通过超前预报技术可以检测掌子面前方的地质构造,预测隧道开挖过程中的不利地质条件,从而保障施工进度和施工人员安全. 拟VSP方法适用于激发点或者接收点在一条直线上,利用反射波走时曲线与直达波走时曲线的交点推测前方反射界面的位置,而克希霍夫偏移方法可以是任意观测系统. 对垭口隧道的实测数据进行时移校正、滤波、波场分离、拉东变换提取有效反射波等预处理, 对比两种成像结果,获得掌子面前方构造异常分布,结果与实际揭露异常相符. 应用结果表明,拟VSP方法对巷道正前方构造位置预测准确,但不能预测构造走向,克希霍夫偏移方法需要速度扫描获得偏移速度信息,根据反射波能量确定反射界面,反射界面与隧道交点为隧道正前方构造位置. 两者结合应用可更准确地确定构造走向与位置.%The technology of advanced geological prediction can detect the geological structure of the tunnel face and predict the ad-verse 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 ra-don 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.
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