A method for detecting the effect of pre-grouting on the ground of vertical shaft using cross-hole resistivity CT

Abstract

The present invention discloses a method for detecting the effect of pre-grouting on the ground of a vertical shaft by using cross-hole resistivity CT. The method comprises the following steps: preparing a cross-hole resistivity CT test system; completing the construction of the grouting hole before grouting; arranging the cross-hole resistivity CT test system; before grouting, performing a test using the cross-hole resistivity CT test system, inverting the result into a map for guiding the grouting construction; and after grouting, performing another test using the cross-hole resistivity CT test system, analyzing the changing trend of the resistivity before and after grouting, and evaluating the grouting water-blocking effect. Using the cross-hole resistivity CT technology to detect the water-blocking reinforcement effect of pre-grouting on the ground of a vertical shaft provides an advanced, simple, and reliable effect evaluation method, provides more formation condition information and guidance for the construction of pre-grouting projects on the ground of a vertical shaft, provides a reliable basis for the acceptance of grouting projects, and provides better technical support for the application of pre-grouting technology on the ground of a vertical shaft and the safe and rapid construction of vertical shaft shafts.

Description

Technical Field

[0001] The present invention relates to the technical field of methods for detecting the effect of pre-grouting on the ground of a vertical shaft, and in particular to a method for detecting the effect of pre-grouting on the ground of a vertical shaft using cross-hole resistivity CT. Background Art

[0002] Vertical shafts are widely used in mining, transportation, tunnels, water conservancy and other fields. When encountering aquifers or soft and broken rock formations, pre-grouting on the shaft surface is a commonly used water-blocking and reinforcement technology. That is, using ground drilling, the prepared slurry is injected into the above-mentioned rock formation through a grouting pump and a grouting pipeline. After the slurry solidifies, it blocks the water channel or consolidates the loose and broken rock mass, forming a curtain within a certain range around the shaft, thereby playing a role in water blocking or reinforcement, ensuring the safe and rapid construction of the shaft. The current depth of pre-grouting on the ground of vertical shafts has exceeded 1000m, and most conventional ones exceed 500m. Pre-grouting on the ground of vertical shafts is an underground concealed project. Due to the complexity and unevenness of geological conditions, there has been no reliable and effective means to inspect and evaluate the grouting effect. At present, there are mainly two methods for inspecting the effect of pre-grouting on the ground of vertical shafts:

[0003] (1) Hydrological test

[0004] Through the final grouting hole, water pressure, injection, or pumping tests are conducted on the injected formation. Hydrological parameters such as the permeability coefficient or water permeability of the injected formation after grouting are calculated, the remaining water inflow in the wellbore is deduced, and the improvement in water conductivity is evaluated to evaluate the grouting effect. Hydrological test calculation methods are based on certain assumptions, such as uniformity and isotropy. Due to the complexity and heterogeneity of the formation conditions, the hydrological calculation results often have large errors, making it impossible to accurately evaluate the grouting water blocking effect and the grouting reinforcement effect.

[0005] (2) Actual excavation inspection

[0006] After grouting is completed, actual observations during shaft excavation and masonry work are used to calculate the remaining water inflow, observe rock mass consolidation, and evaluate the effectiveness of grouting for water blocking and reinforcement. This method is the most intuitive and accurate, but it is a post-inspection and cannot guide preventive measures, adjustments, or remedial measures for ground pre-grouting, hindering the quality of ground pre-grouting work.

