Comprehensive exploration method for surface, line and point karst of sea area stratum shield tunnel

Abstract

The invention discloses a comprehensive exploration method for surface, line and point karst of a sea area stratum shield tunnel. The method comprises the following steps: S1, calculating the diameter D of a shield tunnel structure; s2, arranging two sea surface transient electromagnetic method verification measuring lines; s3, preliminarily confirming parameters of a sea surface transient electromagnetic method; s4, laying verification geological exploration drill holes according to the interpretation data of the sea surface transient electromagnetic method in the unrevealed abnormal sections of the primary exploration drill holes and the detailed exploration drill holes; s5, arranging three transient electromagnetic measuring lines within the tunnel structure range; s6, according to results of the two verification measuring lines and the three measuring lines, data obtained through geophysical prospecting form simulated BIM three-dimensional data; s7, carrying out seismic CT exploration by adopting cross survey lines; and S8, analyzing a result. According to the karst comprehensive survey method, on the basis of the result of early-stage initial survey, detailed survey and comprehensive general survey, line scanning is conducted on the verification survey line and the formal survey line through the sea surface transient electromagnetic method, cross-hole CT and follow-up supplementary survey drill hole specific point position exploration are used, and the problem that sea area karst exploration is inaccurate is effectively solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of submarine tunnel engineering construction. BACKGROUND

[0002] Compared with land tunnel engineering, the precision of karst cave detection is poor under the condition of electromagnetic shielding and dynamic noise interference of seawater.

[0003] The main differences between submarine tunnel engineering and bridge pile and marine port engineering are as follows: (1) submarine tunnel is a long-distance linear engineering, bridge pile is a spaced point position, and marine port engineering is a block, resulting in different ranges of geological exploration; (2) tunnel engineering is a structure that horizontally penetrates a local stratum, while bridge pile and marine port engineering is a structure that vertically penetrates the stratum; (3) tunnel structure is a cavity structure with use requirements, while bridge pile and marine port engineering is a solid structure; (4) tunnel structure construction and use period have higher requirements for structure deformation and water leakage, while bridge pile and marine port engineering construction and use period have lower requirements.

[0004] The above differences result in different focuses of submarine tunnel engineering and bridge pile and marine port engineering on submarine geology and different attention to karst geological problems. For example, bridge pile and marine port engineering generally drills holes at the structure site, while submarine tunnel engineering generally drills holes outside the tunnel structure to avoid forming a water gushing channel during the later shield construction stage, which brings inconvenience to construction and operation.

[0005] Different engineering requirements for karst exploration have different focuses. Bridge pile and marine port engineering make overall judgments on the engineering area and verify the structure range and specific karst conditions of the bridge pile structure and port structure position by drilling holes one by one. Submarine tunnel engineering needs to determine the specific karst conditions of the tunnel structure and the surrounding several meters of horizontal and vertical range and the entire length of the tunnel.

[0006] The purpose of tunnel karst is to find out the distribution, shape and development law of karst caves within the influence range of the shield tunnel. The existing tunnel karst exploration method uses single transient electromagnetic method and cross-hole CT. Transient electromagnetic method and cross-hole CT can not set holes within the tunnel structure range to avoid forming a water gushing channel during the later shield construction stage, which brings inconvenience to construction and operation. However, sea surface transient electromagnetic method has limited exploration of small-scale karst caves. Cross-hole CT has a detection blind area between each measuring line, resulting in insufficient precision. SUMMARY

[0007] In order to solve the problem of insufficient precision of the existing single geophysical exploration method of submarine tunnel, the present application provides a sea area stratum shield tunnel surface, line and point karst comprehensive exploration method.

[0008] The technical solution adopted by this invention to achieve the above objectives is: a comprehensive karst exploration method for shield tunnels in marine strata, including the methods for surface, line, and point surveys, characterized by comprising the following steps:

[0009] S1: Calculate the diameter D of the shield tunnel structure. The diameter of the preliminary exploration and detailed exploration boreholes is 3m outside the diameter D, that is, the lateral spacing is D+2*3=D+6m; S2: Along the detailed exploration borehole points, lay out two sea surface transient electromagnetic method verification survey lines, which coincide with the lines connecting the detailed exploration borehole points respectively.

[0010] S3: Adjust the parameters of the transient electromagnetic method on the sea surface until the consistency rate between the geophysical exploration results interpretation data and the geological data of the previous detailed exploration boreholes reaches more than 80%, and preliminarily confirm the parameters of the transient electromagnetic method on the sea surface.

