A method for detecting and evaluating high-angle bedrock type fault structures in a coastal city

Abstract

The present application relates to the field of geological exploration, in particular to a method for detecting and evaluating high-angle bedrock-type fault structure in coastal cities, comprising: 1) collecting geological data, preliminarily obtaining fault zone spatial distribution characteristic parameters through geophysical prospecting test and interpretation; 2) arranging directional drilling and vertical drilling according to the tendency and inclination of the fault zone, locking the occurrence elements of the fault zone; 3) performing full-hole wall digital imaging, calculating the tendency and inclination of the structural plane, and obtaining the occurrence distribution law of the rock mass joint fissure; 4) dividing lithologic sections, identifying the internal structural units of the fault zone, and analyzing the geological structure characteristics, activity properties and evolution history of the fault zone; 5) constructing a high-angle bedrock-type fault structure engineering geological zoning model showing systematic changes of each zoning system. Through the full-hole wall digital imaging technology, the problem that the drilling method cannot accurately reveal the occurrence of faults and stratigraphic structural planes is successfully solved, and the occurrence elements of the rock mass structural plane in the fault zone can be accurately obtained.

Description

Technical Field

[0001] This invention relates to the field of geological exploration, specifically to a method for detecting and evaluating high-angle bedrock fracture structures in coastal cities. Background Technology

[0002] Fault structures are a key factor affecting urban geological safety. In coastal areas, numerous NE-NNE trending Neocathaysian faults are present. In geological surveys and engineering explorations of coastal bedrock-type cities, the exploration of high-angle bedrock fault zones has always faced significant challenges. For example, some fault zones have dip angles generally greater than 70°, even approaching vertical, and are quite wide, typically 30-60 meters. Traditional vertical drilling techniques have the following problems for exploring such high-angle, wide bedrock faults: 1. High penetration difficulty: Vertical drilling requires traversing deep strata to penetrate high-angle fault zones, and the designed hole depth often exceeds 400m, resulting in high drilling costs and long cycles.

[0003] 2. Low core recovery rate: The rock mass within the fault zone is severely fractured, and the core recovery rate is only about 20% to 50%, making it impossible to accurately obtain key geological parameters such as lithology, layer depth, and structural plane occurrence.

[0004] 3. The orientation of structural planes is difficult to determine accurately: Drilling and coring cannot measure the orientation of fractures and joints in situ, making it difficult to accurately determine the spatial distribution characteristics of fractures.

[0005] 4. Fault zone characteristics are difficult to fully reveal: The angle between vertical boreholes and high-angle fault zones is small, making it difficult to fully reveal the internal structure of the fault zone and easily leading to the loss of important geological information.

[0006] Currently, technologies such as directional drilling and full-hole wall digital imaging are rarely used in fault zone exploration. Therefore, there is an urgent need for an efficient and accurate method for detecting and evaluating high-angle bedrock-type fault structures. Summary of the Invention

[0007] In view of the problems existing in the prior art, the purpose of this invention is to provide a method for detecting and evaluating high-angle bedrock fracture structures in coastal cities that can solve the technical problem that traditional vertical drilling technology is unable to completely and accurately reveal high-angle bedrock fracture structures.

[0008] To achieve the above objectives, the technical solution adopted by this invention is: a method for detecting and evaluating high-angle bedrock fracture structures in coastal cities, comprising the following steps: Step 1: Collect existing geological data in the survey area, and preliminarily determine the distribution location of the fault zone to be investigated based on comprehensive analysis of the data. By analyzing the effects and suitability of different geophysical exploration methods on urban geological structure detection, select a geophysical exploration scheme for the concealed fault structure of coastal bedrock type cities under complex conditions, and obtain the spatial distribution characteristic parameters of the fault zone. Step 2: Based on the geophysical interpretation results, determine the dip and dip angle of the fault zone, arrange directional boreholes on the hanging wall of the fault zone to expose the internal structure of the fault zone, and arrange vertical boreholes near the footwall of the fault zone to lock the fault zone's attitude elements together with the directional and inclined boreholes. Step 3: Clean the drilled borehole, use a panoramic high-definition intelligent borehole television tester to perform full-hole wall digital imaging, stitch the images together to generate a two-dimensional unfolded diagram and a three-dimensional columnar curved surface diagram of the borehole wall, calculate the dip and dip angle of the structural planes, perform statistical analysis on each structural plane within the fault zone, and obtain the occurrence distribution law of rock mass joints and fractures. Step 4: Systematically log the drill core samples, divide the lithological intervals, identify the internal structural units of the fault zone, collect representative samples for rock and mineral testing, and analyze the geological structural characteristics, activity nature and evolution history of the fault zone by combining mineralogical and microstructure characteristics. Step 5: Integrate multi-source data to determine the spatial distribution and engineering geological characteristics of the fault zone, and construct a high-angle bedrock-type fault structure engineering geological zoning model that presents the systematic changes of each zone, so as to provide geological support for the engineering planning and construction of similar fault structure sites.

