下荆江二元结构河岸土体特性及崩岸机理  

Soil properties and erosion mechanisms of composite riverbanks in Lower Jingjiang Reach

作　　者：夏军强[1] 宗全利[1,2] 许全喜 邓春艳[1] 

机构地区：[1]武汉大学水资源与水电工程科学国家重点实验室,湖北武汉430072 [2]石河子大学水利建筑工程学院,新疆石河子832000 [3]长江水利委员会水文局,湖北武汉430010

出　　处：《水科学进展》2013年第6期810-820,共11页Advances in Water Science

基　　金：国家自然科学基金资助项目(51079103);国家重点基础研究发展计划(973计划)资助项目(2012CB417001)~~

摘　　要：三峡水库蓄水后下荆江河段河床冲刷下切,局部河段崩岸险情频繁发生。为研究下荆江二元结构河岸的土体特性及崩岸机理,结合近期该河段崩岸情况,现场查勘了6个崩岸点,并对河岸土体进行了室内土工试验。试验结果表明下荆江河岸土体的垂向组成具有典型的二元结构特征:下部非粘性土(沙土)层较厚,上部粘性土(低液限粘土)层较薄且松散。以河岸崩塌过程分析为基础,提出了二元结构河岸发生绕轴崩塌时上部土层稳定性的计算方法。结合近岸水动力条件计算及土工试验结果,定量分析了二元结构河岸的崩塌机理及其影响因素:①下部沙土层的起动流速比近岸流速小得多,故该土层容易受水流冲刷;②上部粘性土层崩塌前抗冲强度很大,但多为低液限粘土且相对松散,崩塌后堆积在岸边容易分解并被水流带走;③河岸稳定安全系数在一个水文年内呈周期性变化,落水期安全系数最小,故容易引发崩岸,该计算结果与近期崩岸实际统计结果一致。The Lower Jingjiang Reach （LJR） is experiencing problems with continuous channel degradations, and lo- cal riverbank erosion occurs frequently. In order to investigate quantitatively the soil properties and erosion mecha- nisms of composite riverbanks, a field survey is conducted at 6 sections of riverbank collapses along the LJR. An in- door soil experiment is also performed, and both physical and mechanical properties of soil samples are analyzed. The analysis reveals that the vertical profile of soil compositions in the LJR can be characterized as being a typical compos- ite structure. The lower layer is thicker with non-cohesive soils, and the upper is thinner and loose with cohesive soils. A new method for calculating the safety parameter of overhanging block in a composite riverbank is then pro- posed. The method uses the principle of cantilever stability with the bank stability degree being closely related to the unit weight of the overhanging block and the corresponding tensile strength. Based on the calculated near-bank hydro- dynamic conditions and the experimental results from the indoor soil tests, bank stability degrees and influencing fac- tors of a typical composite riverbank in the I,JR are investigated quantitatively. The following conclusions can be drawn from the study. The incipient velocity for the non-cohesive lower layer is obviously less than the mean bank-toe veloci- ty, which easily lead to the occurrence of severe fluvial erosions. The cohesive upper layer betore failure has sufficient strength to resist from direct fluvial scour. However, the failed soil blocks deposited in the near-bank zone would be broken down and transported downstream by the near-bank fluvial entrainment due to the soil properties of loose struc- ture and low liquid-limit clay. The safety parameter measuring the degree of the bank stability at each stage during a hydrological year varies periodically and is calculated. The lowest value at the flood recession stage is obtained, which is consistent to the recent

关 键 词：二元结构河岸 土体特性 崩岸机理 河岸稳定性 下荆江 落水期 

分 类 号：TV122[水利工程—水文学及水资源]