Four-dimensional electrical method detection method for internal cracks of grotto cliff body

Abstract

The invention discloses a four-dimensional electrical method detection method for internal cracks of a grotto cliff body. The method comprises the following steps: firstly, acquiring electrical method data at different times before and after filling water into cracks in a grotto cliff body by using the same three-dimensional observation system to form four-dimensional electrical method data; thirdly, acquiring an internal resistivity image of the cliff body by using the same processing inversion parameter for the data acquired at different times; and finally, identifying the distribution condition of the internal fractures by utilizing the characteristic that the resistivity before and after the fractures are filled with water is high resistance and low resistance respectively. According to the method, the problem of accurate detection of the crack target in the grotto cliff body is solved, the characteristic of resistivity difference before and after the crack of the cliff body is filled with water is fully utilized, the distribution condition of the internal crack can be clearly identified by utilizing the detection result, and the detection accuracy of the crack in the grotto cliff body is improved.

Description

Technical Field

[0001] The invention relates to the field of cultural relics protection, and in particular to a four-dimensional electrical detection method for internal cracks in a cave cliff. Background Art

[0002] Grottoes are an important cultural heritage resource with important historical and cultural value. Due to their age, there are often cracks inside the grotto cliffs. These cracks become seepage channels for water, which cause serious corrosion and damage to the grottoes. Through scientific and technological means, the distribution of cracks inside the grotto cliffs can be identified so that necessary sealing measures can be taken to effectively protect the grotto cultural relics. At present, the geophysical technologies used for detecting cracks inside the grotto cliffs mainly include: ground penetrating radar, electrical method and ultrasonic method. Among them, the electrical method has been proven to be an effective method for detecting cracks inside the grotto cliffs. However, the current method uses a single detection of the grotto cliffs, and on this basis, the distribution of cracks inside the cliffs is inferred. The detection accuracy is low, and even misjudgment occurs. Summary of the invention

[0003] In view of the deficiencies in the prior art, the present invention aims to provide a four-dimensional electrical detection method for internal cracks in a cave cliff.

[0004] The object of the present invention is achieved through the following technical scheme: A four-dimensional electrical detection method for internal cracks in a cave cliff body, comprising the following steps:

[0005] Step 1. Collection of four-dimensional electrical data: Three-dimensional electrical data are collected before and after the internal cracks of the cave cliff are filled with water. The two sets of three-dimensional electrical data together constitute the four-dimensional electrical data;

[0006] Step 2. 4D electrical data processing: Use data visualization tools to process the 4D electrical data obtained in step 1, remove data outliers, import them into inversion software, and calculate the resistivity inversion model of each underground point before and after water filling;

[0007] Step 3. Identification of crack distribution based on the inversion results of four-dimensional electrical data: Compare the resistivity inversion models of the cracks in the cave cliff before and after water filling to obtain the distribution of the cracks.

[0008] Furthermore, the step 1 is specifically as follows:

[0009] The three-dimensional electrical method is used to collect data before and after the cracks inside the cave cliff are filled with water. The number of measuring lines and measuring points is calculated according to the size of the cliff area. Metal foil is used as an electrode, and the electrode is fixed on the cliff surface at each measuring point. The wire is fixed on the metal foil, and the wire leading out of each electrode is connected to the multi-channel electrical method system. For all electrodes, one pair of electrodes is selected as the power supply electrodes each time, and the remaining electrodes are used as receiving electrodes to complete the collection of electrical data.

[0010] Furthermore, the three-dimensional electrical method has an electrode distance of 0.25 m and a measurement line distance of 0.5 m.

[0011] Furthermore, the multi-channel electrical method system is a GD-20 multi-channel resistivity imaging system.

[0012] Furthermore, the step 2 is specifically as follows: using DataMap 2000 software to process the four-dimensional electrical data obtained in step 1, first defining and loading the observation system of the original data; then using the Despiking filtering function to remove the abnormal values ​​(data mutation points, showing sharp pulse characteristics) in the data; importing the processed data into the inversion software RES3DINV, setting the inversion damping coefficient and the threshold value of the inversion error, performing inversion calculation and obtaining the resistivity inversion model; the resistivity inversion model displays the true resistivity value of each point underground.