[0009] The suitability analysis in step 1 of the above-mentioned method for detecting and evaluating high-angle bedrock fracture structures in coastal cities includes site condition requirements, anti-interference ability, construction convenience, detection depth range, and application of results.

[0010] The aforementioned methods for detecting and evaluating high-angle bedrock-type fault structures in coastal cities include a combination of geophysical exploration schemes for concealed fault structures in coastal bedrock-type cities under complex conditions: microkinetic exploration, high-density electrical resistivity tomography, and shallow seismic reflection wave analysis. In relatively intact bedrock, seismic surface wave velocities are high, while in fault zones, due to the fractured rock mass and rich groundwater, geological bodies with low velocity characteristics are formed. Therefore, the micro-motion exploration method, which is based on the difference in surface wave velocity and the theory of stationary random process, is used. When reflected waves pass through fault fracture zones, they are often accompanied by abnormal phenomena such as seismic wave diffraction, the appearance of fault waves, changes in wave group intervals, dislocation of in-phase axes and sudden increases, decreases and disappearances in number, arching, bifurcation, twisting, phase transition, occurrence and sudden changes in energy. In such cases, the shallow seismic reflection wave method, which distinguishes tectonic fracture zones and other geological anomalies based on the kinematic and dynamic characteristics of seismic waves, is used. The presence of fault fracture zones formed by fracturing activity within the bedrock is accompanied by an increase in porosity and water content within the rock mass, as well as the presence of metal oxides such as iron and manganese. This leads to a decrease in resistivity, resulting in a low-resistivity anomaly zone lower than that of the intact rock mass. When the resistivity gradient transitions sharply, high-density electrical resistivity methods are used for detection.

[0011] The above-mentioned method for detecting and evaluating high-angle bedrock-type fault structures in coastal cities, in step 1, can detect low-velocity zone anomalies or geological anomaly areas with drastic gradient changes in wave velocity values ​​at the fault zone using micro-motion exploration, high-density electrical resistivity tomography, and shallow seismic reflection wave method. When the anomaly areas detected by the three methods overlap or partially overlap, it is preliminarily determined that there is a fault structure in the overlapping area. At the same time, spatial distribution characteristic parameters including the width, dip angle, dip direction, and strike of the fault zone can be obtained.

[0012] The above-mentioned method for detecting and evaluating high-angle bedrock-type fault structures in coastal cities involves arranging directional boreholes on the hanging wall of the fault zone. The borehole azimuth is perpendicular to the dip of the fault zone, the borehole dip angle is equal to the fault zone dip angle minus 5°, and the borehole depth is calculated based on the estimated width and dip angle of the fault zone. The borehole depth must penetrate the fault zone and enter the intact rock mass of the footwall by at least 20m.

[0013] The above-mentioned method for detecting and evaluating high-angle bedrock fracture structures in coastal cities, in step 3, involves using a high-definition panoramic fisheye camera concave reflection image method for full-hole wall digital imaging. The camera rotates once to acquire annular well wall images, which are then continuously spliced ​​to generate full-hole wall images. The probe is raised at a constant speed to continuously acquire well wall images. On the two-dimensional unfolded diagram of the well wall, the structural surface that completely cuts the borehole is identified, which appears as a sinusoidal curve. The amplitude and phase of the sinusoidal curve are extracted, and combined with depth coordinates and azimuth information, the sinusoidal curve is fitted on the two-dimensional unfolded diagram of the well wall to obtain the dip angle α and dip direction β of the structural surface. The calculation formula is as follows: α = arctan(H / D), β = initial azimuth ± 90° Where H is the amplitude of the sine curve, D is the borehole diameter, and the starting azimuth is the azimuth corresponding to the lowest point of the sine curve.

