| dc.description.abstract | Resistivity Image Profiling (RIP), a mature technique and that provides stable quality data, can acquire a continuous subsurface image. Moreover, it is sensitive to water and fine content. In general, the significant results can be produced at landslide due to high contrast of resistivity between colluvium and bedrock. Combining RIP, groundwater mobility obtained from E-Logging, geological and groundwater level data, the mechanism and hydrogeological model of landslide can be further determined.
The southeastern part of Lishan and Gangxianxiang landslide areas of central Taiwan were chosen as study sites. The following conclusions can be drawn:
1. The southeastern part of Lishan landslide area:
Based on RIP and rock samples collected from boreholes results, three electrical strata are recognized; colluvium, the shear zone composed of shear gouges and shattered slate, and the undisturbed slate formation. The steep shear zone serves as aquitard, it forms a natural barrier which blocks and retains groundwater flowing down the slope. Groundwater will brim over the barrier when the water level is high. Sufficient supply of groundwater from Fushoushan Farm creates a dynamic balance of groundwater with a stable water level where is higher than shear zone. A series of curved basal surface of the colluvium associated with the main slope failure shown from resistivity variation indicated that the slope migrated upwards, this may be caused by the uplift of the tectonic movement.
2. Gangxianxiang landslide area:
The trend of iso-resistivity line in bedrock is similar to the bedding plane, it indicates that lithological characters dominate resistivity. The low permeable bedrock with poor developed joint and fracture can be further inferred. The groundwater within the bedrock lowers the negative effect on slope stability. When a large quantity of groundwater accumulates in the colluvium; this increases the downward force of the slope and decreases the resistance of surface between colluvium and bedrock. The sliding surface occurred from colluvium down to shallower bedrock. The open release joint of rock slope, highly weathered, near upslope Huoshaoping Terrace is well developed. The rock body, cut by joints, collapse easily, it must be related to groundwater flow with higher gradient from Huoshaoping Terrace.
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