Study on the Method of Advanced Water Prediction for Underground Mine Expansion Using the Transient Electromagnetic Method and the Field Test: A Case Study of the Huize Lead–Zinc Mine

Abstract

Mine water disaster is one of the main natural disasters in underground mining operations, and seriously threatens the safety of mine production and personnel’s life, affecting mine safety and sustainable development. The research on the prevention and control of the disaster of water inrush in fractured rock mass has become a major international frontier issue in the field of underground engineering, and it is also a major national demand. The key to effectively preventing and controlling disasters is to reveal the mechanisms of disasters. Taking the Huize lead–zinc mine as an example, this paper deeply studies the application method of the transient electromagnetic method (TEM) in advance water detection in shaft and roadway development and field test results. In view of the complicated hydrogeological conditions of the mine and the serious threat of water damage, this paper puts forward a kind of advanced water detection technology for the Huize lead–zinc mine based on the mine transient electromagnetic method. The technology uses the principle of electromagnetic induction to detect the water-bearing structure ahead by placing the transmitting and receiving coils in the shaft. In the field test, the multi-turn small wire frame device is used to detect the direction of the roof, bedding and floor of the roadway head on. In roadway excavation, if the site meets the detection requirements, the abnormal low-resistance area in the test area can be exposed by drilling first. The degree of structural development and the peak value of water gushing in the target area have been mastered. Then, it is determined whether it is necessary to increase borehole exploration in other relatively high-resistance low-risk areas. The experimental results show that the mine transient electromagnetic method can accurately identify the low-resistance water in front, and provide reliable technical support for mine water disaster prevention. The research in this paper not only enriches the application field of the mine transient electromagnetic method, but also provides a useful reference for mine water damage prevention under similar conditions.

1. Introduction

In the process of mine mining, the geological structure and hydrological conditions in front of the roadway are important factors affecting the safety of production [1,2]. Especially in complex geological environments, water-bearing structures such as faults, the fissure development zone, karst and the collapse column often bring great safety risks to roadway excavation [3,4]. With the development and future development needs of the mine, the exploration and infrastructure projects of the Huize lead–zinc mine will pass through high-risk areas such as strong aquifers and water-bearing structures. Many water inrush points were revealed in the process of related engineering, which increased the drainage pressure of the mine. Meanwhile, the possibility of water inrush events caused by poor engineering control cannot be ruled out. Therefore, the advanced detection and prediction technology of roadway plays a vital role in safe mining [5,6]. The transient electromagnetic method, as a fast, efficient and convenient detection method, has been widely used in mine advance detection [7,8,9].

Mine geophysical detection methods mainly include the seismic method, the mine transient electromagnetic method, the mine direct current method, electromagnetic wave CT, geological radar and infrared temperature measurement [10,11,12]. The transient electromagnetic method (TEM) is a time-domain electromagnetic method based on the principle of electromagnetic induction [13,14]. In this method, a pulsed electromagnetic field is emitted into the ground by the transmitting coil. During the interval of the pulsed electromagnetic field, the secondary eddy current field is observed by the receiving coil, and the electrical characteristics and spatial distribution of the underground geologic body are inferred. The transient electromagnetic method is especially suitable for mine roadway advance detection because of its small volume effect, strong detection direction, high resolution and sensitivity to water-bearing geological bodies. Wright et al. (2003) [15] proposed the multi-transient electromagnetic method (MTEM). The MTEM integrates data acquisition, processing and interpretation methods in seismic exploration, geometric measurement and induction measurement techniques in electromagnetic exploration, and has become a promising electromagnetic exploration method in the field of petroleum and mineral resources exploration. By studying the key technical difficulties in the application of the TEM in coal mine hydrogeological exploration, Han et al. (2011) [16] made full use of the TEM’s characteristics such as sensitivity to low-resistance bodies, high lateral resolution and fast speed, and improved the accuracy of transient electromagnetic detection. The transient electromagnetic method has been used to locate the water inrush structure quickly and accurately in the rescue of water inrush in coal mines. The TEM has saved time in coal mine emergency rescue and also has significant social and economic benefits. Based on the smoke ring effect of the transient electromagnetic field, the principle of the transient electromagnetic method for advanced detection of hidden water-bearing structures in coal mines was proposed [17]. A small multi-loop structure applied in coal mines is presented, and the field program of semi-circle sector scanning is given. Lu et al. (2021) [18] analyzed the difference in electromagnetic response between multi-grounded devices and single-grounded devices. The results show that the electromagnetic response of multiple ground sources is larger. The transient electromagnetic signal is located by combining multiple ground sources, and the detection capability is enhanced successfully.

