scholarly journals Study on observation system of seismic forward prospecting in tunnel: A case on tailrace tunnel of Wudongde hydropower station

2022 ◽  
Vol 14 (1) ◽  
pp. 1-12
Author(s):  
Senlin Yang ◽  
Hongyi Cao ◽  
Yi Zhang ◽  
Lei Chen ◽  
Xinji Xu ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Space Environment ◽  
Hydropower Station ◽  
Observation System ◽  
Tunnel Face ◽  
Field Environment ◽  
Single Side ◽  
Imaging Results ◽  
Seismic Detection ◽  
Tailrace Tunnel

Abstract Seismic method is a major approach for detecting the seismic geological features ahead of the tunnel, understanding the distribution of unfavorable geology, and ensuring the safety of tunnel construction. Observation system is the key for seismic detection, many studies have been conducted to optimize the observation system; however, most of them focused on the surface seismic investigation and numerical simulation rather than in tunnel field environment (limited aperture and full space environment). How to obtain better wavefield information with limited observation aperture is a great challenge. In this study numerical simulation and instrumental techniques (GPR, DC, etc.) were implemented to further check the result of seismic detection at the 1# tailrace tunnel at the Wudongde hydropower station. In the field case, observation detectors were arranged spatially in the tunnel and source points were placed in four ways: linearly along a single side, on the tunnel face, in front of the detectors, and behind the detectors. Then, after data acquisition, the data processing is conducted to carry out the migration results. The imaging results indicate that the observation system with sources and detectors in liner arrangement (with equal interval) helps to suppress artifacts, further supporting the advantages of spatial observation system with liner observation line (detectors). Moreover, the study provides suggestions for geological prospecting in similar tunnel projects.

Experiment of 3D Seismic Reflection Technique for Forward Probing on TBM Tunnel Face

2019 ◽  
Vol 24 (4) ◽  
pp. 609-619
Author(s):  
Ao Song ◽  
Bin Song ◽  
Rongyi Qian
Keyword(s):  
High Resolution ◽  
Tunnel Boring Machine ◽  
Detection Accuracy ◽  
3D Seismic ◽  
Engineering Project ◽  
Tunnel Wall ◽  
Tunnel Face ◽  
Detection Depth ◽  
Imaging Results ◽  
Geological Conditions

Geophysical technologies are used to mitigate geological hazard caused by adverse geological conditions in front of a tunnel face. The prevailing method for forward probing for tunnels constructed by a tunnel boring machine (TBM) for advance prediction is based on seismic detection. Conventional tunnel seismic prediction technology uses P- and S-waves with sources fired on the tunnel wall or face and layout receivers on the tunnel wall to acquire the reflected waves. However, the results show that most of these methods have different deficiencies that are in either low detection accuracy, short detection depth, and/or multiplicity in imaging. This paper proposes a new high resolution tunnel advance prediction technology on the face based on 3D seismic wave detection. It arranges the 3D high-density source and recording geometry on the tunnel face to receive reflected P-waves for 3D imaging. By using the 3D numerical simulation, we first analyze the energy distribution and propagation characteristics of the wave field, which proves that our method is feasible. Compared with the conventional technologies, the seismic energy propagating towards the tunnel face is stronger and produces rich reflected information. The reflected wave has the advantages of bandwidth, strong energy and little interferences from surface wave, so that the seismic phases are easy to be identified. On this basis, we present the high resolution true 3D prediction technology to obtain more comprehensive and abundant azimuth information. Our approach is further validated by an application experiment in a real-world engineering project of water conveyance tunnel. The results show that the new technique has a greater detection length, higher detection accuracy and more reliable imaging results.

The Numerical Simulation Research about the Deformation and Stability of Cut-Off Wall´s Foundation Trench Zhikong Hydropower Station, Tibet, China

2013 ◽  
Vol 353-356 ◽  
pp. 2506-2510 ◽  
Author(s):  
Qing Song Huang ◽  
Yu Sheng Li ◽  
Song Ye
Keyword(s):  
Numerical Simulation ◽  
Large Deformation ◽  
Hydropower Station ◽  
Simulation Research ◽  
Supporting System ◽  
Construction Scheme ◽  
Deformation State ◽  
Major Factors

Through the numerical simulation research about the deformation and stability of cut-off wall´s foundation trench in Zhikong Hydropower Station China [1]. The text explained the major factors which were construction scheme and the strength of interior bracing structure of the deformation and stability about the foundation trench. In the early construction, the two reasons caused the large deformation. When adjusted the construction scheme and the strength of interior bracing structure, the deformation state of foundation trench and supporting system became much better.

