A shield cutting steel reinforced concrete pile foundation cutter fracture avoidance method

Abstract

This invention provides a method for avoiding cutter fracture when a tunnel boring machine (TBM) is cutting reinforced concrete pile foundations. The method includes: S1, establishing a numerical model of the cutter cutting reinforced concrete, wherein the numerical model is used to obtain the ultimate stress state and corresponding impact load at the instant the cutter contacts the reinforcing steel; S2, determining the impact load on the cutterhead during cutting the reinforcing steel through geometric analysis; and S3, establishing a theoretical model of the dynamic response of the TBM tunneling, wherein the theoretical model is used to solve for the theoretical threshold of the acceleration response at the cutterhead bearing position under impact load. X T S4, Install an acceleration sensor on site. The sensor is used to acquire the acceleration response at the position of the shield cutterhead bearing. S5, Process the acceleration data in real time using a vibration analysis system to obtain the measured peak acceleration response. X P S6, compared to the measured peak value of acceleration response. X P Compared with theoretical threshold X T The magnitude between these values, dynamically adjusted tunneling parameters will affect the measured peak value of the acceleration response. X P Controlled within the theoretical threshold X T The following aims to prevent tool breakage.

Description

Technical Field

[0001] This invention relates to the field of tunnel and underground engineering technology, and in particular to a method for avoiding tool fracture when shield tunneling reinforced concrete pile foundations based on acceleration response threshold. Background Technology

[0002] my country's underground engineering has developed rapidly, with various underground structures intertwined. During shield tunnel construction, situations often arise where the tunnel passes through existing bridge pile foundations and other structures. With the continuous improvement of shield tunneling technology, directly cutting reinforced concrete pile foundations with shields has proven entirely feasible. However, existing shield pile cutting engineering practices show that the impact load generated at the moment of contact between the cutter and the reinforcing steel often induces a large number of cutter fragments on the cutterhead to break. How to avoid cutter fragmentation during shield pile cutting is a common problem of concern in the engineering community. During the process of shield cutters cutting reinforced concrete pile foundations, the changes in tunneling parameters such as thrust and torque are relatively small, failing to reflect the interaction between the cutter and the reinforcing steel, and making it impossible to determine whether the impact load during the current cutting of the reinforcing steel will induce cutter fragmentation based on thrust and torque.

[0003] Based on the principles of structural dynamics, the acceleration response of a tunnel boring machine (TBM) is extremely sensitive to the impact load of the cutting tool cutting the reinforcing steel. Therefore, it is necessary to propose a method for avoiding TBM cutter fracture in reinforced concrete pile foundations based on the acceleration response threshold. This method enables real-time assessment of the impact load during TBM pile cutting, dynamic adjustment of tunneling parameters, and reduction of cutter fracture during TBM pile cutting. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention discloses a method for avoiding tool fracture when tunneling reinforced concrete pile foundations using a shield tunneling machine.

[0005] The specific plan is as follows:

[0006] A method for avoiding cutter fracture when tunneling through reinforced concrete pile foundations using a shield tunneling machine includes the following steps:

[0007] S1. Based on the cutting tools and reinforced concrete materials used in shield tunneling pile cutting in actual engineering, a dynamic numerical model of the cutting tool cutting reinforced concrete coupled body is established. The stress state and impact load of the cutting tool cutting the steel bar under different penetration depths and cutting speeds are calculated to obtain the impact load threshold that meets the ultimate stress requirements of a single cutting tool.

[0008] S2. Through geometric analysis, the number of tools on the cutter head that are simultaneously cutting steel bars is determined. Finally, the impact load acting on the cutter head is the sum of the impact loads of the tools that are simultaneously cutting steel bars.

[0009] S3. Establish a theoretical model of the dynamic response in the tunnel boring machine (TBM) direction. Using the accumulated impact load as the input load, solve the theoretical model of the dynamic response in the TBM direction using the Newmark method to obtain the theoretical threshold X of the acceleration response at the cutterhead bearing position. T .

[0010] S4. In actual engineering, an acceleration sensor is installed at the position of the cutterhead bearing of the tunnel boring machine to collect the acceleration response of the cutterhead bearing in the tunneling direction.

[0011] S5 uses a vibration analysis system to analyze the data monitored by the acceleration sensor in real time and compares and analyzes its waveform response peak value X. P Compared with the theoretical threshold X T Size.

[0012] S6, dynamically adjust tunneling parameters, if the measured waveform response peak value X P <Theoretical threshold X T If the current speed is maintained during tunneling, and the measured waveform response peak value X P >Theoretical threshold X T To ensure the measured waveform response peak X is maintained, the feed speed and cutterhead speed are reduced. P <Theoretical threshold X T This achieves the goal of avoiding tool breakage.

