山區道路落石危險度與危害度之評估與預測

Abstract

台灣山區道路為聯外交通重要通道，但由於沿線邊坡地質破碎，每逢豪雨過後，落石意外不斷傳出，影響民生，阻斷交通，危及通過人車安全。影響落石的成因繁多，包括地形、地質、氣候與環境等因素。過去落石傳統危險度評估方法多將評估因子採絕對確定性之分級劃分，但相較於大地工程其它範疇領域，落石的問題有較高的不確定存在，因此應將落石天生的隨機性考慮進去較為合理。本研究藉由利用傳統落石危險度評估法則，加入不確定性考量，利用可靠度分析原理評估出落石破壞發生機率。同時，本研究也探討雨量對於落石發生潛能之影響，並收集研究區域中部橫貫公路谷關至德基段歷年雨量資料與災害資料，嘗試以不同氣象因子（如累積雨量、落石當日降雨量）與邊坡災害特性，尋找彼此間關連性，以建立雨量對落石造成之危險度預測模式。落石破壞機率的計算乃採用安全餘額的觀念而得，藉由門檻指標與落石危險度指標間的差距大小，來評估出發生落石可能性。利用過去災害案例最佳化學習，本研究中乃假設門檻指標為常態分佈型態。而整個方法以中部橫貫公路谷關至德基路段為研究學習路段，評估與預測結果尚令人滿意。此外，本研究採用風險評估觀念，針對落石對通過人車、鄰近設施、阻斷交通所造成之危害程度，建立一簡單可行之危害度評估模式。

Rockfall often occurs along mountainside road slopes, especially during or after a heavy rainfall. Occasionally, the occurrence of a rockfall results in traffic interruption, property damage, and personal injury or death. The consequence of a rockfall incidence may be very serious and unacceptable for a community. The hazard potential of a rockfall depends on various factors including geology, topography, and weather, among many environmental factors. In the conventional approach, the hazard potential of rockfall is usually evaluated in a deterministic manner. Compared to other aspects of geotechnical engineering, the rockfall problem has a higher degree of uncertainty. It seems reasonable to take the probabilistic nature of rockfall problem into account. This thesis makes use of reliability analysis to investigate the probability of rockfall hazard. It also examines the influence of rainfall on hazard potential. By collecting relevant information concerning the factors that affect the rockfall hazard, this thesis attempts to establish a probabilistic model for evaluating rockfall hazard associated with the condition of rainfall. It establishes an empirical correlation between the minimum rockfall hazard rating and rainfall characteristics (including the cumulative rainfall and the daily rainfall at the time of rockfall). The probability of rockfall is calculated from the safety margin (the difference between the threshold index and the rockfall potential index). The threshold index is assumed normally distributed; it is calibrated from real rockfall records using an optimization procedure. The proposed approach is applied in evaluating the rockfall hazard along the central cross-ridge route. The comparison of the predicted results and the actual case records shows very good agreement. In addition, this thesis adopts the concept of risk analysis and suggests an approach to evaluate the potential for traffic interruption, human life loss and property damage due to a rockfall occurrence.