[0007] The rapid development of geophysical exploration technology has brought new hope for ground pre-grouting effectiveness inspection. Geophysical exploration, or geophysical prospecting, refers to the exploration method of investigating geological conditions such as stratum lithology and geological structure by studying and observing changes in various geophysical fields. Because different rock media comprising the Earth's crust often exhibit differences in density, elasticity, electrical conductivity, magnetism, radioactivity, and thermal conductivity, these differences cause corresponding local variations in geophysical fields. By measuring the distribution and variation characteristics of these physical fields and analyzing and studying them in combination with known geological data, it is possible to infer geological properties. Geophysical exploration technology is widely used in mineral resource exploration, stratigraphic division and structural exploration, hydrogeological surveys, geological anomaly investigations, and engineering geological surveys. Common geophysical exploration methods such as ultrasonic sounding, geological radar, transient electromagnetic sounding, magnetotelluric sounding, cross-hole radio-wave sounding, and cross-hole acoustic sounding are not suitable for vertical shaft ground pre-grouting effectiveness inspection due to their limited depth and low resolution. Cross-hole seismic CT has also not been adopted due to its high cost. Summary of the Invention

[0008] To this end, the technical problem to be solved by this invention is to provide a method for detecting the effectiveness of pre-grouting in vertical shafts using cross-hole resistivity CT. Through cross-hole resistivity CT testing, the changing trends of resistivity before and after grouting on a cross-section can be determined, and the improvement in water content in the injected strata can be interpreted and analyzed. This allows for the evaluation of grouting effectiveness (primarily water blocking), guidance of grouting construction, and serves as an important basis for acceptance of grouting projects.

[0009] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0010] A method for detecting the effect of pre-grouting on the ground of a vertical shaft using cross-hole resistivity CT includes the following steps:

[0011] (A) Preparation of cross-hole resistivity CT test system;

[0012] (B) Complete the construction of the grouting holes before grouting;

[0013] (C) Arrangement of cross-hole resistivity CT testing system;

[0014] (D) Before grouting, a cross-hole resistivity CT test system is used to perform tests and generate inversion images to guide grouting construction;

[0015] (E) After grouting, the cross-hole resistivity CT test system is used to analyze the resistivity change trend before and after grouting and evaluate the grouting water blocking effect.

[0016] In the above-mentioned method of detecting the effect of pre-grouting on the ground of a vertical shaft by cross-hole resistivity CT, in step (A), the cross-hole resistivity CT testing system includes an instrument host, a portable computer, cables and electrodes;

[0017] The instrument host is used to complete testing and data acquisition under the control of a portable computer. The portable computer is installed with resistivity CT testing software, which controls the instrument host testing and acquisition, stores and processes data, and inverts it into readable images. The cable is used for power supply, testing, and data transmission. The electrodes are formed by pressing the ends of each core conductor in the cable. Each cable is tapped at a certain interval within the test section to form a number of electrodes, which are used for power supply and measurement in the formation between holes.

[0018] One end of the cable is equipped with a cable lowering counterweight, and the other end of the cable is connected to an instrument host, which is in turn connected to a portable computer.

[0019] In the above-mentioned method for detecting the effect of pre-grouting on the ground of a vertical shaft by using cross-hole resistivity CT, in step (B), one to two pairs of grouting holes are selected as cross-hole resistivity CT test holes; and construction of the selected pairs of grouting holes is completed;

[0020] Adjust the flushing fluid in time to complete the flushing of the selected pairs of grouting holes, ensure that the rock cuttings precipitation and flushing fluid concentration in the grouting holes are within the allowable range, and ensure that the designed test depth is reached and the safety in the hole is guaranteed.

[0021] The above-mentioned method of detecting the effect of pre-grouting on the ground of a vertical shaft by cross-hole resistivity CT, in step (C), comprises the following steps:

[0022] (C-1) Arrange a drilling tower on the ground, pass the cable through the lower pulley and upper pulley on the drilling tower, and lower it to the designed depth of the grouting hole under the traction of the cable lowering counterweight;

[0023] (C-2) Place the instrument host and portable computer in a safe location between the two paired test grouting holes;

[0024] (C-3) Make good line connections: connect the upper aviation connectors of the cables in the two paired test grouting holes to the instrument host respectively; and connect the instrument host to a portable computer.

[0025] In the above-mentioned method of detecting the effect of pre-grouting on the ground of a vertical shaft by cross-hole resistivity CT, the electrodes on the cable are located in two paired test grouting holes, and the test sections are lowered to the same depth.