[0013] As a further improvement of the present invention, the dynamic numerical model of the cutting tool cutting the reinforced concrete coupling is used to obtain the impact load and stress state of the tool at the instant of contact between the tool and the reinforcing steel; the dynamic response theoretical model of the shield tunneling direction is used to solve the theoretical threshold X of the acceleration response at the cutterhead bearing position under the impact load. T The acceleration sensor is used to acquire acceleration response data of the shield tunnel cutterhead bearing position in actual engineering; the vibration analysis system is used to process the acceleration data in real time to obtain the acceleration response waveform and response peak value X. P Real-time analysis of peak acceleration X P and theoretical threshold X T By reducing the tunneling speed and cutterhead rotation speed, the peak acceleration X can be reduced. P Control at threshold X T The following steps aim to prevent tool breakage.

[0014] As a further improvement of the present invention, in step S1, both concrete and reinforcing steel are modeled using dynamic constitutive models. Specifically, concrete uses the RHT (Riedel-Hiermaier-Thoma) constitutive model, reinforcing steel uses the Johnson-Cook constitutive model, and the cutting tool uses an elastic constitutive model. Bond failure contact is established between the reinforcing steel and concrete to ensure the accuracy of the calculated impact load.

[0015] The RHT constitutive model used to describe the dynamic response behavior of concrete consists of three development stages. As stress increases, the material first passes through the elastic stage to reach the elastic yield surface. Subsequently, the material undergoes plastic deformation and enters the linear hardening stage, exhibiting strain hardening characteristics until it reaches the failure surface. When the equivalent stress intensity exceeds the failure stress intensity, the material begins to accumulate damage, entering the damage softening stage, and finally reaches the residual strength surface.

[0016] Its yield surface is described using compressive strength, regularized yield function, and Willam-Warnke function:

[0017]

[0018] in, It is the normalized yield function, f c R represents uniaxial compressive strength, R3 represents the Williams-Warnke function, and θ l It's Cape Lord, F r It is the dynamic strain rate increase coefficient. It is normalization pressure. P0 is the hydrostatic pressure. It is strain rate. It is an effective plastic strain.

[0019] Strain rate significantly affects the strength of rock. In this model, the dependence of uniaxial compressive strength on strain rate is given by the following equation:

[0020]

[0021] in, It is the reference strain rate under compression. It is the reference strain rate under tension. f t It is tensile strength, β c and β t These are the material constants under compression and tension, respectively.

[0022] The failure surface is represented as:

[0023]

[0024] in, For normalized intensity, A1 and N1 are failure surface parameters.

[0025] When the stress state reaches the ultimate strength of the material at the failure surface, damage accumulates during further inelastic deformation or plastic strain. The plastic strain at failure is shown below:

[0026]

[0027] in It is the plastic strain at failure. It is the minimum damage residual strain. It is the failure cutoff pressure, D r D1 and D2 are the damage variables in the RHT model, and D1 and D2 are the damage constants.

[0028] Damage variable is defined as plastic strain ε p Accumulation:

[0029]

[0030] The Johnson-Cook constitutive formulation used to describe the dynamic response behavior of reinforcing bars is as follows:

[0031]

[0032] In the formula, the first bracket represents the elastoplastic term, indicating work hardening; A is the initial yield stress (MPa); and B is the work hardening coefficient. The first part represents the equivalent plastic strain, where n is the strain hardening exponent; the second part in parentheses represents the viscous term, indicating the increase in material flow stress at high strain rates; and C is the strain rate sensitivity coefficient. For equivalent plastic strain rate, The reference strain rate is used.

[0033] The steel bar chip separation criterion adopts the shear failure criterion built into the Johnson-Cook model. This criterion compares the equivalent plastic strain value at the element integration point with the equivalent failure strain value at that point. Material failure occurs when the failure parameter D is greater than 1. The failure rule is expressed as follows:

[0034]

[0035] In the formula, It is the equivalent plastic strain increment. It is the equivalent failure strain.

[0036] Equivalent failure strain Determined by the following formula:

[0037]

[0038] In the formula, p is the compressive stress, and q is the Mises stress. d1 to d4 are the reference strain rate and material failure parameters.

[0039] The failure rule for the bond between steel reinforcement and concrete is as follows:

[0040]

[0041] In the formula, σ nornal For the normal force at the interface between the steel reinforcement and the concrete, σ shear F is the shear stress at the interface between the steel reinforcement and the concrete. S F is the limit value of normal tensile stress. D This represents the shear stress limit value.

