澜沧江上游河谷哑贡倾倒变形体形成机制及过程

陡倾层状岩体的深层倾倒变形是我国西南深切河谷常见的一种地质现象。第四纪以来，伴随青藏高原隆升，强烈的河谷下切是导致这一现象的重要原因。以澜沧江上游河谷哑贡倾倒变形体为例，采用底摩擦重力试验和数值计算的方法，对河谷下切过程中该倾倒变形体的形成机制和过程进行了研究。结果表明:该边坡随着河谷下切、岩体卸荷及边坡应力场的重新分布，岩体中形成了较深的应力松弛区，主应力方向调整为重力方向，应力松弛区中陡倾的层状岩体向河谷方向发生倾倒变形。根据物理试验特征及数值分析结果，倾倒变形演化过程可归纳为:卸荷（回弹拉裂阶段）、变形（裂隙发育阶段）及折断（裂隙贯通阶段）。

A study on mechanism and process of Yagong toppling fracture in the upper reaches of Lancang River

Deep-seated toppling deformation of steep stratified rock mass is a commonly-seen geological phenomenon in deeply incised valleys in Southwest China. Primarily contributing to this is severe valley downcutting in the wake of uplift of Qinghai-Tibet Plateau since the Quaternary period. In the present paper, taking the case study on the Yagong toppling fracture in the upper reaches of Lancang River as an example, bottom-friction gravity test and numerical calculation were employed to probe into the mechanism and process of how such toppling fracture has formed during valley downcutting. The study has drawn conclusions mainly as follows: the side slope moved along with the valley while downcutting; rock mass loaded off and the field of stress of side slope was re-distributed; a deep-seated area of stress relaxation took shape in the rock mass; and the direction of primary stress re-aligned with gravity direction, under the effect of which deep-seated stratified rock mass in the area of stress relaxation was made topple and deformed towards the valley. The study, on the basis of physical testing features and numerical analysis results, finally concludes that the evolution of such toppling and deformation has the stage of unloading-rebound tension fracture, the stage of deformation-crack development, and the stage of fracture-crack penetration.