Full-wave-field tunnel advanced detection method based on rock physical constraint

Abstract

The invention belongs to the technical field of tunnel engineering geophysical prospecting, and particularly relates to a full-wave-field tunnel advanced prospecting method based on rock physical constraint, which comprises the following steps of: constructing an initial geologic model, sampling on an upper interface of a layer section where a tunnel is located and carrying out longitudinal and transverse wave velocity measurement to obtain a longitudinal wave velocity Vp and a transverse wave velocity Vs; combining all sampled longitudinal wave velocities Vp and transverse wave velocities Vs, calculating longitudinal wave velocities and transverse wave velocities of a target layer section, obtaining elastic parameters of the target layer section, importing the obtained elastic parameters into an initial geologic model, obtaining a parameter inversion initial model, constructing a forward wave field and a simulated seismic record, and making a difference between an actual observation record and a simulation record, so as to obtain an initial geologic model; and conjugate gradient inversion is carried out. According to the method, all wave field information excited by the shield tunneling machine is fully utilized, and high-precision parameter inversion is carried out under rock physical constraints, so that more accurate tunnel front geological prediction can be provided, and a scientific basis is provided for safe and efficient construction of the shield tunneling machine.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel engineering geophysical exploration, and in particular relates to a full-wavefield tunnel advance exploration method based on rock physics constraints. Background Art

[0002] During tunnel construction, the prediction and prevention of geological disasters are key issues to ensure construction safety and efficiency. Although traditional tunnel advance detection technologies, such as geological radar and electromagnetic wave detection, can provide geological information ahead of the tunnel to a certain extent, they often have problems such as limited detection distance and poor adaptability to complex geological conditions. With the development of shield machine technology, how to use the shield machine itself as a seismic source and combine it with seismic wave detection technology to achieve accurate prediction of the geological conditions ahead of the tunnel has become a research hotspot.

[0003] Seismic wave detection technology, especially full-wavefield seismic wave detection technology, is widely used in the field of geological exploration because it can provide richer underground medium information. Full-wavefield seismic wave detection technology can effectively identify and predict the heterogeneous structure in front of the tunnel, such as caves and faults, by analyzing the propagation characteristics of seismic waves in underground media. However, due to the complexity of the tunnel construction environment and the weak amplitude characteristics of seismic signals, traditional full-wavefield seismic wave detection technology faces many challenges in practical applications.

[0004] The existing patent CN202410667104.1 proposes a three-dimensional inversion method for transient electromagnetic tunnel advance detection based on a finite element algorithm. This method obtains formation information data by installing multiple loop sources in the area near the tunnel face, and uses the finite element structure tetrahedron partitioning method to partition the area near the tunnel face to establish a three-dimensional inversion model. The electromagnetic response is calculated by the forward modeling method, and the quasi-Newton algorithm is used for iterative solution to improve the efficiency of three-dimensional inversion. Although this method has achieved certain results in improving the inversion efficiency, its prediction distance is limited, and the accuracy of the inversion result is limited by the setting of the initial value;

[0005] Another patent, CN118311656A, introduces a method for attenuation of seismic reflection wave fields in tunnel advance detection using high-order staggered grids and PML. This method solves the first-order velocity-stress elastic wave equation by using a high-order staggered grid finite difference method, and adopts a PML absorption boundary processing method with a new attenuation function to effectively absorb seismic waves and avoid reflection, thereby ensuring the stability and accuracy of the simulation. However, this method is limited to forward modeling and cannot be directly applied to actual tunnel advance detection. Therefore, it has limitations in predicting abnormal bodies in front of the tunnel.

[0006] In view of the deficiencies of the prior art, the present invention proposes a full-wavefield tunnel advance exploration method based on rock physics constraints. Summary of the invention

[0007] The purpose of the present invention is to provide a full-wavefield tunnel advance exploration method based on rock physics constraints, which combines rock physics experimental data and actual geological conditions, constructs an initial model of inversion parameters, and solves the problem of inaccurate acquisition of initial parameter models in traditional methods. By making full use of all wavefield information excited by the shield machine and performing high-precision parameter inversion under rock physics constraints, it is possible to provide a more accurate geological prediction of the front of the tunnel, providing a scientific basis for the safe and efficient construction of the shield machine.