[0042] The stress state of the cutting tool is calculated using elastic constitutive methods:

[0043] σ=E·ε

[0044] In the formula, σ is the tool stress, E is the tool elastic modulus, and ε is the tool strain.

[0045] Among them, the ultimate stress of the tool is the allowable stress at which the tool material will not fracture in actual engineering.

[0046] By calculating the impact load and stress state of the tool cutting reinforced concrete under different penetration depths and cutting speeds, the impact load under the ultimate stress state of the tool is obtained.

[0047] As a further improvement of the present invention, in step S2, the number of tools simultaneously cutting the reinforcing bars on the cutter head is determined through geometric analysis. The tool arrangement on the cutter head and the relative positions of the tools and the reinforcing cage are consistent with actual engineering. Finally, the impact loads acting on the cutter head are obtained by summing the impact loads of all tools cutting the reinforcing bars.

[0048] As a further improvement of the present invention, in step S3, the theoretical model of the shield tunneling direction dynamic response is modeled using the lumped mass method, considering the elastic stiffness and damping between the cutterhead, the cutterhead main bearing, and the shield body. The impact load acting on the cutterhead is used as the input load, and the theoretical model of the shield tunneling direction dynamic response is solved using the Newmark method to obtain the theoretical threshold X of the cutterhead bearing position acceleration response. T .

[0049] As a further improvement of the present invention, in step S4, to avoid damage to the acceleration sensor, an acceleration sensor is installed at the cutterhead bearing position of the tunnel boring machine in actual engineering to collect the peak acceleration response X at the cutterhead bearing position in the tunnel boring direction. P .

[0050] As a further improvement of the present invention, in step S5, the data monitored by the acceleration sensor is analyzed in real time through a vibration analysis system, and its waveform response peak value X is compared and analyzed. P Compared with the theoretical threshold X T Size.

[0051] As a further improvement of the present invention, step S6 includes the following steps:

[0052] Compare the peak value of the measured waveform response X P and theoretical threshold X T Size;

[0053] If the measured waveform response peak value X P <Theoretical threshold X T If so, continue tunneling at the current speed;

[0054] If the measured waveform response peak value X P >Theoretical threshold X T To ensure the measured waveform response peak X is maintained, the feed speed and cutterhead speed are reduced. P <Theoretical threshold X P ;

[0055] Ultimately, this achieves the goal of preventing tool breakage.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] 1. This invention is safe and efficient, overcoming the shortcomings of traditional shield tunneling parameters such as thrust and torque, which cannot be used to determine the interaction state between the cutter and the reinforcing steel.

[0058] 2. This invention creatively proposes to evaluate the magnitude of the instantaneous impact load on the cutting tool when cutting steel bars by using the acceleration response of the shield cutterhead bearing.

[0059] 3. This invention calculates the impact load that meets the stress requirements of the cutting tool by using a dynamic numerical model of cutting reinforced concrete. Then, using this as the input load, the Newmark method is used to solve the dynamic response theoretical model of the tunnel boring machine in the tunneling direction to obtain the acceleration response threshold that meets the stress requirements of the cutting tool.

[0060] 4. This invention, through an acceleration response analysis system, can achieve real-time automatic monitoring of impact loads during tunneling, propose tunneling parameter control suggestions, and avoid tool breakage during shield tunneling pile cutting.

[0061] 5. This invention has extremely high value for promotion and popularization, and can provide a brand-new solution for avoiding shield cutter breakage.

[0062] 6. This invention creatively combines the dynamic numerical model of the cutting tool cutting reinforced concrete coupled body, the theoretical model of the shield tunneling acceleration response, the measured acceleration response, and the tool fracture control, which helps to reduce the tool fracture induced by impact load during the shield tunneling of reinforced concrete pile foundations. Attached Figure Description

[0063] The invention can be further understood from the following description taken in conjunction with the accompanying drawings, in which the components are not necessarily drawn to scale, but rather the focus is on illustrating the principles of the embodiments.

[0064] Figure 1 This is a flowchart illustrating a method for avoiding cutter fracture when a shield tunneling machine cuts a reinforced concrete pile foundation, as described in this disclosure.

