Method for determining interface between thick layer of colluvial deposit and strongly weathered rock
By combining geological mapping, mechanical drilling, and geophysical seismic refraction profiles, and optimizing the exploration process, the accuracy and safety issues in determining the interface between thick colluvial deposits and strongly weathered rocks were resolved, achieving efficient and safe exploration results.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHAANXI RAILWAY ENG SURVEY CO LTD
- Filing Date
- 2023-05-17
- Publication Date
- 2026-05-29
AI Technical Summary
Existing technologies have problems such as lack of comparative verification, limited applicability, and great influence from topographic conditions when determining the interface between thick colluvial deposits and strongly weathered rocks, resulting in inaccurate exploration results and significant safety hazards.
By combining on-site geological mapping, mechanical drilling, and geophysical seismic refraction profiles, the boundary was determined through three-way comparison and verification. The exploration procedure was optimized to improve accuracy and safety by utilizing the uneven density and wave velocity differences between the colluvial deposits and the strongly weathered rocks.
It achieves accuracy and efficiency in exploration results, reduces safety hazards, is suitable for exploration under complex terrain conditions, and provides accurate basic data support.
Smart Images
Figure CN116755147B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of geotechnical engineering investigation technology, specifically to a method for determining the interface between thick colluvial deposits and strongly weathered rock. Background Technology
[0002] The geological conditions of railway or highway slope engineering in mountainous areas are complex and variable. Therefore, clarifying the disaster-causing mechanisms of adverse geological bodies affecting track safety and providing economical and effective slope prevention and protection recommendations is a primary task. Accumulated deposits, as one of the most common adverse geological bodies in slope engineering, have their formation, thickness, and material composition determining the engineering treatment plan. Two issues must be considered first in the engineering treatment plan: first, assessing the possibility of slope slippage along the soil-rock interface; and second, whether it can be technically treated to serve as a foundation bearing layer. Therefore, determining the thickness of the accumulated deposit and its boundary with the underlying bedrock is particularly important.
[0003] Traditionally, the thickness of slope deposits has been determined primarily through drilling. This involves first determining the extent of the deposit cover through geological mapping in the field, then drilling along a predetermined direction on the slope based on the mapped cover, creating multiple exploration profiles. These profiles then reveal the stratigraphic conditions, allowing for the analysis of the deposit's material composition and thickness, thereby determining the soil-rock interface. This method has the following drawbacks:
[0004] (1) The exploration methods are conventional and simple, usually relying on field geological mapping as an auxiliary means, mainly depending on the results of mechanical drilling, and lacking comparative verification. Especially for thick colluvial deposits, mechanical disturbance during rotary drilling and core sampling, as well as the placement of cores, often result in the cores being taken and placed that do not fully reflect the actual strata. In particular, the cores presented in gravelly soil strata and fractured zones of strongly weathered rock strata deviate significantly from the actual strata, leading to misjudgments by geologists regarding core identification and actual strata, or difficulty in distinguishing between the two, making it impossible to accurately determine the soil-rock interface, thus affecting the quality of exploration, investigation, and design.
[0005] (2) Exploration methods are limited by the formation and coverage of the deposits, which means that when the deposits cover a large area, more exploration profiles need to be laid out and the amount of exploration needs to be increased, which will lead to the extension of the construction period and the increase of costs. In addition, due to the special nature of colluvial deposits, the particle skeleton itself is uneven in density and may even be discontinuous. During the exploration process, it is very easy to cause the loss of filling material and the instability of the skeleton. With the increase of exploration volume and the extension of exploration period, it will bring great safety hazards.
[0006] (3) On-site mechanical drilling is greatly affected by terrain conditions. If the terrain of some exploration points on the slope accumulation is steep, it is extremely difficult to relocate the equipment, resulting in low work efficiency or no drilling site, which leads to the loss of pre-arranged exploration profile points, reduced exploration accuracy, and failure to achieve the expected exploration purpose. Summary of the Invention
[0007] The purpose of this invention is to provide a method for determining the interface between thick colluvial deposits and strongly weathered rock, in order to solve the problems of lack of comparative verification, weak applicability, and great influence from terrain conditions in the current method of determining the interface by drilling.
[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:
[0009] A method for determining the interface between thick colluvial deposits and strongly weathered rock, the method comprising:
[0010] Conduct on-site geological mapping of the target slope site to obtain the geological distribution and structural characteristics of the thick colluvial deposits.