[0008] The technical solution adopted by the present invention is as follows:

[0009] A full-wavefield tunnel advance exploration method based on rock physics constraints includes the following steps:

[0010] S1: construct initial geological model;

[0011] S2: Take samples at the upper interface of the tunnel layer and measure the longitudinal and transverse wave velocities to obtain the longitudinal wave velocity Vp and the transverse wave velocity Vs;

[0012] S3: According to the VRH theory, all the sampled P-wave velocities Vp and S-wave velocities Vs are combined to calculate the P-wave and S-wave velocities of the target layer segment and obtain the elastic parameters of the target layer segment;

[0013] S4: importing the obtained elastic parameters into the initial geological model to obtain a parameter inversion initial model;

[0014] S5: construct forward wavefield and simulated seismic records;

[0015] S6: Subtract the actual observation record from the simulated record and perform conjugate gradient inversion.

[0016] The technical effects achieved by the present invention are:

[0017] The present invention combines rock physics experimental data and actual geological conditions to construct an initial model of inversion parameters, solving the problem of inaccurate initial parameter model acquisition in traditional methods. By making full use of all wave field information excited by the shield machine and performing high-precision parameter inversion under rock physics constraints, it can provide a more accurate geological prediction ahead of the tunnel, providing a scientific basis for safe and efficient construction of the shield machine. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is the overall flow chart of the present invention;

[0019] Figure 2 It is a schematic diagram of the target geological exploration overview of the present invention;

[0020] Figure 3It is a schematic diagram of tunnel sampling in the present invention;

[0021] Figure 4 It is a schematic diagram of the longitudinal wave velocity of the tunnel sampling in the present invention;

[0022] Figure 5 It is a schematic diagram of the shear wave velocity structure of tunnel sampling in the present invention;

[0023] Figure 6 It is a schematic diagram of the initial velocity model in the present invention;

[0024] Figure 7 It is a schematic diagram of the forward wave field in the present invention;

[0025] Figure 8 It is a schematic diagram of simulated earthquake recording in the present invention;

[0026] Fig. 9 It is a schematic diagram of the actual observed earthquake record in the present invention;

[0027] Fig.10 It is a schematic diagram of the inversion result of the longitudinal wave velocity in the present invention;

[0028] Fig.11 is a schematic diagram of the inversion result of the shear wave velocity in the present invention;

[0029] Fig.12 It is a comparison diagram between the inversion results and the transient electromagnetic results in the present invention. DETAILED DESCRIPTION

[0030] In order to make the purpose and advantages of the present invention more clearly understood, the present invention is specifically described below in conjunction with embodiments. It should be understood that the following text is only used to describe one or several specific embodiments of the present invention, and does not strictly limit the scope of protection of the specific claims of the present invention.

[0031] like Figure 1-Figure 12 As shown, a full-wave field tunnel advance exploration method based on rock physics constraints includes the following steps:

[0032] S1: Conduct geological surveys and build an initial geological model. Detailed geological surveys include collecting geological data along the tunnel, such as stratum distribution, lithology, geological structure, etc. This can be obtained through a variety of means, such as consulting regional geological reports, conducting on-site geological mapping, and geophysical exploration. For example, use geological radar to conduct preliminary surface detection to understand the approximate stratification of underground strata, such as the attached Figure 2 As shown, the revealed position is the current position of the shield machine;

[0033] S2: Take samples at the upper interface of the tunnel layer and conduct P-wave and S-wave velocity measurements. Select representative locations for sampling in the corresponding layer above the tunnel design route. To ensure the accuracy and reliability of the data, the sampling points should be evenly distributed and cover different lithology areas, such as the adjacent Figure 3 As shown in the figure, the longitudinal wave velocity Vp and the shear wave velocity Vs are obtained. Figure 4 as well as Figure 5 As shown;

