隧道工程勘察中的超前预报成像方法研究

针对地下工程领域隧道超前预报地震波波场传播与成像中存在的问题，通过数值模拟，构建二维含低速异常的隧道介质模型，研究隧道弹性波场传播规律和异常体边界成像准确性.首先，利用一阶速度-应力波动方程和高阶交错网格有限差分计算方法，导出隧道超前预报数值模拟的稳定性条件和边界条件，对上述隧道模型进行数值模拟，识别波场特征；其次，利用叠前逆时偏移成像方法，对压制噪音干扰后的波场在互相关成像条件下，对隧道模型中的异常体边界进行逆时偏移成像.研究结果表明：采用高阶交错网格有限差分正演获得异常体边界清晰的反射波和角点产生的散射波；逆时偏移算法获得隧道内异常体准确成像结果，从而大大提高隧道超前预报的分辨率与准确性；靠近掌子面单一震源、多道接收观测系统对异常体成像效果最佳，为隧道内高效数据采集提供理论依据.

Advanced prediction migration method research in tunnel engineering investigation

In this study, a two-dimensional tunnel model with low-velocity bodies was constructed to investigate elastic wave field propagation in tunnels, and pre-stack reverse time migration was used to conduct imaging. The stability and boundary conditions for advanced tunnel prediction numerical stimulation were obtained via the high-order staggered-grid finite-difference method and the first-order velocity-stress elastic wave equation to numerically simulate the wave field of the tunnel model. The pre-stack reverse time migration method, which is widely utilized in petroleum exploration, was applied for imaging of the tunnel model with the cross-correlation imaging condition and noise suppression technique. The modeling and migration results show that, reflection wave from abnormal body boundary and scatter wave from breakpoint are clear using the high-order staggered-grid finite-difference numerical modeling, the more accurate imaging results are obtained using reverse time migration method, which improves the resolution and accuracy for tunnel advanced prediction, and the observation system of single source closed to tunneling face with multi-channel receiver brings out the optimal abnormal body imaging, which provides theoretical basis for efficient data acquisition of advanced prediction in tunnel.