A full-wavefield tunnel advanced exploration method based on rock physical constraint

Abstract

The present application belongs to the field of tunnel engineering geophysical prospecting technology, and particularly relates to a full-wave field tunnel advanced exploration method based on rock physics constraints, which comprises the following steps: constructing an initial geological model, sampling at the upper interface of the tunnel layer and carrying out longitudinal and transverse wave velocity measurement to obtain longitudinal wave velocity Vp and transverse wave velocity Vs, combining all the sampled longitudinal wave velocity Vp and transverse wave velocity Vs according to the VRH theory to calculate the longitudinal and transverse wave velocities of the target layer, obtaining the elastic parameters of the target layer, importing the obtained elastic parameters into the initial geological model to obtain a parameter inversion initial model, constructing a forward wave field and simulated seismic record, making a difference between the actual observation record and the simulated record, and carrying out conjugate gradient inversion. The present application can provide more accurate tunnel front geological prediction by fully utilizing all the wave field information excited by the shield machine and carrying out high-precision parameter inversion under the rock physics constraints, thereby providing a scientific basis for safe and efficient construction of the shield machine.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of tunnel engineering geophysical prospecting technology, and particularly relates to a full-wave field tunnel advanced exploration method based on rock physical constraints. BACKGROUND

[0002] In the process of tunnel construction, the prediction and prevention of geological disasters are key issues to ensure construction safety and efficiency. Although traditional tunnel advanced exploration techniques, such as geological radar and electromagnetic wave detection, can provide some geological information in front of the tunnel, they often have 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 combined with seismic wave detection technology to achieve accurate prediction of the geological conditions in front of the tunnel has become a research hotspot.

[0003] Seismic wave detection technology, especially full-wave field seismic wave detection technology, is widely used in geological exploration because it can provide more information about underground media. Full-wave field seismic wave detection technology can effectively identify and predict the heterogeneous structures 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-wave field seismic wave detection technology faces many challenges in practical applications.

[0004] The existing patent CN202410667104.1 proposes a transient electromagnetic tunnel advanced exploration three-dimensional inversion method based on finite element algorithm. This method installs multiple loop sources near the working face to obtain stratum information data, and uses a finite element structure tetrahedral subdivision method to subdivide the area near the working face to establish a three-dimensional inversion model. The electromagnetic response is calculated by the forward 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 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 high-order staggered grid and PML tunnel advanced exploration seismic reflection wave field attenuation method. This method solves the first-order velocity-stress elastic wave equation by high-order staggered grid finite difference method, and uses a new attenuation function PML absorbing boundary treatment method to effectively absorb seismic waves and avoid reflection, ensuring the stability and accuracy of the simulation. However, this method is limited to forward simulation and cannot be directly applied to actual tunnel advanced exploration, so it has limitations in predicting abnormal bodies in front of the tunnel.

[0006] The present application proposes a full-wave field tunnel advanced exploration method based on rock physical constraints to overcome the shortcomings of the prior art. SUMMARY

[0007] The purpose of the present application is to provide a full-wave field tunnel advanced exploration method based on rock physical constraints, which combines rock physical experimental data and actual geological profiles, constructs an initial model of inversion parameters, and solves the problem of inaccurate parameter initial model acquisition in traditional methods.

[0008] The technical solutions adopted by the present application are as follows:

[0009] A full-wave field tunnel advanced exploration method based on rock physical constraints, comprising the following steps:

[0010] S1: constructing an initial geological model;

[0011] S2: sampling and carrying out longitudinal and transverse wave velocity measurement on the upper interface of the tunnel layer, obtaining longitudinal wave velocity Vp and transverse wave velocity Vs;

[0012] S3: according to the VRH theory, combining all the sampled longitudinal wave velocity Vp and transverse wave velocity Vs to calculate the longitudinal and transverse wave velocities of the target layer, and obtaining the elastic parameters of the target layer;

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

[0014] S5: constructing a forward wave field and simulating seismic records;

[0015] S6: differencing the actual observation records and the simulated records, and carrying out conjugate gradient inversion.

[0016] The technical effects achieved by the present application are as follows:

[0017] The present application combines rock physical experimental data and actual geological profiles, constructs an initial model of inversion parameters, and solves the problem of inaccurate parameter initial model acquisition in traditional methods. By fully utilizing all wave field information excited by the shield machine and carrying out high-precision parameter inversion under rock physical constraints, more accurate geological prediction in front of the tunnel can be provided, and scientific basis for safe and efficient construction of the shield machine is provided. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is the overall flowchart of the present application;

[0019] Figure 2 is a schematic diagram of target geological exploration profiles of the present application;

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

[0021] Figure 4 is a schematic diagram of P-wave velocity structure of tunnel sampling in the present application;

[0022] Figure 5 is a schematic diagram of S-wave velocity structure of tunnel sampling in the present application;

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

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

[0025] Figure 8 is a schematic diagram of simulated seismic record in the present application;

[0026] Figure 9 is a schematic diagram of actual observed seismic record in the present application;

[0027] Figure 10 is a schematic diagram of inversion result of P-wave velocity in the present application;

[0028] Figure 11 is a schematic diagram of inversion result of S-wave velocity in the present application;

[0029] Figure 12 is a comparison diagram of inversion result and transient electromagnetic result in the present application. DETAILED DESCRIPTION

[0030] In order to make the objects and advantages of the present application clearer, the present application will be specifically described below in combination with embodiments. It should be understood that the following text is only used to describe one or several specific embodiments of the present application, and does not strictly limit the specific protection scope of the present application.

