elastic modulus of the rock samples were measured, and the experimental results are shown in Table 1.

[0064] Table 1 Cutting Experiment Results The rock-breaking experiment was conducted using a roller cutter linear test bench. The vertical pressure value of the roller cutter was measured by a strain gauge pressure sensor located on the vertically connected guide flange, with a maximum range of 3000 kN.

[0065] The composite rock sample is clamped, and the hydraulic cylinder is adjusted to push the sample box under the roller cutter with an output pressure of 8 MPa. The height of the roller cutter is adjusted downwards using the lift, so that the bottom of the roller cutter contacts the surface of the rock sample. When the vertical pressure value on the control system interface becomes 0.001T, the vertical displacement of the roller cutter is reset in the control panel, so that the vertical displacement value is 0.00mm. After adjustment, the rock is reset, and the initial penetration depth of the roller cutter is set to -3mm using the lift. The horizontal movement speed of the rock sample is set to 350mm / s. The total length of the composite rock sample is 500mm (250±1mm for soft rock section and 250±1mm for hard rock section). The hydraulic station motor is started, and the hydraulic pressure is increased to 16MPa.

[0066] After the cutting was completed, the test results were derived for this cutting experiment. The test result curve is shown below. Figure 6 As shown.

[0067] Calculate the stress change at the lower part of the cutter as it passes the interface using test parameters of AB-type composite rock mass with a bonded interface, and substitute the parameters into the following formula: The resultant normal force of the hob is obtained by integration. The theoretical calculation results are then analyzed and compared with the hob normal force data obtained from experimental monitoring. The results are as follows: Figure 5 , Figure 6 As shown.

[0068] Figure 5 The calculated stress distribution is consistent with the actual distribution, exhibiting characteristics of stress concentration and the presence of zero-load zones on both sides. Furthermore, the stress concentration phenomenon is further intensified when the cutter passes through the transition zone and contacts the hard rock. During the process of the cutter moving from soft rock to hard rock, the vertical angle of the resultant force of the cutter is [not specified]. β The force distribution at the interface shows a pattern of first increasing and then decreasing, which is consistent with the actual situation.

[0069] Figure 6 To compare the experimental and theoretical results of the normal force of the cutter during the entire rock-breaking process, the theoretical results were calculated considering only the damage evolution effect and the damage and lateral shear zone failure effects. The theoretical analysis did not consider the influence of the free interface on both sides, therefore there are no zero values ​​on both sides of the experimental results. The normal load considering the lateral shear zone failure effect at the interface (…) F N + F Nl The calculated theoretical model is more closely matched with the experimental results, which corresponds to the phenomenon of composite rock mass failure at the interface during the rock breaking test.

[0070] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention and within the spirit and principles of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for determining the impact load of shield tunnel cutterhead in composite strata with soft upper layer and hard lower layer, characterized in that, This method Includes the following steps: S1, using a cavity expansion model, the rock is divided into multiple concentric circular regions. The radius of each region is determined, and the relationship between the damage state of the rock mass at different locations and the distance from the cutter center is obtained. In the analysis, the failure evolution of the rock mass below the cutter is described from the perspective of damage mechanics. The central vertical crack expands in a semi-circular shape with a radius of [missing information]. r c A composite formation rock breaking mechanical model based on damage effects was constructed. A cavity expansion model was constructed, dividing the soft rock region below the hob into multiple concentric circular regions from the center point of the cutter ring's cutting edge; based on the differences in the failure mechanisms of each region, from the inside out, the regions are as follows: outer radius is... r d The dense core region, with a width of 2 w Keep it consistent; outer radius is r p The fractured area; outer radius r c The cracked area has an outer radius of... r e The elastic zone is the outermost undisturbed zone, and the confining pressure of the rock mass at infinity is the outermost zone. σ 0; Damage and failure occur within the rock mass as the dense core expands. Based on the zoning of the damage mechanics and cavity expansion model, when the equivalent attenuation coefficient of the rock mass has a linear relationship with the average degree of damage and failure, and the damage changes linearly along the expansion direction, a damage factor is used to describe the damage state of the rock during this process, establishing the damage state at different locations in the soft rock mass. D S ( r Distance from the center of the blade r The relationship is expressed as: ； In the formula, the superscript S represents soft rock. The absolute value symbol represents... r It is a non-negative number; This represents the truncation function, when... x When >0, ;when x When <0, ; The radius of the radial crack zone in the soft rock. The radius of the soft rock fracture zone; Damage status at different locations of soft rock mass D S ( r Distance from the center of the blade r The relationship is averaged to obtain the equivalent damage at different locations in the soft rock. ; ； From the relationship between material damage and damage state, the relationship between the equivalent attenuation coefficient and damage state of soft rock mass is obtained as follows: ； In the formula, The attenuation coefficient of the fractured rock mass is... The attenuation coefficient of the undisturbed intact rock mass. This is the equivalent attenuation coefficient for soft rock mass; S2, Introducing the influence of cross-sectional penetration, based on the difference in damage between the vertical crack zone and the dense core zone during the rock breaking process of the cutter, the damage state of the cutter cross-section at the distance from the center of the cutter edge within the lower contact area of ​​the cutter is determined, and the damage distribution state of the lower hard rock side of the cutter during the vertical crack propagation process at the interface is obtained. S3, based on the CSM model, derives an expression for the stress change in the transition section and, combined with the influence of lateral shear zone failure, realizes the prediction of impact load when the shield cutter passes through a composite stratum of soft upper and hard lower.