In addition, scholars have conducted in-depth research on the depth definition, inversion methods, and data processing of the transient electromagnetic method, which have promoted the continuous development of transient electromagnetic method technology [19,20,21]. Feng et al. (2024) [22] effectively applied the ground to the air transient electromagnetic method to carry out a hydrogeological engineering geological survey of a mine subsidence area. The method provides accurate and reliable basic data support for rescue operations and post-disaster reconstruction, and also provides a valuable reference for similar exploration projects. Yu et al. (2017) [23] used multi-component analysis method to simulate transient electromagnetic response (FDTD) of underground roadway by using finite difference time domain method. The transient electromagnetic advance detection of roadway is carried out by physical simulation method. This shows that it is feasible to interpret transient electromagnetic data by using the horizontal component. Therefore, transverse component method can be used as a new method for TEM data processing and interpretation in coal mines. Based on the propagation theory of “smoke ring effect”, transient electromagnetic technology is applied in coal mines to detect the water-bearing structural anomaly area in the top and bottom of the coal seam and in front of driving roadway [24]. The results show that this technology can detect the horizontal and vertical development law of abnormal water in a certain depth below the bottom of the coal seam, and can also detect abnormal low-resistance water in a certain distance from the roof. Yu et al. (2018) [25] used inversion technology to interpret TEM data, proving that the large-loop transient electromagnetic method is an effective method to detect water-rich goaf under complex terrain conditions, and provides more detailed geological information for coal mining enterprises to further safely arrange coal mining work.

Moreover, the occurrence of mine water inrush is often accompanied by the pollution of mine wastewater [26]. Mines globally obtain their water from various sources including rivers, lakes, groundwater, precipitation, and runoff, which contribute to 2 to 4.5 percent of the national water requirements in major mineral-producing nations [27]. Instances where mining operations withdraw water without ensuring safe disposal often lead to disputes between mining companies and other water users, such as local communities, farmers, and environmental groups [28]. Mining activities, such as excavation, can lead to a lowering of the water table, as well as the water inrush, discharge, storage, and management of wastewater, chemicals, reagents, and fuels, all of which may have an impact on both surface water and groundwater quality [29]. Currently, the swift escalation in the extraction of essential minerals presents novel hazards, with 16% of these mines situated in countries experiencing high or extremely high levels of water stress [30].

As one of the important metal mineral bases in China, the Huize lead–zinc mine has complicated geological conditions and prominent hydrogeological problems. In the process of roadway excavation, water-bearing structure is often encountered, which brings serious threat to safety production. Therefore, it is of great significance to improve the safety level of production, shorten the time of roadway excavation and save costs to carry out the research on the advanced water exploration method of mine tunnel development by the transient electromagnetic method and the field test. Taking the Huize lead–zinc mine as an example, this paper introduces the application method of the mine transient electromagnetic method to advance water exploration in tunnel development, and verifies its detection effect through the field test. At the same time, combined with geological and hydrogeological data, this paper presents a comprehensive analysis of the detection results to provide scientific basis for mine water disaster prevention.

2. Materials and Methods

2.1. Case Study

The Huize lead–zinc mine is located approximately 46 km northeast of Huize County, Yunnan Province, China (Figure 1). The main geological formations in the mining area are the Ordovician System, Cambrian System, Devonian System, Carboniferous System, Permian System, and Quaternary System, as listed in Table 1.

The Huize lead–zinc mine is a massive sulfide deposit mainly composed of lead–zinc and associated with silver and germanium. The morphology, occurrence, scale and regularity of mineralization and enrichment of ore bodies are obviously controlled by the multi-group structures during the mineralization period. The orebodies are mainly distributed in the interstratified fault zone of northeast strike. The Lower Carboniferous Baizuo Formation (C1b) is the main ore formation in the mining area. Its scale increases to the depth, its grade increases, and its boundary with the surrounding rock is obvious. The size of the ore body is very different, with the strike of 5°~25° and the inclination of 60°~70°. The strike length of ore body is approximately 800~1600 m, the vertical extension is more than 800~1100 m, and the thickness varies between 0.7 and 40 m.

With the gradual development of deep resource exploration work, the exploration and tunnel engineering have been conducted below the minimum erosion base level of the mining area. Some projects have exposed the Qixia-Maokou Formation and Sinian karst fissure water aquifer, and the water inflow of the mine has increased significantly. At present, the deep exploration and mining projects of the two mines are located under the Niulanjiang contact zone, the lowest base level of local erosion. The main aquifers are distributed with alternating strength and weakness in both horizontal and vertical directions, and the water conductivity and water richness of each aquifer are very uneven. The direct water-filled aquifer of the deposit is water rich and water permeable in the Carboniferous and Devonic carbonate karst fissure aquifer. The carbonate karst fissure aquifer overlying Qixia-Maokou Formation and underlying Sinian Dengying Formation + Doushantuo Formation has weak to medium water richness and strong water permeability due to local structural influences. The high water head difference between the indirect top and bottom karst fissure aquifer and the direct aquifer is the main factor threatening the safety of mine production. The groundwater in the carbonate fissure aquifer of Qixia Maokou Formation is closely related to the surface water of Niuman River. If the groundwater of Qixia Maokou Formation is drained in advance with large discharge, the Niuman River water may be triggered and the consequences will be serious.