[0065] Figure 2 This is a numerical model of the dynamics of the cutting tool in the reinforced concrete coupling in the embodiments of this disclosure;

[0066] Figure 3 The ultimate stress state of the tool and the corresponding impact load in the embodiments of this disclosure;

[0067] Figure 4 This is a geometric analysis case for a cutting tool cutting a reinforcing steel cage provided in an embodiment of this disclosure;

[0068] Figure 5 The impact load acting on the cutter head in this embodiment of the present disclosure;

[0069] Figure 6 This is the theoretical model of the dynamic response of the tunnel boring machine in the tunneling direction in the embodiments of this disclosure;

[0070] Figure 7 This is the process of solving the theoretical model of the dynamic response of the shield tunneling direction using the Newmark method in the embodiments of this disclosure;

[0071] Figure 8 X is the theoretical threshold value for acceleration in the tunnel boring direction in this embodiment of the present disclosure. T ;

[0072] Figure 9 In this embodiment, an accelerometer and a vibration analysis system are installed on-site.

[0073] Figure 10 In the embodiments disclosed herein, the measured data X of the shield tunnel acceleration response are shown. P . Detailed Implementation

[0074] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0075] As shown in the figure, this invention provides a method for avoiding tool fracture when tunneling through reinforced concrete piles, comprising the following steps:

[0076] S1. Based on the cutting tools and reinforced concrete materials used in shield tunneling pile cutting in actual engineering, a dynamic numerical model of the cutting tool cutting reinforced concrete coupled body is established. The stress and cutting load of the cutting tool cutting the steel bar under different cutting speeds and penetration depths are calculated, and the impact load corresponding to the ultimate stress state of a single cutting tool is obtained.

[0077] S2. Through geometric analysis, the number of tools on the cutter head that are simultaneously cutting steel bars is determined. Finally, the impact load acting on the cutter head is the sum of the impact loads of the tools that are simultaneously cutting steel bars.

[0078] S3. Establish a theoretical model of the dynamic response in the tunnel boring machine direction. Using the accumulated impact load as the input load, solve the model using the Newmark method to obtain the theoretical threshold X for the acceleration response at the cutterhead bearing position. T .

[0079] S4. In actual engineering, an acceleration sensor is installed at the position of the cutterhead bearing of the tunnel boring machine to collect the acceleration response of the cutterhead bearing in the tunneling direction.

[0080] S5 uses a vibration analysis system to analyze the data monitored by the acceleration sensor in real time and compares and analyzes its waveform response peak value X. P Compared with the theoretical threshold X T Size.

[0081] S6, dynamically adjust tunneling parameters, if the measured waveform response peak value X P <Theoretical threshold X T If the current speed is maintained during tunneling, and the measured waveform response peak value X P >Theoretical threshold X T To ensure the measured waveform response peak X is maintained, the feed speed and cutterhead speed are reduced. P <Theoretical threshold X T This achieves the goal of avoiding tool breakage.

[0082] The numerical dynamic model of the cutting tool cutting the reinforced concrete coupling is used to obtain the ultimate stress state of the tool and the corresponding impact load; the theoretical dynamic response model of the shield tunneling direction is used to solve the theoretical threshold X of the acceleration response at the cutterhead bearing position under impact load. T The acceleration sensor is used to acquire acceleration response data of the shield tunnel cutterhead bearing position in actual engineering; the vibration analysis system is used to process the acceleration data in real time to obtain the acceleration response waveform and response peak value X. P Real-time analysis of peak acceleration X P and theoretical threshold X TBy reducing the tunneling speed and cutterhead rotation speed, the peak acceleration X can be reduced. P Control at threshold X T The following steps aim to prevent tool breakage.

[0083] In S1, both concrete and reinforcing steel are modeled using dynamic constitutive models. Concrete uses the RHT (Riedel-Hiermaier-Thoma) constitutive model, while reinforcing steel uses the Johnson-Cook constitutive model. The cutting tool uses an elastic constitutive model. Bond failure contact is established between the reinforcing steel and concrete to ensure the accuracy of the calculated impact load.

[0084] The RHT constitutive model used to describe the dynamic response behavior of concrete consists of three development stages. As stress increases, the material first passes through the elastic stage to reach the elastic yield surface. Subsequently, the material undergoes plastic deformation and enters the linear hardening stage, exhibiting strain hardening characteristics until it reaches the failure surface. When the equivalent stress intensity exceeds the failure stress intensity, the material begins to accumulate damage, entering the damage softening stage, and finally reaches the residual strength surface.

[0085] Its yield surface is described using compressive strength, regularized yield function, and Willam-Warnke function:

[0086]

[0087] in, It is the normalized yield function, f c R represents uniaxial compressive strength, R3 represents the Williams-Warnke function, and θ l It's Cape Lord, F r It is the dynamic strain rate increase coefficient. It is normalization pressure. P0 is the hydrostatic pressure. It is strain rate. It is an effective plastic strain.

