High-density Electrical Method Research Articles

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.

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.

Internet-of-things-based four-dimensional high-density electrical instrument for geophysical prospecting

Abstract. The high-density electrical method is a primary method used in shallow geophysical prospecting. Due to the rapid industrial development that has taken place in recent years, the function and performance of high-density electrical instruments have been considerably improved in several aspects. However, most of the electrical instruments currently available on the market still exhibit some shortcomings, such as being bulky, heavy, limited in their data acquisition accuracy, and difficult to connect to the Internet for remote monitoring. To address these problems, this study developed a new multifunctional four-dimensional (4D) high-density electrical instrument based on remote wireless communication technology. The system is small and lightweight, includes an integrated transceiver, has high data acquisition accuracy, and is capable of remote wireless real-time control. In this study, the hardware circuit was designed. The Arm all-in-one (AIO) LJD-eWinV5-ST7 with a 154.4 cm × 87 cm, 800 × 480 high-brightness wide-temperature-range display is used as the host computer, which has the advantages of small size, low power consumption, and abundant hardware resources. Internet of things (IoT) technology is incorporated in the system, and a 4G module is employed to provide a real-time remote control and data acquisition monitoring system based on the cloud platform. Tests showed that this instrument is stable and convenient to use and can meet the requirements for use in field prospecting.

Analysis of shallow landslide mechanism of expansive soil slope under rainfall: a case study

An expansive soil slope of a high-speed railway under construction in Yunnan suffered a local collapse after a heavy rainfall. The expansive soil on this slope surface is prone to slip and collapse under the action of rainfall. The analysis of water sensitivity reveals the attenuation law of the shear strength of the expansive soil. With the increase in the water content, the shear strength of the expansive soil decreases significantly. Wet–dry cycles also significantly lower the shear strength of the expansive soil. In addition, a high-density electrical method test is performed on the expansive soil slope to determine the structural characteristics of the internal soil. The test results indicate that the internal soil of the slope exhibits poor mechanical properties and contains fissures and cracks, which are also the factors that caused the landslide. The finite element software, ABAQUS, is used to analyze the impact of rainfall on the expansive soil slope. The results reveal that the soil at a depth of approximately 2 m below the surface reaches complete saturation after 24 h of rainfall, and the plastic failure zone is mainly distributed on the surface and toe of the slope. Based on the electrical test results, the slope soil material is classified into saturated, fissured, and non-fissured soil zones. The stability analysis results reveal that the sliding surface is circular and in the shallow layer of the slope, and the sliding depth is 2–3 m. Although the depth of the landslide mass is not large, almost the entire slope surface soil undergoes plastic failure, resulting in a large area of ​slippage.

A Comparative Study on the Exploration Depth and Resolution of Winner and Schlenberg Methods Based on Potential, Current and Field Fields

High-density electrical method is widely used in hydrology, engineering, environment, and other fields. It is of great practical significance to study its exploration depth and resolution. The traditional theoretical research is to analyze and explore the exploration depth and resolution through the current density. Based on the theory of field theory, this paper proposes to study the depth and resolution of high-density electrical exploration based on a stable DC electric field. First, the derivation of the three field quantities of potential, current, and field lines in the normal field was completed, and related numerical simulation calculations were realized. Through theoretical model calculation and analysis, qualitative comparison conclusions of the two methods of Winner and Schlumberger are obtained. It is believed that the detection depth and resolution of the Winner method are lower than those of the Schlumberger, but the observation accuracy of the Winner method is higher than the Schlumberger method. Furthermore, the reliability of this conclusion is verified by physical model experiments. At the same time, the feasibility of the research on exploration depth and resolution based on the three electric field components of potential, current, and field lines is also proved.

A new landslide classification method based on electrical differences and relevant examples

A new landslide classification method based on electrical differences is proposed in this paper. The electrical parameters are obtained by the high-density electrical method, which is commonly used in landslide exploration. In this paper, landslides are divided into four categories based on the electrical difference between overburden and bedrock, and on this basis, the landslides are further divided into four categories according to the local electrical difference of landslides, totally eight kinds of landslides. The high-density resistivity method works well for exploration of both type I and type II slides. However, for type III and type IV, other geophysical methods should be supplemented. For type V-VIII landslides, they are simplified into type I-IV landslides in sections according to their electrical characteristics. As for complex landslides caused by multiple factors, more survey lines need to be laid systematically, combined with various methods, as well as information of drilling and trenching for comprehensive prospecting. The landslide classification method proposed in this paper provides some basis and reference for landslide exploration.