逆向斜交坡中不同節理組特性對楔形岩體變形及破壞機制影響之探討

以往在討論楔形破懷的機制時，常會將岩石邊坡簡化成被兩道節理面截切，楔形岩塊再沿著交線滑出的模式。但經過實際的現地野外調查，我們觀察到形成岩楔崩落的因素，常常不僅只有截切岩體的兩道弱面，而是連同解壓節理形成的後方邊界，再因楔形岩體下方的趾部侵蝕，多種因素的結合才造成岩體沿著不連續面之交線滑出，形成真正在岩石邊坡中觀察到的楔形岩體變形與破壞產狀。本研究將透過在傾斜儀上堆疊擺放菱形柱體的研磨石，模擬受節理組截切之岩石邊坡，以研磨石與研磨石間的接觸面作為岩石邊坡中的層面及節理，並藉由將一定比例之間隙以白膠黏著及改變傾斜儀的傾斜角度，探討在不同節理延續性以及不同交線傾伏角的狀況下，對楔形岩體變形與破壞發展機制的影響。接著本研究將採用三維離散元素法模擬分析軟體3DEC (Three-Dimensional Distinct Element Code)，在與物理模型試驗之結果進行校核及驗證後，試著於數值模型中改變不同節理延續性、節理面交角、交線傾伏角角度及兩弱面在空間中的不對稱性，比較初始階段中楔形岩體中各岩塊的速度以及崩落後之崩積材料堆積型態，觀察並探討楔形岩體的變形趨勢以及影響範圍，以了解不同節理組特性及傾角在楔形岩體變形機制中所扮演的角色。最後再以東北角南雅里台2線82k處之公路旁邊坡作為實際案例，將研究結果套用於現地邊坡中，進而驗證及探討實際存在於邊坡中之節理組對楔形破壞的坡壞機制之影響。

關鍵字

逆向-斜交坡；楔形破壞；位態判釋；節理延續性； 3DEC

並列摘要

The mechanisms of wedge failures were often considered as a simplified rock slope cut through by two joints, followed by the sliding of the rock wedge along the intersection line. However, wedge failures were induced by more complicated factors according to field investigation. The rear boundary issued from the unloading of the joints and the toe erosion at the bottom of the wedges both led to the sliding of the rock mass along the intersection line, which eventually turned into the wedge deformation and the failure as observed. This study carried out a series of model tests to evaluate the failure mechanism of rock wedges under different joint persistence and different plunge of the intersection line. Diamond-cylindrical blocks were piled to simulate a rock slope with bedding and joints. The interface between the blocks simulates the bedding and the joints. The persistence of the joints was controlled by gluing part of the blocks while the plunge of the intersection line was adjusted by tilting the inclined deck. The results of the model tests were used to verify the numerical model. A three-dimensional distinct element software 3DEC (Three-Dimensional Distinct Element Code) was used to investigate the effects of different joint properties and plunge of the intersection line on the failure mechanism of the rock wedges. The persistence and the plunge of the intersection line were varied in the numerical model, as was done in the physical model tests. Additionally, the effect of the unsymmetrical characteristic between two joints was also evaluated in the numerical model. Afterwards, the model was introduced to simulate a slope located at 82 km of the Provincial Highway No.2, Nanya village, Taiwan. The effect of the joints on the failure mechanism of rock wedges in a real slope was thus discussed and verified.