[0014] In the above-mentioned method for detecting and evaluating high-angle bedrock-type fracture structures in coastal cities, in step 5, the internal structural units include fault gouge zones, fault breccia zones, breccia zones, and breccia-altered zones, and the rock and mineral testing includes scanning electron microscopy imaging and electron microscopy imaging.

[0015] In the above-mentioned method for detecting and evaluating high-angle bedrock-type fault structures in coastal cities, in step 5, the multi-source data includes geophysical exploration, drilling, whole-hole wall imaging, and rock and mineral testing data, and the spatial distribution and engineering geological characteristics include the occurrence elements, width, geological structure, and lithological contact relationship of the fault zone.

[0016] The beneficial effects of this invention's method for detecting and evaluating high-angle bedrock fracture structures in coastal cities are as follows: Through directional inclined borehole trajectory design, it accurately and completely penetrates high-angle fracture zones with a limited drilling depth of 200m. Compared to traditional vertical drilling techniques with a minimum of 400m, this significantly saves drilling depth and improves detection efficiency by up to 50%, efficiently penetrating high-angle fracture zones. By employing full-hole wall digital imaging technology, it successfully solves the problem of drilling methods failing to accurately reveal the attitude of fractures and stratigraphic structural planes. It can accurately obtain the attitude elements of rock mass structural planes within the fracture zone and accurately measure the attitude of structural planes in situ. By integrating multi-source data such as geological data, geophysical interpretation, core drilling, rock and mineral testing, and digital imaging, it accurately determines the spatial distribution and engineering geological characteristics of fracture zones, including their attitude elements, width, geological structure, and lithological contact relationships, thus precisely revealing the geological features of the fracture zones. Attached Figure Description

[0017] Figure 1 This is a technical roadmap of the method of the present invention; Figure 2 A profile diagram of the results interpreted by the micro-motion exploration method; Figure 3 A cross-sectional view of the interpretation results of shallow seismic reflection method; Figure 4 A cross-sectional view of the high-density electrical resistivity tomography (EDT) interpretation results; Figure 5 A schematic cross-sectional design for the relationship between directional drilling and the fault zone; Figure 6 The diagram shows the indoor integrated rock and mineral testing and analysis methods and results, where (a) is the borehole imaging diagram, (b) is the unfolded diagram, and (c) is the processed diagram. Figure 7 This is a schematic diagram of an engineering geological zoning model for high-angle bedrock-type fracture structures. Detailed Implementation

[0018] To enable those skilled in the art to better understand the technical solution of the present invention, the following detailed embodiments and appendices are provided. Figure 1 -Appendix Figure 7 The technical solution of the present invention will be described.

[0019] Example 1 A method for detecting and evaluating high-angle bedrock-type fault structures in coastal cities includes the following steps: Step 1: Collect existing geological data of the survey area, and preliminarily determine the distribution location of the fault zone to be investigated based on comprehensive analysis of the data. Analyze the effectiveness and suitability of different geophysical exploration methods for urban geological structure detection, including site requirements, anti-interference ability, construction convenience, detection depth range, and application of results.

[0020] A geophysical exploration scheme for concealed fault structures in coastal bedrock-type cities under complex conditions was selected to obtain the spatial distribution characteristics of the fault zone. The scheme includes a combination of micromotion exploration method, high-density electrical resistivity tomography, and shallow seismic reflection wave method.

[0021] In relatively intact bedrock, seismic surface wave velocities are high. In fault zones, due to the fractured rock mass and rich groundwater, geological bodies with low velocity characteristics are formed. Therefore, the micro-motion exploration method, which is based on the difference in surface wave velocity and the theory of stationary random process, is used.