[0031] As shown in Figures 1-12 , a full-wave field tunnel advanced exploration method based on rock physical constraints comprises the following steps:

[0032] S1: carry out geological survey and construct initial geological model, detailed geological survey includes collecting geological data along the tunnel line, such as stratum distribution, lithological characteristics, geological structure and other information. It can be obtained by consulting regional geological report, conducting field geological surveying and mapping, and geophysical exploration and other means. For example, the ground is preliminarily detected by using geological radar to understand the general stratification of underground stratum, as shown in the attached Figure 2 , the starting position is the current position of the shield machine;

[0033] S2: Take samples at the interface above the tunnel layer and carry out P and S wave velocity measurement. In the corresponding layer above the tunnel design route, select representative positions for sampling. To ensure the accuracy and reliability of the data, the sampling points should be evenly distributed and cover different lithology areas, as shown in FIG. 2. Get the P wave velocity Vp and the S wave velocity Vs, as shown in FIG. 3 and FIG. 4, respectively. Figure 3 Vp Figure 4 Figure 5

[0034] S3: According to the VRH theory, combine all the sampled P wave velocity Vp and S wave velocity Vs to calculate the P and S wave velocity of the target layer, obtain the elastic parameters of the target layer, and construct the initial model, as shown in FIG. 5. Vp Vs Figure 6

[0035] VRH theory (Voigt-Reuss-Hill averaging method) is an effective method for calculating the elastic properties of polycrystalline materials. According to this theory, first, statistical analysis is performed on the P wave velocity Vp and S wave velocity Vs of each sample. Through specific mathematical formulas, the velocity data of all samples are integrated to obtain the average P and S wave velocity of the target layer. Further, using these velocity data, combined with the relevant formulas of rock physics, the elastic parameters of the target layer are calculated, such as Young's modulus and Poisson's ratio. These elastic parameters will be used to further improve the initial geological model. The VRH theory is the existing technology, which will not be described here;

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

[0037] S5: Construct the forward wave field and simulate the seismic record, as shown in FIG. 6 and FIG. 7. Figure 7 Figure 8 The construction of the forward wave field is based on the wave equation to carry out time-domain forward modeling of seismic wave field propagation, and the calculation formula is:

[0038]

[0039]

[0040] is the forward operator of the elastic wave equation, which is determined by the form of the elastic wave equation used in the forward process, and is related to the model parameters, is the forward wave field, which is related to the spatial position and the time , is the source vector.

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

[0042]

[0043] Among them, simulation recording It is a forward-transmitting Tron. In space Wave field at position.

[0044] S6: Record the actual observations (as attached) Figure 9 (as shown) and simulation records (as attached) Figure 8 (As shown) Perform the subtraction and conjugate gradient inversion, and the result is as follows. Figure 10 and attached Figure 11 As shown below:

[0045] The wave field is propagated backwards based on observation records. With simulation recording The residuals between the two equations and the equation in equation (1) are used to calculate the back propagation wavefield. Its relationship with spatial location and time The relevant process is as follows:

[0046]

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

[0048] A1: Define the objective function and calculate the gradient as follows:

[0049]

[0050] in, It is the objective function. Representing all receiver points in space, to ensure that the objective function takes into account all spatial location information, By replacing it with an anti-propagating wave field Through forward propagation wave field Instead, the gradient of the objective function is:

[0051]

[0052] in, It is the forward wave field for specific inversion parameters The partial derivatives, for example, the parameters Longitudinal wave velocity Vp Or transverse wave velocity Vs Or other elastic parameters;

[0053] A2: Update parameters using the conjugate gradient method :

[0054]

[0055] wherein, is a step size, is the first update result of the model parameter, is the first result of the model parameter. S7: compare the obtained result with the transient electromagnetic result, as shown in the accompanying drawings, it can be seen that the result is consistent, but the prediction distance of the present application is farther and the accuracy is higher.

[0056] Figure 12 The present application constructs an initial model of inversion parameters according to actual geological profiles and rock physical experiments, solves the problem that the initial model of parameters cannot be accurately obtained in the related method of traditional tunnel advanced exploration, and fully utilizes all wave fields excited by a shield machine, and then realizes high-precision inversion of parameters under rock physical constraints, and provides an accurate initial velocity field in a rock physical manner, and on this basis, parameter inversion is carried out based on full-wave field observation data, and tunnel advanced exploration prediction is realized.

