Heavy rainfall regularly occurs in Taiwan during the typhoon season in the summer and fall, and this rainfall causes large-scale natural disasters such as landslides, rockslides, and mudflows. Using a geophysical survey
with both invasive and noninvasive methods, this study was conducted to preliminarily understand the hydrogeological
characteristics of a landslide area and locate potential failure surfaces to strengthen slope failure prevention. The landslide area of Babaoliao region in Chiayi County of Taiwan was selected as the research site. Core drilling and analysis were conducted at the site; the results revealed that the 1–2-m-thick upper layer is composed of soil and weathered rock, which is similar to the conclusion reached through resistivity image profiling. Analysis of three boreholes (BH-01–3) determined a 2–3-m-thick layer of shear gouge in the subsurface layer between 18.3 and 26.5 m below ground.Investigation of the fractured rock masses in BH-02 and BH-03 revealed that the region has a large dip angle. Furthermore,geophysical survey of the boreholes demonstrated that both the outer and inner geological layers of the region are composed of silt-bearing marlstone that is not prone to cementation, causing a potential rupture surface. Inspection of BH-03 in terms of groundwater velocity and direction revealed a potential decrease in slope stability under heavy rain due to the rise in pore water pressure caused by the high hydraulic head connected to the borehole through fractures.
The flow path formed by the soil–rock interface at 4 m below ground is a potential rupture surface.
Keywords: Drilling, geophysical approach, invasive and noninvasive methods