湖口崩塌地位於新竹縣新埔鎮湖口臺地南緣，在地質年代上屬於上新至更新世之地層，由節理不發達、膠結不良的砂岩、泥岩及砂泥岩互層之岩層組成。湖口崩塌地邊坡常常於豪雨過後發生邊坡滑動，其中以1990年4月23日所發生的大規模地層滑動最為嚴重，屬地滑活動相當頻繁之區域。由地形與地質研判湖口臺地崩塌區共可計三次的大型滑動，三個滑動面均位於同一不透水泥岩層。滑動面依序由下而上可分為第一階滑動面、第二階滑動面與第三階滑動面，其滑動面的位置、深度皆為已知，提供本研究一個邊坡正、逆分析之題材。 本研究嚐試由湖口崩塌地現況水文地質模型，藉由現地水壓計監測資料，進行降雨滲流水文地質概念模式及地層水力參數校正，並利用校正後之水文地質數值模式與地層水力參數，進行1990年崩塌前之滲流模擬及第一階滑動面邊坡穩定逆分析以校正地層強度參數。校正後之地層水力參數及強度參數，再經由第二階滑動面與第三階滑動面崩塌水文地質數值模式加以驗證，以確保水文地質概念模型與地層水力參數、強度參數之合理性。最後，基於數值模式分析結果，本研究建立湖口崩塌地之地層滑動與水文地質條件之關連性，並瞭解水文地質因素及特性對湖口臺地滑動之影響。結果發現，水力-力學特性之異質性與異向性，對於湖口臺地豪雨誘發之滑動扮演重要角色。 Hukou landslide is located in the southern margin of Hukou terrace at Hsinpu, Hsinchu. Pliocene to Pleistocene formation composed of the poorly cemented sandstone, mudstone, and sandstone mudstone interbeded. Hukou landslide triggered by heavy rainfall in April 23, 1990. according to the topography and geological analysis, three distigable sliding mainly along an impermeable beding plane are identified. From the bottom-up, The sliding surfaces were chartegorized as the first slip surface, the second slip surface and the third slip surface. With knowing exact positions of the sliding surfaces, it is possible to conducte forward and back analysis of slope stability. A hydro-geological model of Hukou landslide was proposed. The conceptual model and the hydraulic parameters were calibrated using the rainfall data and monitored pore water pressure. Moreover, using the calibrated numerical hydro-geological model, the strength of the first sliding surface was back calculated. The back calculated hydraulic and strength parameters were verified to ensure the rationality of the conceptual hydro-geological and slope stability model during the second and the third retrived sliding. Finally, based on the numerical experiments, the hydrological and geological factors influencing the slope failure were discussed. It is demonstrated that the hydro-mechanical heterogeneity and anisotropy of poorly cemented rock play a major role on the instability of Hukou terrace during heavy rainfall.
