基于稀土元素示踪技术的库岸崩滑土体堆积特征研究

Characterizing reservoir sediment deposition caused by bank collapse with REE tracer

降雨和库水位变化是库岸崩滑的重要诱发因素。以黄河中游土质库岸为研究对象,在由3°缓坡、40°陡坡和70°急坡组成的概化岸坡上,利用稀土元素(REE)示踪技术,研究降雨和库水位升降作用下库区堆积土体的来源,分析离岸方向上的土体堆积特征。结果表明:在水位下降、水位上升、降雨作用-水位下降和降雨作用-水位上升4种工况下,同一组地形经过5场试验后,库区内来源于缓坡、陡坡、急坡的土量以及堆积土体总量均与堆积土体和库岸之间的距离存在负指数函数关系,且相关性较高;急坡是库区堆积土体的主要来源,其中水位变化条件下尤为明显;在水位上升和水位下降工况下,同一组地形5场试验后来源于急坡的堆积土量平均约占总堆积土量的71%;急坡对库区堆积土体的泥沙贡献率在坡脚处基本达到最高,各组地形5场试验后急坡对临岸堆积体泥沙量的平均贡献率约为66%。因而,在水库蓄水或放水时,需重点做好对急坡的防护。

Rainfall and water level fluctuations are critical triggering factors for reservoir bank failures.Taking the soil reservoir bank in the middle reaches of the Yellow River as the case study,this paper investigates the effects of rainfall action and water level fluctuations on the source of sediment deposition and the soil accumulation characteristics of the offshore direction in the reservoir area.By means of the rare earth element(REE)tracer technique,concept bank slopes containing the gentle slope of 3°,steep slope of 40°and abruptly steep sidewall of 70°were investigated.Four different conditions are designed for the analysis,including falling water level,rising water level,the coupled effect of ongoing rainfall and falling water level,and the coupled effect of ongoing rainfall and rising water level.The results show that after five experiments in the same group of terrain,soil productions from the gentle slope,steep slope,abruptly steep sidewall,and the total soil accumulation are strongly correlated with the distance between the sediment deposition and the bank,which can be expressed by the negative exponential function.The abruptly steep sidewall is a dominant source of sediment deposition in reservoir areas,particularly under the condition of water level fluctuations.The average mass of sediment deposition from the abruptly steep sidewall accounted for 71%of the total sediment deposition mass after five experiments in the same terrain group under rising and falling water levels.Furthermore,the sediment contribution of the abruptly steep sidewall to the mass of sediment deposition is basically highest at the toe of the slope,and its average contribution accounted for approximately 66%.Hence,it is advisable to protect the abruptly steep sidewall of the reservoir banks when impounding and releasing.