The dynamic change characteristics of groundwater in the mining area reveal the nature of the hydrogeological problems in the mining area: the direct water-filled aquifer of the deposit has poor permeability and low water richness, while the indirect water-filled aquifer of the deposit has strong permeability and high water richness. Once the water barrier roof and floor are exposed in the mining area, the water inflow in the mine will surge. The protection of water-proof roof and floor of deposit is the key to solve the problem of mine hydrogeology engineering geology.

2.2. Technical Principle of the Mine Transient Electromagnetic Method

The transient electromagnetic method is a time-domain electromagnetic induction method, as shown in Figure 2. A current pulsed square wave is supplied on the sending loop, and a primary magnetic field propagating in the direction of the normal of the transmitting loop is generated when the square wave descends behind it. Under the excitation of the primary magnetic field, the geologic body will produce eddy current, the size of which depends on the degree of conductivity of the geologic body. After the primary field disappears, the eddy current will not disappear immediately, and it will have a transition (attenuation) process. In this transition process, a secondary magnetic field with attenuation is propagated to the geological body, and the secondary magnetic field is received by the receiving loop. The change in the secondary magnetic field will reflect the electrical distribution of the geological body.

The basic principle of the mine transient electromagnetic method and the ground transient electromagnetic method is the same, and all devices and parameters of ground electromagnetic method can be used in theory. However, due to the influence of the underground environment, the data acquisition and processing of the mine transient electromagnetic method and the ground TEM are very different. Due to the influence of the mine track, the high pressure environment and small-scale wire frame device, the exploration depth in the underground is very limited, and the effective interpretation distance is generally approximately 100 m. In addition, the ground transient electromagnetic method is a semi-spatial transient response, which comes from the half-space layer below the surface, while the mine transient electromagnetic method is a full-space transient response, which comes from the strata above and below the loop plane (or both sides), which brings great difficulties in determining the location of the abnormal body. The actual data interpretation must be combined with the specific geological and hydrogeological situation comprehensive analysis. Specifically, the mine transient electromagnetic method has the following characteristics:

• (1). Due to the influence of mine roadway, the mine transient electromagnetic method can only use a multi-turn small loop device with side length of 1.5–2 m, which has less labor intensity, light measuring equipment, high working efficiency and low cost compared with the ground transient electromagnetic method.

• (2). In order to ensure the quality of the data, reduce the influence of the volume effect and improve the exploration resolution, especially the lateral resolution, the small loop device system is used. When arranging the measuring points, the point distance must be controlled, and make the measuring points as dense as possible when considering the work intensity.

• (3). The downhole measurement device is closer to the abnormal body, which greatly improves the signal-to-noise ratio of the measurement signal. Experience shows that the signal strength of the downhole measurement is 10–100 times stronger than the signal of the same device and parameter setting on the ground. The interference signal in the mine is approximately zero relative to the useful signal, while the surface measurement signal is covered by the interference signal after attenuation to a certain period of time, and the useful abnormal signal cannot be identified.

• (4). Generally, the wire frame can only be placed flat on the ground for measurement in surface TEM exploration, while the underground TEM can place the coil on the floor of the roadway for measurement to detect the vertical and horizontal development law of the abnormal water-bearing body in a certain depth of the floor, or it can be placed upright in the roadway. When the wire frame surface is parallel to the front of the roadway, advance detection can be carried out. When the coil is parallel to the seam on the side of the roadway, the development law of the water-bearing low-resistivity abnormal body in a certain range of the side wall and the roof and floor can be detected (Figure 3).

2.3. The Mine Transient Electromagnetic Instrument (YCS1024)

The YCS1024 transient electromagnetic instrument (Chongqing Research Institute of China Coal Science and Industry Group, Chongqing, China) for mining is adopted, as shown in Figure 4. The YCS1024 transient electromagnetic instrument is composed of a main engine and a transmitting and receiving coil, which is an integrated design and easy to carry. The primary magnetic field is sent underground through the transmitting coil, and the secondary magnetic field stimulated by the underground water-rich strata, structures and other low-resistivity anomalies is received by the receiving coil, and the apparent resistivity is calculated, and then the degree of water-rich water is judged by the analysis of the apparent resistivity. The main technical parameters are: (1) transmission current: up to 4.2 A; (2) transmission frequency: 2.5 Hz, 6.25 Hz, 12.5 Hz, 25 Hz, and 62.5 Hz; (3) overlay times: 1–9999 times optional; (4) A/D conversion: double 24 Bit; (5) operation interface: HD color LCD screen; (6) effective detection distance: not less than 100 m.

The YCS1024 transient electromagnetic instrument has the characteristics of anti-interference, lightweight and high degree of automation. The data acquisition is controlled by microcomputer, recorded and stored automatically, and the data playback can be realized by connecting with microcomputer. Because the probe uses a small wire frame, the point distance can vary according to the requirements of the exploration mission. In the actual measurement, multi-turn wire frame is used, transmitting wire frame and receiving wire frame are different turns, common center point overlapping loop device, in order to produce the best coupling response with the underground abnormal body.

