通过现场调查,结合边坡的地形地貌、坡体结构、变形破坏和江岸纹泥沉积特征,分析认为滑坡在变形破坏后高速下滑,撞击对岸山体并堰塞堵江,在经历长期的河湖相沉积后逐渐溢流溃决,部分滑体分别残留于左、右岸山坡上。根据恢复的原始地形,通过刚体极限平衡分析可知滑坡为地震诱发,为了进一步研究滑坡堵江成因和变形破坏机理,运用离散元数值软件进行模拟分析。研究表明天然状态下坡体浅表部沿层面和缓倾坡外优势结构面产生卸荷拉裂,地震作用使坡体内部层面拉裂并沿缓倾坡外优势结构面剪断破坏,其破坏堵江过程可概括为前缘剪切变形、后缘震动拉裂→滑面贯通、高速下滑→铲刮河床、刨蚀对岸山体→前缘受阻隆起、后缘坐落下滑、中部堰塞堵江→震后停积自稳,坡体具有明显的动力放大效应。
Abstract
Through field investigation and according to the topography and landform characteristics, structural characteristics of slope, deformation characteristics of slope and deposits characteristics on riverbank, we conclude that the ancient landslide slid down with a high speed after failure, then hit the hill on the opposite bank and blocked river. After a long time of fluvio-lacustrine deposit, the barrier dam overflowed broke down with stepwise scour and the debris were still left on the left and right side of the river. Restoring the original terrain and using general limit equilibrium method, we analyze that the landslide is inducted by earthquake. To further research the formation of blocking river and deformation failure mechanism of the landslide, we employ discrete element method to simulate the landslide process. Results reveal that under natural circumstance, relaxed-tension cracks in shallow surface of the slope developed along the bedding plane and preferred gently-inclined plane; while under earthquake condition, tensioned fracture occurred inside the slope and shear failure happened along the gently-inclined structural plane. The slope experienced the following stages (1) shearing deformation happened in the leading edge and vibration-tension cracks occured in the back edge of the slope; (2) sliding plane penetrated through and the slope slid in high speed; (3) the landslide scraped the riverbed and ploughed the hill on the opposite bank; (4) the leading edge of landslide uplifted for impediment, the back edge stood and glided, and the middle part blocked the river; (5) the landslide self-stabilized after earthquake. The slope has an obvious amplification effect under the action of seismic dynamic load.
关键词
古滑坡 /
变形破坏机理 /
堵江特征 /
离散元数值模拟 /
放大系数
Key words
ancient landslide /
deformation and failure mechanism /
characteristics of blocking river /
discrete element numerical simulation /
amplification coefficient
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