本文利用PFC2D模擬岩石節理面承受直接剪力下之力學行為，節理面之幾何型態包括：不同粗糙角之規則節理面及Barton JRC不規則節理面；探討變因包括：不同正向應力、尺寸、微觀參數；觀察的項目包括：剪力阻抗與剪位移之關係、剪力強度參數、裂縫發展及破壞模態。在分析方面，本文之模擬結果分別與Patton (1966)及張文城(1988)之規則節理面模式及Barton (1977)不規則節理面模式進行比較。結果顯示：在高、低正向應力時，模擬結果符合Patton (1966)雙線性剪力強度模式及張文城(1988)剪力強度模式。在臨界正向應力時，張文城(1988)剪力強度模式與本文模擬結果相符。破壞模態之分布上，模式I破壞發生在低正向應力；模式III破壞發生在臨界正向應力；模式IV破壞發生在高正向應力。不規則節理面分析上使用Barton (1977)提出之剪力強度模式，在正向應力3MPa前，數值模擬結果與Barton (1977)預測值相當吻合；在高正向應力時(3MPa以上)，此模式會高估節理面之剪力強度。不規則節理面的剪力強度並不隨著節理面尺寸增加而改變，與Ueng et al. (2010)、鄒岳展(2002)實驗觀察相似。

This paper used Particle Flow Code in 2 dimension (PFC2D) to simulate shear behaviors of rock joints under direct shear tests. Geometry of joints include (1) regular joints in different roughness angles and (2) irregular joints of Barton’s JRC profiles. Controlled variables involves different normal stresses, specimen sizes, and micro parameters. Shear resistance-shear displacement relation, shear strength parameters, crack propagation, and failure modes were observed in this paper. For regular joint models, the simulation results compared well with Patton (1966) and Chang (1988) shear strength models in higher and lower normal stresses, but only compared well with Chang (1988) in critical normal stresses. For irregular joint models, simulation results compared well with Barton (1977) estimation in low normal stresses (< 3MPa). In higher normal stresses (≧3MPa), Barton (1977) will overestimate this paper simulations. Three failure modes were observed in this paper, (1) Mode I, failure occurs in lower normal stress; (2) Mode III, failure occurs in critical normal stress; (3) Mode IV, failure occurs in higher normal stress. Scale effects were not be observed in this paper, as same as Ueng et al. (2010) and Zou (2002) experimental tests.

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