[0022] When reflected waves pass through fault fracture zones, they are often accompanied by abnormal phenomena such as seismic wave diffraction, the appearance of fault waves, changes in wave group intervals, dislocation of in-phase axes and sudden increases, decreases and disappearances in number, arching, bifurcation, twisting, phase transitions, and sudden changes in attitude and energy. In such cases, the shallow seismic reflection wave method, which uses the kinematic and dynamic characteristics of seismic waves as a basis, is used to distinguish tectonic fracture zones and other geological anomalies.

[0023] The presence of fault fracture zones formed by fracturing activity within the bedrock is accompanied by an increase in porosity and water content within the rock mass, as well as the presence of metal oxides such as iron and manganese. This leads to a decrease in resistivity, resulting in a low-resistivity anomaly zone lower than that of the intact rock mass. When the resistivity gradient transitions sharply, high-density electrical resistivity methods are used for detection.

[0024] Micro-motion exploration, high-density electrical resistivity tomography, and shallow seismic reflection wave method can all detect low-velocity zone anomalies or geological anomaly areas with drastic gradient changes in wave velocity values ​​at fault zones. When the anomaly areas detected by the three methods overlap or partially overlap, it can be preliminarily determined that there is a fault structure in the overlapping area. At the same time, spatial distribution characteristic parameters including the width, dip angle, dip direction, and strike of the fault zone can be obtained.

[0025] Wave velocity values ​​in the target area are measured using specialized geophysical equipment. Low-velocity anomalies or areas of abrupt gradient changes in wave velocity values ​​are then read and interpreted using specialized software. Combined with local experience, parameters such as the location, width, and attitude of the fault zone are preliminarily determined. (See details...) Figures 2-4 Interpretation results are as follows: The micro-motion exploration equipment adopted the GN209 remote real-time intelligent micro-motion system, and the interpretation was performed using Feisheng micro-motion processing software (3D version); the high-density electrical resistivity tomography equipment adopted the E60DN high-density electrical resistivity tomography instrument, and the interpretation was performed using RES2D inversion software; the shallow seismic reflection wave method equipment adopted the Minisis48A integrated engineering detector, and the interpretation was performed using Jiaojia software.

[0026] Step 2: Based on the geophysical interpretation results, preliminarily determine the dip and dip angle of the fault zone. Deploy directional boreholes in the hanging wall of the fault zone to expose its internal structure. When deploying directional boreholes in the hanging wall, the borehole azimuth should be opposite to the fault zone dip, and the borehole dip angle should be equal to the fault zone dip angle minus 5°. The borehole depth should be calculated based on the estimated fault zone width and dip angle, and the borehole depth should penetrate the fault zone into the intact rock mass of the footwall by at least 20m. Deploy vertical boreholes near the footwall within the fault zone, together with the directional dipping boreholes, to pinpoint the fault zone's attitude.

[0027] Step 3: Clean the drilled borehole, use a panoramic high-definition intelligent borehole television tester to perform full-hole wall digital imaging, stitch the images together to generate a two-dimensional unfolded diagram and a three-dimensional columnar curved surface diagram of the borehole wall, calculate the dip and dip angle of the structural planes, perform statistical analysis on each structural plane within the fault zone, and obtain the occurrence distribution law of rock mass joints and fractures.

[0028] Full-hole wall digital imaging employs a high-definition panoramic fisheye camera concave reflection image method. The camera rotates one revolution to acquire images of the annular well wall, which are then stitched together through continuous lifting to generate a full-hole wall image. The probe rises at a constant speed, continuously acquiring well wall images. On the two-dimensional unfolded diagram of the well wall, the structural surface completely cutting the borehole is identified, exhibiting a sinusoidal curve shape. The amplitude and phase of the sinusoidal curve are extracted, and combined with depth coordinates and azimuth information, the sinusoidal curve is fitted on the two-dimensional unfolded diagram of the well wall to obtain the dip angle α and dip direction β of the structural surface. The calculation formula is as follows: α = arctan(H / D), β = initial azimuth ± 90° Where H is the amplitude of the sine curve, D is the borehole diameter, and the starting azimuth is the azimuth corresponding to the lowest point of the sine curve.