[0011] An exploration profile was laid out at the target slope site, including mechanical borehole profiles and geophysical seismic refraction profiles.
[0012] Drilling is carried out by arranging boreholes in the mechanical borehole profile and geophysical exploration is carried out in the geophysical seismic refraction profile.
[0013] By combining the results of on-site geological mapping, drilling, and geophysical exploration, a three-way comparative verification was conducted to determine the interface between the thick colluvial deposits and the strongly weathered rock.
[0014] Furthermore, on-site geological mapping was conducted on the target slope site to obtain the geological distribution and structural characteristics of the thick colluvial deposits, including:
[0015] Conduct on-site geological mapping of the slope topography and geomorphology of the target slope site;
[0016] To obtain the geological distribution and structural characteristics of thick colluvial deposits, including delineating the coverage area of thick colluvial deposits and estimating the thickness of thick colluvial deposits.
[0017] Furthermore, exploration profiles are laid out at the target slope site, including mechanical borehole profiles and geophysical seismic refraction profiles, including:
[0018] Based on the geological distribution and structural characteristics of thick colluvial deposits, exploration profiles were laid out.
[0019] Mechanical drilling profiles are arranged for typical cross-sections;
[0020] For general terrain, mechanical borehole profiles and geophysical seismic refraction profiles are alternately arranged.
[0021] Furthermore, drilling is carried out by arranging boreholes in the mechanical borehole profile, including:
[0022] Drilling was carried out by arranging boreholes in the mechanical drilling profile, and the drilling depth penetrated the strongly weathered layer and entered the moderately weathered bedrock.
[0023] Points on the mechanical borehole profile where there is no drilling site or where equipment relocation is extremely difficult are considered special locations. Geophysical transient surface waves are deployed at these special locations to replace the boreholes.
[0024] Furthermore, combining the results of on-site geological mapping, drilling, and geophysical exploration, a three-way comparative verification was conducted to determine the interface between the thick colluvial deposits and the strongly weathered rock, including:
[0025] Based on the results of on-site geological survey, the material composition and block size of the thick colluvial deposits were determined;
[0026] Based on the drilling results and the condition of the core samples, the location of the interface between the thick colluvial deposits and the strongly weathered rock was preliminarily determined.
[0027] Based on the results of geophysical exploration, the exact location of the interface was further determined by utilizing the differences between the uneven density or high porosity of colluvial deposits and the fractured but dense nature of strongly weathered rocks, through changes in stratigraphic wave velocity.
[0028] Furthermore, based on the drilling results and core condition, the location of the interface between the thick colluvial deposit and the strongly weathered rock was preliminarily determined, including:
[0029] Identify the location of the interface between moderately weathered and strongly weathered rocks;
[0030] Core identification was performed above the interface of moderately weathered rock.
[0031] Determine the location of the interface between the thick colluvial deposit and the strongly weathered rock.
[0032] Furthermore, the exact location of the interface is further determined by the variation in formation wave velocity, including:
[0033] Seismic refraction contour maps are generated based on field data, reflecting the undulations of shallow strata.
[0034] For a given interface, check whether there is an abnormal gradient zone of wave velocity within the range of the interface on the seismic refraction contour map. If there is a clear gradient zone at a certain depth, then that depth is determined to be the location of the interface.
[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0036] (1) The exploration results are more accurate and efficient.
[0037] The method of this invention integrates drilling and geophysical exploration, complementing each other's advantages. It greatly improves the efficiency of field exploration while ensuring the accuracy of exploration results, providing accurate and effective basic data support for slope protection and route detour suggestions.
[0038] 2) It has greater applicability and flexibility.
[0039] The method of this invention breaks through the limitations of terrain and space in field drilling, realizing a flexible and effective exploration method for complex terrain. It can be widely applied to steep slopes with complex terrain conditions, difficult relocation, and limited site, effectively making up for the shortcomings of difficult drilling access.
[0040] 3) Security is significantly improved.
[0041] The method of this invention optimizes the exploration layout scheme, namely by reasonably increasing the amount of geophysical exploration and reducing the drilling tasks, which will further shorten the drilling period and minimize the safety risks of drilling on accumulation bodies with significant safety hazards, thus significantly improving the safety of field exploration. Attached Figure Description
[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other embodiments can be obtained from these drawings without creative effort.
[0043] Figure 1 This is a flowchart of the method of the present invention.
[0044] Figure 2 It is a map delineating the extent of the accumulation.
