[H-TT20] New Developments in Shallow Geophysics

[HTT20-P06] Relationships between leakage areas through basement and the distribution of a covering layer detected by geophysical exploration

*Kyosuke Onishi¹, Yusuke Oishi¹, Kobayashi Takayuki² (1.Public Works Research Institute, 2.OYO Corporation)

Keywords:leakage, ground-penetrating radar, resistivity survey, covering layer

Water leakage through basement is one of a main cause of dike break. For decreasing flood damage which increases gradually in these days in Japan, it is required that areas with high potential to generate leakage are identified. However, many levees do not have enough information such as the history of making dikes, therefore it is difficult to identify the region with high potential to break a dike. Also, boring results are not continuous information for space and cannot identify higher potential areas of water leakage. Therefore, geophysical exploration methos must become effective ways to identify the weak zone for leakage.

This report shows records of ground-penetrating radar (GPR) and electric measurement in the damaged levee which had water leakage through basement. First, we show GPR record which was acquired near a levee and indicates rugged layers in the ground. We can find that the edges of area crossing with a high permeable layer and the ground surface are located at water leakage points from the survey record. In general, the water leakage has high potential in the area that the width of the covered layer with low permeability is thin. Thus, we will show records of GPR and electric measurement to identify the thickness distribution of a covered layer. When a high permeable layer in basement is identified by boring, we can determine the region with high potential for water leakage using geophysical exploration.