為探討市道172線42K+300處邊坡在不同降雨強度與三個地震紀錄下之邊坡穩定性，並評估兩者造成複合型災害的影響。本研究首先使用GMS (Groundwater Modeling System)建立研究區域的三維地層模型與常時地下水位面，再輸入FLAC3D(Fast Lagrangian Analysis of Continua in 3 Dimensions)進行降雨入滲與地震模擬，探討此區域邊坡之安全性。並將分析結果、現地監測資料與二維模型分析結果進行比較，顯示本研究過程與結果的合理性。
本研究以四種不同降雨強度(100、200、350、500 mm/day)與2022年9月18日台東地震(ML= 6.8)及2024年4月3日花蓮地震(ML= 7.2)進行模擬。在降雨入滲的模擬結果顯示水位上升約0.43~2.93公尺，隨著降雨強度的增加，坡面飽和度的範圍越大，從下邊坡往中邊坡延伸，導致東側邊坡有崩塌可能性，而商家與民宅區域相對穩定；在地震模擬中，先以距離研究區域最近的沄水國小測站紀錄(PGA約為61gal)進行分析。結果顯示對於本研究區域商家與民宅影響不大，而東側邊坡則處在較於不穩定的狀態。
在降雨入滲與地震聯合作用模擬下，結果顯示地震前的降雨入滲造成邊坡飽和度增加與地下水抬升，導致邊坡穩定性降低，相繼發生的地震使邊坡情況更加惡化，變得更加難以預測，崩塌範圍隨著震前累積降雨量的增加而持續擴大。依滑動方向趨勢結果，東側邊坡崩塌時會影響商家與民宅區域，使其處在危險之中。

This study applies the shear strength reduction method to investigate three-dimensional slope stability with rainfall infiltration and earthquake on the slope at 42K+300 of County Highway 172 in Tainan City. First, GMS (Groundwater Modeling System) was used to build the realistic three-dimensional stratigraphic model and water table of the study area, and then FLAC3D (Fast Lagrangian Analysis of Continua in 3 Dimensions) was used to analyze slope stability with rainfall infiltration and earthquake.
In the simulation of the combined action of rainfall infiltration and earthquake, the results show that rainfall infiltration before earthquake causes the increase of slope saturation and groundwater uplifting, which leads to the decrease of slope stability. Successive earthquakes aggravate the slope situation and make it more difficult to predict. The collapse range continues to expand with the increase of accumulated rainfall before earthquake. As a result of the sliding trend, the collapse of the eastern side slope will affect businesses and residential areas, putting them at risk.

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