[0029] The main function of the three-dimensional columnar surface map is to restore the three-dimensional morphology of the rock mass inside the borehole, which can generate an "electronic core". It can automatically identify and extract geometric parameters such as the rock mass and the occurrence of its structural planes. At the same time, it can switch between analysis of the inside and outside of the borehole, avoiding the time-consuming and laborious manual extraction of parameters, which may also be subject to human error. This lays the foundation for the digital and intelligent processing of geological information.

[0030] Step 4: Systematically log the drilled core samples, divide the lithological sections, identify the internal structural units of the fault zone, including fault gouge zone, fault breccia zone, breccia zone, and breccia zone, collect representative samples for rock and mineral testing using scanning electron microscopy and electron microscopy, and analyze the geological structure, activity, and evolution history of the fault zone by combining mineralogical and microstructural characteristics.

[0031] Step 5: Integrate multi-source data including geophysical exploration, drilling, whole-hole imaging, and rock and mineral testing data to determine the spatial distribution and engineering geological characteristics of the fault zone, including its occurrence elements, width, geological structure, and lithological contact relationships. Construct a high-angle bedrock-type fault structure engineering geological zoning model that presents the systematic changes of each zone, providing geological support for the engineering planning and construction of similar fault structure sites.

[0032] Example 2 A method for detecting and evaluating high-angle bedrock-type fracture structures in coastal cities includes the following steps.

[0033] Step 1: Geological data collection and analysis.

[0034] Collect existing geological data for the survey area, including regional geological maps, fault structure distribution maps, and previous research results; based on a comprehensive analysis of all previous research data, preliminarily determine the distribution location of the fault zone to be investigated, and provide a scientific basis for the deployment of subsequent geophysical exploration, drilling and other work.

[0035] Step 2: Multi-source geophysical interpretation.

[0036] By analyzing the effects of different geophysical exploration methods on urban geological structure detection, as well as their suitability in terms of site conditions, anti-interference ability, construction convenience, detection depth range, and application of results, the optimal geophysical exploration scheme for concealed fault structures in coastal bedrock-type cities under complex conditions is selected as: microkinetic exploration + high-density electrical resistivity tomography + shallow seismic reflection wave method.

[0037] Geophysical exploration methods and technical principles: In coastal bedrock cities, high-density electrical resistivity tomography (EDT) is a highly efficient method for geological structural detection. If fault fracture zones exist within the bedrock due to fracturing activity, they are often accompanied by increased porosity and water content within the rock mass, along with the presence of iron and manganese oxides, leading to a decrease in resistivity and the appearance of low-resistivity anomaly zones lower than those of intact rock masses, with a sharp gradient in resistivity values. Shallow seismic reflection wave methods, based on the kinematic and dynamic characteristics of seismic waves, distinguish tectonic fracture zones and other geological anomalies. A key indicator of fault presence is the lateral variation of the phase axis of the reflected wave. When the reflected wave passes through a fault fracture zone, it is often accompanied by anomalies such as seismic wave diffraction, the appearance of fault waves, changes in wave group intervals, phase axis misalignment and sudden increases, decreases, and disappearances in the number of phase axes, upward arching, bifurcation, twisting, phase transitions, and sudden changes in attitude and energy. The micro-motion exploration method is based on the theory of stationary random processes and takes the difference in surface wave velocity as a premise. In relatively intact bedrock, the surface wave velocity of seismic waves is relatively high, while in fault zones, due to the characteristics of rock fragmentation and rich groundwater, geological bodies with low velocity characteristics can often be formed.

[0038] In summary, all three geophysical exploration methods can detect low-velocity anomalies or geological anomalies with drastic gradient changes in wave velocity values ​​at fault zones. When the anomaly zones detected by the three methods overlap or partially overlap, it can be preliminarily determined that the probability of a fault structure existing in the overlapping area is greater than 90%. Simultaneously, spatial distribution characteristics such as fault zone width, dip angle, dip direction, and strike can be obtained (preliminary determination: fault zone width approximately 60m, dip angle approximately 80°, dip direction NW), ultimately providing a basis for directional drilling design. Typical interpretation results are attached. Figure 2 -Appendix Figure 4 .

[0039] Step 3: Design and construction of directional drilling trajectory.