In order to make the detection range more comprehensively reflect the abnormal distribution of rock water in front of the roadway head and meet the requirements of the detection geological task, according to the actual mining conditions, five advance detection directions (elevation direction of 60°, elevation direction of 45°, horizontal direction, depression angle of 30° and depression angle of 60°) are arranged at the roadway head position. According to the actual situation on site, 13 detection angles are arranged in each detection direction (90° on the left side of the roadway −90° on the right side of the roadway, with an angle every 15°) to control the distribution of rock formation water in the whole space within 100 m in front of the head position. The schematic diagram of the detection device is shown in Figure 5.

3. Experimental Results and Discussion

3.1. Experimental Study on the Mine Transient Electromagnetic Method and Equipment Effectiveness Detection

3.1.1. Detection Parameter Analysis

This paper mainly deals with the parameter selection of superposition times and signal acquisition time.

• (1). Stacking number

In the process of data acquisition, there is random interference. Therefore, in order to suppress the random electromagnetic signal interference and improve the signal-to-noise ratio of the observed data, the transient electromagnetic instrument adopts the “cumulative average” value technology. That is, multiple measurements are made for each measuring point, and the average value of multiple measurements is finally obtained as the final data of the measuring point. The number of measurements at each measuring point is called the “stacking number”. Increasing the number of superposition can reduce the interference noise level in the observed data, but increasing the number of superposition will increase the observation time and reduce the observation speed. Therefore, under the premise of ensuring the quality of data, the number of superposition should be selected comprehensively.

• (2). Acquisition time

From the basic principle of transient electromagnetic method, it can be seen that the transient electromagnetic field of the mine is the change characteristic of the underground secondary electromagnetic field with time by using the ungrounded loop. Therefore, in order to obtain the information of underground geologic bodies, a certain collection time is needed. In theory, the longer the acquisition time, the greater the detection depth. However, the water content of mine strata is large, the electromagnetic wave attenuates quickly, and the signal attenuates basically to 0 at the end, and the attenuation curve does not change basically, so the observation quality of the late signal cannot be guaranteed. Therefore, although a large collection time is adopted, the corresponding large depth data has no guiding effect, which requires us to adopt a reasonable collection time length.

3.1.2. Stacking Frequency Effect

Under the same acquisition time, the induced electromotive force attenuation curves of 32 times and 64 times were compared, and the comparison results were shown in Figure 6. As can be seen from the figure, as the number of superposition increases, the late detection signal (red circle position) becomes more stable, that is, when the number of superposition is 64 times, the data quality is better.

Under the same acquisition time, the induced electromotive force attenuation curves of 64 times and 128 times superposition were compared, and the comparison results were shown in Figure 7. As can be seen from the figure, the data quality of 64 times superposition and 128 times superposition is relatively high. Considering the time cost and signal quality, 64 times superposition.

3.1.3. Effect of Acquisition Time

The attenuation curve and detection results are analyzed, respectively.

• (1). Attenuation curve analysis

After the stacking times were fixed at 64 times, the induced electromotive force attenuation curves of the acquisition time 40 ms and 80 ms were compared, and the comparison results were shown in Figure 8. As can be seen from the figure, as the acquisition time increases, the late detection signal (the position of the red solid line in Figure 8b) becomes weaker (approaching 0). The more the attenuation curve is affected by interference in the late stage, the worse the quality of the signal (red solid line position) and the lower the accuracy of the detection result. As can be seen from Figure 8c, the late signal quality does not improve despite the increase in the number of overlays. For the YCS1024 mine transient electromagnetic instrument, when the stacking times are ≥64 times and the acquisition time is 40 ms, the geophysical exploration results are in the best agreement with the field conditions. Therefore, the follow-up study will be mainly carried out with the above parameters.

3.1.4. Analysis of Detection Result

Figure 9 shows the detection results in the 924 m middle section with acquisition time of 40 ms and 80 ms, respectively. As can be seen from Figure 9a, in front of the roadway, in the direction of −45° on the left side to 45° on the right side, and within the detection range of 20–70 m, the apparent resistivity is characterized by low resistance, which is inferred to be caused by water in the rock formation.

In the detection results of 80 ms acquisition time shown in Figure 9b, it can be seen that the characteristics of shallow low resistance and deep high resistance are displayed in the entire detection range. The lack of resistivity details cannot be used as a basis for the inference of water anomalies.

After drilling verification, the error of detection results is large when the acquisition time is 80 ms. Therefore, the collection time of 40 ms was mainly used in the follow-up research.

Better detection results can be obtained by selecting appropriate acquisition parameters in different geological environments. For the YCS1024 mine transient electromagnetic instrument, when the stacking times are over 64 times and the acquisition time is 40 ms, the geophysical exploration results are in the best agreement with the field conditions.

3.2. The 1274 m Middle Section Detection Test

The transient electromagnetic method was used to detect and test the Lower Permian Qixia-Maokou formation in the middle section of 1274 m, as shown in Figure 10.

