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Improving the safety of personnel and boosting productivity are fundamental drivers for the coal mining industry. Automated mining is seen as providing the ultimate outcome, with reliable sensing technology being a key enabler to this strategy. However present automation capability is being limited by a lack of sensing instrumentation that can reliably measure coal-strata geological structure. A related...
The health status of a railway tunnel should be regularly inspected during its service period for safe operation. The frequency of periodic inspection should be increased when the tunnel has become aged. For the coverage tunnels, health assessment is more essential. Ground penetrating radar (GPR) has been used as a key tunnel health detecting technique; however, so far, such (GPR) techniques are in...
The finite-difference method (FDM) algorithm with staggered grid greatly improved the computational efficiency of solving differential equations in two dimensional simulation of GPR, but the strict Courant-Friedrich-Levy (CFL) condition must be satisfied. In three dimensional simulation of GPR, a maximum time-step size will lead to a serious numerical dispersion, while a minimum time-step size will...
Full-waveform inversion of GPR data has shown a high potential in many applications to obtain accurate and quantitative high resolution images of the subsurface. We implemented a new full-waveform inversion that combines an accurate 3D forward modeling approach with a shuffled complex evolution method that incorporates the complicated wave interactions and interferences that cannot be resolved by...
Provided that the frequency of the GPR antenna is properly selected, detecting rock fractures is generally an achievable task because most of the investigated rocks are resistive. On the other hand, fractures can be generally envisaged as thin-beds embedded in a homogenous rock formation, thus yielding a complex reflection pattern caused by the reverberation of the GPR signal back and forth within...
This paper presents a crosshole radar system and its model experiment for underground structure's defect detection. The system was built using a vector network analyzer (VNA), cylinder dipole antennas, and a radio frequency (RF) amplifier. The VNA enables the radar to work in a stepped frequency mode. The antenna, which has a carefully designed diameter of 32 mm, is compatible with most boreholes...
In this paper, according to the two design principles of uniform distribution and less element shadowing for effective aperture, a novel two-dimensional (2-D) sparse ultra-wideband (UWB) multiple-input-multiple-output (MIMO) antenna array topology is proposed for near-field high-resolution imaging. Compared with another different array having the same number of transceivers, the proposed optimal array...
Application of the finite-difference reverse time migration (FD-RTM) to ground penetrating radar (GPR) data may generate high-resolution imaging for complex geologic bodies. However, in conditions of complex topography, due to topographic roughness it is very difficult to get clear images of near-surface internal structure with the traditional approach of “static correction + flat datum migration”...
Polarization is a property of electromagnetic waves, and polarimetric GPR can obtain the co-polarization and cross-polarization information coinstantaneously. In this paper, we use a polarimetric migration imaging method to research LNAPLs contamination in soil. The polarimetric migration algorithm is a merging of the Pauli polarimetric decomposition technique with the Kirchhoff migration equation,...
The microwave interferometer used in the present study is capable of multiple-point displacement measurements for bridge health monitoring. In this paper, two highway bridges were monitored once a year for a period of five to six years. The first case is an extradosed bridge with prestressed concrete (PC) multicell box girders. The second case contains prestressed concrete box girder with tapered...
The detection of subsurface cracks and moisture in blast-holes is an important problem to be solved in open-cut coal mining. During the overburden removal process at open-cut coal mines, blast-holes are drilled and filled with ANFO explosive. Any explosive that extends into surrounding cracks within the blast-hole has the potential to remain unexploded during the detonation process, which results...
A high-efficiency scheme based on both time division multiplexing (TDM) and parallel processing of FPGA is proposed in this paper to address the problem of high scanning rate in high-speed measurements with UWB array GPR. The merit of this new scheme is that all trigger signals of all the channels can be delayed in a controllable step through the same delay chip at different times. Each channel of...
The interpretion of GPR data is usually limited by the attenuated signal and noise interference. The signal-to-noise ratio (SNR) of the received GPR data is influenced by the characteristics of GPR systems, the target signatures, the properties of the medium, and by incoherent random noise. The original attributes of the data will be distorted by noise. Usually, noise removal is conducted by employing...
This paper focuses on the affection of the curved surface media. In order to study it, the continuous wave penetrating radar (CWPR) is applied to detect targets buried in the spherical media. The antennae move in a plane above the spherical surface and execute two dimensions sampling. Different from planar media, this special geometry makes the echoes of the surface interfere, and several circular...
The NeTTUN (New Technologies for Tunnelling and Underground Works) Project involves a consortium of 23 industrial, research & development laboratories and small and medium enterprise organizations across 9 countries in Europe; the ultimate goal is to enable groundbreaking change in the construction and maintenance of tunnels. Most existing ground prediction methods require the stopping of excavation...
In order to evaluate our developing 3D directional borehole radar system, ReflexTracker®, we carried out experimental studies on its capability to detect foundation piles in poor subsoil in the Tokyo area, and cavities beside a housing complex in Aichi Prefecture, central Japan. To evaluate foundation pile detectability, we took omnidirectional and directional borehole radar measurements in two boreholes...
Ultra-wideband (UWB) pulse generators based on an avalanche transistor are widely used in time domain ground penetrating radar(GPR). For shallow subsurface detection, it is essential to increase the pulse amplitude while maintaining the pulse width in order to improve the spatial resolution of GPR. Eliminating pulse trailing is also necessary to improve GPR performance. In this paper, a simple nanosecond...
Ground Penetrating Radar (GPR) has proved to provide a high reliability in detecting several subsurface features such as water and gas pipes, energy and telecommunication supplies, water reservoirs or air voids. The present work uses a comparison between different central frequencies of investigation to reconstruct the network of utilities located underneath a paved surface and to understand the best...
In this paper, we deal with the problem of the size of the investigation domain in a 2D linear inversion algorithm applied to GPR data. Linear inverse scattering approaches involve the problem of the computational burden associated with the inversion of a matrix when regularization schemes are adopted. In real GPR applications, the domain of interest is significantly large in terms of probing wavelength...
This study is devoted to the electromagnetic (EM) characterization of concrete mixes within the ground penetrating radar frequency band. Defining two specific experimental designs, water and chloride contents are studied in order to establish their relative sensitivity compared to the other parameters describing the mixes. The evaluation of the complex dielectric properties is carried out in laboratory...
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