Rayleigh波椭圆极化与地震映像在城市地层扰动探测中的数值模拟和应用

Numerical simulation and application of Rayleigh wave elliptic polarization and seismic imaging in urban stratum disturbance detection

为研究瑞利面波椭圆极化频散方法的探测效果,首先,利用有限元方法对基于工程实例的城市盾构隧道及土层扰动简化二维模型进行数值模拟,分析各隧道模型的点震源波场特征和瑞利面波椭圆极化频散特征;其次,利用传统地震映像方法对比验证结果的可靠性;最后,结合盾构隧道施工前后场地实测主动源地震数据,分析隧道开挖前后的瑞利面波椭圆极化特征。研究结果表明:在盾构隧道模型及隧道土层扰动模型的模拟地震波场中,隧道边界及塌落空洞区域产生了椭圆极化频散现象,在空洞边界处出现了“左高右低”椭圆极化率数值异常分布特征,相应模型的地震映像剖面验证了模拟结果的可靠性;在工程实例中,隧道开挖前后场地的椭圆极化频散特征也与地震映像及现场勘察结果相对应,验证了瑞利面波椭圆极化方法在盾构隧道场地扰动探测的有效性。

To study the non-destructive testing effect of the Rayleigh surface wave elliptically polarized dispersion method,a simplified two-dimensional model of urban shield tunnel and soil disturbance based on an engineering case was firstly simulated by the finite element method. The characteristics of point source wave field and elliptical polarization dispersion of Rayleigh surface wave of each tunnel model were analyzed. Secondly, the reliability of the results was verified by comparing the traditional seismic imaging methods. Finally, the elliptical polarization characteristics of Rayleigh surface waves before and after tunnel excavation were analyzed by combining the active source seismic data measured on site before and after shield tunnel construction.The results show that elliptical polarization dispersion occurs at the tunnel boundary and collapse cavity area in the simulated seismic wavefield of the shield tunnel model and tunnel soil disturbance model. "High left and low right" elliptical polarizability numerical abnomaly distribution characteristics appear at the boundary of the model cavity. Seismic image profiles of the corresponding models validate the reliability of the simulation results. In engineering examples, the elliptical polarization dispersion characteristics of the site before and after tunnel excavation also correspond to seismic images and field survey results, which verifies the effectiveness for the detection effect of the Rayleigh surface wave elliptical polarization method on shield tunnel site disturbance.