隧道衬砌背后脱空识别的改进瞬变电磁雷达法

Improved transient electromagnetic radar method of void identification behind tunnel lining

针对衬砌背后脱空检测图像特征不显著、脱空定位及范围识别准确性较低等技术难题,以瞬变电磁理论为基础,结合隧道衬砌结构检测需求,提出了隧道衬砌背后脱空识别的改进瞬变电磁雷达法;通过改善发射系统关断时间增大探测深度;利用接收线圈等效电路及弱信号增强算法提升成像分辨率;在剔除强干扰信号并增大发射磁矩基础上,采用圆滑滤波处理及多周期叠加采样抑制数据噪声;基于视电阻率差异建立衬砌结构相关介质的TER图谱,通过不同类型混凝土构件的多种组合进行室内衬砌缺陷模拟检测试验,初步评估改进TER法检测衬砌背后脱空的可行性及其检测精度;在北京市地铁6号线郝北隧道进行了现场实际检测与应用,综合对比了TER检测图像与管片钻芯取样结果,以验证改进TER法检测衬砌背后脱空的有效性。研究结果表明:改进TER法具有较高的成像分辨率与较好的缺陷辨识效果,可直观清晰地反映衬砌背后脱空缺陷的实际特征,能有效识别衬砌厚度、钢筋埋深、衬砌背后脱空及衬砌内部空洞的具体位置及范围;可定量化描述10~20 cm的脱空缺陷,并对小于10 cm的脱空缺陷进行定位及脱空量级判定,对于衬砌背后深度达30 cm以上目标体的识别结果具有较好的参考性;改进TER法受金属介质干扰较小,在大范围连续性检测中,可对脱空范围大于30 cm的衬砌背后脱空缺陷进行精确定位。

In view of the technical problems of detection behind the tunnel lining such as insignificant image features,and the low accuracies of void location and range identification,an improved transient electromagnetic radar(TER)method to detect the void behind the lining was proposed based on the transient electromagnetic theory and the detection requirements of tunnel lining structure.The detection depth was increased by improving the turn-off time of the transmitting system.The image resolution was improved by using the equivalent circuit of receiving coil and weak signal enhancement algorithm.On the basis of eliminating the strong interference signal and increasing the transmitting magnetic moment,the data noise was suppressed by smooth filtering and multi-period superimposed sampling.Based on the difference in the apparent resistivity,the TER map of the relevant medium of lining structure was established,and the indoor lining defect simulation test was carried out through the different combinations of various concrete components.The detection accuracy and feasibility of the improved TER method to detect the void behind the lining were preliminarily evaluated.A field application was carried out in Haobei Tunnel of Beijing Metro Line 6.By comparing the test results of TER images with the sampling results of drilling,the effectiveness of the improved TER method to detect the void behind the lining was further verified.Analysis results show that the improved TER method has higher imaging resolution and better defect identification effect.It can directly and clearly reflect the actual characteristics of the void defects behind the lining and effectively identify lining thickness,buried depth of steel bar,and specific locations and scopes of the voids behind and inside the lining.It can quantitatively describe 10-20 cm voids and locate and determine the magnitude of the voids less than 10 cm.Besides,it has a good reference for the identification result of the target body with a depth of more than 30 cm behind the lining.Meanwhile,the improved TER method is less disturbed by metal mediums and can accurately locate the void defects behind the lining with a void range greater than 30 cm in a wide range of continuous detection.