[0026] In the above-mentioned method of detecting the effect of pre-grouting on the ground of a vertical shaft by cross-hole resistivity CT, in step (D),

[0027] Before grouting test, the instrument host is controlled by a portable computer, the test is carried out through the electrodes, and the test data is transmitted to the instrument host through the cable. The instrument host transmits the collected data to the portable computer, which stores, processes and interprets the data and inverts it into a readable result map to guide the grouting construction;

[0028] After the test is completed, disconnect the cable from the instrument host and pull the cable and electrode out of the grouting hole.

[0029] The above-mentioned method of using cross-hole resistivity CT to detect the effect of pre-grouting on the ground of a vertical shaft comprises grouting holes, selecting 1 to 2 pairs of grouting holes, and then drilling paired grouting holes after the grouting is completed according to steps (B) to (D), arranging a cross-hole resistivity CT testing system, conducting cross-hole resistivity CT testing after grouting, and processing and interpreting the data.

[0030] In the above-mentioned method of using cross-hole resistivity CT to detect the effect of pre-grouting on the ground of a vertical shaft, in step (E), a comparative analysis is performed on the data obtained by the cross-hole resistivity CT test system before and after grouting. Based on the changing trend of the resistivity in the cross-hole profile before and after grouting, combined with the geological conditions and grouting construction parameters, a comprehensive analysis is made on the improvement of the water-containing characteristics of the grouting section before and after grouting to evaluate the grouting water blocking effect.

[0031] The above-mentioned method of using cross-hole resistivity CT to detect the effect of pre-grouting on the ground of a vertical shaft has the following evaluation criteria for the grouting effect: after grouting, if the resistivity of the water-rich area of ​​the injected layer increases significantly, the resistivity value tested after grouting is more than 50% higher than the resistivity value tested before grouting, and the low-resistance abnormal area existing before grouting on the cross-hole resistivity CT profile is significantly weakened or disappears after grouting, and there is no new obvious low-resistance abnormal area, combined with other geological data and grouting construction data, it can be determined that the water content is significantly reduced and the grouting water blocking effect is achieved.

[0032] The technical solution of the present invention achieves the following beneficial technical effects:

[0033] The present application provides a method for detecting the effect of pre-grouting on the ground of a vertical shaft using geophysical exploration technology. Through cross-hole resistivity CT testing, the changing trend of resistivity before and after grouting on the profile is grasped, and the improvement of the water content of the injected stratum is interpreted and analyzed, thereby evaluating the grouting effect (mainly the water blocking effect), guiding the grouting construction and serving as an important acceptance basis for the grouting project.

[0034] The use of cross-hole resistivity CT technology in the detection of the water blocking and reinforcement effect of pre-grouting in vertical shaft ground provides an advanced, simple and reliable means of evaluating the effect of pre-grouting in vertical shaft ground, overcoming the shortcomings of large errors in current hydrological tests and delayed timeliness of excavation measurements, providing more information and guidance on formation conditions for the construction of pre-grouting projects in vertical shaft ground, providing a reliable basis for the acceptance of grouting projects, and providing better technical support for the application of pre-grouting technology in vertical shaft ground and the safe and rapid construction of vertical shaft shafts. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A schematic structural diagram of the cross-hole resistivity CT testing system of the present invention;

[0036] Figure 2 Layout plan of vertical shaft grouting holes and cross-hole resistivity CT;

[0037] Figure 3 Schematic diagram of cross-hole resistivity CT detection electrode distribution in this embodiment;

[0038] Figure 4 The cross-hole resistivity CT test output results in this embodiment are: a comparison of the resistivity CT sections of S9-S3 and S2-S10 before and after grouting.