• (1). Detection results

Figure 11 shows the results of advanced detection of the mine transient electromagnetic method. In the figure, the horizontal coordinate at 0 m corresponds to the position of the roadway head. The positive horizontal axis corresponds to the left side and the negative horizontal axis corresponds to the right side. The vertical axis is the distance in front of the head along the detection direction. The site is affected by the empty chamber on the right side of the head, and the horizontal detection angle is ±45°.

Figure 11a shows the detection results in the direction of the roof elevation angle of 60° in front of the head. As can be seen from the figure, on the slope of the roof elevation of 60° in front of the roadway, in the direction of −15°~0° on the left side, the apparent resistivity of the detection distance is low in the range of 10~40 m, reflecting weak water richness. In the direction of 30°~40° on the right side, the apparent resistivity is low in the range of 20~80 m for the detection distance, which is a weak water-rich reflection.

Figure 11b shows the detection results in the direction of roof elevation angle 30° in front of the head. As can be seen from the figure, on the slope of the roof elevation of 30° in front of the roadway, in the direction of −30° on the left side to 5° on the right side, the apparent resistivity of the detection distance is low in the range of 20~50 m, reflecting weak water richness.

Figure 11c shows the detection results of the alignment direction in front of the head. In the direction of the horizontal strata in front of the roadway, in the direction of −40° on the left side to 10° on the right side, the resistivity of the detection range is low in the range of 20~50 m, reflecting weak water richness.

Figure 11d shows the detection results of direction on the inclined plane with 30° depression angle of the front floor. On the inclined plane with a depression angle of 30° in front of the roadway, in the direction of −20°~0° on the left side, the resistivity of the detection distance is low in the range of 20~40 m, which is a weak water-rich reflection.

Figure 11e shows the detection results of direction on the inclined plane with a depression angle of 60°. On the inclined plane of the floor with a depression angle of 60° in front of the roadway, the resistivity of the detection distance is low in the range of 20~40 m, which is a weak water-rich reflection.

Therefore, the excavation of the tunnel within 50 m may be affected by weak water-rich rock formations.

• (2). Water detection and verification

Water exploration at this location is as follows: (1) The overall 50 m is relatively medium–low resistance, weak water-rich reflection, and no extremely low-resistance abnormal water-rich area is shown. (2) According to the disclosure of water exploration holes in Table 2, the overall water quantity is at a small value. The increase in water gushing in the last 50 m is less than that before 50 m, and the results are consistent with the combination of bedding and depression angle of 30°. (3) According to the initial disclosure of hole No. 1 in the bedding layer, the increase of 6 m–56 m water surge is 1.4 m³/h, the increase of 56 m–98 m water surge is 0.8 m³/h, and the water richness of 60 m–100 m is weaker than before, and the corresponding is more consistent. (4) According to the excavation and disclosure of the site, the test area is partially flooded from 0 to 35 m. Among them, the area of 4 m, 20 m and 33 m is relatively obvious water leaching, and the rock mass of 35 m–100 m is dry and has no water leaching phenomenon (see Figure 12). The results are consistent with those obtained by the transient electromagnetic method.

3.3. The Mine Transient Electromagnetic Method Detection Effectiveness Test and Field Verification

The above research work has shown that the mine transient electromagnetic method can play an important role in the advance water exploration of shaft and roadway development in the Huize lead–zinc mine. Based on the research of detection parameters, it is now applied to the effectiveness test and field detection verification in other locations.

Field Verification of Main Pulse Head Detection in the Middle Section of 924 m

The roof of the main vein head in the 924 m middle section of the Huize lead–zinc mine is seriously flooded. When the mine transient electromagnetic method is used for detection, elevation angle 30°, bedding direction angle 30°and depression angle 30° are selected in the vertical detection direction. The detection scheme is shown in Figure 13, and the field work is shown in Figure 14.

• (1). Detection results

Figure 14 shows the results of advanced detection of the transient electromagnetic method in the 924 m midsection head-on mine. During the detection process, there was water at the bottom of the lane near the palm face, and the roof was obviously flooded, which had a certain influence on the detection.

Figure 14a shows the detection results of the roof elevation angle of 30° in front of the 924 m middle section. On the slope of the roof elevation of 30° in front of the roadway, in the direction of the left side −45° to the right side 45°, in the detection range of 20~80 m, the apparent resistivity is characterized by low resistance.

Figure 14b shows the detection results of the alignment direction in front of the mid-section of 924 m. In front of the roadway, in the direction of the left side −45° to the right side 45°, in the detection range of 20~70 m, the apparent resistivity is characterized by low resistance.

Figure 14c shows the detection results of 30° depression angle of the front floor in the middle section of 924 m. On the inclined plane of the floor with a depression angle of 30° in front of the roadway, in the direction of the left side −90° to the right side 50°, in the detection range of 20–80 m, the apparent resistivity is characterized by low resistance.

