Difference between rainy and dry year in Relations of activity and hydraulic parameters of landslide prone area: A case study in Xinzhuang, Southern Taiwan

The landslide prone area, Xingzhuang has been identified as a deep-seated landslide prone area by Taiwan authorities. Where covers a 10.3 hectares’ area with an average slope of 22.8 degrees and 20 buildings around the slope toe. The majority lithology of upper slope is sand-shale interbedded with highly sand contented, which differs from lower slope in shale with mud contented. In order to grasp the activities of this area, we have installed a real-time compound monitoring station including GNSS, biaxial tiltmeter, ground water level meter, and rain gauge.

The rainfall depth of 2021 and 2022 was 4,175 mm and 1,691 mm respectively. The difference was larger than 2400 mm in our study area which might induced the different activity behaviors. In this study, we discussed the relations of slope activity and hydrological parameters in last two years. The results show (1) The variation of X-direction of tiltmeter were about 7,500 and 3,500 (sec) in 2021 and 2022, respectively. The variation of Y-direction of tiltmeter were about 6,500 and 4,500 (sec) in 2021 and 2022, respectively. (2) In the same 6-hours rainfall intensity, the 6 hours tilt-angle of X and Y direction in 2021 were both two times of 2022. (3) In the same ground water level, the 6 hours tilt-angle of X and Y direction in 2021 were about 2 and 1.5 times of 2022, respectively. (4) In the same variation of 6-hours ground water level, no matter raising or decline ground water level the 6 hours tilt-angle of X and Y direction in 2021 were about 2.2 and 1.5 times of 2022, respectively. And the change rate of the 6 hours tilt-angle would be accelerated when the 6-hours variation of groundwater level was higher than 0.4 meters. On the whole, the rainy year would induce more active than dry year.