[0088] Strain rate significantly affects the strength of rock. In this model, the dependence of uniaxial compressive strength on strain rate is given by the following equation:

[0089]

[0090] in, It is the reference strain rate under compression. It is the reference strain rate under tension. f t It is tensile strength, β c and β t These are the material constants under compression and tension, respectively.

[0091] The failure surface is represented as:

[0092]

[0093] in, For normalized intensity, A1 and N1 are failure surface parameters.

[0094] When the stress state reaches the ultimate strength of the material at the failure surface, damage accumulates during further inelastic deformation or plastic strain. The plastic strain at failure is shown below:

[0095]

[0096] in It is the plastic strain at failure. It is the minimum damage residual strain. It is the failure cutoff pressure, D r D1 and D2 are the damage variables in the RHT model, and D1 and D2 are the damage constants.

[0097] Damage variable is defined as plastic strain ε p Accumulation:

[0098]

[0099] The Johnson-Cook constitutive formulation used to describe the dynamic response behavior of reinforcing bars is as follows:

[0100]

[0101] In the formula, the first bracket represents the elastoplastic term, indicating work hardening; A is the initial yield stress (MPa); and B is the work hardening coefficient. The first part represents the equivalent plastic strain, where n is the strain hardening exponent; the second part in parentheses represents the viscous term, indicating the increase in material flow stress at high strain rates; and C is the strain rate sensitivity coefficient. For equivalent plastic strain rate, The reference strain rate is used.

[0102] The steel bar chip separation criterion adopts the shear failure criterion built into the Johnson-Cook model. This criterion compares the equivalent plastic strain value at the element integration point with the equivalent failure strain value at that point. Material failure occurs when the failure parameter D is greater than 1. The failure rule is expressed as follows:

[0103]

[0104] In the formula, It is the equivalent plastic strain increment. It is the equivalent failure strain.

[0105] Equivalent failure strain Determined by the following formula:

[0106]

[0107] In the formula, p is the compressive stress, and q is the Mises stress. d1 to d4 are the reference strain rate and material failure parameters.

[0108] The failure rule for the bond between steel reinforcement and concrete is as follows:

[0109]

[0110] In the formula, σ nornal For the normal force at the interface between the steel reinforcement and the concrete, σ shear F is the shear stress at the interface between the steel reinforcement and the concrete. S F is the limit value of normal tensile stress. D This represents the shear stress limit value.

[0111] The stress state of the cutting tool is calculated using elastic constitutive methods:

[0112] σ=E·ε

[0113] In the formula, σ is the tool stress, E is the tool elastic modulus, and ε is the tool strain.

[0114] Among them, the ultimate stress of the tool is the allowable stress at which the tool material will not fracture in actual engineering.

[0115] By calculating the impact load and stress state of the tool cutting reinforced concrete under different penetration depths and cutting speeds, the impact load of the tool's ultimate stress state is obtained.

[0116] In S2, the number of cutters simultaneously cutting the reinforcing steel on the cutter head is determined through geometric analysis. The cutter arrangement on the cutter head and the relative positions of the cutters and the reinforcing steel cage are consistent with the actual engineering. Finally, the impact loads acting on the cutter head are obtained by summing the impact loads of all cutters cutting the reinforcing steel.

[0117] In S3, the theoretical model of the dynamic response of the tunnel boring machine (TBM) in the tunneling direction is modeled using the lumped mass method, considering the elastic stiffness and damping between the cutterhead, cutterhead main bearing, and shield body. The impact load acting on the cutterhead is used as the input load, and the theoretical model of the dynamic response of the TBM in the tunneling direction is solved using the Newmark method to obtain the theoretical threshold X of the acceleration response at the cutterhead bearing position. T .

[0118] In S4, to avoid damage to the accelerometer, an accelerometer is installed at the cutterhead bearing position of the tunnel boring machine in actual engineering to collect the peak acceleration response X at the cutterhead bearing position in the tunneling direction.P .

[0119] In S5, the vibration analysis system analyzes the data monitored by the acceleration sensor in real time and compares and analyzes its waveform response peak value X. P Compared with the theoretical threshold X T Size.

[0120] S6 includes the following steps:

[0121] Compare the peak value of the measured waveform response X P and theoretical threshold X T Size;

[0122] If the measured waveform response peak value X P <Theoretical threshold X T If so, continue tunneling at the current speed;

[0123] If the measured waveform response peak value X P >Theoretical threshold X T To ensure the measured waveform response peak X is maintained, the feed speed and cutterhead speed are reduced. P <Theoretical threshold X P , ;

[0124] Ultimately, this achieves the goal of preventing tool breakage.