[0034] S3: According to the VRH theory, all the sampled P-wave velocities Vp and S-wave velocities Vs are combined to calculate the P-wave and S-wave velocities of the target layer, and obtain the elastic parameters of the target layer. The initial model is as shown in the attached figure. Figure 6 As shown;

[0035] Among them, VRH theory (Voigt-Reuss-Hill average method) is an effective method for calculating the elastic properties of polycrystalline materials. According to this theory, the longitudinal wave velocity Vp and the shear wave velocity Vs of each sample are first statistically analyzed. Through a specific mathematical formula, the velocity data of all samples are comprehensively calculated to obtain the average longitudinal and shear wave velocities of the target layer. Then, using these velocity data, combined with the relevant formulas of rock physics, the elastic parameters of the target layer, such as Young's modulus, Poisson's ratio, etc., are calculated. These elastic parameters will be used to further improve the initial geological model. The VRH theory is an existing technology and will not be repeated here;

[0036] S4: The elastic parameters obtained, such as velocity, are put into S1 and imported into the initial geological model to obtain the parameter inversion initial model;

[0037] S5: Construct the forward wave field and simulated seismic records, as shown in the attached Figure 7 and attached Figure 8 As shown;

[0038] The construction of the forward wave field is based on the wave equation to carry out the forward modeling of the seismic wave field propagation time domain, and the calculation formula is:

[0039] Lu=f (1)

[0040] Among them, L is the forward operator of the elastic wave equation, which is determined by the form of the elastic wave equation used in the forward modeling process and is related to the model parameters. u is the wave field, which is related to the spatial position x and time t, and f is the source vector.

[0041] The generation of the simulated seismic record is based on the finite element method, and using the equation in formula (1), the simulated record can be obtained as:

[0042] d cal =u x＝xi (2)

[0043] Among them, d cal It is the wave field of the forward wave field u at the spatial position xi.

[0044] S6: Record the actual observations (such as Fig. 9 ) and simulated records (as shown in Figure 8 As shown in the figure, the difference is made and conjugate gradient inversion is performed. The result is as follows Fig.10 and attached Fig.11 As shown below:

[0045] Transmit the wave field back, based on the observation record d obs With analog recording cal The residual between and the equation in formula (1) is used to calculate the back propagation wave field w, which is related to the spatial position x and time t. The process is:

[0046] Lw=d obs -d cal (3)

[0047] The conjugate gradient inversion is carried out according to the following steps:

[0048] A1: Define the objective function and find the gradient:

[0049]

[0050] Where E is the objective function, ∑ i Represents all the detection points in space. In order to take all the position information of the objective function into account, d obs By replacing the back propagation field, d cal By replacing the forward wave field, the gradient of the objective function is:

[0051]

[0052] in, is the partial derivative of the forward wave field with respect to a specific inversion parameter m. For example, the parameter m can be the P-wave velocity Vp or the S-wave velocity Vs, or other elastic parameters;

[0053] A2: Update the parameter m using the conjugate gradient method:

[0054]

[0055] Where α is the step size, m k is the kth update result of the model parameters, m k+1 is the k+1th result of the model parameters.

[0056] S7: Compare the obtained results with the transient electromagnetic results, as shown in the attached Fig.12As shown, it can be seen that the results are consistent, but the prediction distance of the present invention is farther and the accuracy is higher.

[0057] The present invention constructs an initial model of inversion parameters based on actual geological conditions and rock physics experiments, which solves the problem that the initial model of parameters cannot be accurately obtained in traditional tunnel advance exploration related methods, and makes full use of all wave fields excited by the shield machine. Under the constraints of rock physics, high-precision inversion of parameters is achieved, and an accurate initial velocity field is provided through rock physics. On this basis, parameter inversion is performed based on full wave field observation data to achieve tunnel advance exploration prediction.

