荆江河段崩岸机理及多尺度模拟方法

三峡工程运用后,进入荆江河段的水沙条件大幅度改变,导致近期崩岸频繁发生,影响局部河段的河势稳定及河道防洪安全。荆江段河岸组成一般为上层黏性土、下层沙土的二元结构,在近岸水流冲刷及河道水位涨落过程中受多种因素作用而发生崩塌。以往崩岸模拟考虑因素少,且相关参数难以量化确定。将河流动力学与土力学结合,提出了荆江段河岸土体物理特性与抗剪、抗冲及抗拉强度三大力学特性的量化指标,建立了上、下荆江二元结构河岸稳定性的计算方法,揭示了坡脚冲刷、潜水位变化等因素对岸坡稳定性的影响;提出了河岸崩退过程的多尺度模拟方法,将崩岸力学模型与水沙数学模型耦合,不仅能模拟河道内水沙输移及床面冲淤过程,而且还能模拟不同二元结构河岸的崩退过程。将建立的模型应用于荆江河段典型断面、长河段及局部河段的崩岸过程模拟,计算结果与实测值总体符合较好。提出的多尺度模拟方法为荆江崩岸预测提供了理论与技术基础。

Bank collapse mechanism of Jingjiang River reach and multi-scale simulation

After operation of TGP, the flow and sediment conditions in the Jingjiang River changed greatly, causing frequent bank collapse in recent years and influencing the stability of the local river regime and the safety of river channel flood control. The river bank is a dual structure of clay in upper layer and sandy soil in lower layer and is prone to collapse influenced by various factors in the processes of near-bank flow scouring and water level fluctuation. The simulation in the past considered less factors and the correlative parameters were difficult to be quantified. Combining river dynamics and soil mechanics, this paper puts forward three main quantified mechanics indexes of anti-shear, anti-scouring and anti-tensile, and establishes the stability calculation method for the dual-structure bank of the upper Jingjiang and lower Jingjiang rivers. The results reveal the influential factors of the bank stability such as bank toe scouring, potential water level change etc. and suggest the multi-scale simulation method for the river bank collapse and retreat. Coupled bank collapse mechanics model and flow-sediment mathematical model not only simulate the processes of flow-sediment transport in river channel and river bed scouring, but also simulate the collapse and retreat process of dual-structure bank. The bank collapse simulation results in the typical cross-sections of the Jingjiang River, long scale reach and the local reaches with the model are well accordance with the measured results in general. The suggested multi-scale simulation method provide theoretical and technical basis for bank collapse prediction of the Jingjiang River.