High-density Electrical Method Research Articles

Evaluation of water richness in coal seam roof aquifer based on factor optimization and random forest method.

Water richness evaluation of coal seam roofs is a crucial prerequisite for preventing and controlling water hazards in coal seam roofs. For this purpose, Spearman correlation and GeoDetector were employed for factor optimization to investigate the significance of lithological and structural factors and the impact of interactions among different factors on the water richness of coal seam roofs. Water richness evaluation models of coal seam roofs were separately established via the entropy weight method (EWM), coefficient of variation method (CVM), and random forest method (RFM), and the predictive accuracies of these models were compared. Eleven lithological and structural factors were collected. Through Spearman correlation analysis, 6 factors were identified to have significant influences on water richness. By utilizing the interaction detection of GeoDetector, the effects of interfactor interactions on water richness were explored, and 3 combination factors were selected. AICc was used to determine the model's superiority. The evaluation results of the study area based on factor optimization and three methods were further compared and validated via pumping tests, workface water inflow tests, and three-dimensional high-density electrical method. The results indicated that the RFM exhibited higher prediction accuracy than did the entropy weight and coefficient of variation methods. Additionally, within each method, factor optimization led to improved model accuracy.

Monitoring and Evaluation of Debris Flow Disaster in the Loess Plateau Area of China: A Case Study

The Loess Plateau area, with complex geomorphological features and geological structure, is highly prone to geologic disasters such as landslides and debris flow, which cause great losses. To investigate the initiation mechanism of landslide and debris flow disasters and their spreading patterns, historical satellite images in the Laolang gully were collected and digitized to generate three-dimensional topographic and geomorphological maps. Typical landslides were selected for landslide thickness measurement using a standard penetrometer and high-density electrical method. Numerical models were established to simulate the occurrence and development of landslides under different working conditions and to evaluate the spreading range based on the propagation algorithm and friction law. The results show that the 10 m resolution DEM data are well matched with the potential hazard events observed in the field site. The smaller the critical slope threshold, the greater the extent and distance of landslide spreading. The larger the angle of arrival, the greater the energy loss, and therefore the smaller the landslide movement distance. The results can provide scientific theoretical guidance for the prevention and control of rainfall-induced landslide and debris flow disasters in the Loess Plateau area.

Study on the Distribution Law of External Water Pressure with Limited Discharge during Shield Construction of Soft Rock Tunnel in Western Henan Province

When shield tunneling is carried out in poor geological areas with high water head and low strength, there is a great construction risk, and the external water pressure is one of the key factors affecting the stability and safety of the tunnel during shield tunneling. Taking the Yinguruxin tunnel of Xin’an County as the engineering background, the geological conditions and water-bearing characteristics of the water-rich area in the tunnel excavation path are analyzed by means of drilling and high-density electrical method, and the pumping test is used to evaluate the groundwater linkage in the water-rich area. The 2022 version of Midas GTS NX is used to study the distribution characteristics of external water pressure during tunnel excavation in fault zones, and the influence of different drainage rates on the external water pressure of the tunnel is analyzed. The results show that the rock mass in the unfavorable geological section of the tunnel excavation is broken and rich in water, but the complexity of the stratum leads to uneven water richness in the axis direction of the tunnel. The drainage rate is the key to affecting the external water pressure of the lining. The drainage rate is the key to affecting the external water pressure of the tunnel. The correct drainage rate is an effective measure to reduce the external water pressure of the tunnel. The internal and external water pressure of the tunnel decreases with the increase of the drainage rate. When the drainage rate reaches 66.67% of the water inflow, the external water pressure of the tunnel can be reduced to 0.3 MPa to ensure the safety of the earth pressure balance shield machine in the tunneling process. The conclusion provides a useful reference for the high water pressure control of the tunnel shield tunneling process.

Diagnosis and Monitoring of Tunnel Lining Defects by Using Comprehensive Geophysical Prospecting and Fiber Bragg Grating Strain Sensor.

Tunnel excavation induces the stress redistribution of surrounding rock. In this excavation process, the elastic strain in the rock is quickly released. When the maximum stress on the tunnel lining exceeds the concrete's load-bearing capacity, it causes cracking of the lining. Comprehensive geophysical exploration methods, including seismic computerized tomography, the high-density electrical method, and the ultrasonic single-plane test, indicated the presence of incomplete distribution of broken rock along the tunnel axis. Based on the geophysical exploration results, a carbon-fiber-strengthened tunnel simulation model was established to analyze the mechanical characteristics of the structure and provide a theoretical basis for sensor deployment. Fiber Bragg grating (FBG) strain sensors were used to measure the stress and strain changes in the second lining concrete after carbon reinforcement. Meanwhile, one temperature sensor was installed in each section to enable temperature compensation. The monitoring results demonstrated that the stress-strain of the second lining fluctuated within a small range, and the lining did not show any crack expansion behavior, which indicated that carbon-fiber-reinforced polymer (CFRP) played an effective role in controlling the structural deformation. Therefore, the combined detection of physical exploration and FBG sensors for the structure provided an effective monitoring method for evaluating tunnel stability.

