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.