Study On Advanced Detection Technology Of Highway Tunnel Based On Ground Penetrating Radar In Karst Area

The landform is various and the geological structure is complex in karst area. During the construction, because of the geological conditions and other elements, unfavorable geological body such as karst cave, fault, underground river, broken zone and geological risks such as water-inrush, mud-burst, collapse are happened frequently, and endangers the safety of staff and construction equipment, also restricts the construction progress and affects the quality. Therefore, how to detect the unfavorable geological body and take related countermeasure more effectively and reduce the construction risk and guarantee the safety are urgent key technique issues during the construction.In order to improve the practicability and precision of GPR(Ground Penetrating Radar) advanced detection of highway tunnel in karst area, the method of theoretical analysis, field measures and numerical calculation were taken to systematically study the GPR advanced detection technology for unfavorable geological body. The main research contents and achievements are as follows:1) On the basis of field geological investigation and GPR detection, the three types of unfavorable geological body was defined, as cavity karst cave, filled karst cave and broken zone.2) By means of theoretical analysis and field measure to study the detection applicability of GPR in terms of electromagnetic loss and dispersion, the distribution range of surrounding rock water content that is suitable for GPR detection was put forward.3) According to the detection theory of GPR, the field detection method for unfavorable geological body in side wall and little body within the scope of tunnel face was analyzed, and the detection principle was formulated, the layout form of survey line and survey point and the detection parameters were given.4) Based on the field water content comparison of surrounding rock, the method of regression analysis was adopted to correct the calculate parameter of TOPP formula when the GPR was applied to detect the surround rock water content of broken zone, and the parameter range was ascertained.5) According to the statistic analysis of distribution range of reflection amplitude and frequency of field measure data, the reflection strength and frequency was defined, and the range was achieved.6) In accordance with field measure data and theory, the wave-form property under different water content of cavity karst cave, filled cave, water-rich broken zone and weathered limestone was analyzed synthetically and quantitatively, and the wave-form property and interpretation standard related to unfavorable geological body was proposed.7) On the basis of relevant theory of image and signal processing, according to the color eigenvector corresponding with electromagnetic reflection energy, amplitude and frequency, the technique of CONTOURLET and K-MEANS++ were applied to extract and analyze the raw property of GPR data, and the interpretation standard based on image and signal property was proposed.8) The construction safety distance of unfavorable geological body was numerically analyzed with the software of FLAC3 D, and the safety distance under different support conditions of karst cave and broken zone was given. The judgment method of distribution scale of karst cave and broken zone was researched on the basis of field geological investigation and GPR detection, and put forward the estimation method based on geological investigation and wave-form property. According to water-prevention rock pillar failure theory and broken rock zone detection, the estimation model of water-inrush and collapse quantity was established and calculation formulas were deduced. The risk rank was classified statically according to relational domestic research achievements.Achievements can provide beneficial reference for GPR detection of karst highway tunnel and other underground engineering in future.