基于椭圆展开共反射点叠加的隧道地震波超前探测成像方法与应用

采用地震波法探明隧道前方断层、溶洞等不良地质体,是隧道施工安全的重要保障,而有效的成像方法则是关键。椭圆展开是一种新型的偏移成像方法,已在地表地震勘探中得到应用,然而尚未被引入隧道地震探测中。针对隧道环境,基于非标准椭圆方程,构建了隧道空间观测方式椭圆展开方法,同时重新设定隧道轴线方向为椭圆展开法向出射点方向,实现了对隧道掌子面前方区域地质的成像;通过共震源点地震记录的椭圆展开及相干叠加,最终实现掌子面前不良地质的识别和定位,形成了基于椭圆展开共反射点叠加的隧道地震波超前探测成像方法。在此基础上,基于交错网格有限差分方法,对岩性界面和断层进行了系统的正演成像研究,分析了不同地质模型的成像特征;最后,依托现场进行了探测试验,探测结果与开挖揭露情况基本一致,验证了成像方法的有效性和实用性。

Imaging method of seismic advanced detection in tunnels based on ellipse evolving CRP stacking and its application

The seismic advanced detection of tunnels is a common method to estimate faults, karst caves and other adverse geologies, and is an important method to guarantee the safety of tunnel construction. The ellipse evolving is a new migration method and has been applied in seismic data processing in surface investigation. For the observation system of seismic advanced detection in complicated construction environment, a new ellipse evolving CRP method is developed based on the non-standard elliptic equation. Meanwhile, the tunnel axis is set as the direction of normal emergent point, and the geology ahead of tunnel face is prospected by this way. Then, an imaging method for the seismic advanced detection method based on the ellipse evolving CRP stacking is proposed, which is suitable for the observation system in tunnel environment. Moreover, based on the staggered grid finite difference method, numerical modeling of interfaces with different inclinations and faults with different shapes is conducted. The proposed imaging method is used to obtain the imaging results. The imaging characteristics of different models are analyzed. Finally, the method is applied in a spillway tunnel, and the detection results are the same as what the geology exposes, which verifies the validity and practicability of the proposed imaging method.