多场跨孔CT联合反演成像的城市地铁隧道盾构区孤石探测研究

Shield method is usually used in city metro construction because it has the advantages of high efficiency, low cost, high automation, high quality and less harm to the surface culture buildings. Using tunnel boring machine (TBM) to construct a tunnel is very quick and safe in uniform stratum. However, if there are boulder stones in the uniform stratum, the cutter of the TBM can be easily damaged, and it is very hard to reassemble the cutter, which not only increases the expenses, but also delay the project. Boulder stones are the natural hazards for metro shield, especially in Shenzhen, Guangzhou, Xiamen, Fuzhou city etc. However, it is very difficult for accurate detection of boulder stones for metro shield tunnel project because of the small size of boulder stone. This project is aimed to the basic research of boulder detection method for metro shield zone using multi-fields including cross-hole resistivity tomography(CT) and cross-hole seismic wave tomography(CT) techniques. The numerical modeling, physical simulation, and field experiment will be used to solve relevant basic scientific issues of boulder detection in metro shield tunnel region. The numerical and physical models of normal composite stratum and boulders are established for numerical modeling, physical simulation and field experiment. The simulation results will be analyzed for geophysical field response characteristics, data acquisition array, data processing and boulder information recognition. We will study a three-dimensional joint inversion algorithm of cross-hole resistivity tomography and cross-hole seismic tomography data with cross-gradient constraints, which will be effectively overcome the weak consistency of single inversion of resistivity CT or seismic CT, and will enhance the resolution and accuracy of boulder detection in metro shield zone.

孤石（花岗岩球状风化核体）会使盾构刀盘严重磨损甚至损坏，是城市地铁隧道盾构施工的安全隐患之一，其中我国南方城市（深圳、广州、厦门、福州等）尤其突出，严重影响地铁隧道工程的安全生产，而准确探测孤石空间形态和孤石三维定位是城市地铁盾构隧道工程中的重要课题和难题。本项目主要利用数值计算、物理模拟、现场试验等多种途径、多方法进行研究，解决地铁盾构隧道区孤石探测相关基础科学问题。建立正常复合地层和孤石体的数值模型和物理模型，进行多场（地震波场和电场）数值计算和物理模拟，研究三维空间条件下孤石异常体的地球物理场响应特征，研究数据采集、数据处理、地球物理场信息识别方法，研究基于交叉梯度耦合约束的三维跨孔电阻率CT与地震波CT数据的联合反演成像算法，提高地铁盾构区孤石异常体的三维定位精度和成像分辨率，为城市地铁隧道工程勘察奠定理论基础。

为准确探测城市地铁盾构隧道区间孤石空间形态和分布的工程难题，本项目重点研究了基于交叉梯度耦合约束的跨孔电阻率CT和地震波CT数据的联合反演成像算法，包括基于有限差分的三维跨孔电阻率CT正演算法、基于共轭梯度的三维跨孔电阻率反演成像算法、2.5维跨孔电阻率CT正演算法、2.5维跨孔电阻率CT反演算法、正则化因子在反演成像中的影响、基于直射线追踪的三维跨孔地震波CT正演和反演成像算法、基于Moser曲射线追踪的三维跨孔地震波CT正演和反演成像算法、2.5维跨孔电阻率CT和地震波CT交叉梯度联合反演算法、三维跨孔电阻率CT和地震波CT交叉梯度联合反演算法、交叉耦合因子在反演成像中的影响、跨孔电磁波CT正演和反演成像算法。基于以上算法，进行了大量数值模拟、物理模拟和现场试验等多种途径，研究了城市地下空间多地球物理方法联合探测地下孤石的分辨率和探测效果。跨孔电阻率CT和地震波CT联合使用，可提高城市地铁盾构隧道区间孤石探测效果，还可以推广在城市地下空间岩溶和其他地质不良体探测中的应用。