[0045] Figure 3 It is an exploration profile and point layout diagram.
[0046] Figure 4 It is an earthquake refraction contour map.
[0047] Figure 5 It is a cross-sectional diagram of earthquake refraction interpretation.
[0048] Figure 6 This is a core image from ZK4. Detailed Implementation
[0049] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.
[0050] It should be noted that similar labels and letters indicate similar items; therefore, once an item is defined in one embodiment, it does not need to be further defined and explained in subsequent embodiments. Furthermore, the term "comprising" and any variations thereof are intended to cover non-exclusive inclusion, such as including a series of indicators, factors, or steps, not necessarily limited to a clearly listed list of all indicators, factors, or steps, but may include other indicators, factors, or steps used to implement the method that are not clearly listed.
[0051] This invention provides a method for determining the interface between thick colluvial deposits and strongly weathered rocks. It innovatively combines geophysical transient surface wave and seismic refraction tomography methods with traditional exploration techniques. Based on the unique loose skeletal characteristics of colluvial deposits, which distinguish them from other types of sedimentary bodies, the method utilizes the wave velocity variations caused by seismic waves excited by artificial sources at different interfaces to reflect the spatial distribution of different stratigraphic interfaces. Combined with the stratigraphic distribution revealed by drilling, it provides reasonable and accurate interpretation results. By effectively combining multiple methods, such as field geological mapping, mechanical drilling, and geophysical exploration (seismic refraction and transient surface wave), the exploration process is optimized to achieve more accurate, efficient, and safe exploration results.
[0052] The method described is applicable to the investigation of adverse geological bodies in geotechnical engineering. It involves a comprehensive method for determining the interface between thick colluvial deposits and strongly weathered rock, which fully leverages the advantages of different exploration methods. This solves the problems of traditional single mechanical drilling methods for thick colluvial deposits, which are easily limited by site conditions, have low work efficiency, pose significant safety hazards, and lack comparative verification of results. The method specifically includes the following steps:
[0053] S1: Field Geological Survey
[0054] The organization will conduct on-site geological mapping of the surrounding environment of the target slope site, supplemented by manual excavation when necessary, to obtain the geological distribution and structural characteristics of the thick colluvial deposits, including:
[0055] S101: Conduct on-site geological mapping of the slope topography and geomorphology of the target slope site;
[0056] S102: Obtain the geological distribution and structural characteristics of thick colluvial deposits, including delineating the coverage area of thick colluvial deposits, estimating the thickness of thick colluvial deposits, and making a preliminary judgment on the geological distribution and structure of colluvial deposits.
[0057] S2: Determine and optimize the exploration plan:
[0058] Based on the topographic conditions, exploration profiles are laid out at the target slope site. These profiles include mechanical borehole profiles and geophysical seismic refraction profiles, including:
[0059] S201: Based on the geological distribution and structural characteristics of thick colluvial deposits, an exploration profile is laid out;
[0060] Optimization measures include:
[0061] S202: Mechanical borehole profiles are laid out for typical sections to conduct control exploration;
[0062] S203: For general areas, mechanical borehole profiles and geophysical seismic refraction profiles are alternately arranged for verification exploration. The spacing and length of the two types of exploration lines are reasonably controlled to ensure the accuracy of the exploration.
[0063] S3: On-site implementation:
[0064] Drilling is conducted using mechanically drilled boreholes along the borehole profile, and geophysical exploration is carried out using geophysical seismic refraction profiles, including:
[0065] S301: Drilling shall be carried out by arranging boreholes in the mechanical borehole profile. The core recovery rate of each borehole shall meet the requirements (≥65%). The borehole depth shall penetrate the strongly weathered layer and enter the moderately weathered bedrock.
[0066] S302: Hole locations on the mechanical borehole profile where there is no drilling site or where equipment relocation is extremely difficult are designated as special locations. Geophysical transient surface waves are deployed at these special locations to replace the boreholes.
[0067] S303: Conduct geophysical exploration at the geophysical seismic refraction profile, and carry out geophysical field data acquisition, data processing and geological interpretation.
