摘要
2008年5月28日14时28分,四川汶川发生Ms8.0级地震,由于震级高,持续时间长,释放能量大,震区地质环境脆弱,地震诱发了大量崩塌、滑坡等次生地质灾害,其中四川安县大光包滑坡是规模最大,初步估算滑坡体积在7.42亿m3左右,成因机理最为复杂的地质灾害体。
通过现场详细地质调查测绘及定性分析,运用三维离散元软件,对坡体动力作用进行全过程数值模拟再现,得到如下基本结论及认识:
(1)大光包巨型滑坡是在地震过程中,一次性整体溃裂滑动破坏后高速运动产生,不存在次级或多级大规模滑塌破坏迹象;
(2)大光包滑坡具有多项典型独特地质现象,主要有①主滑体运动1.6km后任未完全解体;②未完全解体滑体前端逆冲推覆变形,形成鼓丘及岩层反翘,产生强烈挤压剪切缝及长大拉张裂缝;③门槛石沟南侧坡面一定高度范围内的植被及浅层土层“不翼而飞”,变形破坏原因独特;④滑坡北侧断壁背坡发育多条长大拉张裂缝,多处见深宽拉陷槽,后壁背坡却完好无损。
(3)滑坡动力形成机制及运动特征具有以下特点和阶段:①坡体震裂松弛,产生微张裂缝并不断向深部扩展;②后缘破裂面和滑面及北侧破裂边界贯通,滑床底部岩体在上覆厚重山体及地震竖向应力的反复拉压作用下被碾碎,由于摩擦产生的高温作用,已变成近似炭状颗粒;③坡体由静摩擦向动摩擦状态转变,处于不断被加速启动过程;当坡体被加速超过滑动临界值,发生整体溃屈式滑动破坏,滑体进入高速运动阶段;④滑体高速冲过黄洞子沟过程中,发生“气垫效应”;⑤高速运动滑体的前端与迎面山体强烈冲撞,岩体溃喷式解体形成碎屑流,整体刚性骤然降低,主滑体中段及后段岩体产生逆冲推覆变形,缓冲减速,顺利实现“软着陆”,保持整体完整。
(4)数值模拟分析结果表明:①滑坡形成及运动特征与定性分析及现场实际地质现象基本吻合;②各监测点位移动力响应及速度和加速度动力响应时程曲线形态特征及变化趋势具有整体一致性特点,这一点可以证明滑坡是一次性发生的;③坡体高高程及特殊地形位置地震动力响应强烈,尤其是条形单薄山脊端部较为明显;④地形起伏大及高程较高的位置加速度放大系数明显增大,沟谷放大不明显。
At 2:28 p.m. on May 28, 2008, Ms8.0 earthquake occurred in Wenchuan Sichuan,Because of high magnitude, long duration, large energy release, seismic zero vulnerability of the geological environment, the earthkuake induced a large number of fallings、landslides and other secondary geological disasters,in the ological disasters,Da guang bao landslide lying in An County Sichuan province is the largest and most complex mechanism body of geological disasters. the volume of landslide is preliminarily estimated about at 742 million m3.
Detailed geological mapping by field survey and qualitative analysis, The use of 3D discrete element software is to reach the role of slope dynamic numerical simulation of the whole process of reproduction, Obtain the following basic conclusions and the knowledge:
(1) In the earthquake process Daguangbao massive landslide is the one-time production after the shattering for high speed movement, there is no large-scale secondary or several level collapse or failure phenomena;
(2) Da guangbao landslide has typical and unique geological phenomenon:they are :①The main landslide body after its’movement 1.2km is not fully disintegrated;②The front sliding body of incomplete disintegration reached to thrust deformation, rock drumlin formation and anti-Alice Produced a strong extrusion shear fractures and raised tension fracture;③The south slope plane of vegetation within a certain height and the shallow soil are "missing",the reason of Deformation and failure are perfect unique;④The back slope of the north failure surface develope a number of tension fracture, many see pull trapped deep groove width, but the back slope of landslide back scarp is intact.
(3) Landslide dynamic formation mechanism and the movement characteristics has the following characteristics and stages:①Stage of slope shatering cracking and loosing, slightly open cracks starts to appear and to continue to produce more deep cracks extended;②Posterior fracture surface、south skid surface and north side of failure surface break through the border,Rock in the bottom of Sliding bed were crushed, after the overlying heavy mountain and seismic vertical stress produce repeated tension and compression, As the high temperature generated by friction,the rack have become a near carbon-like particles;③Slope from the static friction to dynamic friction state changes, at the start of the process of constantly being accelerated, When the slope is accelerated over the threshold,Daguangbao slope overally produced shattering-sliding rupture;④During the process of the landslide High-speedly crossing huangdongzi valley,“Air-cushion effect”occurred;⑤High speed front-end landslide body strongly collides the face of the mountain,the rock collapse jet and are broken up debris flow ; the overall stiffness suddenly reduce,because of the process the middle and back rock of landslide body produce thrust deformation, the buffer reduction speed, successfully realize "soft landing" to maintain the overall integrity.
(4)Numerical simulation results show that:①Landslide formation and sporting characteristics and qualitative analysis and field geological phenomenon are actually in good agreement;②the displacement、speed and acceleration dynamic response curves of changes are basicly consistent in morphological characteristics and the tendency, which has demonstrated that a one-time landslide occurred;③In high elevation and slope position of special terrain,the rock have strong dynamic response ,especially in thin ridge bar ends ,the responses are more obvious;④At the large terrain and high-elevation position acceleration amplification factor significantly increased, no significant amplification in the valley.
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