[0125] Specifically, such as Figure 1 As shown, a method for avoiding cutter fracture during shield tunneling of reinforced concrete pile foundations is disclosed, which is used to prevent cutter fracture during the shield tunneling of reinforced concrete pile foundations. Specifically, it includes the following steps:

[0126] S1: Figure 2 This embodiment presents a numerical model of the dynamics of a cutting tool cutting a reinforced concrete coupled body. Parameters such as tool geometry, rebar diameter, concrete grade, and rebar grade are derived from actual field engineering conditions.

[0127] Based on the actual on-site engineering, in this embodiment, the cutting tool width is 10mm, the rebar diameter is 25mm, and the pile foundation concrete strength grade is C25. To ensure the accuracy of the calculated impact load, both concrete and rebar are modeled using dynamic constitutive models. The concrete uses the RHT constitutive model, the rebar uses the Johnson-Cook constitutive model, and the cutting tool uses an elastic constitutive model. Changes in cutting temperature are not considered in the calculation. The numerical parameters corresponding to the elastic constitutive model of the rebar are shown in Table 1, and the parameters corresponding to the RHT constitutive model of C25 concrete are shown in Table 2. The parameters corresponding to the elastic constitutive model of the cutting tool are shown in Table 3.

[0128] Table 1. Parameter values ​​for the JOHNSON-COOK material model of reinforcing steel.

[0129]

[0130] Table 2. Parameter values ​​for the RHT material model of concrete.

[0131]

[0132]

[0133] Table 3. Parameter values ​​for the PLASTIC-KINEMATIC material model of the cutting tool.

[0134]

[0135] Figure 3 This embodiment describes the ultimate stress state of the cutting tool and the corresponding impact load. In this embodiment, the cutting tool is made of 42CrMo alloy, and the allowable ultimate stress to prevent tool fracture is 2.8 GPa. The numerical model calculation results of the cutting tool's dynamics of the reinforced concrete coupling show that when the impact load during the cutting process exceeds... Figure 3 The tool will fracture under the impact load given in the text.

[0136] S2: Figure 4 This embodiment of the present disclosure provides a geometric analysis of a cutting tool cutting a reinforcing cage. This analysis is based on actual shield tunneling pile cutting engineering, focusing on the geometric relationship during the initial contact between the shield cutter and the pile foundation's reinforcing cage when cutting the first reinforcing bar. In this embodiment, the pile foundation is offset from the cutter center by 360mm. Based on the cutter arrangement on the cutterhead and the positional relationship between the cutter and the first reinforcing bar, it is calculated that during the cutting of the first reinforcing bar, only one cutter cuts the first reinforcing bar at any given moment, and the time interval between adjacent cutters cutting the first reinforcing bar is 0.083s. Therefore, the time interval for the impact load is also 0.083s. Figure 5 This refers to the impact load acting on the cutter head in this embodiment of the present disclosure. This load is the cumulative result of the impact loads on the cutting tool cutting the reinforcing steel within 1 second.

[0137] S3: Figure 6 This embodiment presents a theoretical model for the dynamic response of the tunnel boring machine (TBM) in the tunneling direction. Using the lumped mass method, the cutterhead, bearings, and shield body are treated as equivalent lumped mass points, establishing an equivalent dynamic model of the cutterhead-bearing-shield system in the tunneling direction. Considering the actual mechanical connections of the TBM in the tunnel boring machine pile cutting project of this embodiment, the elastic coefficients K1, K2, and K3 are taken as 1.44e10 N / m, 3.6e12 N / m, and 1e12 N / m, respectively, and the damping coefficients C1, C2, and C3 are taken as 1.15e... 6 N·s / m, 7e 5 N·s / m, 1e8N·s / m, cutter head mass m c Cutter head bearing mass m r Shield mass md The values ​​are 60,000 kg, 70,000 kg, and 255,000 kg, respectively. Figure 7 This embodiment describes the process of solving the theoretical model of the dynamic response of the tunnel boring machine (TBM) in the tunneling direction using the Newmark method. In this embodiment, the impact load acting on the cutterhead is used as the input load. The theoretical model of the dynamic response of the TBM in the tunneling direction is obtained using the Newmark method, with a time interval Δt of 0.000332 s. The theoretical threshold X for the acceleration response at the cutterhead bearing position that satisfies the ultimate stress requirement of the cutterhead is calculated. T . Figure 8 X is the theoretical threshold value for acceleration in the tunnel boring direction in this embodiment of the present disclosure. T In this embodiment, the theoretical threshold X for acceleration response is... T It is 0.6g.