[0011] S4: In areas where no anomalies were revealed by the preliminary and detailed exploration boreholes, verification exploration boreholes were set up based on the sea surface transient electromagnetic method interpretation data. The accuracy of the sea surface transient electromagnetic method interpretation data in this area was determined by drilling through the boreholes.

[0012] S5: Three transient electromagnetic survey lines are deployed within the tunnel structure. One survey line is along the tunnel centerline, and the other two lines pass through the centers of the inscribed circles of the blind zones on both sides of the cross-hole CT scan. That is, the distances of the two survey lines from the tunnel centerline are respectively...

[0013]

[0014] S6: Based on the results of 2 verification survey lines and 3 survey lines, and by combining the preliminary exploration and detailed exploration drilling results, the data obtained from the geophysical exploration will be used to form pseudo-BIM 3D data;

[0015] S7: Delineate the karst development zone within each mileage range, determine the cross-hole CT geophysical exploration range, lay out CT boreholes, and conduct seismic CT exploration using cross-line surveying.

[0016] S8: Based on transient electrical measurement results, select characteristic points after cross-hole CT drilling to perform three-dimensional digital imaging inside the borehole, and analyze the results;

[0017] S9: Based on the karst density distribution, karst exploration boreholes are arranged to determine key and uncertain areas. Based on the preliminary exploration, detailed exploration, two sea surface transient electromagnetic method verification lines, three sea surface transient electromagnetic method lines, cross-hole CT method, and karst exploration borehole data, the BIM three-dimensional data results are obtained.

[0018] In step S3, the geophysical results interpretation data are one-dimensional and pseudo-two-dimensional inversion images obtained by removing outliers, denoising, and smoothing filtering of ocean transient electromagnetic data.

[0019] In step S6: the data obtained from geophysical exploration include the three-dimensional coordinates of the karst cave space, the filling condition, and the stratigraphic interface data.

[0020] In step S7, for the strongly karst-developed area delineated by transient electromagnetic geophysical exploration, CT holes are laid out laterally for 3m along both sides of the tunnel structure with a spacing of 10m for detailed seismic CT exploration; for the moderately karst-developed area delineated by transient electromagnetic geophysical exploration, CT holes are laid out laterally for 3m along both sides of the tunnel structure with a spacing of 20m for seismic CT exploration.

[0021] In step S7, due to the multiple source methods of cross-hole CT, cross-hole CT verification is carried out to determine the specific source of the cross-hole CT. Let the longitudinal spacing of the cross-hole CT boreholes along the tunnel direction be L, the diameter of the inscribed circle of the triangle formed by the intersection of CT survey lines in the blind zone be d, and the diameter of the lateral blind zone be d1.

[0022]

[0023] Front blind zone diameter d2:

[0024]

[0025] In step S8, after cross-hole CT is performed, the accuracy of the CT is verified by drilling the verification borehole, and the accuracy of the sea surface transient electromagnetic survey is verified by calibrating the sea surface transient electromagnetic survey. Based on the BIM three-dimensional data results obtained by the comprehensive geological analysis method, the sea surface transient electromagnetic method, and the cross-hole CT method, karst exploration boreholes are arranged to determine the key areas and uncertain areas according to the karst density distribution.

[0026] This invention provides a comprehensive karst exploration method for shield tunnels in marine strata, including surface, line, and point surveys. Based on the results of preliminary and detailed surveys, this method uses the transient electromagnetic method on the sea surface to scan the verification and formal survey lines, and employs cross-hole CT and subsequent supplementary drilling to explore specific points. This comprehensive karst exploration method effectively solves the problem of inaccurate karst exploration in marine areas. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the tunnel's longitudinal section.

[0028] Figure 2 This is a schematic diagram of the planar layout of the sea surface transient electromagnetic survey line, the cross-hole CT survey line, and the blind zone.

