岩溶区富水破碎带探地雷达频谱特征研究

Study on Spectrum Characteristics of GPR for Water-rich Crushed Zone in Karstic Area

受到地质条件、施工条件以及施工控制等因素的影响,隧道在岩溶地区施工建设过程中会存在一定的风险。超前地质预报能够为隧道安全提供重要保证,当前研究成果主要为岩溶区富水破碎带反射波形的定性特征分析,缺乏振幅及频率大小分布的定量性特征研究。基于此,以广西六河高速公路瑶寨隧道为工程依托,基于电磁波传播特性,结合探地雷达探测原理,开展了大量的现场探测。从振幅与频率的最值及振幅一定取值范围的比例特征出发,对实测数据进行了系统的统计分析,直观、详细地描述并定量揭示了岩溶区富水破碎带的探地雷达频谱特征,为探地雷达判读提供了新的参考方法。现场探测数据分析结果表明:雷达反射振幅的最小值和最大值基本在0. 25和0. 96左右波动,振幅最大值逼近于满幅值1. 0,表现出极其显著的强反射;反射频率的最大值不超过110 MHz,最大反射频率平均值为105 MHz;反射振幅的最大值达到0. 8的扫描点比例高达约95%,而其最小值达到0. 4却较难,体现了反射振幅的强烈性。将研究结果应用于实际工程的判读,通过对比验证,判读结论与隧道的实际开挖结果吻合较好,说明研究结果能有效地为雷达判读提供指导,为保证隧道的施工与建设安全提供了重要支撑。

Because of the influence of geological condition,construction condition and other factors,there wifl be some risks during the tunnel construction in karst area tunnel.Tunnel geological prediction can provide important guantee for tunnel construction safety.Recently,the qualitative characteristics of reflection waveform through the water-rich crushed zone of karst area are analysed mostly,but lacking of its quantitative characteristics study.Therefore,based on the Yaozhai Tunnel on Liuzhai-Hechi expressway in Guangxi ,according to the propagation property of electromagnetic wave and combining with the GPR detection principle,a great deal of field detection is carried out.From the maximal and the minimal vibration amplitudes and freqriencies as well as the ratio of vibration amplitude range,the measured data are systematic statistical analysed,and the spectral characteristics of GPR in water-rich fracture zone in karst area are revealed quantitatively and described intuitively and in detail,which provides a new reference method for GPR interpretation.The analysis result of field detection data shows that (1)the minimum and the maximum of the GPR reflection vibration amplitude fluctuated around 0.25and 0.96respectively,the maximum vibration amplitude approached the full amplitude 1.0,which shows the extremely strong reflection ;(2)the maximum reflection frequency is less than 110MHz,and the average is 105MHz;(3)the proportion of the scanning points whose the maximum rettecnon amplitude reached O.8is as high as about 95%,but the minimum value is difficult to reach 0.4,which reflects the imensity of the reflection amplitude.The result is applied to the interpretation of the practical project,and the comparative verification shows that the interpretation is in consistent with thereal excavation,and the research can provide effective guidance for GPR interpretation,which provides an important support for ensuring the safety of tunnel construction.