为实现隧道超前方向不良地质体真三维精细探测成像，提出宽照明高信噪比隧道三维地震超前预报方法，设计3D对称观测系统（symmetric observation system,STSP），并采用数值模拟方法、地震照明分析和3D逆时偏移方法评价观测系统的合理性和优势。不规则空洞体模型和软弱夹层模型的分析结果表明STSP的优势为： 1）3D STSP的炮点呈线性排列，有利于使用方向滤波方法提取超前方向的反射波，数据信噪比高； 2）对于目的层的照明能量和照明范围而言，3D STSP要优于3D TRT（3D true reflection tomography）； 3）3D STSP的偏移成像精度较高，而3D TRT对地质体倾向和走向的成像明显不足。
Three-dimensional (3D) tunnel geological
advance prediction methods currently face several challenges: (1) The
arrangement of shot and geophone points is complex and nonlinear, preventing
the use of directional filtering techniques to extract reflected waves in the
advance direction, which results in a low signal-to-noise ratio (SNR); (2) the direct wave arrival is unsuitable for
estimating the surrounding rock velocity; and (3) geophones are positioned on
the tunnel walls, far from the tunnel face, leading to low illumination energy
for the target body in the forward direction, which decreases the accuracy of
anomaly imaging. To enable true 3D fine detection and imaging of unfavorable
geological bodies in the tunnel advance direction, the author proposes a 3D
seismic advance prediction method for tunnels with wide illumination and high
SNR. A 3D symmetric observation system (STSP) is designed, and its advantages
are evaluated through numerical simulation, illumination analysis, and 3D
reverse time migration method. Results from the analysis of irregular karst
cave and weak interlayer models highlight the following advantages of STSP: (1)
The shot points in 3D STSP are arranged linearly, which facilitates extracting
reflected waves in the advance direction via directional filtering, resulting
in high data SNR. (2) In terms of illumination energy and range of the target
layer, 3D STSP outperforms 3D true reflection tomography (TRT). (3) 3D STSP
provides high offset imaging accuracy, whereas TRT shows insufficient accuracy
in imaging the inclination and trend of geological bodies.