[0029] In the picture:

[0030] 001. Sea surface; 002. Seabed overburden; 003. Karst cave; 01. Tunnel structure; 011. Tunnel centerline; 012. Tunnel edge line; 021. Preliminary and detailed exploration boreholes; 022. Connection line between preliminary and detailed exploration boreholes; 023. Verification survey line for transient electromagnetic method on sea surface; 024. Survey line for transient electromagnetic method on sea surface (centerline); 025. Survey line for transient electromagnetic method on sea surface (waistline); 031. Cross-hole CT point; 032. Cross-hole CT survey line; 033. Central blind zone of cross-hole CT; 034. Side blind zone of cross-hole CT. L is the longitudinal spacing of cross-hole CT boreholes along the tunnel direction, and D is the diameter of the shield tunnel excavation. Detailed Implementation

[0031] This invention presents a comprehensive karst exploration method for shield tunnels in marine strata, focusing on the surface, lines, and points. Karst is primarily controlled by factors such as rock solubility, geological structure, and corrosive groundwater. Rock composition, stratification conditions, structure, and texture directly influence the degree and rate of karst development. Generally, karst development is strong, with complete forms and large scale in pure, thick rock strata; karst development is weaker in rock strata containing argillaceous material or other impurities; karst development is more pronounced in rocks with coarse crystalline grains, while it is weaker in rocks with fine crystalline grains. Solid filling materials in marine karst caves are generally saturated with water, while unfilled caves are filled with water. The longitudinal wave velocity of water is approximately 1500 m / s, while the longitudinal wave velocity of the medium within the cave is between 1700 m / s and 2100 m / s, showing a significant difference in wave velocity compared to the original rock (limestone).

[0032] Tunnel longitudinal section as Figure 1 As shown, before the formal commencement of the exploration work, cross-hole electromagnetic wave CT tests were conducted in the coastal land section to verify the adaptability of different CT emission sources. Based on the tests, a suitable emission source was selected; this invention selects an inter-hole elastic plate CT based on the test results. The longitudinal wave velocities of different strata within the engineering site were statistically calculated through the tests. The spatial distribution pattern of karst caves within 5m below the building's structural foundation was investigated as a key focus.

[0033] Based on stratigraphic lithology, karst is primarily controlled by factors such as rock solubility, geological structure, and corrosive groundwater. Rock composition, stratification conditions, structure, and tectonics directly influence the degree and rate of karst development. Generally, thick, pure rock strata exhibit strong karst development with complete forms and larger scale; rock strata containing argillaceous material or other impurities show weaker karst development; rocks with coarse-grained crystals show more developed karst, while rocks with fine-grained crystals show weaker karst development. The degree of dissolution development on each profile generally varies with the undulation of the soluble rock surface, with areas of greater surface undulation showing higher levels of dissolution development. When a large area of ​​karstified dolomitic limestone exists, the probability of surrounding caves is extremely high. However, for small-scale caves, the electrical anomalies in geophysical data are not obvious, making them undetectable. This indicates that the geophysical method has limited interpretation capabilities for small-scale caves.

[0034] Strong karst development: (1) There are many karst collapses, funnels, depressions and springs on the surface; (2) Dense distribution of solution channels, solution troughs and karst buds, with free faces between adjacent boreholes and a bedrock surface height difference greater than 5m; (3) Underground underground rivers and underground streams; (4) Boreholes show a porosity greater than 30% or a linear karst rate greater than 20%; (5) Solution channels or beaded vertical karst caves develop to a depth of more than 20m. Slightly developed karst: (1) No karst collapses or funnels on the surface; (2) Solution channels and solution troughs are relatively developed; (3) Free faces exist between adjacent boreholes and a bedrock surface height difference less than 2m; (4) Boreholes show a porosity less than 10% or a linear karst rate less than 5%.

[0035] Karst exploration boreholes were used to conduct on-site drilling in key and unexplored areas based on the results of cross-hole CT. The "surface-line-point" marine collaborative exploration technology, based on the results of preliminary and detailed surveys, used the sea surface transient electromagnetic method to conduct line scanning of verification and formal survey lines, and used cross-hole CT and subsequent supplementary drilling to explore specific points. This comprehensive karst exploration method effectively solves the problem of inaccurate marine karst exploration.

[0036] Sea surface transient electromagnetic survey lines, cross-bore CT survey lines, and blind zone layout are as follows: Figure 2 As shown, the method is as follows:

[0037] Geological analysis was conducted, including analysis of the bedrock lithology and mineral composition of the site.

[0038] Preliminary and detailed exploration boreholes were drilled. The diameter of the shield tunnel excavation was D, and the lateral extension on both sides of the structure was 3m. The preliminary and detailed exploration data were summarized and analyzed. The diameter of the shield tunnel structure D was calculated. Subsequent preliminary and detailed exploration boreholes were drilled with an extension of 3m beyond diameter D on each side, i.e., the lateral spacing was D + 2 * 3 = D + 6m. This was the limited length and could not be compressed or reduced.