[0058] The following two examples are further explanations of this application:

[0059] Embodiment 1:

[0060] Project background: The mountain tunnel project is 3 kilometers long and passes through a variety of complex strata, including sandstone, shale and limestone;

[0061] Implementation process: Through geological survey, it was found that there were many small faults in the area. Samples were collected in different lithology areas above the tunnel to measure the P- and S-wave velocities. The elastic parameters of the target layer were calculated using the VRH theory. The source was set to Ricker wavelet with a frequency of 50 Hz. Preliminary simulation results were obtained through forward wave field construction and simulated seismic record generation. After multiple conjugate gradient inversion iterations, relatively accurate model parameters were finally obtained.

[0062] Implementation effect: By comparing the inversion results with the actual excavation conditions, the prediction accuracy of the geological conditions within 200 meters ahead reached more than 90%, and the location and occurrence of multiple faults were successfully predicted, providing reliable geological information for tunnel construction.

[0063] Embodiment 2:

[0064] Project background: Urban subway tunnel project, passing through soft soil and sand layers.

[0065] Implementation process: An initial geological model is constructed by combining urban geological data and preliminary survey data, and special coring equipment is used to sample the soft soil layer and sand layer above the tunnel, respectively, to measure the longitudinal and transverse wave velocities, and calculation and inversion are performed in sequence according to the method of the present invention;

[0066] Implementation effect: Compared with the actual construction situation, the stratum changes within 150 meters ahead were accurately predicted, and the water-rich areas in the sand layer were predicted in advance, which provided a basis for taking corresponding water-stopping measures during construction and effectively avoided the occurrence of water gushing accidents.

[0067] The above is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principles of the present invention, and these improvements and modifications should also be considered as the protection scope of the present invention. The structures, devices and operating methods not specifically described and explained in the present invention shall be implemented according to the conventional means in the art unless otherwise specified and limited.

Claims

1. A full-wavefield tunnel advance exploration method based on rock physics constraints, characterized in that: The following steps are involved: S1: construct initial geological model; S2: Take samples at the upper interface of the tunnel layer and measure the longitudinal and transverse wave velocities to obtain the longitudinal wave velocity Vp and the transverse wave velocity Vs; S3: According to the VRH theory, all the sampled P-wave velocities Vp and S-wave velocities Vs are combined to calculate the P-wave and S-wave velocities of the target layer segment and obtain the elastic parameters of the target layer segment; S4: importing the obtained elastic parameters into the initial geological model to obtain a parameter inversion initial model; S5: construct forward wavefield and simulated seismic records; S6: Subtract the actual observation record from the simulated record and perform conjugate gradient inversion.

2. The full-wavefield tunnel advance detection method according to claim 1, characterized in that: In S5, the construction of the forward wave field is based on the wave equation to carry out the forward modeling of the seismic wave field propagation time domain, and the calculation formula is: Lu=f (1) Among them, L is the forward operator of the elastic wave equation, which is determined by the form of the elastic wave equation used in the forward modeling process and is related to the model parameters. u is the wave field, which is related to the spatial position x and time t, and f is the source vector.

3. The full-wavefield tunnel advance detection method according to claim 2, characterized in that: The generation of the simulated seismic record is based on the finite element method, and using the equation in formula (1), the simulated record can be obtained as: d cal =u x＝xi (2) Among them, d cal It is the wave field of the forward wave field u at the spatial position xi.

4. The full-wavefield tunnel advance detection method according to claim 3 is characterized in that: In S6, the wave field is transmitted back, and according to the observation record d obs With analog recording cal The residual between and the equation in formula (1) is used to calculate the back propagation wave field w, which is related to the spatial position x and time t. The process is: Lw⼝d obs -is cal (3)。 5. The full-wavefield tunnel advance detection method according to claim 4, characterized in that: In S6, conjugate gradient inversion is performed according to the following steps: A1: Define the objective function and find the gradient: Where E is the objective function, ∑ i Represents all the detection points in space. In order to take all the position information of the objective function into account, d obs By replacing the back propagation field, d cal By replacing the forward wave field, the gradient of the objective function is: in, is the partial derivative of the forward wave field with respect to a specific inversion parameter m; A2: Update the parameter m using the conjugate gradient method: Where α is the step size, m k is the kth update result of the model parameters, m k+1 is the k+1th result of the model parameters.

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