2. The method for determining the cutterhead impact load of a shield tunneling machine in a composite stratum with soft upper and hard lower formations according to claim 1, characterized in that, In step S2, the model is analyzed according to the plane strain problem: based on the analysis method of plane strain problem, the radial stress inside the soft rock mass is analyzed. With tangential stress According to the equilibrium equation and the relationship between stress and displacement Obtain the general solution In the formula, , These are the elastic modulus and Poisson's ratio of the material, respectively. For radial displacement, r s The distance between the center of the cutting edge in soft rock is denoted as C1 and C2, which are integral constants determined by the boundary conditions. Relationship 1: Based on stress boundary conditions , ,have to: , ,in, For soft rock, the tensile strength of the rock. Represents the pressure of the surrounding rock at infinity; The surrounding rock pressure at infinity for soft rock; and Substituting the general solution Based on the elastic zone displacement boundary condition Obtain the radius of the elastic zone in soft rock. Radial crack zone radius The relation is: ; Relationship 2: Stress conditions in the radial crack zone , Substituting into the equilibrium equation, the stress in the radial crack zone is obtained. , Uniaxial compressive strength of soft rock; based on boundary stress continuity condition ,in , These are the limiting approximation methods for the inner and outer radii of the interface between the radial crack zone and the fractured zone, respectively, to obtain the radius of the radial crack zone in soft rock. With the radius of the fracture zone The relation is: ; Relationship 3: Fractured zone based on Mohr-Coulomb strength criterion Perform calculations, and The correlation coefficient is ,and The relevant uniaxial compressive strength of rock is , σ θ For tangential stress, The internal friction angle of the rock mass. c The material's cohesion; substituting the Mohr-Coulomb strength criterion into the equilibrium equation, when the rock inside the crushed zone generates vertical stress due to yielding and failure... p and horizontal stress q If the dense core region is equivalent to the roller penetration load being transmitted in the form of hydrostatic pressure, then... p = q = p 0, p 0 is the reference pressure; according to the stress boundary conditions , The radius of the fractured zone in soft rock was obtained. radius of dense core region The relation is: ; This is a coefficient related to the internal friction angle corresponding to soft rock. This is the reference pressure for soft rock.

3. The method for determining the cutterhead impact load of a shield tunneling machine in a composite stratum with soft upper and hard lower formations according to claim 2, characterized in that, In step S2, based on the geometry of each zone of the soft rock and the radius of the elastic zone in the soft rock... Radial crack zone radius Relationship, radial crack zone radius With the radius of the fracture zone Relationship, radius of the broken zone radius of dense core region The relationship determines the distribution and change of the damage range inside the soft rock during the roller cutter cutting process, and obtains the range of each damage area in the hard rock after the roller cutter has completely entered the hard rock through the interface. As the cutting tool gradually approaches the interface between the soft rock and the hard rock in the soft rock, the damaged and disturbed zone of the soft rock comes into contact with the hard rock. This is typical of composite rock masses. Therefore, the damaged zone in the soft rock will be interrupted at the interface, and a dense core zone will be reformed in the hard rock when the cutter makes point contact with the hard rock. When the cutter fully penetrates the hard rock in the pressure zone, the lower damaged area expands to the level of the homogeneous rock mass. The size of the expansion range during this process is approximately equal to the length of the cutter. L The size of the contact zone entering hard rock Proportional to the damage distribution of hard rock during the propagation process, the relationship between the equivalent attenuation coefficient of soft rock and the damage state is used to obtain the damage distribution of hard rock during the propagation process. ; ； In the formula, the superscript H indicates hard rock. The length of the first half of the contact area of ​​the hob. The length of the contact zone into hard rock. For in position r The basic damage distribution function at the location, This is the hard rock damage distribution function after scaling transformation; when At that time, through The location parameter r is scaled and then substituted into the hard rock foundation damage distribution function. In this context, it is used to describe the length L of the front half of the contact zone of the hob exceeding the length of the contact zone entering the hard rock. The distribution of hard rock damage varies with scale.

4. The method for determining the impact load of shield tunnel cutterhead in composite strata with soft upper and hard lower formations according to claim 3, characterized in that, In step S2, based on the constructed rock-breaking force model of the roller cutter, the vertical crack zone in soft rock is determined according to the rock-breaking process of the roller cutter. With dense core region The impact of damage differences leads to the derivation of the distance from the center of the cutting edge within the lower contact area of ​​the hob. r Damage state of the hob section ,in r > 0; ； In the formula, 、 The parameters for linear cutting tests with roller cutters in soft rock are determined, and their range depends on the properties of the rock mass and the degree of crack development; among them, soft rock... =0.3, =0.95, hard rock =0.35, =0.95, the penetration relationship of the hob section at a distance r from the center of the cutting edge. , Let the hob radius be... The penetration depth of the section where the hob is located at the center of the cutting edge. For position parameters, This indicates the location of the interface between soft and hard rocks.