[0013] Furthermore, the step 3 is specifically as follows: when the cracks in the cliff body of the cave are not filled with water, the cracks are filled with air and present high resistance (resistance value is greater than 100 ohm-meters); when the cracks in the cliff body of the cave contain water, they present low resistance characteristics (resistance value is less than 50 ohm-meters); compare the resistivity inversion models of the cracks in the cliff body of the cave before and after they are filled with water to obtain the distribution of the cracks. When the cracks in the cliff body of the cave are not filled with water, the inversion model corresponds to a high-resistance area. If the area shows low resistance after the cracks in the cliff body of the cave are filled with water, these areas are marked as cracks, and the two sets of resistivity data inversion models in the non-crack area are both high-resistance.

[0014] The present invention also provides a four-dimensional electrical detection device for internal cracks in a cave cliff, comprising one or more processors for implementing the four-dimensional electrical detection method for internal cracks in a cave cliff.

[0015] The present invention also provides a computer-readable storage medium on which a program is stored. When the program is executed by a processor, it is used to implement the four-dimensional electrical detection method for internal cracks in a cave cliff body.

[0016] The beneficial effects of the present invention are as follows: the present invention draws on the time-lapse geophysical observation method, proposes to collect electrical data at different times before and after the fracture is filled with water, and forms four-dimensional electrical data. On this basis, a comparative analysis is performed on the resistivity inversion model before and after water filling, which can make full use of the difference in resistivity of the fracture area before and after water filling and accurately identify the distribution of the fracture. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flow chart of the present invention;

[0018] Figure 2 It is a schematic diagram of the electrode positions during three-dimensional electrical acquisition;

[0019] Figure 3 It is the resistivity slice diagram before the crack is filled with water;

[0020] Figure 4 This is the resistivity slice diagram after the crack is filled with water. DETAILED DESCRIPTION

[0021] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Instead, they are merely examples of devices and methods consistent with some aspects of the present invention as detailed in the appended claims.

[0022] The terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The singular forms "a", "the" and "the" used in the present invention and the appended claims are also intended to include plural forms unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0023] It should be understood that although the terms first, second, third, etc. may be used in the present invention to describe various information, these information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of the present invention, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Depending on the context, the word "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining".

[0024] The present invention is described in detail below in conjunction with the accompanying drawings. In the absence of conflict, the features of the following embodiments and implementations can be combined with each other.

[0025] Example 1

[0026] like Figure 1 As shown: This embodiment provides a four-dimensional electrical detection method for internal cracks in a cave cliff, comprising the following steps:

[0027] 1. Collection of four-dimensional electrical data: Use three-dimensional electrical data to collect data before and after the cracks inside the cave cliff are filled with water, and calculate the number of measuring lines and measuring points according to the size of the cliff area; use metal foil as an electrode, fix the electrode on the cliff surface at each measuring point, fix the wire on the metal foil, and connect the wire led out of each electrode to the multi-channel electrical system; for all electrodes, select one pair of electrodes as power supply electrodes each time, and the remaining electrodes as receiving electrodes to complete the collection of electrical data.

[0028] 2. Four-dimensional electrical data processing: The four-dimensional electrical data obtained in step 1 are processed. First, the observation system of the original data is defined and loaded; the outliers in the data are removed; the processed data is imported into the inversion software, the inversion damping coefficient and the threshold value of the inversion error are set, the inversion calculation is performed and the resistivity inversion model is obtained; the resistivity inversion model shows the true resistivity value of each point underground.

[0029] 3. Identification of crack distribution based on the inversion results of four-dimensional electrical data: When the cracks in the cave cliff are not filled with water, they show high resistance because the cracks are filled with air; when the cracks in the cave cliff contain water, they show low resistance characteristics; compare the resistivity inversion models of the cracks in the cave cliff before and after they are filled with water to obtain the distribution of the cracks. When the cracks in the cave cliff are not filled with water, the inversion model corresponds to the high-resistance area. If the area shows low resistance after the cracks in the cave cliff are filled with water, these areas are marked as cracks. The two sets of resistivity data inversion models in the non-crack area are both high-resistance.