[0039] The reference numerals in the figure are as follows: 1-instrument host, 2-portable computer, 3-lower pulley, 4-upper pulley, 5-drilling tower, 6-cable, 7-grouting hole casing, 8-electrode, 9-grouting hole, 10-cable lowering counterweight. DETAILED DESCRIPTION

[0040] Cross-hole resistivity CT is a recently developed ultra-high-density direct current electrical exploration method. It belongs to the array exploration method and is an electrical tomography method that combines electrical profiling and electrical depth sounding. This method primarily studies the distribution of conductive current in the ground under the influence of an applied electric field based on differences in the electrical conductivity of rocks (or minerals). This method can infer the occurrence of geological bodies with different resistivities underground.

[0041] Cross-hole resistivity CT involves placing cables with electrodes simultaneously within the same depth range in two boreholes to collect apparent resistivity data from any electrode arrangement, i.e., all possible combinations of current and potential points. Using inversion techniques, resistivity imaging profiles are obtained and geological interpretation is performed. This method differs from other high-density resistivity methods in the following ways: ① Conventional high-density resistivity methods employ surface survey lines to map the distribution and variation of rock resistivity within a certain depth, while cross-hole resistivity CT employs survey lines placed in two boreholes that penetrate the test rock formation, directly contacting and measuring the resistivity distribution and variation of the target rock formation, resulting in a more accurate and reliable method. ② Cross-hole resistivity CT involves large-scale data acquisition, resulting in more comprehensive, accurate, and reliable inversion imaging. Its high resolution, low multi-solution coefficient, and fully automated, rapid acquisition methods ensure reliable exploration of high-precision, small-target areas.

[0042] The resistivity of the rock formation is mainly related to the lithology, water content, and formation water salinity. For the same aquifer or water-bearing area, the resistivity before grouting should be relatively low, and a low-resistance abnormal area will appear on the resistivity CT profile. After grouting, the water-bearing voids within the curtain range are filled with slurry, and the groundwater is isolated. The original low-resistance anomaly should be significantly weakened or disappear, and there will be no new obvious low-resistance abnormal area. This is the basic principle of cross-hole resistivity CT detection of grouting effect.

[0043] This application takes the Xianglushan Tunnel, Section 2 of the Dianchi Water Diversion Project in Dali I, as an example for explanation.

[0044] 1. Overview

[0045] The Dianzhong Water Diversion Project is a landmark project among my country's major water conservation and supply projects. It consists of two components: a water source project and a water transmission project. The water source project, located in Shigu Town, Yulong County, draws water from the Jinsha River, approximately 1.5 kilometers upstream. Pumping stations pump water to the main canal. The water transmission project begins at Wangchengpo in Shigu Town, Lijiang, and passes through Lijiang City, Dali Prefecture, Chuxiong Prefecture, Kunming City, and Yuxi City, ending at Xinpobei in Honghe Prefecture.

[0046] The Xianglu Mountain Tunnel of the Dali I Section 2 Construction Project of the Dianchi Water Diversion Project is located in Lijiang City. In order to speed up the construction progress, a vertical shaft was added at the Xianglu Mountain Tunnel. The vertical shaft passes through the strata mainly composed of Triassic Beiya Formation limestone, dolomite limestone and Tertiary intrusive rock andesitic basalt. The surrounding rock stability conditions are poor and the groundwater is abundant. In order to ensure the construction safety and the smooth progress of the project, grouting and water blocking reinforcement treatment is required around the shaft before construction.

[0047] The wellbore surface grouting project design utilizes a straight hole + S-hole approach. Straight holes are used for grouting treatment in the upper and middle strata within the wellbore depth. After completion, the drilling rig is moved farther from the wellbore center, and an S-hole approach is used to grout treatment in the lower and middle strata within the wellbore depth. While the S-hole approach is being constructed, the wellbore excavation and masonry work can begin, allowing the excavation and masonry work of the upper wellbore to proceed simultaneously with the grouting treatment of the lower wellbore, shortening the overall wellbore construction period.

[0048] After the borehole is formed, the downward segmented grouting method is used to treat the aquifer around the wellbore to form a water-blocking curtain. Clay cement slurry is mainly used for grouting, combined with a certain amount of single-liquid cement slurry to reinforce large caves and broken formations.

