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Tunnel seismic prediction is widely used in the field of tunnel seismic advance detection. The illumination of the target and the signal‐to‐noise ratio of the data are two key factors affecting the precision of data interpretation. Current seismic prospecting has shortcomings on sites: (1) The lighting shots are solely towards one side of the tunnel wall, (2) the geophones are placed far away from the tunnel face and (3) the surface waves from the tunnel wall dominate over the reflection waves, lowering the signal‐to‐noise ratio of the data at the tunnel wall. This paper proposes a tunnel symmetrical geometry to tackle the above challenges. The arrangement is to place 12 sources uniformly on each side of the tunnel wall and six geophones on the tunnel wall and face. Results of simulated data and measured data show that the proposed method enables (1) broad illumination of the target body, (2) the enhancement of illumination energy of the target body, and (3) higher data signal‐to‐noise ratio. The proposed symmetrical geometry method provides better interpretation in terms of broader coverage, higher quality and greater distance of investigation. [ABSTRACT FROM AUTHOR]

Transient electromagnetic (TEM) soundings are being increasingly used in engineering applications of environmental and regional surveys and shallow metal detection. Efficient and real time of the processing of the observed TEM data is the trend for the engineering geophysical prospecting and detection instrument in modern times. This letter presents a fast resistivity imaging method of TEM using artificial neural networks. The input–output mapping relations of neural networks are established based on the TEM response characteristics under different transmitter loop devices. The built network could map the recorded TEM data and quickly obtain the resistivity image. The proposed method offers accuracy and fast computation for resistivity imaging, and only 9.003 s costs for the calculation of 142 measured points’ data. Feasibility and technical attractiveness of the proposed method in fast resistivity imaging of TEM mean that it is well suited for instantaneous of survey results to a client. The proposed TEM imaging method can be used in real time so that the recorded TEM data can be calculated without retraining, which avoids time-consuming iteration and inversion computation. [ABSTRACT FROM AUTHOR]

A wavelet edge detection method is introduced to image the topology of grounding grids and locate the grounding conductors from measured magnetic induction. Theoretical analysis of the magnetic field and calculation method of discrete wavelet transform are described. Since the sharpest variation of the magnetic field perpendicular to the ground surface occurs right above a conductor, the gradient vector modulus maximum of the vertical component can be calculated to extract the position information about the conductor. This scheme is derived from the Canny edge detection. A 2-D discrete à trous algorithm is used to perform equivalent edge detection as the wavelet transform avoids partial derivative. The method is robust to noise and would extract more stable and distinct edge. Extensive simulation and experimental examples demonstrate that the proposed method can accurately draw the topology of grounding grids and locate the conductors. [ABSTRACT FROM AUTHOR]

Faults in the grounding grid are a hidden danger to the safety of power systems and cause significant economic loss every year. This paper presents a new means to locate faults in grounding grids using the transient electromagnetic imaging method. The method compares the distribution characteristics of the equivalent resistivity of the underground covered by grids for the no-fault case and those with break points. We describe why and how the proposed method can be used for the break-point diagnosis of grounding grids. Simulation was performed using the Ansoft finite-element method package, and a field experiment was conducted to verify the effectiveness of the proposed method. This study provides a practical means for break-point diagnosis with no requirement of power shut down or soil excavation. Moreover, the proposed method does not require the design drawings of grounding grids. [ABSTRACT FROM PUBLISHER]