The Simulation and Imaging of Cross-borehole Elastic Wave for Boulders Detection

In urban rail transit system development, the granite spherical weathering bodies (boulders), which can undermine the relative uniformity of granite weathering profiles, will cause potential safety problems in shield construction. In order to remove this hidden danger, we must detect the shape and distribution of the boulders before the shield construction. Cross-borehole elastic wave plays an important role in urban engineering geophysical exploration as it can avoid the interference of surface conditions, residential and industrial electricity. Through numerical and physical simulation, we select several geological models to prove the feasibility of the technology in which the cross-borehole elastic wave is used to detect the boulders and discuss the ways to improve the imaging precision. (1) Both of the numerical and physical simulation experiments show that the cross-borehole elastic wave works well in boulders imaging, (2) When decreasing the borehole distance/depth ratio, it is easier to identify boulders because the energy of imaging results will be more concentrated.