[0068] S4: Comparative Verification Analysis:
[0069] Based on the results of on-site geological mapping, drilling, and geophysical exploration, a three-way comparative verification was conducted to determine the interface between the thick colluvial deposits and the strongly weathered rock, including:
[0070] S401: Based on the results of on-site geological mapping, determine the material composition and block size of the thick colluvial deposits. Specifically, based on the results of on-site geological mapping, on the one hand, the thickness of the deposits collected at the observation points, combined with topographic features, can provide a reference for determining the thickness of the deposits in the nearby exploration profiles; on the other hand, determine the material composition and block size of the thick colluvial deposits. If the lithology of the deposits is diverse, the material composition above the interface will be diverse and mixed in color, while the lithology below the interface will be uniform. This can provide a reference for identifying the interface in drilling cores. If the lithology of the deposits is uniform, there is no obvious interface between it and the underlying strongly weathered rock. In this case, it is necessary to combine drilling and geophysical exploration to determine the location of the interface.
[0071] S402: Based on the drilling results and core condition (color, density, block size), preliminarily determine the location of the interface between the thick colluvial deposit and the strongly weathered rock, including:
[0072] Typically, core identification begins by examining the condition of each borehole core, such as color, composition, integrity, and hardness, to preliminarily classify the stratigraphy. Then, based on the stratigraphic division results of the remaining boreholes on the profile, combined with stratigraphic occurrence and topographic features, a comprehensive analysis is conducted to arrive at a reasonable stratigraphic division conclusion.
[0073] 1) First, identify the location of the interface between moderately weathered and strongly weathered rocks. Generally, the joint surfaces of moderately weathered bedrock cores are fresh, and the cores are mostly columnar or short columnar. The joint surfaces of strongly weathered rocks are corroded and old, and the cores are mostly blocky. Based on this, determine the location of the interface between the bedrock and the lower moderately weathered rocks, and narrow down the identification range of the upper soil-rock interface.
[0074] 2) Focus on core identification above the moderately weathered interface. If the sedimentary material has diverse lithologies, the material above the soil-rock interface will have diverse compositions and mixed colors, while the lithology below the interface will be uniform. This can be used to determine the location of the interface. If the sedimentary material has uniform lithologies, and due to mechanical disturbance during drilling and core placement, there may be no clear interface between the sedimentary material and the underlying strongly weathered rock. In this case, a comprehensive comparison of cores from other boreholes at the same stratum (within a certain range above the moderately weathered interface) can be made to roughly determine the location or range of the interface.
[0075] S403: Based on the results of geophysical exploration (transient surface waves and seismic refraction), utilizing the difference between the uneven density or high porosity of colluvial deposits and the fractured but dense nature of strongly weathered rocks, the exact location of the interface is further determined by changes in stratigraphic wave velocity, including:
[0076] Seismic refraction contour maps are generated based on field data. These contour maps effectively reflect the undulations of shallow strata (0–30 meters). The focus is on verifying the presence of wave velocity anomaly gradient zones within the boundary range determined by drilling. If a significant gradient zone is found at a certain depth, that depth can be identified as the boundary location. This method offers significant advantages; the results obtained after data interpretation are linear lithological boundaries. Traditional drilling only yields lithological boundary points from a single borehole, requiring the connection of multiple borehole boundaries to obtain the boundary line. For areas without boreholes, the delineation accuracy is clearly lower than that of geophysical methods.
[0077] The method of this invention considers two aspects. First, it replaces mechanical drilling with geophysical transient surface wave exploration, ensuring at least one mechanical borehole on each exploration profile to improve work efficiency and solve the problems of low efficiency caused by site conditions in field drilling. Second, it considers alternating arrangements of mechanical borehole profiles and geophysical seismic refraction profiles, with the two methods complementing each other and being compared and verified to greatly improve the accuracy of exploration results. Simultaneously, it effectively reduces drilling workload and shortens the exploration cycle, minimizing the safety risks of field drilling for colluvial deposits with uneven density and unstable frameworks.
[0078] Example:
[0079] In a highway project in Yunnan, a colluvial landslide has a certain impact on the route. It is now necessary to determine the thickness of the colluvial landslide and the location of the soil-rock interface in order to assess the stability of the slope and provide basic data support for prevention and control measures and route detours.
[0080] See Figure 2 and Figure 3 The method of the present invention includes the following steps:
[0081] S1: Field Geological Survey
[0082] Geologists conducted on-site mapping of the slope's topography, geomorphology, and stratigraphy, and collected data from eight observation points in the area. Figure 2 The deposits are located between GCD-1 and GCD-8. Observation points GCD-1, GCD-2, GCD-5, GCD-6, and GCD-8 (supplemented by manual excavation) and the nearby gully scour surfaces show a relatively thick deposit (greater than 15m). Observation points GCD-3, GCD-4, and GCD-7 show exposed bedrock or shallow bedrock. This roughly delineates the perimeter of the deposit, with an average length of approximately 260m and an average width of approximately 195m, as shown by the sawtooth lines in the figure. Simultaneously, manual excavation revealed that the deposit (rubble) is mainly composed of argillaceous sandstone fragments interbedded with silty clay.
