9. Shallow/Near-Surface Structural Applications
Estimating Underground Tilt Variations under Some Loading Conditions on the Surface using FEM
Takeshi Shimizu, Kyosuke Onishi, Yasuhiro Yamada and Toshihumi Matsuoka
Kyoto University, Japan.
Abstract
The high-resolution tilt meter is a kind of level meter. Tilt-signal is affected significantly by noise, which arise from various causes, but the signal due to the surface noise decreases with increasing of the tilt meter installation depth. From this reason, the tilt meter has been installed in a vertically drilled hole at some depth. Advancements in tilt meter technologies are of significance, especially in this decade. High-resolution tilt meters are available for estimating underground tilt variations, which are affected by rainfalls or snow fall on the surface. So, it is effective for various types of underground imaging and evaluation. But, in order to image and evaluate, it is indispensable to estimate elastic modulus such as the Young's modulus. As one of the application, the moveable loading experiment can be proposed. For example, using the weight of a dump truck as an artificial load from the surface. A dump truck comes up to the high-resolution tilt meters installed in a hole. A set of tilt-time record is obtained by such a movable loading experiment. The analysis on the tilt-distance relation data will provide the deformability modulus of a huge scale rock mass, for example the value of the Young's modulus. In this study, we simulate underground tilt variations under some loading conditions on the surface provided snow fall and estimate the Young's modulus by using finite element method (FEM), and we evaluate this simulation by comparing the result of calculation with the strict solution based on elasticity theory. From this simulation, we know that amount of tilt at 12m depth is about 20 micro radian under a load of about 5 tons on the surface. We will try to check the method in field observation under the condition of typical surface soil. This method is available for imaging geological discontinuities, such as faults.
Last modified: Tue May 23 08:59:24 2006