粉煤灰模型沙的试验研究

 泥沙模型应正确复演原型河道演变特点和规律，模型沙的选择是起关键作用的。为此，通过室内土力学试验、物理化学性能分析、玻璃水槽试验和泥沙模型验证试验结合理论分析等方法，对粉煤灰模型沙进行了试验研究，取得了以下主要成果和结论。(1)采用光学显微镜和电镜观察成果分析了粉煤灰的细观结构和理化特性，明确了d＞0.076 mm的粉煤灰分散性较好；(2)用定量数值对比了粉煤灰干重度及土力学特性变化规律与天然泥沙的差异，阐述了选用凝聚力较低的粉煤灰粒径组作模型沙的机理；(3)粒径为0.027～0.11 mm的粉煤灰模型沙的干重度和起动流速随时间增加有限，不致引起模型沙明显的板结和起动相似偏离；(4)南水北调中线穿黄泥沙模型验证试验表明，粉煤灰模型沙能够较好地满足模型试验要求，模型挟沙水流物理特性和运动规律与原型相似；(5)采取控制干重度使模型沙不发生板结现象的方法，可解决类似模型试验问题。

Investigation of flyash model sands

Because sediment model is required to correctly replicate the characteristics and regularity of river bed evolution in prototype,the selection of model sands plays the role of key.For this purpose,by means of the methods of laboratorial soil mechanics tests,the analyses of physical chemistry properties, combining the experiment results obtained in the glass flume and sediment model tests with theory analysis ,etc.,the tests for flyash model sands were carried out.The primary results and conclusions are as following:(1)The results on the fine structure and physical chemistry properties of flyash were obtained and analysed using the optical microscope and eletronic microscope,it was demonstrated that the decentralization property of flyash with partical size d >0.076mm is better;(2)Through contrasting the differences in values between flyash and nature sands in their dry unit weight and soil mechanic characteristic variation,the mechanism of selecting flyash partical size groups,in which cohesion is rather low,as model sands is represented;(3)The increase of the dry unit weight and the incipient velocity of flyash with time(partical size ranges from 0.027 mm to 0.11mm)is very small so as to not generate obvious consolidation effect and similarity departure;(4)The results obtained from sediment model tests for Diversion Project from South to North China crosscut the Yellow River showed that the flyash model sands can meet the requirements of model test well,and the physical properties and regularity of silt carrying flow on model are silimar to prototype;(5)Employing the method of controlling dry unit weight to keep model sands not generate consolidation phenomenon,this kind of model sands may solve the problems of analogic model test.