[0083] S2: Determine and optimize the exploration plan:
[0084] Based on the extent and potential thickness of the colluvial deposits delineated by S1, three exploration profiles were laid out longitudinally along the slope, with a spacing of approximately 70m between profiles and a length of approximately 280m for each profile, extending beyond the perimeter of the deposits. The layout scheme is shown in [reference needed]. Figure 3 .
[0085] Optimized exploration profile layout: Based on the S1 mapping results, the thickness of the deposit is greatest in the middle section of the slope, gradually thinning towards both sides. Considering topographic conditions, drilling efficiency, and safety risks, three profiles in S2 were optimized. The central section uses mechanical drilling profile ZT-1 as the control profile. In steep terrain areas, to reduce on-site implementation difficulty, surface wave geophysical surveys were used instead of boreholes. Geophysical seismic refraction profiles DZ-1 and DZ-2 were arranged on the left and right sides. To ensure exploration effectiveness, mechanical boreholes or surface wave surveys were also deployed on profiles DZ-1 and DZ-2 for comparative verification. The optimized exploration plan includes 5 mechanical boreholes, 4 surface wave surveys, and 2 seismic refraction survey lines. Exploration point locations are shown below. Figure 3 .
[0086] S3: On-site implementation:
[0087] Conduct field drilling and geophysical data collection.
[0088] a: Drilling is carried out according to the hole locations, and process inspections are conducted to ensure that the core recovery rate meets the requirements (≥65%). The final hole depth is confirmed on-site based on the depth of entry into moderately weathered bedrock.
[0089] b: Conduct geophysical seismic refraction field data acquisition according to the profile length and direction. The data acquisition process should comply with relevant geophysical specifications and procedures. At the same time, data processing and geological interpretation should be carried out in conjunction with drilling results.
[0090] S4: Comparative Verification Analysis:
[0091] A comprehensive analysis was conducted, comparing and verifying the results of field geological mapping, drilling, and geophysical exploration.
[0092] a: According to the survey results and manual excavation, the strata of the slope deposit are gravelly soil, composed of reddish-brown muddy sandstone fragments and a small amount of silty clay. The composition is relatively simple (when the composition is complex, it can provide a reference for distinguishing the boundary between the gravelly soil layer and the strongly weathered layer).
[0093] b: Drilling results show that the gravelly soil strata are mainly blocky and short columnar, with gravel particles of 2-6 cm accounting for approximately 20-35% of the total, and particles of 6-8 cm accounting for 40-60%. The remainder is filled with a small amount of silty clay. The gravel skeleton is relatively loose, and the overall structure is slightly dense to medium dense. The lower strongly weathered argillaceous sandstone has well-developed joints and fissures. The core samples are blocky and short columnar, with particle diameters ranging from 4-10 cm, and the overall structure is dense. Because the core samples of the upper gravelly soil layer and the lower strongly weathered rock layer are very similar, judging the boundary between the two based on this is likely to lead to misjudgment.
[0094] c: By utilizing geophysical results (transient surface waves and seismic refraction), namely surface wave dispersion curves and seismic refraction comprehensive interpretation profiles, the differences between the uneven density or high porosity characteristics of colluvial deposits and the fractured but dense characteristics of strongly weathered rocks are fully utilized to verify the reliability of the stratigraphic information revealed by drilling, thereby achieving the goal of refining and accurately locating the precise depth of the interface; taking the seismic refraction profile DZ-1 as an example, through the seismic refraction wave velocity contour map ( Figure 4 ), and obtained the seismic refraction comprehensive interpretation cross-section diagram ( Figure 5 The seismic refraction method clearly and intuitively reflects the stratigraphic layering, demonstrating good exploration results. The interpreted stratigraphic distribution closely matches the core data revealed by the control borehole ZK4, proving the reliability and practicality of using the seismic refraction method on this slope. However, some discrepancies exist. The interface location determined by on-site core analysis of borehole ZK4 is at 21.0m (core photographs are shown below). Figure 6 The boundary location is particularly difficult to determine accurately in the range of 21–28.2 m. Therefore, using seismic refraction wave velocity contour maps, the variation of strata wave velocity in the 21–28.2 m range was studied in detail. An abnormal gradient zone was found at a depth of 26.5 m, indicating that the boundary location should be at 26.5 m.