5. The method for determining the cutterhead impact load of a shield tunneling machine in a composite stratum with soft upper and hard lower formations according to claim 4, characterized in that, In step S2, the damage state after the hob has fully entered the hard rock. D H ( x , r )and D S ( x , r ) consistent, among which When the vertical crack is close to the interface between soft and hard rock in the contact area of ​​the lower part of the cutter, it will be interrupted. After contacting the hard rock in the contact area, it will propagate again in the hard rock. The propagation law of the fracture damage zone satisfies the linear variation law of the damage distribution assumption of the hard rock. Combined with the damage state of the cutter section, the damage distribution state of the hard rock side of the lower part of the cutter during the vertical crack propagation process at the interface is obtained. ； In the formula, 、 The parameters for linear cutting tests of hard rock roller cutters are related to the properties of the rock mass and the degree of crack development. , .

6. The method for determining the cutterhead impact load of a shield tunneling machine in a composite stratum with soft upper and hard lower formations as described in claim 5, is characterized in that... In step S3, the dynamic change of the cutter force at the composite stratum interface is based on the CSM model used in homogeneous hard rock strata. By analyzing the influence of system deformation and composite rock mass damage on the pressure distribution and penetration of the cutter at the bottom, a predictive model for the impact load of the cutter in composite strata is constructed. The contact stress at the bottom of the CSM model is expressed as: ； ； ； ； in, φ θ is the contact angle between the cutter and the rock; C is a dimensionless coefficient. S The distance between the blades; σ c , σ t These are the rock mass compressive and tensile strengths, respectively. p s This represents the distributed contact stress at the bottom of the cutter ring; It is an integral variable used to describe the contact area from the beginning to the angular range; ψ This is the pressure distribution coefficient at the tool tip, ranging from -0.2 to 0.2, and varies with the tool tip width. T If the increase is due to the increase in size, 0.1 should be taken first. Integrating the load at the bottom of the hob, simplifying the expression... To obtain the stress changes in the soft rock section for: ； Similarly, the stress changes in the hard rock section can be obtained. for: ； The stress on the transition section is divided into two parts: the force of the soft rock section and the force of the intrusive hard rock section. By solving and summing the forces of the two parts separately, the stress variation formula of the transition section is obtained. ; ； In the formula, the superscript T represents the composite interface. , .

7. The method for determining the cutterhead impact load of a shield tunneling machine in a composite stratum with soft upper and hard lower formations as described in claim 6, is characterized in that... In step S3, the contact area length between the rock-breaking cycle and the cutter head is... L Consistently, as the cutter advances, the normal component provided by the shear zone continuously increases; when the shear zone fails, this component becomes zero. Limit force equilibrium analysis of the rock mass shear zone at the cutter's central section yields the following: ； In the formula, The angle between the bottom of the shear zone and the horizontal plane. θ c The cutting edge angle of the hobbing cutter. p l It is subjected to lateral force; According to the Mohr-Coulomb violation criterion ,Will Substitute to get ;right Find the partial derivative Substituting into the calculation, we get , bring back Lateral force Based on the contact geometry between the front half of the hob contact area and the shearing zone, the normal force component provided by the shearing zone is obtained. F Nl, as the shear zone breaks down F The amplitude of Nl fluctuates; according to trigonometric function representation, the rock breaking period is consistent with the size of the cutter contact zone. To simplify the calculation of rock mass parameters, the position of the cutter centroid is used for judgment. Therefore: ； Based on the cavity expansion model, the stress change process of the transition section of the composite strata is analyzed from the perspective of damage mechanics, and the normal force component provided by the shear zone is calculated based on the failure effect of the lateral shear zone. The process will cause the transition section to be subjected to force. Normal force caused by lateral shear failure Summation to establish the final calculation formula + ; 。 8. A system for determining the impact load of shield tunnel cutterhead in composite strata with soft upper layer and hard lower layer, characterized in that, This system is used to regulate the method for determining the cutterhead impact load of shield tunneling in composite strata with soft upper and hard lower formations as described in any one of claims 1-7. The system comprises: The rock partitioning module is used to divide the rock into multiple concentric circular regions using a cavity expansion model, determine the radius of each partition, and obtain the relationship between the damage state of the rock mass at different locations and the distance from the center of the cutting edge. The damage state determination module is used to introduce the influence of the section penetration. Based on the influence of the damage difference between the vertical crack zone and the dense core zone during the cutter rock breaking process, it determines the damage state of the cutter section at the distance from the center of the cutter edge within the lower contact area of ​​the cutter, and obtains the damage distribution state of the lower hard rock side of the cutter during the vertical crack propagation process at the interface. The impact load prediction module derives the expression for the stress change in the transition section based on the CSM model, and combines the influence of lateral shear zone failure to realize the impact load prediction when the shield cutter passes through a composite stratum with soft upper and hard lower layers.

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