[0030] Example 2

[0031] 1) Collection of four-dimensional electrical data:

[0032] The experiment was conducted on the cliff wall of a grotto site. During the rainy season, water was found to flow out of the surface of the grotto, but it was not clear whether there were cracks inside the cliff and whether water was seeping along the cracks. The 4D electrical data were collected at the place where water flowed out of the grotto surface. The working area is a rectangular area, such as Figure 2As shown in the figure, four measuring lines were laid out along the width direction, with the interval between adjacent measuring lines being 0.5m. 23 electrodes were laid out along each measuring line along the length direction, with the interval between adjacent electrodes being 0.25m. Metal foil was used as the electrode. Bentonite was used to fix the electrode on the surface of the cliff at each measuring point. The wire was glued to the metal foil with tape, and the wire led out of each electrode was connected to the GD-20 multi-channel resistivity imaging system. First, when there was no rain for nearly a month (which can be regarded as the cracks not being filled with water), the laid electrodes were used to collect three-dimensional electrical data. For all electrodes, one pair of electrodes was selected as the power supply electrodes each time, and the remaining electrodes were selected as the receiving electrodes to complete the collection of electrical data. Then in the rainy season, when it rained for three consecutive days or more (which can be regarded as the cracks being filled with water), water was found to flow out of the surface of the cave, and the same method as above was used to collect three-dimensional electrical data. In addition to the three-dimensional spatial coordinates, the data collected in these two times also include different time information, which can be regarded as four-dimensional electrical data. The two sets of data collected before and after the cracks were filled with water are shown in Tables 1 and 2, respectively.

[0033] Table 1: Example of data collected before fracture filling

[0034]

[0035] Table 2: Example of data collected after fracture filling with water

[0036]

[0037]

[0038] 2) Four-dimensional electrical data processing

[0039] The same processing method is used to process the two sets of three-dimensional electrical data collected before and after water filling. First, the software DataMap 2000 is used for data preprocessing. In DataMap 2000, the raw data is loaded by defining the observation system, and then the outliers in the data body are removed by filtering technology, such as the "Despiking" function. DataMap 2000 can also form an apparent profile image, which shows the apparent resistivity value at each depth. By observing the apparent profile image, the parameters in the filtering process can be further modified to achieve the purpose of smoothing the data body without removing effective information. The preprocessed data are imported into the inversion software RES3DINV, and the inversion results are calculated. The inversion method used by RES3DINV software is the least squares Newton method, which has fast calculation speed and high inversion accuracy. It is widely used in electrical data inversion, so this software is selected for electrical data inversion. The inversion parameters are set as follows: the damping parameter is 0.3, the lower limit of the root mean square error is 10%, and the number of iterations is less than 10 times. Perform inversion calculations and obtain inversion results, which show the true resistivity values ​​of each underground point.

[0040] 3) Identification of fracture distribution based on the inversion results of four-dimensional electrical data

[0041] When the cracks in the grotto cliff are not filled with water, they show high resistance because the cracks are filled with air; when the cracks in the grotto cliff contain water, they show low resistance characteristics. The high-resistance areas corresponding to the inversion model when the cracks in the grotto cliff are not filled with water, if the areas show low resistance after the cracks in the grotto cliff are filled with water, these areas can be identified as cracks. Figure 3 and Figure 4 The resistivity slices at a depth of 0.25m below the surface of the cave are shown. The blue area represents low resistance, which is a water-bearing feature; other colors represent high resistance areas, which are non-water-bearing features. Figure 3 and Figure 4 It can be found that there are two strip-shaped anomalies with high resistance before water filling and low resistance after water filling in the length direction of 0.8m-1.2m and 3.2m-3.6m, which can be inferred to be caused by internal cracks in the cliff. Using the same method, by comparing the resistivity models before and after water filling, the distribution of internal cracks in the cliff can be identified.

[0042] An embodiment of the present invention further provides a four-dimensional electrical detection device for internal cracks in a cave cliff, comprising one or more processors for implementing the four-dimensional electrical detection method for internal cracks in a cave cliff of the embodiment.

[0043] The embodiment of the present invention further provides a computer-readable storage medium on which a program is stored. When the program is executed by a processor, it is used to implement the four-dimensional electrical detection method for internal cracks in a cave cliff body of the embodiment.