• (2). Water detection and verification

In order to clearly reflect the electrical variation characteristics of the 924 m middle section and verify the accuracy of the detection results, the measured resistivity along the bedding direction was distributed on the mining engineering plan based on the detection results of different acquisition times, as shown in Figure 15. As can be seen from the figure, it can be inferred that the low-resistance anomaly in front is caused by strong water-rich rock formations, which will be affected by water-rich rock formations during roadway excavation.

The data of water exploration holes are shown in Table 3. It can be seen from Table 3 that with the increase in drilling depth, the water inflow is increasing, which is consistent with the transient electromagnetic detection results of the mine.

4. Discussion

By analyzing the results of mine transient electromagnetic detection at different locations of the Huize lead–zinc mine, it shows that the location of rich water can be effectively detected by using the mine transient electromagnetic method. Based on the above, this chapter sums up a set of water inflow prediction methods by combining the water inflow situation of water exploration boreholes and the resistivity value of corresponding position.

4.1. Analysis of the Relationship Between Water Inflow and Resistivity

The verification of mine transient electromagnetic detection in different locations of the Huize lead–zinc mine can be divided into two cases: one is to adopt direct excavation and verify according to excavation disclosure. The second is the use of water exploration holes, according to the drilling water surge verification. In order to obtain the corresponding relationship between water inflow and resistivity, the locations with water inflow from drilling holes (924 m middle section, 1274 m middle section, 924 m middle main vein head and 924M-08 line small drilling chamber) were selected for comparative analysis.

According to the recorded water inflow of the borehole, the increase in water inflow in different positions is calculated. Then, the resistivity of the corresponding position is extracted, and the corresponding curve of the resistivity—water surge increase is obtained, as shown in Figure 16. The horizontal coordinate is the different positions of the drilling hole, the left vertical coordinate is the resistivity, and the right vertical coordinate is the increase in water gushing. The red curve is the resistivity change curve, and the blue curve is the change curve of the increase in water gushing. It can be found that the resistivity of rock strata is inversely proportional to the water inflow, that is, when the resistivity is large, the increase in water inflow is small, whereas when the resistivity is small, the increase in water inflow is large.

4.2. Establishment of the Regression Model

Generally, the relationship between variables can be divided into two kinds: a functional relationship and a correlation relationship. In mathematics, most of the variables are functional relationships with explicit mathematical expressions. In natural science, there are a large number of correlation relations, that is, variables cannot maintain a one-to-one correspondence under some functional relationship, but they show a strong law of change. For a certain region, the change in groundwater aquifer characteristics will cause the change in transient electromagnetic response and unit water inflow, and there is a correlation between the two. Using the regression analysis method, the statistical model is established by using the apparent resistivity obtained by transient electromagnetic response and the increase in water gushing obtained by water exploration boreholes in the study area, and the statistical relationship between them is studied.

After measuring a certain position by using transient electromagnetic detection technology of mines, the test of boreholes is carried out. According to the increase in water gushing in different depths of boreholes, the recorded depth is selected as the test depth, and the apparent resistivity of corresponding depth in the transient electromagnetic measurement data of the mine is found.

The apparent resistivity and the increase in water inrush were analyzed by regression. The water inrush q was the dependent variable and the resistivity ρ was the independent variable. The characteristics of the measured data are analyzed, the appropriate regression model is selected, and the regression equation is established. For a given observation $(x_i,y_i),i=1,2,3,\cdots \cdots ,n$, the general formula of the regression equation can be obtained:

$y_i=f(x_i,\theta )+{\epsilon }_i$

where $y_i$ is the dependent variable, that is, the increase in water gushing q, $x_i$ is the independent variable, that is, the apparent resistivity ρ, $\theta$ is the unknown parameter number, ${\epsilon }_i$ is a random error and satisfies the independent co-distribution assumption.

Differentiation can be used when a function is assumed to be continuously differentiable with respect to parameters. Set up equations to make the formula reach the minimum $\widehat{\theta }$.

$Q(\theta )={\displaystyle \sum _{i=1}^n{(y_i-f(x_i,\theta ))}^2}$

Taking the partial derivative of the Q function with respect to the parameter $\theta$ and setting it to 0 yields p + 1 equations. In this case, the least square estimation is the solution of the regression equation, and the regression equation can be obtained eventually.

The resistivity and water gushing increase at different positions in the middle section of 924 m, 1274 m, 924 m and small drilling chamber of line 924M-08 were calculated. Using the regression analysis method, the scatter plot of resistivity and water surge increase was made (Figure 17).

From the scatter plot, we can see that the sample data roughly fall near a parabola, indicating that there is a significant correlation between water inflow and apparent resistivity. But the relationship is not so exact that with a given resistivity there is a unique unit of water inflow corresponding to it. In this way, to solve the regression equations, we can obtain the regression equation between the two variables as follows:

$y=0.00111x^2-0.15127x+5.13496$

The regression curve is shown in Figure 18.

According to the detection results of the mine transient electromagnetic instrument in different locations of the Huize lead–zinc mine, combined with the water inflow of exploration and release boreholes, the research on water inflow prediction method and anomaly evaluation system is carried out. Through the regression analysis of apparent resistivity and water gushing increase, the regression equation of water gushing prediction is obtained, which can be used as the technical basis for advance water exploration in the Huize lead–zinc mine.