[0138] S4: Figure 9 In this embodiment, an accelerometer and a vibration analysis system are installed on-site. In this embodiment, the accelerometer is installed at the cutterhead bearing location to acquire the acceleration direction of the tunnel boring machine in real time.

[0139] S5: Figure 10 In the embodiments disclosed herein, the measured peak value of the shield tunnel acceleration response X P In this embodiment, the data collected by the acceleration sensor is analyzed in real time using a vibration analysis system to obtain the measured peak value X of the acceleration response. P The peak acceleration response X at that moment. P It is 0.48g.

[0140] S6: Current measured peak acceleration response X P Less than the theoretical threshold X T There is no need to reduce the impact load by decreasing the tunneling speed and cutterhead rotation speed; the first steel bar can be cut according to the current tunneling parameters.

[0141] Ultimately, the goal of avoiding tool breakage is achieved.

[0142] The above-described embodiments are merely one implementation of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this invention should be determined by the appended claims.

Claims

1. A method for avoiding cutter fracture when tunneling reinforced concrete pile foundations using a shield tunneling machine, characterized in that, Includes the following steps: S1. Based on the cutting tools and reinforced concrete materials used in shield tunneling pile cutting in actual engineering, a dynamic numerical model of the cutting tool cutting reinforced concrete coupled body is established. The stress and cutting load of the cutting tool cutting the steel bar under different cutting speeds and penetration depths are calculated to obtain the impact load corresponding to the ultimate stress state of a single cutting tool. S2. Through geometric analysis, the number of tools on the cutter head that are simultaneously cutting steel bars is determined. Finally, the impact load acting on the cutter head is the sum of the impact loads of the tools that are simultaneously cutting steel bars. S3, a dynamic response theoretical model of the tunneling direction of the shield is established, the accumulated impact load is taken as an input load, the Newmark method is used for solving, and a theoretical threshold X of the acceleration response of the bearing position of the cutter head is obtained T ; S4. In actual engineering, an acceleration sensor is installed at the position of the cutterhead bearing of the tunnel boring machine to collect the acceleration response of the cutterhead bearing position in the tunneling direction. S5, through the vibration analysis system, real-time analysis of acceleration sensor monitoring data, comparative analysis of its waveform response peak X P With the size of the theoretical threshold X T ; S6, dynamically adjust tunneling parameters, if the measured waveform response peak value X P <Theoretical threshold X T If the current speed is maintained during tunneling, and the measured waveform response peak value X P >Theoretical threshold X T To ensure the measured waveform response peak X is maintained, the feed speed and cutterhead speed are reduced. P <Theoretical threshold X T This achieves the goal of avoiding tool breakage.

2. The method for avoiding cutter fracture when tunneling reinforced concrete pile foundations using a shield tunneling machine according to claim 1, characterized in that, The numerical dynamic model of the cutting tool in the reinforced concrete coupling is used to obtain the impact load and stress state of the tool at the instant of contact between the tool and the steel reinforcement. The theoretical model of dynamic response in the tunnel boring machine direction is used to solve for the theoretical threshold X of acceleration response at the cutterhead bearing position under impact load. T ; The acceleration sensor is used to acquire acceleration response data of the shield cutterhead bearing position in actual engineering. The vibration analysis system is used to process acceleration data in real time, obtaining the acceleration response waveform and the peak response X. P ; Real-time analysis of peak acceleration X P and theoretical threshold X T By reducing the tunneling speed and cutterhead rotation speed, the peak acceleration X can be reduced. P Control at threshold X T The following steps aim to prevent tool breakage.