[0039] Two verification survey lines for the transient electromagnetic method on the sea surface were laid out along the detailed exploration borehole locations, coinciding with the lines connecting the detailed exploration borehole locations, to verify and adjust the parameters of the transient electromagnetic method on the sea surface.

[0040] The transient electromagnetic data of the ocean is processed by removing outliers, denoising, and smoothing filtering. Then, one-dimensional and quasi-two-dimensional inversion imaging is performed to form geophysical interpretation data. If the agreement rate between the geophysical interpretation data and the geological data from previous detailed drilling is above 80%, the parameters of the transient electromagnetic method on the sea surface (variables, regression analysis, thresholds, etc.) are preliminarily confirmed.

[0041] In areas where no anomalies were revealed by the preliminary and detailed exploration boreholes, verification boreholes were laid out based on the interpretation data of the transient electromagnetic method on the sea surface to determine whether the interpretation data of the transient electromagnetic method on the sea surface in this area was correct.

[0042] Comparing the results of the verification borehole, the interpretation data and results of the transient electromagnetic method on the sea surface are generally limited for the exploration of caves below 2-5m.

[0043] Three transient electromagnetic survey lines were deployed within the tunnel structure. One line was along the tunnel centerline. Based on the blind zone characteristics of the later cross-hole CT geophysical exploration, the other two lines passed through the centers of the inscribed circles of the blind zones on both sides of the cross-hole CT, meaning the distances from the tunnel centerline to the two survey lines were respectively... To achieve the optimal effect of minimizing blind spots.

[0044] Based on the results of two verification survey lines and three survey lines, and taking into account the preliminary and detailed exploration drilling results, the data such as the three-dimensional coordinates of the karst cave space, the filling situation, and the stratigraphic interface obtained from the geophysical exploration were used to calculate the difference and form pseudo-BIM three-dimensional data.

[0045] The karst development zones within each mileage section were delineated to determine the key areas for the next step of cross-hole CT geophysical exploration. For the intensely karst development zones delineated by transient electromagnetic geophysical exploration, CT boreholes were laid out laterally for 3 meters along both sides of the tunnel structure at 10-meter intervals for detailed seismic CT exploration. For the moderately karst development zones delineated by transient electromagnetic geophysical exploration, CT boreholes were laid out laterally for 3 meters along both sides of the tunnel structure at 20-meter intervals for seismic CT exploration to further determine the karst conditions.

[0046] Because there are many types of seismic sources for cross-hole CT, cross-hole CT verification was carried out to determine the specific seismic source for cross-hole CT.

[0047] Based on the algorithm, the lateral and longitudinal spacing of cross-hole CT boreholes is calculated, and the blind zone is minimized as much as possible within a certain cost.

[0048] The algorithm is based on the shield tunnel excavation diameter D, with a lateral extension of 3m on both sides of the structure, i.e., the lateral spacing D+2*3=D+6m. This is the limited length and cannot be compressed or reduced.

[0049] For cross-hole CT, if the longitudinal spacing of the boreholes along the tunnel direction is L, then the blind zone of the cross-hole CT is the diameter of the inscribed circle of the triangle formed after the CT lines intersect, and the diameter of the lateral blind zone is d1.

[0050]

[0051] Front blind zone diameter d2:

[0052]

[0053] Cross-hole CT survey lines are used.

[0054] Since existing boreholes in the sea area cannot be reused, when conducting cross-hole CT drilling in the sea area, the initial and detailed exploration boreholes should be avoided as much as possible. The preferred boreholes should have a total length of not less than 2m to allow more boreholes to reveal karst caves.

[0055] Based on transient electrical logging results, characteristic points were selected for 3D digital imaging within the borehole after cross-hole CT drilling. Verification boreholes were drilled after cross-hole CT to verify the accuracy of the CT, and the accuracy of the survey lines was verified by sea surface transient electrical logging. Integrating the results of geological analysis, sea surface transient electromagnetic methods, and cross-hole CT, specialized karst exploration boreholes were deployed to determine key and uncertain areas. Karst exploration boreholes were then used to conduct on-site drilling in key and unexplored areas based on the cross-hole CT results.

[0056] Based on the karst density distribution, karst exploration boreholes were arranged to determine key and uncertain areas. Based on data from preliminary exploration, detailed exploration, two sea surface transient electromagnetic method verification lines, three sea surface transient electromagnetic method verification lines, cross-hole CT method, and karst exploration boreholes, BIM three-dimensional data results were obtained.

[0057] This invention has been described through embodiments. Those skilled in the art will understand that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of this invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, this invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of this invention.