[0049] The design parameters of grouting holes are shown in Table 1 and Figure 2 :

[0050] Table 1 Drilling design parameters

[0051]

[0052] According to the analysis of the current research status at home and abroad, there has been no inspection and evaluation of the ground pre-grouting effect of the vertical shaft through geophysical exploration methods. Therefore, this project decided to study the method of detecting and evaluating the grouting effect by cross-hole resistivity CT.

[0053] 2. Specific detection plan

[0054] In order to study the soft rock grouting technology and evaluate the grouting effect, geophysical exploration work was carried out in the same area before and after grouting. The grouting effect was evaluated by the changes in physical properties before and after grouting.

[0055] The specific method is as follows:

[0056] (A) Preparation of cross-hole resistivity CT test system;

[0057] like Figure 1 and Figure 3 As shown, the cross-hole resistivity CT testing system includes an instrument host 1, a portable computer 2, a cable 6 and an electrode 8;

[0058] The instrument host 1 is used to complete testing and data acquisition under the control of a portable computer. The portable computer 2 is installed with resistivity CT testing software, which controls the testing and acquisition of the instrument host 1, performs data storage and processing, and inverts the data into a readable image. The cable 6 is used for power supply, testing, and data transmission. The electrodes 8 are formed by pressing the tapped ends of each core conductor in the cable 6. Each cable 6 is tapped at a certain interval within the test section to form a plurality of electrodes for power supply and measurement in the inter-hole formation.

[0059] One end of the cable 6 is installed with a cable lowering counterweight 10 , and the other end of the cable 6 is connected to the instrument host 1 , and the instrument host 1 is connected to the portable computer 2 .

[0060] (B) completing the construction of the grouting hole 9 before grouting;

[0061] Before grouting, select two holes S3 and S9 that were completed at about the same time, and perform cross-hole resistivity CT detection on the S3-S9 profile; complete the construction of the selected paired holes S3 and S9;

[0062] Adjust the flushing fluid in time to complete the flushing of the selected pair of grouting holes 9 (boreholes S3 and S9), ensure that the rock cuttings precipitation and flushing fluid concentration in the grouting holes 9 (boreholes S3 and S9) are within the allowable range, and ensure that the designed test depth is reached and the safety of the hole is guaranteed. Figure 3 .

[0063] (C) Arrangement of cross-hole resistivity CT testing system;

[0064] like Figure 1 As shown in FIG. 1 : (C-1) a drilling tower 5 is arranged on the ground, a cable 6 is passed through the lower pulley 3 and the upper pulley 4 on the drilling tower 5, and is lowered to the designed depth of the grouting hole 9 under the traction of the cable lowering counterweight 10; electrodes 8 on the cable 6 located in two paired test grouting holes 9 (boreholes S3 and S9) are lowered to the same depth in the test section.

[0065] (C-2) Place the instrument host 1 and the portable computer 2 in a safe position between the two paired test grouting holes 9 (drilling holes S3 and S9);

[0066] (C-3) Make good line connections: The upper aviation connectors of the cables 6 located in the two paired test grouting holes 9 (drilling holes S3 and S9) are respectively connected to the instrument host 1; the instrument host 1 is connected to the portable computer 2.

[0067] Cross-hole resistivity CT data acquisition: Place a multi-core cable 6 in each hole, connect the electrodes 8 in series to the ground and connect to the control instrument host 1. Each electrode has 32 electrodes, the electrode spacing is 3m, the measurement section length is 93m, the power supply voltage is 90V or 250V, and the data is collected at one time after setting the working parameters. See the electrode distribution diagram for details. Figure 4 .

[0068] The cross-hole resistivity CT test section is 360-460m.

[0069] (D) Before grouting, a cross-hole resistivity CT test system is used to perform tests and generate inversion images to guide grouting construction;

[0070] Automatic cross-hole resistivity testing is carried out through the control of a portable computer. Before grouting, the instrument host 1 is controlled by the portable computer 2, the test is carried out through the electrode 8, and the test data is transmitted to the instrument host 1 through the cable 6. The instrument host 1 transmits the collected data to the portable computer 2. The portable computer 2 stores, processes and interprets the data, and inverts it into a readable result map to guide the grouting construction.