[0040] Based on the geophysical interpretation results, the dip and dip angle of the fault zone were determined. Directional boreholes were drilled on the hanging wall of the fault zone, with the borehole azimuth angle designed to intersect the fault zone dip direction. The borehole dip angle was set to equal the fault zone dip angle minus 5°, ensuring the boreholes penetrated the fault zone at a large angle to fully expose its internal structure. Then, vertical boreholes were drilled near the footwall within the fault zone. Their purpose, along with the directional and dipping boreholes, was to pinpoint the fault zone's dip angle and other attitude parameters. The directional and vertical borehole trajectory designs are attached. Figure 5 .

[0041] A drilling rig capable of directional drilling was used, equipped with a screw motor drill string and an inclinometer, to carry out directional drilling according to the designed trajectory; vertical drilling was then carried out after completely penetrating the fault zone. During drilling, mud wall protection, hydraulic single-action double-tube drill strings, and wireline coring were employed to ensure core recovery rate; the borehole inclination and azimuth were measured every 25m to control borehole trajectory error, with an allowable error of 2° per 100m inclination; and borehole depth measurement and correction were performed every 50m and at the end of the drilling.

[0042] The drilling rig selected is an XY-4 type drilling rig or equipment with equivalent performance. Its technical parameters should meet the following requirements: maximum drilling depth ≥ 850m, drilling inclination angle adjustment range 0-360°, maximum vertical shaft lifting force ≥ 80kN, and maximum vertical shaft pressure ≥ 60kN.

[0043] The screw motor drill bit consists of four components: a bypass valve, a motor, a universal joint, and a drive shaft. It uses the flushing fluid output from the mud pump to drive the motor rotor to rotate, and transmits torque to the drill bit through the universal joint and drive shaft, thus achieving directional drilling without the need for drill pipe rotation.

[0044] By employing a hydraulic single-action double-tube drill and wireline coring technology, and utilizing directional drilling techniques, cores are extracted throughout the preset depth, significantly improving the core recovery rate. This solves the problem of low core recovery rate and loss of important geological information caused by rock mass fracturing in traditional drilling, thereby enhancing the core recovery rate.

[0045] Step 4: In-situ testing of full-hole wall digital imaging.

[0046] After drilling, the borehole is washed to remove mud cake from the borehole wall. A panoramic high-definition intelligent borehole television testing instrument is used for full-borehole digital imaging. The probe is raised at a constant speed, continuously acquiring borehole wall images. These images are then stitched together by software to generate a two-dimensional unfolded diagram and a three-dimensional columnar surface diagram of the borehole wall. On the two-dimensional borehole unfolded diagram, structural surfaces that completely cut through the borehole are identified, exhibiting a sinusoidal curve shape. The amplitude and phase of the sinusoidal curve are extracted by software, and combined with depth coordinates and azimuth information, the dip and dip angle of the structural surfaces are calculated. Statistical analysis is performed on each structural surface within the fault zone to obtain the distribution pattern of rock mass joints and fractures. The principle of full-borehole digital imaging structural surface attitude measurement is attached. Figure 6 As shown in (a), (b), and (c).

[0047] The full borehole wall digital imaging uses a high-definition panoramic fisheye camera concave reflection image method. The camera rotates once to collect images of the annular well wall, and the images are generated by continuous lifting and stitching.

[0048] As a preferred option, the calculation of the structural plane attitude in step four uses dedicated computer software to fit a sine curve on a two-dimensional borehole development diagram to obtain the dip angle α and dip direction β of the structural plane. The calculation formula is as follows: α = arctan(H / D) β = Initial azimuth ± 90° Where H is the amplitude of the sine curve, D is the borehole diameter, and the starting azimuth is the azimuth corresponding to the lowest point of the sine curve.

[0049] Step 5: Core logging and comprehensive rock and mineral analysis.

[0050] The drilled core samples were systematically cataloged, lithological intervals were divided, and internal structural units of the fault zone were identified, including fault mudstone zone, fault breccia zone, breccia zone, and breccia-altered zone. Representative samples were collected for rock and mineral testing, such as scanning electron microscopy (SEM) and electron microscopy. Combined with mineralogical and microstructural characteristics, the geological structural features, activity properties, and evolutionary history of the fault zone were analyzed.