Claims

1. A method for comprehensive karst exploration of the surface, line, and point of a shield tunnel in marine strata, characterized in that: Includes the following steps: S1: Calculate the diameter D of the shield tunnel structure. The planar position of the borehole points in the preliminary and detailed exploration is 3m outside the diameter D, that is, the lateral spacing is D+2*3=D+6m. S2: Along the detailed exploration borehole locations, two sea surface transient electromagnetic method verification survey lines are laid out, which coincide with the lines connecting the detailed exploration borehole locations respectively; S3: Adjust the parameters of the transient electromagnetic method on the sea surface until the consistency rate between the geophysical exploration results interpretation data and the geological data of the previous detailed exploration boreholes reaches more than 80%, and preliminarily confirm the parameters of the transient electromagnetic method on the sea surface. S4: In areas where no anomalies were revealed by the preliminary and detailed exploration boreholes, verification exploration boreholes were set up based on the sea surface transient electromagnetic method interpretation data. The accuracy of the sea surface transient electromagnetic method interpretation data in this area was determined by drilling through the boreholes. S5: Three transient electromagnetic survey lines are deployed within the tunnel structure. One survey line is along the tunnel centerline, and the other two lines pass through the centers of the inscribed circles of the blind zones on both sides of the cross-hole CT scan. That is, the distances of the two survey lines from the tunnel centerline are respectively... ； S6: Based on the results of 2 verification survey lines and 3 survey lines, and by combining the preliminary exploration and detailed exploration drilling results, the data obtained from the geophysical exploration will be used to form pseudo-BIM 3D data; S7: Delineate the karst development area within each mileage range, determine the cross-hole CT geophysical exploration range, lay out CT boreholes, and conduct seismic CT exploration using cross-line surveying. S8: Based on the transient electrical measurement results, select characteristic points after cross-hole CT drilling to perform three-dimensional digital imaging inside the borehole for analysis; S9: Based on the karst density distribution, karst exploration boreholes are arranged to determine key and uncertain areas. Based on the preliminary exploration, detailed exploration, two sea surface transient electromagnetic method verification lines, three sea surface transient electromagnetic method lines, cross-hole CT method, and karst exploration borehole data, the BIM three-dimensional data results are obtained.

2. The method for comprehensive karst exploration of the surface, line, and point of a shield tunnel in marine strata according to claim 1, characterized in that: In step S3, the geophysical results interpretation data are one-dimensional and pseudo-two-dimensional inversion images obtained by removing outliers, denoising, and smoothing filtering of ocean transient electromagnetic data.

3. The method for comprehensive karst exploration of the surface, line, and point of a shield tunnel in marine strata according to claim 1, characterized in that: In step S6: the data obtained from geophysical exploration include the three-dimensional coordinates of the karst cave space, the filling condition, and the stratigraphic interface data.

4. The method for comprehensive karst exploration of the surface, line, and point of a shield tunnel in marine strata according to claim 1, characterized in that: In step S7, for the strongly karst-developed area delineated by transient electromagnetic geophysical exploration, CT holes are laid out laterally for 3m along both sides of the tunnel structure with a spacing of 10m for detailed seismic CT exploration; for the moderately karst-developed area delineated by transient electromagnetic geophysical exploration, CT holes are laid out laterally for 3m along both sides of the tunnel structure with a spacing of 20m for seismic CT exploration.

5. The method for comprehensive karst exploration of the surface, line, and point of a shield tunnel in marine strata according to claim 1, characterized in that: In step S7, because there are many types of cross-hole CT seismic source methods, cross-hole CT verification is carried out to determine the specific seismic source of the cross-hole CT. Assume the longitudinal spacing of the cross-hole CT boreholes along the tunnel direction is L, the blind zone is the diameter of the inscribed circle of the triangle formed by the intersection of CT survey lines is d, and the diameter of the lateral blind zone is... : ； Front blind zone diameter : 。 6. The method for comprehensive karst exploration of the surface, line, and point of a shield tunnel in marine strata according to claim 1, characterized in that: In step S8, after cross-hole CT is performed, the accuracy of the CT is verified by drilling the verification borehole, and the accuracy of the sea surface transient electromagnetic survey is verified by calibrating the sea surface transient electromagnetic survey. Based on the BIM three-dimensional data results obtained by the comprehensive geological analysis method, the sea surface transient electromagnetic method, and the cross-hole CT method, karst exploration boreholes are arranged to determine the key areas and uncertain areas according to the karst density distribution.

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