gprMax干扰消除方法优化隧道壁后空洞成像特征研究

Optimizing Imaging Characteristics of Voids Behind Tunnel Linings Using gprMax Interference Elimination Method

为解决传统探地雷达图像处理方法在检测隧道衬砌钢筋影响下的壁后空洞时,二维模型不能有效描述空洞三维特征,存在计算效率低、计算精度不足的问题,综合运用平均消除法、指数增益法和时间零点校正法,结合雷达信号随双程窗口时间变化的特点,引入分段函数计算步骤,提出gprMax干扰消除方法,并验证该方法在正演模拟结果处理中的可行性。结合工程实际注浆情况和隧道壁后空洞的检测过程,采用基于时域有限差分法的gprMax软件设计隧道壁后注浆空洞的三维模型,采用gprMax干扰消除方法优化图像结果,对不同工况下的正演模拟图像成像特征进行分析。结果表明:1)gprMax干扰消除方法的正演模拟处理结果与室内混凝土板中圆形空洞结构模型试验的实测结果总体一致;2)水平测线中矩形空洞信号特征呈现出“凹”字形,垂直测线中矩形空洞信号特征呈现出类似直达波的特征,由空洞的三维特征图获取数据可计算得到空洞尺寸和埋深信息;3)gprMax干扰消除方法可以有效增强埋深较大处空洞的电磁信号强度。由研究结果可知,gprMax干扰消除方法在提高了隧道壁后空洞检测数据处理效率的同时保证了计算准确性和精度。

Two-dimensional models are insufficient for capturing the three-dimensional(3D)characteristics of voids behind tunnel linings,primarily due to the interference caused by reinforcement during traditional ground penetrating radar image processing.Additionally,conventional data processing methods are computationally inefficient and have limited accuracy.To address these challenges,the authors integrate average elimination,exponential gain,and time-zero correction techniques to develop the gprMax interference elimination method.The proposed method leverages the temporal variation of radar signals within two-way travel windows and uses piecewise function calculations to enhance computational performance.The feasibility of the proposed method is validated through forward simulations.A 3D model of the voids behind tunnel linings is constructed using gprMax software based on the finite-difference time-domain method to align with real-world grouting conditions and detection processes.The gprMax interference elimination method is used to optimize the imaging results of the forward simulation under varying conditions.The analysis of the imaging characteristics yields the following findings:(1)The forward simulation results using the gprMax interference elimination method closely align with the measured results from model tests of circular cavity structures embedded in indoor concrete slabs.(2)On horizontal survey lines,the rectangular void signal appears as a"concave"shape,whereas on vertical survey lines,it resembles the characteristics of direct waves.The size and burial depth of voids can be derived from the 3D feature maps.(3)The gprMax interference elimination method significantly enhances the electromagnetic signal strength of voids at greater depths.In summary,the proposed gprMax interference elimination method improves the data processing efficiency for voids behind tunnel linings while maintaining calculation accuracy and precision.