陡倾顺层岩质斜坡动力倾倒变形机理研究

通常认为顺层岩质斜坡动力变形破坏以滑移—拉裂、滑移—弯曲模式为主,但是通过现场调研发现,在陡倾顺层斜坡中存在一类特殊的动力变形破坏方式——倾倒变形。为了得出该类型斜坡动力倾倒变形机理,以四川汶川县水磨沟陡倾软硬相间顺层斜坡在"5.12"汶川地震作用下失稳为例,在充分总结滑坡区工程地质条件和分析其动力破坏特征后,利用二维离散元数值模拟方法开展研究。结果表明:在地震荷载作用下,在斜坡表面PGA放大系数随着高程的增加总体表现节律性变化,在坡肩呈现峰值;斜坡失稳机理为坡内软岩和硬岩差异式拉剪破坏导致层面抗剪强度急剧降低,岩土体沿优势层面下滑;由于坡体下部岩层锁固作用,坡体向下滑动受阻,坡脚附近岩土体翘曲隆起,而坡顶震裂松弛岩土体在巨大地震惯性力下沿优势结构面滑动剪出过程中,受坡肩"关键块体"阻挡而向临空面发生倾倒变形,整个斜坡发生滑移—下部弯曲—上部倾倒式失稳破坏。研究成果为类似地区的边坡工程地震失稳分析提供参考和依据。

Study on dynamic toppling deformation mechanism of inclined steep-dip bedding slope

It is generally considered that the dynamicdeformation and failure of inclined bedding rock slope are mainly dominated by the modes of sliding-tensile fracturing and sliding-bending，however，it is found out through the relevant in situ investigation that another kind of dynamic deformation failure mode———toppling deformation is there for the inclined steep-dip bedding slope. In order to obtain the dynamic toppling deformation mechanism of this kind of inclined slope，the instability of the inclined steepdip hard rock and soft rock interbedded slope at Shuimogou of Wenchuan County in Sichuan Province under the effect of 5. 12 Wenchuan Earthquake is taken as the study case，from which the relevant study is carried out with the 2 － D discrete element numerical simulation method after fully summarizing the engineering condition of the landslide area and analyzing its dynamic failure characteristics. The result shows that the PGA amplification factor on the slope surface presents a rhythmic change along with the increase of the elevation，while its peak value occurs at the slope-shoulder. The instability mechanism of the inclined slope is the sudden decline of the shearing strength of the bedding-plane caused by the differential tensile-shear failures of the soft rock and hard rock in the slope，which makes rock-soil mass slide down along the superior bedding-plane therein. Due to the blocking effect of the rock layer at the lower part of the slope，the downward slide of the slope body is restricted and the rock-soil mass warps and protuberates at the slope toe，while the toppling deformation of the shattered and relaxed rock-soil mass at the slope crest to the free-face arisesdue to the obstruction from the“key block”of the slope shoulder during its sliding and shearing out along the superior structural planeunder the great earthquake inertia force，and then the instability failure of the whole inclined slope，i. e. sliding-bedding at the lower part-toppling of the upper part occurs. The study result can provide a basis and reference for the analysis on the slope instability caused by earthquake in the similar region.