基于柱坐标系的隧道空间溶洞探测全波场数值模拟

Full wave filed numerical simulation of karst caves in tunnel space based on cylindrical coordinate system

溶洞作为碳酸盐岩地区常见的一类局部不良地质体,其波场特征常常与形态、填充物、空间方位等因素相关,而受此影响地震类方法对溶洞的探测效果往往不理想.因此,要想实现地震类方法对溶洞的准确探测,首先需要明确不同状态下溶洞的波场特征.针对上述问题,考虑到实际隧道空间形态,本文首次采用柱坐标系下的一阶速度-应力弹性波动方程对隧道空间进行数值模拟,通过通量矫正技术压制频散,同时对已开挖段隧道与围岩的边界采用自由边界条件处理.对不同半径、不同填充物、不同方位的溶洞以及复杂溶洞模型的数值模拟结果及波场特征分析表明:本文提出的方法可实现隧道空间全波场高精度数值模拟,波场特征符合波的运动学与动力学特征;不同情况下溶洞波场特征的差异可有效的指导溶洞的探测与识别.

Karst cave is a kind of local ill geologic body in carbonate rock area.Its wave field characteristics are often related to shape,size,filler,spatial orientation and other factors.The seismic methods affected by these factors are often not ideal for detecting karst caves.Therefore,in order to realize the accurate detection of karst caves by seismic methods,it is necessary to clarify the wave field characteristics of karst caves in different states.In view of the above problems,considering the actual tunnel space form,the first order velocity-stress elastic wave equation based on cylindrical coordinate system is adopted to simulate the tunnel space for the first time.The Flux Correction Technology(FCT)is used to suppress dispersion.At the same time,the boundary between the excavated tunnel and surrounding rock is treated by free boundary conditions(Lateral isotropic medium replacement method).The numerical simulation and wave field characteristics analysis of different radius,filler,azimuth and complex karst cave models show that the proposed method can achieve high-precision numerical simulation of the full-wave field in tunnel space,and the wave field characteristics accord with the kinematics and dynamics characteristics of the wave;the difference of wave field characteristics(e.g.waveform,energy,in-phase axis and so on)in different situations can effectively guide the detection and identification of karst caves.