4.3. Limitation and Future Prospects

4.3.1. Limitation

In the research of water inflow prediction method, the regression equation of water inflow prediction obtained this time only uses the water inflow data of four water exploration holes, which belongs to small sample regression. Therefore, it is necessary to increase the data samples of mine transient electromagnetic detection and water inflow from exploration holes to calculate more accurate regression equation.

4.3.2. Future Prospects

• (1). The classification of water-bearing anomalies in underground transient electromagnetic surveys is relative, and its classification criteria are mainly based on the difference in resistivity. However, there are many factors that cause changes in resistivity, so the area defined as a water-bearing anomaly is only the area where resistivity changes are reflected. Since geophysical methods have multiple solutions, and underground transient electromagnetic surveys are full-space surveys, it cannot be completely ruled out that the anomaly area may be caused by the survey behind the detection area. Therefore, it is suggested that the mine use underground transient electromagnetic surveying in combination with its own hydrogeological characteristics and laws and other known information.

• (2). Due to the poor mining environment with many interferences, and the fact that geological conditions may change with mining and tunneling activities, it is suggested that the mine should pay attention to the location and water changes in low-resistance anomalies in the tunnel excavation process. If geological conditions such as increased water inflow in the surrounding rock are encountered during construction, supplementary exploration should be carried out in a timely manner to ensure safety. In addition, due to the low-resistance shielding effect of transient electromagnetic in the tunnel, it is suggested that the water-rich bodies in front of the tunnel be first treated with grouting before supplementary exploration is carried out.

• (3). The implications of this study are profound for both industry and academia. For industry, it offers practical solutions to enhance safety, efficiency, and sustainability in mining operations. For academia, it provides opportunities for research advancement, interdisciplinary collaboration, and educational enhancement, contributing to the broader scientific understanding of geophysical exploration and mine water management.

5. Conclusions

• (1). The mine transient electromagnetic method is sensitive to low resistivity anomalies, and it is effective for water exploration. A set of geological advance prediction methods suitable for shaft and roadway excavation in the Huize lead–zinc mining area has been preliminarily explored, and a geophysical anomaly evaluation system has been preliminarily established.

• (2). The overall effect of the mine transient electromagnetic method for advanced water exploration in carbonate rock strata in the mining area is good. However, the observation results have timeliness under specific conditions, and the water-rich situation is not invariable. The moisture content of rich water directly affects the accuracy of detection results.

• (3). A set of advanced water detection technologies for shaft and roadway development in the Huize lead–zinc mine is determined. This can be used to realize the three-dimensional space detection of rich water in front of roadway excavation, and provide the basis for mine production work. At the same time, the application of the mine transient electromagnetic method can reduce the drilling workload, reduce the cost and improve the production efficiency.

• (4). According to the experimental results obtained, it can make the construction of mine water exploration holes more purposeful. In roadway excavation, if the site meets the detection requirements, the abnormal low-resistance area in the test area can be exposed by drilling first. The degree of structural development and the peak value of water gushing in the target area have been mastered. Then, it is determined whether it is necessary to increase borehole exploration in other relatively high-resistance low-risk areas.

Author Contributions

Conceptualization, performing tests, and writing—original manuscript preparation, Z.R. and D.L.; methodology, conceptualization and supervision, S.Y.; performing tests, T.H.; validation and writing—review and editing, H.W., R.X. and L.H. All authors have read and agreed to the published version of the manuscript.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Acknowledgments

The authors express their gratitude to the anonymous reviewers for their detailed comments and suggestions, which have greatly enhanced the quality of this paper.

Conflicts of Interest

Zhouhong Ren, Ticai Hu, Hongliang Wang, and Ronghui Xia were employed by Yunnan Chihong Zn&Ge Co., Ltd. Dajin Liu and Lihui Han were employed by North China Engineering Investigation Institute Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Footnotes

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Figures and Tables

Figure 1. Study area. (a) Location of the Huize lead–zinc mine and (b) landform of the mining area.

Figure 2. Schematic diagram of the principle of transient electromagnetic geophysical survey.

Figure 3. Schematic diagram of the transient electromagnetic measuring line and measuring point layout: (a) bottom plate detection, (b) longitudinal detection, (c) top plate detection, and (d) transmitter coil.

Figure 4. The YCS1024 intrinsic safety transient electromagnetic instrument for mining.

Figure 5. Schematic diagram of TEM advance detection of roadway head.

Figure 6. Attenuation curve of the induced electromotive force with different stacking times. (a) Attenuation curve of the induced electromotive force in bedding direction (stacking 32 times, acquisition time 40 ms). (b) Attenuation curve of the induced electromotive force in bedding direction (stacking 64 times, acquisition time 40 ms). Note: Different color curves represent multiple measurements taken at the same measuring point.

