At present, the tunnel geological prediction(TGP) is one of the most commonly used method in advanced geological prediction of the tunnel; and filtering process of TSP data is a key link to decide reliability and stability of forecast results. To obtain the accurate results of TGP, 681cases of TGP data from highway and railway tunnels are counted and analyzed for the influence of filter frequency band range on prediction results, and soft interlayer, water inrush, broken zone and karst cave etc.5 typical geological conditions as examples are analyzed. The results show that: (1) Signal-to-noise ratio of data is high that should select wide-band filtering(appropriately increasing the difference between low pass and high pass or high cut and low cut) to ensure accurate positioning and effective recognition for abnormal body; generally, the main frequency width of 1.5-2.5 times can be used as low pass or high cut value of filter; however, the size of abnormal body is big and the grade of abnormal body is strong that should appropriately compress the filer range(reduce the difference between low pass and high pass) to highlight abnormal body, if wide-band filtering is selected in this case, it is easy to underestimate the geological condition and surrounding rock grade of surrounding rock; thus causing construction risk, and the filtering range should be determined according to the effective width of main frequency. (2) Signal-to-noise ratio of data is low: the dominant frequency is not obvious and no domain frequency, one should select narrow-band filtering so as to eliminate fake abnormality and save real geological conditions, the abnormal bodies still after filtering should be further judged by combined with other advanced prediction methods; the dominant frequency is apparent, one should choose wide-band filtering to avoid shifting of abnormal position and cause error judgement. The above-mentioned filtering method of TGP data has important practical significance for improving the accuracy and stability of TGP results and guiding the safe construction of tunnel.
