Abstract
In this study, first, a finite element analysis was performed for heterogeneous rocks or a homogeneous rock with a mountain/valley on the surface, to know the effects of the mechanical heterogeneity and the surface topography on the surface tilt induced by groundwater flow. Next, an inverse analysis was performed by using the surface tilts obtained for the rocks to estimate groundwater flow under the assumption that the rock mass is a homogeneous half space. The surface tilt in a two-layered rock is greater than that in a homogeneous rock since the vertical deformation at upper depths of the field of groundwater flow is greater than that in the homogeneous rock, to compensate the vertical deformation at lower depths, which is suppressed by the lower layer with higher Young’s modulus. The surface tilt of the rock with a mountain/valley on the surface is smaller/greater than that in a homogenous rock, depending on the distance of the surface to the field of groundwater flow. The surface tilt suddenly decreases beyond a fault since the fault absorbs the volumetric strain induced by the groundwater flow. Although groundwater flow is roughly estimated by the inversion of the tilt data obtained for the heterogeneous rocks under the assumption that the rocks are a homogeneous half space, groundwater flow may be overestimated or underestimated, and furthermore small artifacts appear around the real field of groundwater flow, depending the degree of heterogeneity, the roughness of the surface and the layout of the tiltmeters.
