藉地表位移場推測邊坡滑動面位置之初探

A Preliminary Study on Inferring the Slip Surface of Emerging Landslide from Surface Displacement Field

方星文(Hsing-Wen Fang)

指導教授 ： 潘以文

國立交通大學/工學院/土木工程系所/碩士(2018年)

摘要

邊坡崩塌常有著歷時性短且會毀滅性高的特性，往往造成突發的生命財產損失。針對具有滑動徵兆之邊坡，於邊坡破壞前之調查因此十分重要。而在邊坡調查中，對於滑動面位置之調查，在一般的工程手段都是在鑽探後，安裝監測系統方能確定滑動面之位置。然而若尚不知滑動面所在，於鑽探規劃時卻往往難以決定鑽探孔應布置之位置與深度。也因還不確定滑動面之位置，為求保守可能會浪費鑽探成本，反之若過度樂觀卻可能深度不足。
本研究嘗試在鑽探規劃開始前，利用地表位移分布推測滑動面之概略深度，以利後續調查規劃之參考。本研究計算滑動面位置之方法係建立於地表位移與圓弧形滑動之幾何關係上，因此所研擬之方法限用於滑動位移有限的單一圓弧形滑動面。本研究利用圓弧形滑動面與地表位移量之幾何關係，嘗試反算推估滑動面之位置，並利用地工分析軟體FLAC3D進行模擬驗證，比較場址之地表位移分布情形與FLAC3D計算之位移分布結果是否相符。
本研究以兩處案例測試上述方法之可行性，兩處案例場址分別位於苗栗縣南庄鹿場以及阿里山二萬坪地區。由於鹿場案例缺乏可靠之精確地表位移量測，故僅經由數值模擬計算模擬之字坡區域之地表位移場。並於之字坡剖面假設不同滑動面以進行FLAC3D模擬以得到相對之地表位移場，再以模擬所得之地表位移場來推衍滑動面位置，比較推衍滑動面是否與先前假設之滑動面一致，以驗證推衍滑動面之正確性。就阿里山二萬坪之案例，該處經歷八八風災後，由前後期之DEM可明顯發現滑動跡象，且具有明顯典型圓弧形滑動之特徵，經測試推衍滑動面並與現場條件比較，本研究之方法大致可行。

關鍵字

推衍滑動面 ； 邊坡滑動 ； 地表位移 ； 數值模擬

並列摘要

A landslide failure usually takes place in a short time and may cause sudden disastrous consequence. It is therefore important to investigate the precursor of a landslide before its ultimate failure. The conventional ways for locating the slip surface of a landslide rely very much on placing instrumentation in boreholes. However, one has to assess the depth and the extent of the slip surface before planning the required borehole exploration.
This thesis aims to propose an inferring approach for the slip surface of a landslide from the ground-surface displacement field (GSDF) before planning a borehole-exploration program. The basic principle of the proposed method is the geometric relationship between the GSDF and the rotation of a circular landslide. Owing that this principle is only valid for a circular landslide, the proposed method is only useful for estimating the single slip surface resulting from at least one arc within a circular landslide. For the purpose of verification, this thesis also compared the GSDF corresponding to the inferred slip surface and the GSDF estimated by the software FLAC3D.
This thesis examined the feasibility of the proposed method with two case studies, the first one located in Luchung, Miaoli County and the second in the Erwanping Area in Alishan. In lack of high-resolution GSDF measurement in the first case, this study regarded the numerically simulated GSDF results (by FLAC3D) assuming various slip surfaces in the z-shape slope area in Luchung as the field GSDF. Then, the study used the artificial GSDF to infer the slip surfaces corresponding to each sets of GSDF. Next, the thesis compared the inferred slip surfaces with the slip surfaces assumed in the FLAC3D simulation. For the second case study, the DEM before and after the Morakot typhoon clearly indicates the occurrence of a typical circular sliding. This study compared the slip surface (inferred from the retrieved GSDF) with the field evidence of the actual sliding surface. The comparison of slip surfaces in both case studies support the feasibility of the proposed method.

並列關鍵字

inferred slip surface ； landslide ； surface displacement ； FLAC3D ； Numerical simulation

參考文獻

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2. BISHOP, K. M. (1999). Determination of Translational Landslide Slip Surface Depth Using Balanced Cross Sections. Environmental & Engineering Geoscience, V(2), 147–156.

3. Carter, M., & Bentley, S. P. (1985). The geometry of slip surfaces beneath landslides: predictions from surface measurements. Canadian Geotechnical Journal, 22(2), 234–238.

4. Calvello, M., Cascini, L., & Sorbino, G. (2008). A numerical procedure for predicting rainfall-induced movements of active landslides along pre-existing slip surfaces. International Journal for Numerical and Analytical Methods in Geomechanics, 32(4), 327–351.

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