[0044] The computer-readable storage medium may be an internal storage unit of any device with data processing capability described in any of the aforementioned embodiments, such as a hard disk or a memory. The computer-readable storage medium may also be any device with data processing capability, such as a plug-in hard disk, a smart media card (SMC), an SD card, a flash card, etc. equipped on the device. Furthermore, the computer-readable storage medium may also include both an internal storage unit of any device with data processing capability and an external storage device. The computer-readable storage medium is used to store the computer program and other programs and data required by any device with data processing capability, and may also be used to temporarily store data that has been output or is to be output.

[0045] Those skilled in the art can understand that the above are only preferred examples of the invention and are not intended to limit the invention. Although the invention is described in detail with reference to the above examples, those skilled in the art can still modify the technical solutions recorded in the above examples or replace some of the technical features therein with equivalents. Any modifications, equivalent replacements, etc. made within the spirit and principles of the invention should be included in the protection scope of the invention.

Claims

1. A four-dimensional electrical detection method for cracks inside a cave cliff, characterized in that: The steps include: (1) The three-dimensional electrical data acquisition method was used to collect data before and after the internal cracks of the cave cliff were filled with water, and two sets of three-dimensional electrical data were obtained, which together constituted four-dimensional electrical data; (2) using a data visualization tool to process the four-dimensional electrical data obtained in step (1), remove data outliers, and calculate the resistivity inversion model of each underground point before and after water filling; (3) Compare the resistivity inversion models of the cracks in the cave cliff before and after they are filled with water to obtain the distribution of the cracks.

2. The four-dimensional electrical detection method for internal cracks in a cave cliff according to claim 1 is characterized in that: The step (1) specifically comprises: using a three-dimensional electrical method to collect apparent resistivity data of the internal cracks of the cave cliff before and after water is filled, and calculating the number of measuring lines and measuring points according to the size of the cliff area; fixing electrodes on the surface of the cliff at each measuring point, fixing wires on the electrodes, and connecting the wires led out of each electrode to a multi-channel electrical method system; wherein, for all the electrodes, one pair of electrodes is selected each time as power supply electrodes, and the remaining electrodes are selected as receiving electrodes to complete the collection of electrical method data.

3. The four-dimensional electrical detection method for internal cracks in a cave cliff according to claim 2 is characterized in that: The electrodes are made of metal foil.

4. The four-dimensional electrical detection method for internal cracks in a cave cliff according to claim 2 is characterized in that: The electrode distance of the three-dimensional electrical method is 0.25m and the measurement line distance is 0.5m.

5. The four-dimensional electrical detection method for internal cracks in a cave cliff according to claim 2 is characterized in that: The multi-channel electrical method system is a GD-20 multi-channel resistivity imaging system.

6. The four-dimensional electrical detection method for internal cracks in a cave cliff according to claim 1 is characterized in that: The step (2) is specifically: The four-dimensional electrical data obtained in step (1) are processed using DataMap 2000 software. First, the observation system of the original data is defined and loaded. Then, the outliers in the data are removed using the Despiking filter function, wherein the outliers are data mutation points showing sharp pulse characteristics. The processed data are imported into the inversion software RES3DINV, the inversion damping coefficient and the threshold value of the inversion error are set, and the inversion calculation is performed to obtain the resistivity inversion model. The resistivity inversion model displays the true resistivity value of each underground point.

7. The four-dimensional electrical detection method for internal cracks in a cave cliff according to claim 1 is characterized in that: The step (3) is specifically as follows: when the cracks in the cave cliff body are not filled with water, they present high resistance characteristics because the cracks are filled with air; when the cracks in the cave cliff body contain water, they present low resistance characteristics; compare the resistivity inversion models of the cracks in the cave cliff body before and after they are filled with water to obtain the distribution of the cracks; wherein, when the cracks in the cave cliff body are not filled with water, the inversion model corresponds to a high resistance area; if the cracks in the cave cliff body are filled with water, the area becomes low resistance, then the area is marked as a crack, and the two sets of resistivity data inversion models in the non-crack area are both high resistance.

8. A four-dimensional electrical detection device for cracks inside a cave cliff, characterized in that: It comprises one or more processors for implementing the four-dimensional electrical detection method for internal cracks of a cave cliff body as described in any one of claims 1-7.

9. A computer-readable storage medium having a program stored thereon, characterized in that: When the program is executed by a processor, it is used to implement the four-dimensional electrical detection method for internal cracks in a cave cliff body as described in any one of claims 1-7.

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