【摘要】 为揭示二元结构河岸的崩塌机理,本文采用荆江河岸原型土体为试验材料,开展了上、下荆江二元结构河岸崩塌过程的概化水槽试验,分析了河岸的崩塌过程、机理及崩塌后土体的堆积、分解和输移特点等.试验结果表明:平面滑动破坏在上荆江概化试验中发生频率最高,其崩塌过程包括岸顶竖向拉伸裂隙的出现以及崩塌土体(滑崩体)沿滑裂面的滑动两部分;下荆江概化试验河岸崩塌类型主要为悬臂破坏,发生机理为悬空土块宽度超过其临界值,自身产生的重力矩大于黏土层的抵抗力矩,从而绕中性轴旋转发生崩塌;从试验结果还可看出,上部黏性土层崩塌后大部分土体会暂时堆积在河岸坡脚处,不会被水流立即冲走,在一定时间内对覆盖的近岸河床起到一定保护作用;崩塌后土体在坡脚处呈三角形堆积,其坡度近似等于河岸水下稳定坡比或泥沙水下休止角;堆积土体的体积主要与崩塌土体体积有关,一般占后者的比例在0.38~0.74之间,实际计算中可以按照此比例进行估算.更多还原

【Abstract】 In order to explore the erosion mechanisms of composite riverbanks,a series of flume experiments about the erosion process of Upper Jingjiang Reach( UJR) and Lower Jingjiang Reach( LJR) were conducted using prototype soils of Jingjiang Reach. Through analyzing the experimental results,bank erosion process and mechanism,the deposition,decomposition and transport of the failed block were analyzed. Firstly,the results indicate that planar sliding failure represents the most frequent bank erosion in UJR flume experiment,which the vertical tension cracks will appear firstly on the top of bank and then the failed block will slide along a slip failure plane. Secondly,the main bank failure types are shear failure,beam failure and tensile failure in LJR flume experiment. The mechanical conditions of cantilever failure are that the width of overhanging block is bigger than the critical value and the weight moment of overhanging block is greater than the resistance moment of cohesive layer,which produce rotational motion around the neutral axis toward the direction of river channel. Therefore,the mechanical equilibrium principle of overhanging cohesive layer is the erosion mechanism of bank failure in the LJR. Finally,based on the results of experiment,most failure block of cohesive soil upper bank may deposit on the toe of the bank. They will remain until be broken down or entrained by the flow. The failed block,in turn,may temporarily protect the toe of the bank from erosion. The deposition form of failed block is a triangle,which the slope is approximately equal to the underwater stable slope of bank or underwater repose angle of sediment. The deposition volume of failed block is mainly related to the collapsed volume and the ratio between them is from 0. 38 to 0. 74,which can provide a basis of actual calculation.更多还原