The application of Pseudo VSP method and Kirchhoff migration to the tunnel advanced geological prediction
ZHA Xin-Jie1, WANG Wei2, GAO Xing2
1. College of Computer Science and Technology, Xi'an University of Science and Technology, Xi'an 710054, China;
2. State Key Laboratory of Resources and Environmental Information System, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China
The technology of advanced geological prediction can detect the geological structure of the tunnel face and predict the adverse geological conditions so as to ensure the efficiency and safety of the construction. This paper introduces the theory of Pseudo VSP and Kirchhoff migration imaging respectively, and argues that Pseudo VSP, which takes advantage of the intersection of reflection and P-wave arrival time to predict the position of reflection interface ahead, is suitable for the situation that the sources or the receivers are designed on a straight line; however, Kirchhoff migration method can be used in any observation system. This paper is based on the principle of Kirchhoff migration imaging and Pseudo VSP. Taking the Yakou tunnel as an example, the authors compared the imaging results between the two methods through a series of pretreatments,such as time-shift correcting, filtering, wave field separating, and radon transform. The results show that Pseudo VSP can predict the position of construction accurately, but it cannot predict the structural strike. Kirchhoff migration imaging which gets the information of migration velocity by velocity scan method is on the basis of reflected wave energy to determine the reflection interface, and the intersection of reflection interface and tunnel is the position of construction. Combination of Pseudo VSP and Kirchhoff migration imaging can predict the structural strike and position more precisely.