3. The method for avoiding cutter fracture when tunneling reinforced concrete pile foundations using a shield tunneling machine according to claim 1, characterized in that, In step S1, both concrete and reinforcing steel are modeled using dynamic constitutive models. The concrete uses the RHT constitutive model, the reinforcing steel uses the Johnson-Cook constitutive model, and the cutting tool uses an elastic constitutive model. Bond failure contact is established between the reinforcing steel and the concrete to ensure the accuracy of the calculated impact load. The RHT constitutive model used to describe the dynamic response behavior of concrete consists of three development stages. As stress increases, the material first goes through the elastic stage to reach the elastic yield surface. After that, the material undergoes plastic deformation and enters the linear hardening stage, exhibiting strain hardening characteristics until it reaches the failure surface. When the equivalent stress intensity exceeds the failure stress intensity, the material begins to accumulate damage and enters the damage softening stage, finally reaching the residual strength surface. Its yield surface is described using compressive strength, regularized yield function, and Willam-Warnke function: in, It is the normalized yield function, f c R represents uniaxial compressive strength, R3 represents the Williams-Warnke function, and θ l It's Cape Lord, F r It is the dynamic strain rate increase coefficient. It is normalization pressure. P0 is the hydrostatic pressure. It is strain rate. It is effective plastic strain; Strain rate significantly affects the strength of rock; in this model, the dependence of uniaxial compressive strength on strain rate is given by the following equation: in, It is the reference strain rate under compression. It is the reference strain rate under tension. f t It is tensile strength, β c and β t These are the material constants under compression and tension, respectively; The failure surface is represented as: in, For normalized intensity, A1 and N1 are failure surface parameters; When the stress state reaches the ultimate strength of the material at the failure surface, damage accumulates during further inelastic deformation or plastic strain; the plastic strain at failure is shown below: in It is the plastic strain at failure. It is the minimum damage residual strain. It is the failure cutoff pressure, D r D1 and D2 are the damage variables in the RHT model, and D1 and D2 are the damage constants. Damage variable is defined as plastic strain ε p Accumulation: The Johnson-Cook constitutive formulation used to describe the dynamic response behavior of reinforcing bars is as follows: In the formula, the first bracket represents the elastoplastic term, indicating work hardening; A is the initial yield stress; and B is the work hardening coefficient. The first part represents the equivalent plastic strain, where n is the strain hardening exponent; the second part in parentheses represents the viscous term, indicating the increase in material flow stress at high strain rates, and C is the strain rate sensitivity coefficient. For equivalent plastic strain rate, For reference strain rate; The steel bar chip separation criterion adopts the shear failure criterion built into the Johnson-Cook model. This criterion compares the equivalent plastic strain value at the element integration point with the equivalent failure strain value at that point. Material failure occurs when the failure parameter D is greater than 1. The failure rule is expressed as follows: In the formula, It is the equivalent plastic strain increment. It is the equivalent failure strain; Equivalent failure strain Determined by the following formula: In the formula, p is the compressive stress, and q is the Mises stress. This is the reference strain rate, and d1 to d4 are material failure parameters; The failure rule for the bond between steel reinforcement and concrete is as follows: In the formula, σ nornal For the normal force at the interface between the steel reinforcement and the concrete, σ shear F is the shear stress at the interface between the steel reinforcement and the concrete. S F is the limit value of normal tensile stress. D This represents the shear stress limit value. The stress state of the cutting tool is calculated using elastic constitutive methods: σ=E·ε In the formula, σ is the tool stress, E is the tool elastic modulus, and ε is the tool strain; Among them, the ultimate stress of the tool is the allowable stress that the tool material will not fracture in actual engineering. By calculating the impact load and stress state of the tool cutting reinforced concrete under different penetration depths and cutting speeds, the impact load under the ultimate stress state of the tool is obtained.

4. The method for avoiding cutter fracture when tunneling reinforced concrete pile foundations using a shield tunneling machine according to claim 1, characterized in that, In step S2, the number of cutting tools that simultaneously cut the reinforcing bars is determined by geometric analysis in combination with the relative positions of the actual engineering tools and the reinforcing bars in the pile foundation. The impact loads of the cutting tools are accumulated to obtain the impact loads acting on the cutter head.

5. A method for avoiding cutter fracture when tunneling reinforced concrete pile foundations using a shield tunneling machine, as described in claim 2, is characterized in that... In step S3, the lumped mass method is used to represent each part of the cutterhead, bearing, and shield as a concentrated mass point, establishing an equivalent dynamic model of the cutterhead-bearing-shield system in the tunneling direction. The impact load acting on the cutterhead is used as the input load, and the dynamic model is solved using the Newmark method to obtain the theoretical threshold X of the cutterhead bearing position acceleration response that satisfies the cutter stress requirements. T .

6. A method for avoiding cutter fracture when tunneling reinforced concrete pile foundations using a shield tunneling machine, as described in claim 2, is characterized in that... In step S4, an acceleration sensor is installed at the cutterhead bearing position in the actual project to obtain the acceleration response in the tunnel boring direction. The sensor base is equipped with a strong magnet that can be quickly attracted to the cutterhead bearing.

7. The method for avoiding cutter fracture when tunneling reinforced concrete pile foundations using a shield tunneling machine according to claim 2, characterized in that, In step S5, the vibration analysis system receives and analyzes the data collected by the acceleration sensor in real time via the Internet, and compares and analyzes its waveform response peak value X. P Compared with the theoretical threshold X T Size.

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