以坡地土壤厚度及垂直結構探討淺層崩塌潛勢區位

Assessment of the Location of Potential Shallow Slope Failure with Soil Depth and Vertical Soil Structure Data

詹孟浚(Meng-Chun Chan) ； 梁偉立(Wei-Li Liang)

《中華水土保持學報》 45卷2期 (2014/06) Pp. 85-94

https://doi.org/10.29417/JCSWC.201406_45(2).0002

摘要

判斷淺層崩塌潛勢的因子中，地表下不可視的土壤厚度、土壤垂直結構和基岩面地形等因子各別有不同的促崩機制和影響力。本研究利用簡易貫入試驗調查坡地的土壤垂直結構、土壤厚度及推估基岩面地形，瞭解這些因子的空間變異，並以樣區中發生的小崩塌為基礎探討各個因子對淺層崩塌潛勢區位的判釋能力。結果顯示土壤厚度具有空間變異，說明土壤厚度調查的重要性。在崩塌單一因子的分析中，以土壤厚度評估高崩塌潛勢區域（PSFL）所得的分布面積最小，且皆分布於崩塌位置附近，說明土壤厚度在崩塌潛勢的預測中佔有相當重要的角色。由崩塌地的貫入試驗和崩塌剖面觀察所得土壤垂直結構資訊，推測水分垂直移動受硬度較高的土壤層、塊石、基岩面阻擋，使得局部孔隙水壓上升進而引發淺層崩塌。這顯示土壤結構的影響力，也說明了相同的崩塌機制亦可能發生在具有同類土壤垂直結構的區域。根據本研究結果，建議就評估臺灣坡地水文過程及坡地穩定而言，應重視土壤厚度及土壤結構異質性在評估淺層崩塌潛勢區位的影響力。

關鍵字

基岩面地形 ； 淺層崩塌 ； 土壤厚度 ； 土壤垂直結構

並列摘要

The factors related to shallow slope failures include soil depth, vertical soil structure, and bedrock topography. In this study, we surveyed spatial variations of soil depth and vertical soil structure by conducting simplified penetration tests, and then estimated bedrock topography in a newly-planted hillslope. We analyze the ability of these three factors to detect potential slope failure locations (PSFL) on the basis of information from a shallow slope failure which occurred at the study site during the survey period. The results show that soil depth varies spatially on the hillslope. However, there are no obvious correlations between soil depth and any topographic factor. This finding differs from the results suggesting an inverse correlation between soil depth and slope in some previous studies. Comparing the three factors, the area of PSFL determined by soil depth is the smallest. This implies that soil depth plays an important role in predicting the potential of a shallow slope failure. According to information about vertical soil structure, we presume that vertical rainwater infiltration is impeded by local hard soil layers, rocks, and the soil-bedrock interface, and following increase of pore water pressure might trigger shallow slope failure. This indicates that vertical soil structure has implications for vertical soil water movement and PSFL. Consequently, we suggest that the spatial variations of soil depth and vertical soil structure should be carefully considered when assessing potential locations for shallow slope failures in Taiwan.

並列關鍵字

Bedrock topography ； shallow landslide ； soil depth ； vertical soil structure