[0071] After the test is completed, the cable 6 is disconnected from the instrument host 1 , and the cable 6 together with the electrode 8 is pulled out from the grouting hole 9 .

[0072] (E) After grouting, adjacent boreholes S2 and S10 were selected for cross-hole resistivity CT detection of the S2-S10 profile. Cross-hole resistivity CT testing was then performed using a cross-hole resistivity CT testing system to analyze the resistivity change trend before and after grouting and evaluate the grouting water blocking effect.

[0073] The two surveys before and after grouting used the same working device, data acquisition parameters and processing methods. Figure 4 .

[0074] Detection result analysis:

[0075] Before grouting, the cross-hole resistivity CT detection of S3-S9 section was carried out. After the grouting was completed, the resistivity CT detection of S2-S10 section was carried out. Through inversion imaging, two resistivity distribution profiles were formed. Figure 3 , through comparative analysis, explore the effect of price grouting.

[0076] When performing geological analysis on cross-hole resistivity CT profiles, the primary focus is on resistivity contour anomalies. Resistivity values ​​are defined using color saturation within the profile. To highlight anomalies, color scales may vary between profiles. Generally, dark and light blue define low-resistance areas, red, yellow, and green define high-resistance areas, and blue represents low-resistance areas.

[0077] The resistivity CT profiles S9-S3 before grouting show significant low-resistivity anomalies in the original formation between 384-392 m and 418-425 m, and a medium-low resistivity anomaly in the 450-460 m section, indicating weak water-bearing areas. After grouting, the S2-S10 profiles show no more concentrated low-resistivity anomalies. The resistivity values ​​of the original sections between 384-392 m, 418-425 m, and 450-460 m have significantly increased. Table 2 shows the pre- and post-grouting resistivity comparisons. This indicates that the weak water-bearing areas in the original formation have been effectively sealed, and the significant water-bearing areas have disappeared, demonstrating the grouting effect.

[0078] Table 2 Comparison of resistivity values ​​before and after grouting

[0079]

[0080]

[0081] A comparative analysis was conducted on the data obtained by the cross-hole resistivity CT test system before and after grouting. Based on the changing trend of the resistivity in the cross-hole profile before and after grouting, combined with the geological conditions and grouting construction parameters, a comprehensive analysis was made on the improvement of the water-containing characteristics of the grouting section before and after grouting, and the grouting water blocking effect was evaluated.

[0082] The evaluation criteria for the grouting effect are: after grouting, if the resistivity of the water-rich area of ​​the injected layer increases significantly, the resistivity value tested after grouting is more than 50% higher than the resistivity value tested before grouting, and the low-resistance abnormal area existing on the cross-hole resistivity CT section before grouting is significantly weakened or disappears after grouting, and there is no new obvious low-resistance abnormal area, combined with other geological data and grouting construction data, it can be determined that the water content is significantly reduced and the grouting water blocking effect is achieved.

[0083] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the claims of this patent application.