[0051] A transverse zoning model for engineering geology of high-angle bedrock-type fault structures was constructed, dividing the fault zone into three main zones: fault mud zone, breccia zone, and joint development zone, as well as six sub-zones: strong expansion zone, non-expansion zone, hanging wall breccia zone, footwall breccia zone, hanging wall joint development zone, and footwall joint development zone. Each zone exhibits systematic changes in petrological characteristics, rock mass integrity, and physical and mechanical parameters, and all have clear geological and engineering significance.

[0052] Step Six: Comprehensive Data Analysis and Application of Results.

[0053] By integrating multi-source data from geophysical exploration, drilling, full-hole imaging, and rock and mineral testing, the spatial distribution and engineering geological characteristics of the fault zone, including its attitude, width, geological structure, and lithological contact relationships, are accurately determined. This allows for the construction of an engineering geological zoning model of a high-angle bedrock-type fault structure (as attached). Figure 7 Each zone exhibits systematic changes in petrological characteristics, rock mass integrity, and physical and mechanical parameters, which can provide geological support for engineering planning and construction of areas with similar fault structures.

[0054] This invention employs a technical approach of "multi-source integrated geophysical exploration interpretation and positioning - directional drilling design and implementation - full-hole wall digital imaging in-situ testing - indoor integrated rock and mineral analysis." The main core technologies can be summarized as "one exploration, two drillings, and three imagings." One exploration involves a comprehensive geophysical exploration method combining micro-motion exploration, shallow seismic reflection wave method, and high-density resistivity method. Two drillings involve using a combination of directional inclined and vertical drilling techniques to "see through" the fault zone. Three imagings involve a comprehensive rock and mineral testing method including full-hole wall digital imaging technology, scanning electron microscopy (SEM) imaging, and electron microscopy imaging. This approach enables efficient and accurate detection and evaluation of high-angle bedrock fault structures.

[0055] The above embodiments are merely illustrative of the structural concept and features of the present invention, intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made based on the essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for detecting and evaluating high-angle bedrock-type fracture structures in coastal cities, characterized in that, Includes the following steps: Step 1: Collect existing geological data in the survey area, and preliminarily determine the distribution location of the fault zone to be investigated based on comprehensive analysis of the data. By analyzing the effects and suitability of different geophysical exploration methods on urban geological structure detection, select a geophysical exploration scheme for the concealed fault structure of coastal bedrock type cities under complex conditions, and obtain the spatial distribution characteristic parameters of the fault zone. Step 2: Based on the geophysical interpretation results, preliminarily determine the dip and dip angle of the fault zone, arrange directional boreholes on the hanging wall of the fault zone to expose the internal structure of the fault zone, and arrange vertical boreholes near the footwall of the fault zone to lock the fault zone's attitude elements together with the directional and inclined boreholes. Step 3: Clean the drilled borehole, use a panoramic high-definition intelligent borehole television tester to perform full-hole wall digital imaging, stitch the images together to generate a two-dimensional unfolded diagram and a three-dimensional columnar curved surface diagram of the borehole wall, calculate the dip and dip angle of the structural planes, perform statistical analysis on each structural plane within the fault zone, and obtain the occurrence distribution law of rock mass joints and fractures. Step 4: Systematically log the drill core samples, divide the lithological intervals, identify the internal structural units of the fault zone, collect representative samples for rock and mineral testing, and analyze the geological structural characteristics, activity nature and evolution history of the fault zone by combining mineralogical and microstructure characteristics. Step 5: Integrate multi-source data to determine the spatial distribution and engineering geological characteristics of the fault zone, and construct a high-angle bedrock-type fault structure engineering geological zoning model that presents the systematic changes of each zone, so as to provide geological support for the engineering planning and construction of similar fault structure sites.

2. The method for detecting and evaluating high-angle bedrock fracture structures in coastal cities according to claim 1, characterized in that, In step 1, the suitability analysis includes site conditions, anti-interference ability, ease of construction, detection depth range, and application of results.