Exploration and prediction of high pressure dynamic water hidden collapse column in coal mines

Hidden collapse column associated with high pressure dynamic water is a main cause of major water inrush accidents in North China type coal fields. Taking the structural abnormality area discovered in 11603 working face of Daizhuang Coal Mine as an example, underground three-dimensional high-density electrical method, advanced exploration of underground drilling and curtain grouting were used to detect the existence of collapse column, and analyzed the water conductivity of collapse columns based on the hydraulic connection analysis of the 13th limestone and Ordovician limestone aquifers. Finally, it is determined that this abnormal area is a strong water filling collapse column originating from the upper Ordovician strata runoff zone (inferred to be within a range of 30 to 100 m below the Ordovician limestone top interface), developed to a height of 12th limestone. Based on the fact that the water yield and water pressure of underground directional drilling, the grouting pressure of curtain grouting, and the amount of cement injected are external quantitative factors that reflect the existence of hidden karst collapse columns during the process of detecting hidden karst collapse columns, and in combination with the feature that deep learning can fully independently learn abstract knowledge expression, a prediction model based on convolutional neural networks is constructed. According to the established network model, it was found that among the 12 sets of actual measurement data, only one data point indicated the absence of a collapse column. The prediction accuracy reached 91.6%, which meets the practical needs.

The Application of Three-Dimensional High-Density Electrical Method in Detecting Vertical HDPE Membranes at Landfill Sites

Landfilling is one of the important methods in hazardous waste treatment. In order to prevent the landfill leachate from connecting with external groundwater and prevent leachate from flowing into external polluted water bodies and soil, vertical anti-seepage membranes will be installed along the perimeter of the reservoir area. Given the structural characteristics of vertical HDPE membranes and site conditions, this study proposes the application of three-dimensional high-density electrical resistivity (3D-HDER) tomography for the detection of these membranes. Compared with the traditional resistivity method, the high-density resistivity method can realize automatic switching of electrode device type, electrode spacing and measuring points during the measurement process, thereby improving detection accuracy and work efficiency. By employing 3D-HDER for data collection on vertical HDPE membranes and inverting the subsurface resistivity distribution, the presence of leaks can be inferred based on the distribution of low-resistivity anomalies in the target underground area, thereby facilitating the integrity assessment of the vertical HDPE membranes. This research was applied in a practical investigation at a municipal landfill site in Hunan Province, where field tests were conducted, and the effectiveness of 3D-HDER in detecting vertical HDPE membranes was validated through excavation. The experimental results indicate that: (1) 3DHDER is capable of effectively and accurately locating shallow leaks, and (2) low resistivity anomalies were observed in the vicinity of the leaks.

Comparison between Common Devices and Fusion Devices of High-Density Electrical Method—Taking the Investigation of Surface Matrix of Black Soil in Lishu Area as an Example

Comparison between Common Devices and Fusion Devices of High-Density Electrical Method—Taking the Investigation of Surface Matrix of Black Soil in Lishu Area as an Example

Research and Application of 3D High Density Electrical Method

3D high-density electrical method is a kind of artificial underground stable flow field established by setting electrodes on the ground, which is used to analyze the underground distribution of geological bodies, so as to predict or solve the problems in the planning, design and construction of projects. However, 3D high-density electrical method still has its limitations. In order to study the resolution ability of 3D high-density electrical method in actual underground cavity investigation, a comparative test of two-pole device and dipole device was established in this paper. The results show that the two-pole device can detect large depth but low resolution, while the dipole device is more affected by depth and has better effect in the measurement of low resistance abnormal body.

Research on Numerical Simulation of High-Density Electrical Method Based on Multi-Layer Coal Seam Goaf Area

Research on Numerical Simulation of High-Density Electrical Method Based on Multi-Layer Coal Seam Goaf Area

Epikarst water detection using integrated geophysical methods

When detecting epikarst water using the self-potential method, the actual location of the anomaly center often deviates from the prospecting result due to the interference of the regional background field, which is comprised of geological noise and artificial electromagnetic fields. Ultimately, this makes it difficult to locate the detection target accurately. To address the potential offset of the anomaly center location, in this study we introduce the differential filtering method into the data processing procedure. This method has smoothing and low-pass filtering effects, facilitating the extraction of meaningful anomalies. Meanwhile, based on the anomalous features of different physical parameters, we propose an integrated method system based on differentially filtered horizontal self-potential gradient data, the composite profile method, and the high-density electrical method, which can effectively improve the accuracy of anomaly localization. This newly established method system was applied at the Xiaguantun test site in Longzhou County, Chongzuo, Guangxi Province, China, and its effectiveness and feasibility was confirmed.