Claims

1. A method for detecting the effect of pre-grouting on the ground of a vertical shaft using cross-hole resistivity CT, characterized in that: The steps include: (A) Preparation of the cross-hole resistivity CT test system; (B) completing the construction of the grouting hole (9) before grouting; (C) Arrangement of cross-hole resistivity CT testing system; (D) Before grouting, a cross-hole resistivity CT test system is used to perform a test and generate an inversion map to guide the grouting construction; (E) After grouting, the cross-hole resistivity CT test system is used to analyze the resistivity change trend before and after grouting and evaluate the grouting water blocking effect; In step (A), the cross-hole resistivity CT test system includes an instrument host (1), a portable computer (2), a cable (6) and an electrode (8); the instrument host (1) is used to complete testing and data acquisition under the control of the portable computer; the portable computer (2) is installed with resistivity CT test software, which controls the instrument host (1) to test and acquire, and performs data storage and data processing, and inverts it into a readable image; the cable (6) is used for power supply, testing and data transmission; the electrode (8) is formed by pressing the tap of each core conductor in the cable (6), and each cable (6) is tapped at a certain arrangement interval within the test section length to make a plurality of electrodes for power supply and measurement in the inter-hole formation; one end of the cable (6) is installed with a cable lowering counterweight (10), the other end of the cable (6) is connected to the instrument host (1), and the instrument host (1) is connected to the portable computer (2); In step (C), the following steps are included: (C-1) Arrange a drilling tower (5) on the ground, pass the cable (6) through the lower pulley (3) and the upper pulley (4) on the drilling tower (5), and lower it to the designed depth of the grouting hole (9) under the traction of the cable lowering counterweight (10); (C-2) Place the instrument host (1) and the portable computer (2) in a safe location between the two paired test grouting holes (9); (C-3) Make good line connections: connect the upper aviation connectors of the cables (6) in the two paired test grouting holes (9) to the instrument main unit (1) respectively; The instrument host (1) is connected to the portable computer (2); In step (E), a comparative analysis is conducted on the data obtained by the cross-hole resistivity CT test system before and after grouting. Based on the changing trend of the resistivity in the cross-hole profile before and after grouting, combined with the geological conditions and grouting construction parameters, a comprehensive analysis is conducted on the improvement of the water content characteristics of the grouting section before and after grouting to evaluate the grouting water blocking effect. The evaluation criteria for the grouting water blocking effect are: after grouting, if the resistivity of the water-rich area of ​​the injected layer increases significantly, the resistivity value tested after grouting is more than 50% higher than the resistivity value tested before grouting, and the low-resistance abnormal area existing on the cross-hole resistivity CT section before grouting is significantly weakened or disappears after grouting, and there is no new obvious low-resistance abnormal area, combined with other geological data and grouting construction data, it can be determined that the water content is significantly reduced and the grouting water blocking effect is achieved.

2. The method for detecting the effect of pre-grouting on the ground of a vertical shaft by cross-hole resistivity CT according to claim 1 is characterized in that: In step (B), one to two pairs of grouting holes (9) are selected as cross-hole resistivity CT test holes; the construction of the selected pairs of grouting holes (9) is completed; the flushing fluid is adjusted in a timely manner to complete the flushing of the selected pairs of grouting holes (9), ensuring that the rock cuttings precipitation and the flushing fluid concentration in the grouting holes (9) are within the allowable range, ensuring that the designed test depth is reached and the safety in the hole is ensured.

3. The method for detecting the effect of pre-grouting on the ground of a vertical shaft by cross-hole resistivity CT according to claim 1 is characterized in that: The electrodes (8) on the cables (6) are located in two paired test grouting holes (9), and the test sections are lowered to the same depth.

4. The method of detecting the effect of pre-grouting on the ground of a vertical shaft by cross-hole resistivity CT according to claim 1 is characterized in that: In step (D), before grouting, the test is performed by controlling the instrument host (1) through the portable computer (2), performing the test through the electrode (8), and transmitting the test data to the instrument host (1) through the cable (6). The instrument host (1) transmits the collected data to the portable computer (2), and the portable computer (2) performs data storage, data processing and interpretation, and inverts the data into a readable result map for guiding the grouting construction. After the test is completed, the cable (6) is disconnected from the instrument host (1), and the cable (6) and the electrode (8) are pulled out from the grouting hole (9).

5. The method of detecting the effect of pre-grouting on the ground of a vertical shaft by cross-hole resistivity CT according to claim 4 is characterized in that: The grouting holes (9) are grouting-constructed, 1 to 2 pairs of grouting holes are selected, and then the paired grouting holes (9) are drilled after the grouting is completed, a cross-hole resistivity CT test system is arranged, and cross-hole resistivity CT test after grouting, data processing and interpretation are performed.

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