Imaging the Geology Ahead of a Tunnel Using Seismics and Adaptive Polarization Analysis

2020 ◽  
Vol 25 (2) ◽  
pp. 189-198
Author(s):  
Lei Chen ◽  
Chao Fu ◽  
Xinji Xu ◽  
Lichao Nie
Keyword(s):  
Time Window ◽  
Geophysical Methods ◽  
Weighting Coefficient ◽  
Tunnel Construction ◽  
Polarization Analysis ◽  
Polarization Direction ◽  
Tunnel Face ◽  
Seismic Method ◽  
Imaging Results ◽  
Geological Conditions

The seismic method is one of the main geophysical methods that are widely used to image the geology ahead of tunnels during tunnel construction. However, owing to the complex environment and limited observation aperture in a tunnel, symmetric false results (that appear in imaging results but not in the actual environment) frequently occur in imaging results. In a symmetric false reflection, false and true reflection points are axisymmetric around the tunnel axis. Such false results frequently cause errors in the interpretation of the geological conditions ahead of a tunnel face. To overcome this problem, a seismic method that uses adaptive polarization analysis was adopted to better image geological conditions. Based on an adaptive time window, the polarization characteristics of seismic signals were analyzed to calculate the main polarization direction. The symmetric false results in imaging results were suppressed by adopting a weighting coefficient based on the angle between the main polarization direction and ray direction. Numerical simulations revealed the superiority of the method when applied to synthetic data processing. Moreover, the method was applied to a diversion tunnel. The method successfully identified the fracture zones ahead of the tunnel face, thus significantly enhancing the safety of tunnel construction.

scholarly journals Diffraction Characteristics of Small Fault ahead of tunnel face in coal roadway

2017 ◽  
Vol 21 (2) ◽  
pp. 95-99 ◽  
Author(s):  
Bo Wang ◽  
Shengdong Liu ◽  
Fubao Zhou ◽  
Jun Zhang ◽  
Fangkun Zheng
Keyword(s):  
Acoustic Wave ◽  
Coal Seam ◽  
Fault Prediction ◽  
P Wave ◽  
Mine Safety ◽  
Observation System ◽  
Tunnel Face ◽  
Coal Roadway ◽  
Small Fault ◽  
Channel Wave

Small fault ahead of the tunnel face in coal roadway is the important hidden hazard factor of coal and gas outburst accidents. The study of small fault prediction has important practical significance, which is the urgent demand of coal mine safety production. The diffraction of breakpoint can be used to identify the fault. However, unlike surface seismic exploration, the diffraction is with approximately horizontal incidence when the advanced detection is carried out in the roadway. The common advanced detection system is mainly as the reference of traffic tunnel, without considering the influence of low-velocity coal seam. Considering the influence of an acoustic wave of the roadway cavity and channel wave of the coal seam, the advanced detection model of small fault ahead of tunnel face is established. Diffraction advanced observation system in which sources located in front of tunnel face is constructed, and the numerical calculation of the high-order staggered-grid finite difference is carried out. The simulation results show that: Compared with the data collected by reflection observation system, in seismic records acquired by diffraction observation system, the suppression effect of acoustic wave is appeared. The diffracted P-wave of the breakpoint of component X is clear with strong energy and short-wave group. Multiple diffractions of the breakpoint are not found, but the multiple diffraction of tunnel face endpoint is obvious. The difference between breakpoint diffraction and multiple diffractions of the endpoint is clear, and diffracted P-wave of the breakpoint is easy to identify. The multiple reflected channel wave between the fault and the tunnel face is very obvious, and the reflected channel wave of small fault is so hard to identify. Migration results show that the imaging resolution of diffracted P-wave of small fault is higher than the reflected channel wave, and breakpoint location of imaging is consistent with the actual model.

Geo-Stress Direction Evaluation Method Based on Numerical Simulation

2014 ◽  
Vol 580-583 ◽  
pp. 2011-2014
Author(s):  
Su Chao Xu ◽  
C Y. Jin
Keyword(s):  
Numerical Simulation ◽  
Evaluation Method ◽  
Maximum Shear Stress ◽  
Local Stress ◽  
Surrounding Rock ◽  
Hydropower Station ◽  
Local Stress Concentration ◽  
Stress Direction ◽  
Baihetan Hydropower Station

The phenomenon of spalling at Baihetan Hydropower Station is influenced by such factors as the stress redistribution in surrounding rock, the local stress concentration and also poor properties of disturbed belt. In this paper, a series of numerical simulation were carried out and some beneficial conclusions were gained as follows: 1) the ratio of maximum shear stress and uniaxial compressive strength is more rational in the prediction of spalling and can give confident explanation for “V” shape pits; 2) the in-situ geo-stress direction is in accordance with NNE and NE.

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