Water Distribution Characteristics of Slopes Based on the High-Density Electrical Method

Measuring the water content of slopes is essential because the distribution and migration of water within slopes are important factors of landslide instability. In this study, the relationship between the resistivity, volumetric temperature water content and temperature of landslide soil was modelled. The model was validated by indoor landslide model tests and field tests in Baijiabao to investigate the effect of reservoir water levels on the water content of landslide slopes. Test results showed that, as the reservoir levels rose, the water content of the landslide soil increased. Moreover, a good correspondence between the measured results and the inversion results based on the resistivity data was obtained by using the high-density electrical method in combination with the developed model of the relationship between resistivity, volumetric water content and temperature, indicating that the proposed method is reliable and practicable in hydrodynamic landslide monitoring.

Quantification of solute transport in a fracture-matrix system using geoelectrical monitoring

Solute transport in fracture is easy to diffuse into the matrix due to the permeability of the matrix. The quantification of solute concentration is particularly important during diffusion and is a challenge for the management of pollutants in a fracture-matrix system. In this paper, sodium chloride as solute, the geoelectrical technology was combined with high density electrical method and conductivity acquisition method to conduct a series of sandbox experiments. In the center of the sandbox is a fracture, and on both sides of the fracture is the matrix. The fracture and matrix in the sandbox form a fracture-matrix system. Loading-flushing process of sodium chloride solution in fracture-matrix system was monitored in real-time and non-destructive. The effect of matrix porosity and flow velocity on solute transport in fracture-matrix system was investigated. The results showed that: 1) Mass transfer rate coefficient (α) and fracture/matrix porosity ratio (β), and tailing exponent of residence time distribution (ω) were quantified by pairing bulk electrical conductivity (BEC) and fluid electrical conductivity (FEC), without the requirement of inverse model calibration. In contrast, the single electrical method still lacks resolution or is not representative in determining solute transport parameters in fracture-matrix system. 2) The matrix porosity had a significant effect on solute transport in fracture-matrix system. With the increase of porosity, the mass transfer rate coefficient (α) increased and the residence time in the matrix decreased. 3) An increase of flow velocity led to a decrease of residence time in the matrix and an increase in mass transfer rate coefficient (α). The solute transport in fracture-matrix system can be quantified by electrical conductivity hysteresis. The results can provide a basis for the management of solute transport in fracture-matrix system

Bi-LSTM-GPR algorithms based on a high-density electrical method for inversing the moisture content of landslide

Bi-LSTM-GPR algorithms based on a high-density electrical method for inversing the moisture content of landslide

Water Inrush Mechanism of Roof Induced by the Fault Weakening Effect in the Coal Mining

The northern Guizhou coalfield exhibits complex geological conditions and well-developed structures. Hard rock formations are damaged by faults, causing frequent water inrush accidents. To study the damaging effect of faults on roof key strata and the mechanism of water inrush accidents, this paper chose the 5914 coal mining faces of the Longfeng coal mine as the engineering background, determined the water inrush source and key strata through field investigation, hydrochemical analysis, and theoretical calculation, and used RFPA-flow numerical simulation software to simulate the hydraulic coupling effect. The characteristics of the shear stress, damage degree, and hydraulic gradient were analyzed, and finally, the high-density electrical method was employed for simulation verification. The results indicated that the key stratum can control water inrush, but under the influence of faults, the roof forms multiple separation layers, and several sudden increases in displacement occur (the sudden jump phenomenon). A stress concentration area is formed in the head-end tunnel through the fault, and the number of AE events increased to 1150. The water-force gradient exhibits a uniform local large-scale evolution process, and finally, the height of the water-conducting fracture reaches 60 m through the aquifer. This height is 3 times that without fault influence. The numerical simulation results are consistent with the theoretical calculation and field analysis results, which verifies that the fault imposes a highly significant weakening effect on the key stratum, providing data support for later engineering.

Review and Challenges in the Geophysical Mapping of Coal Mine Water Structure

Generally, the water-bearing structures of coal mines mainly include coal seam, roof, coal seam, floor, and goaf, while the main water-conducting structures include faults, collapsed columns, and collapsed goaf areas. The most commonly used methods for the detection of the above structures include the seismic method, high-density electrical method, controlled source audio-frequency magnetotelluric method, and transient electromagnetic method. Theoretically, the seismic methods have a higher resolution, which can be used to determine the targets’ geometry, but unable to determine whether the target is filled with water, while the electromagnetic methods are capable of this, although with lower resolution. Therefore, it is necessary to adopt the comprehensive geophysical prospecting in the actual field measurement of the coal mine water to guarantee the detection accuracy. Based on this, in the passage, first, we introduced the characteristics of the water-bearing and water-conducting structures and then analyzed the detection results of different methods by examples. Finally, we pointed out that, first, it is essential to develop the mine or airborne methods for the sake of convenience; and second, it is time that we adopt three-dimensional detection technology, multisource and multiresolution detection technology, and electromagnetic big data technology for high accuracy.

