[MIS13-P09] Development of a New Method for Rockfall Analysis using Schmidt Hammer
Keywords:rockfall, Schmidt hammer, SfM, UAV
For the survey of rockfall, geological features such as cracks, rock joins, the slope in the triggering area, the weathering patterns and level, and various other data need to be set, but many are based on qualitative criteria, which makes comparisons between sites difficult. A few quantitative methods exist however, such as the stability assessment of rock mass using hammering sound measurement (Kanbara et al. 2013) and vibration measurement with U-Doppler (Uehan et al. 2012). Nevertheless those studies remain very marginal and it is still necessary to develop further low-cost methods to evaluate the stability of rock masses on slopes and terrains difficult to access. Therefore, in this study, we attempted to evaluate the factors, estimated occurrence time, place of occurrence, and geomorphological environment of rockfall using Schmidt Hammer, UAV, and laser data, which are easy to carry because they are compact and lightweight and because they offer data from a comfortable remote position.
The survey was conducted at Gunbarrel-tributary in the Fox Glacier Valley, located on the west coast of New Zealand, using a single hit method for a giant bolder of 5 to 6 m. The data collected show differences in the Schmidt Hammer rebound values, which we could relate to the difference in the degree of weathering. On the newly broken side of the rock, the rebound value tended to be slightly higher than on the sides that were exposed to erosion for a longer period. Additionally, examining the pattern of weathering based on the Schmidt Hammer data, we can also infer that the rock was partly connected to a non-weathered bedrocks while half of it had been subjected to various weathering processes. This finding also allows us to discard a glacial origin. Indeed as half of the block did not show any weathering, we can infer that the rockfall comes from a late detachment from the bedrock. It was not deposited first by the glacier as an erratic block. Further refinement of the method is certainly needed, but the present results are encouraging.