[0057] The present application constructs an initial model of inversion parameters according to actual geological profiles and rock physical experiments, solves the problem that the initial model of parameters cannot be accurately obtained in the related method of traditional tunnel advanced exploration, and fully utilizes all wave fields excited by a shield machine, and then realizes high-precision inversion of parameters under rock physical constraints, and provides an accurate initial velocity field in a rock physical manner, and on this basis, parameter inversion is carried out based on full-wave field observation data, and tunnel advanced exploration prediction is realized.

[0058] The following two embodiments are further illustrations of the present application: Embodiment

[0059] Engineering background: mountainous tunnel engineering, total length 3 kilometers, passing through multiple complex strata, including sandstone, shale and limestone, etc.

[0060] Implementation process: through geological investigation, it is found that there are multiple small faults in the region, samples are collected in different lithology areas above the tunnel for longitudinal and transverse wave velocity measurement, the elastic parameters of the target layer are calculated by using the VRH theory, the source is set as a Ricker wavelet, the frequency is 50Hz, the forward wave field construction and simulated seismic record generation are carried out, the preliminary simulation result is obtained, and after multiple conjugate gradient inversion iterations, the relatively accurate model parameters are finally obtained.

[0061] Implementation effect: comparing the inversion result with the actual excavation situation, the geological situation prediction accuracy in the range of 200 meters in front reaches more than 90%, and the positions and occurrences of multiple faults are successfully predicted, providing reliable geological information for tunnel construction.

[0062] Embodiment two:

[0063] Engineering background: urban subway tunnel engineering, passing through soft soil strata and sand layers.

[0064] ​Implementation process: combine the urban geological data and the previous survey data to construct an initial geological model, use special coring equipment to sample the soft soil layer and sand layer above the tunnel respectively, measure the longitudinal and transverse wave velocity, and sequentially calculate and invert according to the method of the application;

[0065] Implementation effect: compared with the actual construction situation, the stratum change within the range of 150m in front is accurately predicted, the water-rich area in the sand layer is predicted in advance, which provides a basis for taking corresponding water-stopping measures in construction, and effectively avoids the occurrence of water gushing accidents.

[0066] The above is only the preferred embodiment of the present application, it should be pointed out that for ordinary skilled in the art, without departing from the principles of the present application, can make a number of improvements and refinements, these improvements and refinements should also be considered as the protection scope of the present application. The structure, device and operation method not specifically described and explained in the present application, such as no special description and limitation, are implemented according to the conventional means in the art.

Claims

1. A full wavefield tunnel advance exploration method based on rock physics constraints, characterized in that, The method comprises the following steps: S1: constructing an initial geological model; S2: Take interface samples above the tunnel layer section and carry out longitudinal and transverse wave velocity measurement to obtain longitudinal wave velocity Vp and transverse wave velocity Vs; Vp and transverse wave velocity Vs; S3: According to the VRH theory, the P-wave velocities of all samples are combined with the S-wave velocities of all samples to calculate P-S wave velocities of the target interval, and to obtain the elastic parameters of the target interval. Vp Vs S3: According to the VRH theory, the P-wave velocities of all samples are combined with the S-wave velocities of all samples to calculate P-S wave velocities of the target interval, and to obtain the elastic parameters of the target interval.​ S4: importing the obtained elastic parameters into the initial geological model to obtain a parameter inversion initial model; S5: constructing a forward wave field and simulating a seismic record; In the S5, the construction of the forward wave field carries out seismic wave field propagation time domain forward according to a wave equation, and the calculation formula is: ； wherein, is the forward operator for the elastic wave equation, determined by the form of the elastic wave equation used in the forward process, related to the model parameters, is the forward wavefield, related to the spatial position and time , is the source vector; The generation of the simulated seismic record is based on a finite element method and uses the equation in the formula (1), and the simulated record can be obtained as: ； wherein the analog record is a forward wavefield in space position; S6: subtracting the actual observation record from the simulated record and carrying out a conjugate gradient inversion; In the S6, the wavefield is back-propagated, and the back-propagated wavefield is calculated according to the observation records and the equation in the formula (1) between the simulation records and the equation in the formula (1) between the simulation records and the equation in the formula (1) between the simulation records and the equation in the formula (1) between the simulation records and the equation in the formula (1) between the simulation records ； In the S6, the conjugate gradient inversion is carried out according to the following steps, and the steps are: A1: defining an objective function and calculating a gradient, which is: ； where, is the objective function, represents all the receivers in space, in order to make the objective function consider all the spatial information, we have by the reverse wave field instead, by the forward wave field instead, the gradient of the objective function is: ； wherein, is the partial derivative of the forward wavefield with respect to a specific inversion parameter ; A2: update parameters using the conjugate gradient method : ； wherein, is a step size, is the result of the th update of the model parameters, is the result of the th update of the model parameters.

Images