[0095] The successful application of this method has achieved two main benefits. First, it integrates drilling and geophysical exploration, complementing each other's strengths and greatly improving the efficiency of field exploration. Second, by comparing and verifying the results of both methods, it further enhances the accuracy of the exploration results, providing accurate and effective basic data support for the prevention and protection of the slope deposits and for route detour suggestions. Third, it overcomes the limitations of terrain and space in field drilling, enabling a flexible and effective exploration method for complex terrain, effectively overcoming the difficulties of drilling on-site. Furthermore, the optimized exploration layout, which reasonably increases the workload of geophysical exploration and reduces drilling tasks, effectively reduces the safety risks associated with drilling on loose deposits, significantly improving the safety of field exploration.
[0096] The above examples illustrate the present invention only to aid in understanding it and are not intended to limit the scope of the invention. Those skilled in the art can make various simple deductions, modifications, or substitutions based on the principles of this invention.
Claims
1. A method for determining the interface between thick colluvial deposits and strongly weathered rock, characterized in that: The method includes: Conduct on-site geological mapping of the target slope site to obtain the geological distribution and structural characteristics of the thick colluvial deposits. An exploration profile was laid out at the target slope site, including mechanical borehole profiles and geophysical seismic refraction profiles. Drilling is carried out by arranging boreholes in the mechanical borehole profile and geophysical exploration is carried out in the geophysical seismic refraction profile. By combining the results of on-site geological mapping, drilling, and geophysical exploration, a three-way comparative verification was conducted to determine the interface between the thick colluvial deposits and the strongly weathered rock. in: On-site geological mapping of the target slope site was conducted to obtain the geological distribution and structural characteristics of the thick colluvial deposits, including: on-site geological mapping of the slope topography and geomorphology of the target slope site; obtaining the geological distribution and structural characteristics of the thick colluvial deposits, including delineating the coverage area of the thick colluvial deposits and estimating the thickness of the thick colluvial deposits. An exploration profile is set up at the target slope site. The exploration profile includes mechanical borehole profiles and geophysical seismic refraction profiles. This includes: setting up exploration profiles based on the geological distribution and structural characteristics of thick colluvial deposits; setting up mechanical borehole profiles for typical profiles; and alternating between mechanical borehole profiles and geophysical seismic refraction profiles for general areas. Drilling is carried out by arranging boreholes on the mechanical borehole profile, including: drilling boreholes on the mechanical borehole profile, with the borehole depth penetrating the strongly weathered layer and entering the moderately weathered bedrock; borehole locations on the mechanical borehole profile where there is no drilling site or where it is extremely difficult to relocate equipment are designated as special locations, and geophysical transient surface waves are arranged at these special locations to replace the boreholes.
2. The method according to claim 1, characterized in that: Based on the results of on-site geological mapping, drilling, and geophysical exploration, a three-way comparative verification was conducted to determine the interface between the thick colluvial deposits and the strongly weathered rock, including: Based on the results of on-site geological survey, the material composition and block size of the thick colluvial deposits were determined; Based on the drilling results and the condition of the core samples, the location of the interface between the thick colluvial deposits and the strongly weathered rock was preliminarily determined. Based on the results of geophysical exploration, the exact location of the interface was further determined by utilizing the differences between the uneven density or high porosity of colluvial deposits and the fractured but dense nature of strongly weathered rocks, through changes in stratigraphic wave velocity.
3. The method according to claim 2, characterized in that: Based on the drilling results and core condition, the location of the interface between the thick colluvial deposit and the strongly weathered rock has been preliminarily determined, including: Identify the location of the interface between moderately weathered and strongly weathered rocks; Core identification was performed above the interface of moderately weathered rock. Determine the location of the interface between the thick colluvial deposit and the strongly weathered rock.
4. The method according to claim 3, characterized in that: Further determination of the precise location of the interface by variations in formation wave velocity includes: Seismic refraction contour maps are generated based on field data, reflecting the undulations of shallow strata. For a given interface, check whether there is an abnormal gradient zone of wave velocity within the range of the interface on the seismic refraction contour map. If there is a clear gradient zone at a certain depth, then that depth is determined to be the location of the interface.