强震过程岩体非协调变形及动力扩容效应研究

Existing investigation and exploration work shows the thick interlayer staggered zones are sliding zones of large-scale landslides induced by Wenchuan Earthquake such as Daguangbao landslide, Tangjiashan landslide, etc.. The key factors of landslide formation are rock fragmentation and sharp reduction of friction resistance triggered by strong earthquake in that zone. The studies of the response and slide mechanism of the thick interlayer staggered zone are rarely researched in the process of the strong earthquake. This subject is intended to search the sliding zone by excavating adits in Daguangbao landslide, and then make the study of rock mass structure elaboration and fracture extension regularity. Furthermore, recognized non-coordinate deformation feature caused by seismic wave spreading through hard or soft rock. The micro-fine-macro rockmass structure model will be established in the final. The researchers plan to carry out field rockmass tests, dynamic tri-axial tests and large-scale Geo-centrifuge test. Through these tests we attempt to reveal the starting point and peak value varying regularity of rockmass dilatation under the action of cyclic loading, the dilatation after the peak and fracture development process. Firstly we establish a mechanism about the response of rockmass non-coordinate deformation under the cyclic loading, secondly, discover the effect of the magnifying strength of seismic waves under various depth ,thickness and speed of weak intercalated layers(reveal the effect to seismic wave strength from different weak interlayer thickness, depth and wave velocity), thirdly, reveal the regularity and development laws of excess pore water pressure during the process of rockmass failure and recombination and its contribution to landslide formation. Finally, establish seismic oscillation enlargement - non-coordinate deformation, dynamic dilatation - excess pore water pressure-landslide initiation and evolution mechanism.

汶川地震触发的大光包、唐家山等巨型滑坡，滑带均为厚层间错动带，强震过程滑带岩体碎裂化、摩阻力急剧降低是滑坡形成的关键。但此类厚层间错动带在强震中的响应机理及其致滑机制，还没有深入研究成果。拟申请课题在现有工作的基础上，利用大光包滑坡的开挖平硐追踪滑带，进行岩体结构精细描述和强震裂隙扩展规律研究，辨识地震波在硬、软岩传播过程中引起的非协调变形特征，建立微-细-宏观多层次岩体结构模型。开展现场多手段岩体测试及室内动三轴、大型离心机振动台试验等，揭示循环荷载作用下不同结构岩体的扩容起点与峰值变化规律，及峰后扩容行为与裂隙发展演化过程，建立岩体在循环荷载过程中的非协调变形响应机制；揭示软弱夹层厚度、埋深及其波速对地震波强度的影响规律；阐述岩体结构破坏与重组过程中超孔隙水压力的产生与发展及其对滑坡形成的贡献，揭示地震动放大—非协调变形、动力扩容—超孔隙水压力—滑坡启动演化机制。

我国处于两条全球性地震带的夹持地区，活动断裂十分发育，是全球大陆地震最为集中和活动性最高的地区之一。2008年汶川Ms8.0级大地震产生了迄今为止记录到的，单次地震产生的分布最密集、数量最多、面积最广的滑坡事件，造成了巨大的损失。大光包滑坡是汶川地震触发的最大滑坡，也是全球最大地震滑坡之一，受到国内外广泛关注和持续研究。本项目以大光包滑坡为实例，开展了宏–细–微观调查与测试、室内动力学试验、理论分析和模拟试验，研究了滑坡地质原型、强震过程滑带岩体非协调变形与动力扩容、滑带地震动响应与诱发滑坡启动机理。通过研究，揭示了大光包滑坡滑带背景为斜坡内深埋400m、最大厚度达5m的先期层间构造错动带，该带经历了至少6次构造错动，且具有地下水赋存和运移特征。汶川强震过程中，层间错动带与上下地层产生非协调变形，致使层间错动带受到振动冲压-张拉和振动剪切力，导致其岩体震损扩容。强震过程斜坡潜在通道垂向贯通、高位地下水瞬间挤入层间错动带扩容空间，产生了水击效应，快速降低了层间错动带有效应力和强度。为评估水击力，基于流体力学Joukowsky瞬态流方程建立了扩容软层水击力计算模型，计算结果表明在地下水头70～360 m 范围内可激发水击力达 20 MPa；从而得出，强震过程滑带动力扩容和水击效应可能使得滑坡骤然启动。最后，提出一种大光包滑坡启动的机制模型：强震过程→滑带地震动力破裂扩容→水击效应→滑坡启动。