Rayleigh-to-shear wave conversion at the tunnel face — From 3D-FD modeling to ahead-of-drill exploration
Rayleigh-to-shear wave conversion at the tunnel face — From 3D-FD modeling to ahead-of-drill exploration
复制标题
DOI：
10.1190/1.2785978
复制
发表时间：
2007-11
期刊：
影响因子：
3.3
通讯作者：
T. Bohlen;U. Lorang;W. Rabbel;C. Müller;R. Giese;S. Lüth;S. Jetschny
中科院分区：
文献类型：
--
作者：
T. Bohlen;U. Lorang;W. Rabbel;C. Müller;R. Giese;S. Lüth;S. Jetschny
为了隧道的安全开挖，在施工前预测岩性和结构的非均质性非常重要。传统的隧道地震预测系统利用直接在隧道壁或隧道掘进机 (TBM) 刀头附近产生的体波（纵波和横波）。我们提出了一种通过 3D 弹性有限差分 (FD) 建模发现的新预测策略：到达隧道前端面的瑞利波被转换为向前传播的高振幅 S 波。反射或反向散射的 S 波被转换回瑞利波，可以沿侧壁记录。我们将这些波命名为 RSSR 波。在我们的方法中，正面充当 S 波收发器。一项技术优势是源和接收器都可以放置在 TBM 刀盘后面。模型显示 RSSR 波的振幅明显高于直接反射的体波。开挖破坏区导致 RSSR 波分散，导致多模态反射响应。为了探测前方的地质界面，沿侧壁记录的 RSSR 波会进行色散校正并进行叠加。根据到达时间，可以估计到 S-S 反射点的距离。当隧道接近界面时，循环应用也允许量化反射界面的方向。我们的方法已在圣哥达基线隧道皮奥拉隧道的现场实验中得到成功验证。根据叠加的 RSSR 事件估计的到皮奥拉断层带的距离与地质测量和勘探钻探获得的信息非常吻合。
For safe tunnel excavation, it is important to predict lithologic and structural heterogeneities ahead of construction. Conventional tunnel seismic prediction systems utilize body waves (P- and S-waves) that are directly generated at the tunnel walls or near the cutter head of the tunnel boring machine (TBM). We propose a new prediction strategy that has been discovered by 3D elastic finite-difference (FD) modeling: Rayleigh waves arriving at the front face of the tunnel are converted into high-amplitude S-waves propagating further ahead. Reflected or backscattered S-waves are converted back into Rayleigh waves which can be recorded along the sidewalls. We name these waves RSSR waves. In our approach, the front face acts as an S-wave transceiver. One technical advantage is that both the sources and the receivers may be placed behind the cutter head of the TBM. The modeling reveals that the RSSR waves exhibit significantly higher amplitudes than the directly reflected body waves. The excavation damage zone causes dispersion of the RSSR wave leading to multimodal reflection response. For the detection of geologic interfaces ahead, RSSR waves recorded along the sidewalls are corrected for dispersion and stacked. From the arrival times, the distance to the S-S reflection point can be estimated. A recurrent application, while the tunnel approaches the interface, allows one to quantify the orientation of the reflecting interfaces as well. Our approach has been verified successfully in a field experiment at the Piora adit of the Gotthard base tunnel. The distance to the Piora fault zone estimated from stacked RSSR events agrees well with the information obtained by geologic surveying and exploratory drilling.