3. The method for detecting and evaluating high-angle bedrock fracture structures in coastal cities according to claim 2, characterized in that, The selected geophysical exploration schemes for concealed fault structures in coastal bedrock cities under complex conditions include a combination of microkinetic exploration, high-density electrical resistivity tomography, and shallow seismic reflection methods. In relatively intact bedrock, seismic surface wave velocities are high, while in fault zones, due to the fractured rock mass and rich groundwater, geological bodies with low velocity characteristics are formed. Therefore, the micro-motion exploration method, which is based on the difference in surface wave velocity and the theory of stationary random process, is used. When reflected waves pass through fault fracture zones, they are often accompanied by abnormal phenomena such as seismic wave diffraction, the appearance of fault waves, changes in wave group intervals, dislocation of in-phase axes and sudden increases, decreases and disappearances in number, arching, bifurcation, twisting, phase transition, occurrence and sudden changes in energy. In such cases, the shallow seismic reflection wave method, which distinguishes tectonic fracture zones and other geological anomalies based on the kinematic and dynamic characteristics of seismic waves, is used. The presence of fault fracture zones formed by fracturing activity within the bedrock is accompanied by an increase in porosity and water content within the rock mass, as well as the presence of metal oxides such as iron and manganese. This leads to a decrease in resistivity, resulting in a low-resistivity anomaly zone lower than that of the intact rock mass. When the resistivity gradient transitions sharply, high-density electrical resistivity methods are used for detection.

4. The method for detecting and evaluating high-angle bedrock fracture structures in coastal cities according to claim 3, characterized in that, In step 1, micro-motion exploration, high-density electrical resistivity tomography, and shallow seismic reflection wave method can all be used to detect low-velocity zone anomalies or geological anomaly areas with drastic gradient changes in wave velocity values ​​at the fault zone. When the anomaly areas detected by the three methods overlap or partially overlap, it is preliminarily determined that there is a fault structure in the overlapping area. At the same time, spatial distribution characteristic parameters including the width, dip angle, dip direction, and strike of the fault zone can be obtained.

5. The method for detecting and evaluating high-angle bedrock fracture structures in coastal cities according to claim 4, characterized in that, When directional boreholes are arranged on the hanging wall of the fault zone, the borehole azimuth is opposite to the dip of the fault zone, the borehole dip angle is equal to the fault zone dip angle - 5°, and the borehole depth is determined by calculation based on the estimated width and dip angle of the fault zone. The borehole depth should penetrate the fault zone and enter the intact rock mass of the footwall by no less than 20m.

6. The method for detecting and evaluating high-angle bedrock fracture structures in coastal cities according to claim 5, characterized in that, In step 3, the full-hole wall digital imaging employs a high-definition panoramic fisheye camera concave reflection image method. The camera rotates one revolution to acquire annular well wall images, which are then stitched together through continuous lifting to generate a full-hole wall image. The probe is raised at a constant speed, continuously acquiring well wall images. On the two-dimensional unfolded diagram of the well wall, the structural surface that completely cuts the borehole is identified, which appears as a sinusoidal curve. The amplitude and phase of the sinusoidal curve are extracted, and combined with depth coordinates and azimuth information, the sinusoidal curve is fitted on the two-dimensional unfolded diagram of the well wall to obtain the dip angle α and dip direction β of the structural surface. The calculation formula is as follows: α = arctan(H / D), β = initial azimuth ± 90° Where H is the amplitude of the sine curve, D is the borehole diameter, and the starting azimuth is the azimuth corresponding to the lowest point of the sine curve.

7. The method for detecting and evaluating high-angle bedrock fracture structures in coastal cities according to claim 6, characterized in that, In step 5, the internal structural units include fault gouge zones, fault breccia zones, breccia zones, and breccia zones, and the rock and mineral testing includes scanning electron microscopy imaging and electron microscopy imaging.

8. The method for detecting and evaluating high-angle bedrock fracture structures in coastal cities according to claim 7, characterized in that, In step 5, the multi-source data includes geophysical exploration, drilling, whole-hole imaging, and rock and mineral testing data, and the spatial distribution and engineering geological features include the occurrence elements, width, geological structure, and lithological contact relationships of the fault zone.

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