梨山地滑發生於1990年4月19日,造成臺七甲線73K+150處有長60公尺左右之路段下滑,而使通往宜蘭的交通中斷,地滑地上緣之臺八線、國民旅舍、梨山賓館、臺汽客運站與梨管所活動中心等建築物均有嚴重下陷或龜裂現象。經現況調查後,230公頃的調查範圍分為西、東南和東北三地滑區,每一地滑區都是由數個上下相關連之滑動體構成。機制調查的結果,滑動面型態多為椅子型,深度自15公尺至60公尺不等。發生的機制為在凹谷地形和風化板岩地質的潛因下,連續性的降雨及地下水是地滑的主要誘因。地滑整治規劃的構想為將邊坡的計畫安全係數提昇至1.15~1.20,以地表排水、橫向集水管、集水井及排水隧道工程組合之排水工法為主,另輔以邊坡保護工程及防砂工程,以供後續設計之參考。
The Li-Shan Landslip located on the central crossisland highway in Taiwan happened in April 19, 1990. The occurrence of the landslip endangered the safety of the highway and several buildings.The study area of 230 ha is divided into west, southeast and northeast slip-areas. Each slip-area is composed of several connected sliding blocks. The depth of slip plane ranges from 15m to 60m. The mechanism of landslip was triggered by the groundwater.The remediation measures including surface drainage, horizontal drainage, drainage well, drainage tunnel, sabo dam and steel pipe were planned. Up to now, the supplementary investigation for detailed design was carried out.