Figure 7. Attenuation curve of the induced electromotive force with different stacking times of data acquisition. (a) Attenuation curve of the induced electromotive force in bedding direction (stacking 64 times, acquisition time 40 ms). (b) Attenuation curve of the induced electromotive force in bedding direction (superposition 128 times, acquisition time 40 ms). Note: Different color curves represent multiple measurements taken at the same measuring point.

Figure 8. Attenuation curve of the induced electromotive force with different stacking times of data acquisition. (a) Attenuation curve of the induced electromotive force in bedding direction (stacking 64 times, acquisition time 40 ms). (b) Attenuation curve of the induced electromotive force in bedding direction (stacking 64 times, acquisition time 80 ms). (c) Attenuation curve of the induced electromotive force in bedding direction (superposition 128 times, acquisition time 80 ms).

Figure 9. Comparison of transient electromagnetic detection results at different acquisition times: (a) 40 ms advance detection apparent resistivity profile along the stratification direction; (b) 80 ms advance detection apparent resistivity profile along the stratification direction.

Figure 10. Field test diagram of geophysical exploration water in the middle section of 1274 m.

Figure 11. Apparent resistivity of the mine in the middle section of 1274. (a) Apparent resistivity profile of 60° elevation advance detection. (b) Apparent resistivity profile of 30° elevation advance detection. (c) Apparent resistivity profile for advance detection along the bedding direction. (d) Apparent resistivity profile for advance detection at 30° depression angle. (e) The 60° dip detection apparent resistivity profile.

Figure 12. Field verification: (a) leakage at 33 m and (b) dry after 35 m.

Figure 13. Design diagram and field working diagram of the 924 m middle section main pulse head-on geophysical exploration.

Figure 14. The apparent resistivity of the advanced detection of the transient electromagnetic method in the 924 m middle-level mine. (a) Elevation 30° advanced detection apparent resistivity profile. (b) Stratification direction advanced detection apparent resistivity profile. (c) The 30° dip detection apparent resistivity profile.

Figure 15. Stack of apparent resistivity in front of the middle section of Huize 924 along the formation section.

Figure 16. The corresponding curve of transient electromagnetic resistivity and water inflow increment at different drilling positions (a) in the 924 m middle section mine, (b) in the 1274 m middle section mine, (c) in the main vein head mine in the middle section of 924 m, and (d) in the small drilling chamber of 924 m-08 line.

Figure 17. Scatter plot of resistivity and water surge increase.

Figure 18. Regression curve of resistivity versus increase in water discharge.

Table 1

The comprehensive geological formation in the mining region of the Huize lead–zinc mine.

Erathem	Series	Epoch	Formation	Symbol	Thickness (m)
Cenozoic	Quaternary	/	/	Q	0~71.75
Pz	Permian	Upper Series	Emeishan Basalt Formation	P2β	600~800
		Lower Series	Qixia-Maokou Formation	P1q + m	450~600
			Liangshan Formation	P1l	21.2~49.5
	Carboniferous	Upper Series	Maping Formation	C3m	22.5~78.2
		Middle Series	Weining Formation	C2w	10~69
		Lower Series	Baizuo Formation	C1b	35~89
			Dating Formation	C1d	27~41
	Devonian	Upper Series	Zaige Formation	D3zg	200~365
		Middle Series	Haikou Formation	D2h	4.6~106.5
	Cambrian	Lower Series	Qiongzhusi Formation	∈1q	0~98.5
Pt	Simian	Upper Series	Dengying Formation	Z2dn	>70
			Doushantuo Formation	Z2d	>100

Table 2

Results of water exploration through water exploration holes.

Horizontal Hole 1(2.4 m3/h)		Left Side Hole 2(2.6 m3/h)		Right Side Hole 3(2.1 m3/h)
Depth (m)	Water inflow (m3/h)	Depth (m)	Water inflow (m3/h)	Depth (m)	Water inflow (m3/h)
0–6	0.2	0–22	0	0–16	0.2
6–56	1.4	22–68	0.3	16–19	0.2
		68–71	0.2	19–70	1.1
56–98	0.8	71–90	0.5	70–85	0.2
		90–110	1.6	85–117	0.4

Table 3

Results of water exploration through water exploration holes.

Bedding Water Exploration Boreholes
Depth (m)	Water Inflow (m3/h)	Depth (m)	Water Inflow (m3/h)	Depth (m)	Water Inflow (m3/h)
1–17	1.12	26–27	27.8	38–39	41.2
18	18.5	27–28	28.9	40–41	42.7
19–20	19.7	28–29	29.7	41–42	44.5
20–21	21.3	29–30	30.5	44–45	45.52
21–22	22.6	30–31	31.8	45–46	45.67
22–23	23.4	31–32	35.6	46–47	46.23
23–24	24.15	32–33	35.6	47–48	46.24
24–25	25.6	34–35	36.1	48–49	46.35
25–26	26.4	36–37	38.9	49–50	46.5

Note: The design hole depth is 120 m, and the detection point is located at the 18 m position of the drilling hole. When the drilling construction reaches the 51 m position, the construction will be suspended due to the large water inflow in the whole hole.

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