在隧道超前地质预报中，负视速度法以其简便、快速的特点被广泛应用。常规的方法是直达波时距曲线和反射波时距曲线的交点即为反射界面的位置；但是对于倾斜界面，如果只是单纯的延伸时距曲线，并不能准确地找出界面位置，而且当倾斜角度比较大时，误差更大，这样在实际处理数据时，往往因为处理不当，造成预报的不准确，以致于实际操作出现大的事故。针对此问题，笔者主要研究倾斜界面，采用最新坐标法求反射界面的时距曲线，并对所得时距曲线进行插值拟合，主要包括多项式拟合、一元三点等距插值以及连分式插值。通过大量试验，比较各个插值拟合的特点，最终得出由多项式拟合对时距曲线插值，能够准确地确定反射界面的位置；最后通过几何公式求出界面倾角（视倾角），为负视速度法数据处理提供方便。%With the merits of simplicity and rapidness, the negative apparent velocity method has been used widely in tunnel geological prediction. The regular method indicates that the intersection of time⁃distance curves of direct wave and reflected wave is just the posi⁃tion of reflecting interface. However, for inclined interface, the interface position cannot be identified accurately if we only extend time⁃distance curves. What's more, the more lean the angle, the greater the error. This leads to serious accidents in practice because of inac⁃curate prediction. Aimed at solving the problem, the authors mainly studied the inclined interface, used the newest coordinates method to get time⁃distance curve of reflected interface, and then fitted their interpolation, mainly including polynomial fitting curve, unitary three⁃points isometric interpolation and interpolation by continued fractions. Through a lot of tests and comparisons of the characteristics of all interpolation fittings, the time distance curve interpolation by polynomial fitting can be worked out so as to identify the position of reflected interface accurately. Finally, interface dip ( apparent dip) can be calculated using geometric formula. This method facilitates the data processing by means of negative apparent velocity.
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