利用坡高與坡角反衍岩體強度

Inversions of rock mass strength from slope height and angle

蘇意筑(Yi-chu Su)

指導教授 ： 李錫堤 ； 董家鈞

國立中央大學/地球科學學院/應用地質研究所/碩士(2011年)

摘要

地形反映了地殼抬昇與侵蝕作用，長期以來，源於完整岩石強度很高，因此切蝕被認為是型塑地形的最重要因素。近年來研究卻發現，大尺度岩體強度將遠低於室內岩石實驗獲得之強度，因此，岩體強度極可能是限制地形高差的另外一個重要因素。坡度與坡高常被用於束限岩體強度參數，不論是地球或火星都有一些研究案例。本研究利用岩體強度特性、邊坡穩定性及地表形貌三者之間的關係，透過邊坡反應曲線配合地形推估岩體強度。本研究將RMR岩體分類法結合Mohr-Coulomb破壞準則、GSI地質強度指標結合Hoek-Brown破壞準則，利用邊坡穩定分析計算不同強度材料組成及不同高度之下岩坡之安全係數，找出不同坡高之下安全係數為1時的臨界穩定坡角，並展繪RMR-based以及GSI-based邊坡反應曲線，而其中GSI-based邊坡反應曲線結合了有效應力概念(考慮孔隙水壓對邊坡穩定之影響)，使得GSI-based邊坡反應曲線可用於反推有地下水岩坡的岩體強度。本研究經由實際案例說明，利用邊坡反應曲線，配合現地地形之坡高與坡角資料，逆推獲得之GSI值與現地調查之GSI值差異不大，顯示利用GSI-based邊坡反應曲線反推岩體強度具有可行性。最後，透過敏感度分析得知，單壓強度較低、孔隙水壓較高或是低矮岩坡，利用地形配合邊坡反應曲線推估岩體GSI值時，推估結果之變動範圍較大，因此，GSI值逆推時，對Hoek-Brown破壞準則中其它強度參數的掌握要更準確。

關鍵字

邊坡反應曲線 ； 邊坡穩定 ； 岩體強度

並列摘要

Relief is a fundamental landscape reflecting the influence of uplift and erosion. Contrary to the traditional concept that the relief is dominated by incision, recent research indicated that the landscape-scale material strength play an important role on the landform process. However, it is difficult to obtain a representative strength parameters based on laboratory rock tests. Slope height and slope angle were frequently used to infer the strength of rock mass (both for earth and Mars). In this study, a series of slope response curves are proposed to constrain the rock mass strength. Non-linear Hoek-Brown failure criterion is incorporated into the proposed model where the linear Mohr-Coulomb failure envelop seems oversimplified. Field work (measure the geological strength index; GSI) are conducted to validate the non-linear model which the influence of pore pressure is considered. A difference less than 8% between the GSIs obtained from back analysis and site investigation indicates the feasibility to back calculate the rock mass strength from GSI-based slope performance curve. Consequently, the strength of rock mass could be inferred from the topography. Based on parametric study, slopes with high uniaxial compressive strength, low pore water pressure and high slope height are less sensitive to the back calculations.

並列關鍵字

Rock mass strength ； Slope performance curve ； Slope stability

參考文獻

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