Page - 850 - in Book of Full Papers - Symposium Hydro Engineering

2. VARIATIONS IN AGGREGATE GRADING’S One of the most important benefits of CMDs is the ability to adopt raw and even low-quality materials around the dam site [2], which causes unavoidable variations in aggregate grading and the physical properties of Hardfill materials on the other side. Segregations at Hardfill placement are another defect that could occur in this regard. A solution to reduce these variations and mitigate such segregations is dividing the raw materials in two or three stockpiles. Sands and gravels will then be mixed with pre-specified proportions to produce the best fit of aggregate grading compared to the optimum curves. Obviously, this process will lead to the production of some excess aggregates that can be crushed and used again if desirable. Applying the probabilistic method will be of significant help in order to obtain the optimum sieve number of fractions and mixing proportion since the varieties in the samples are unknown. This method can be summarized in the following steps: - Providing adequate samples of raw materials in the different locations of the borrow area and at different depths of each pit. - Generating the remaining portions instead of the finer material grading tables. - Generating a huge series of aggregate grading tables (e.g. more than 10000) based on the probabilistic approach (one may use a numerical method instead of probabilistic distributions to generate a new series). - Changing the above-mentioned series from the “residue” percentage curves to “finer” percentage curves. - Selecting the base sieve numbers for aggregate fractioning and the proportion of mixing, in a way that the best fit to the desired curves is obtained with minimum excess materials. As a case study, the application of this method in the "Kahir" dam project will be discussed: Riverbed aggregates with MSA=50mm are selected as the raw materials, and the natural grading curves are shown in Fig. 3. The aim is to simplify the construction procedure by reducing the aggregate production process. Fig. 3 Grading curves of raw materials 850