Application and Development of High Density Electrical Method in Engineering Investigation

Application and Development of High Density Electrical Method in Engineering Investigation

Application Analysis of Various Geophysical Methods in Volume Calculation of Different Landfills

Garbage disposal has gradually become a key issue faced by environmental governance. What must be controlled in garbage disposal is the calculation of garbage volume. In this paper, according to the different landfill conditions of a landfill in Anhui, including: covering soil, overlying HDPE membrane, overlying concrete, etc., combined with the physical differences between the rock mass and the garbage at the bottom of the landfill. The landfill covered with HDPE membrane adopts the transient electromagnetic method, the landfill covered with soil layer adopts the high-density electrical method, and the landfill covered with concrete adopts the combination of transient electromagnetic method and ground penetrating radar. At the same time, Combines the borehole data to determine that the resistivity value of the interface between the garbage and the soil was 29 Ω⋅m. Finally, the sections of multiple survey lines can accomplish three-dimensional stereoscopic that calculate the distribution and actual volume of the garbage. This method is used to determine the final investment cost.

Reinforcement of silty soil with permeable polyurethane by penetration injection

Injection of silts is commonly used to improve unfavorable engineering properties. Though the effects of traditional grouting materials on soil improvement have been investigated in recent years, documented research studies on the macro-, micro-level characteristics and engineering application of problematic silt solidified by polyurethane are fairly limited. This study examined the characteristics and application of silt with permeable polyurethane. Micro-level physico-chemical bonding mechanisms were studied. Unconfined compressive strength (UCS) and anti-permeability tests were performed. The UCS increased from 0.2 to 1.2 MPa; their permeability was smaller compared to the untreated soils. Microstructural changes in the soil fabric showed that polyurethane modified the consolidated silt’s porous network. Drilling process monitoring and the high-density electrical method were used for evaluation. The soil resistivity increased from 120 to 300 Ω·m; drilling speed decreased by over 29%. Thus, permeable polyurethane improves an embankment’s compaction degree and mechanical properties.

Research on intelligent monitoring technology of grouting based on dielectric characteristics

The electromagnetic characteristics of the grouting material can be changed to achieve the electrical difference with the surrounding rock, so as to meet the needs of grouting monitoring. The combination of this principle and the high-density resistivity method can be used to detect whether or not the grout is in the diffusion of an underground space, yet still cannot meet the expected grouting monitoring effect. To monitor the grouting process and detect the grouting effect more clearly, in the present study a theoretical method is proposed, and a high-precision distributed monitoring system based on high-density electrical method technology is independently developed to dynamically monitor the grouting process of non-dispersed materials. The system possesses a stronger ability to identify the resistivity difference of underground materials, and can be used to monitor the entire grouting process through networking technology. The system uploads the collected data to the server in real time through the Internet of Things module, then continuously inverts the uploaded data to obtain the real-time apparent resistivity section diagram. Next, through observation and analysis of the apparent resistivity section diagram and data, it detects the mud diffusion in the underground space. Through the analysis in this study, it is proven that the system can be used for grouting monitoring and that it meets the expected performance requirements.

Application of Comprehensive Geophysical Prospecting Method in Water Accumulation Exploration of Multilayer Goaf in Integrated Mine

A coal mine in Datong is an integrated mine. At present, there is goaf in the upper and lower part of the mining coal seam. There is a lot of ponding in the goaf, which has great potential safety hazards for production. In order to find out the scope and location of ponding in goaf, the comprehensive geophysical exploration method combining transient electromagnetic method and high-density resistivity method is used to carry out the research. Firstly, the time-base, turn-off time, receiving delay, current, superposition times, and other parameters of the instrument are tested on the surface of known goaf to obtain the best instrument parameters, and the parameters are used to verify the feasibility of the research scheme; then, the transient electromagnetic method is used for large-area exploration on the surface of the mine, the suspected goaf ponding area is found through comprehensive analysis, and the high-density resistivity exploration is arranged in the suspected goaf ponding area. According to the obtained results, the scope and location of the goaf ponding area are accurately located through comprehensive analysis. The results show that there are two goaf ponding areas in the exploration area, which are located above the 8# coal seam currently mined; the range and location of goaf ponding area can be accurately obtained by using the comprehensive geophysical method of high-density electrical method and transient electromagnetic method. This method can provide reference for mine water prevention and control in Datong area and has great practical significance to ensure coal mine safety production.