Page - 1003 - in Book of Full Papers - Symposium Hydro Engineering

mm, respectively. By considering the mentioned factors, the probability for continuing for erosion has been estimated as 0.01. 3.1.2.3. Progression of erosion from embankment into foundation For assessing the progression of erosion from embankment into foundation, the possibility of forming roof of the piping path and restriction of the flow in piping path in upstream of dam should be determined; - Probability of forming the roof of the piping path (PR); For progression of erosion from embankment into foundation by forming a roof of a pipe path, the core material and erodible layer of soil foundation must be capable of forming and holding the roof of a pipe. The fine content of core/soil foundation (% passing sieve #200, 0.075mm), the plasticity of the soils and the saturation of the soil are the most important factors in forming a roof. According to the grading curve of core material, the fine content of core material is between 30 to 85 % , the average plasticity index is 23 and the fine content of erodible layer of foundation is >15 %. Therefore, by using the reference table and the material characteristic, the probability of forming a roof has been calculated as 0.9. - Probability for no limitation of the flow (PL); In this dam there is a filter and transition zone with fine content < 5% that cannot support a roof in upstream side of core, and also, the hydraulic gradient in upstream side of core is less than 1.0, thus, the probability of no limitation of flow is estimated as 0.01. However, by considering the results of above assessment, the probability of progression of erosion from embankment into soil foundation is obtained 0.009 (P=PR X PL). 3.1.2.4. Breach in the embankment or from embankment into foundation due to erosion In order to assess the probability of breach in the embankment or from embankment into foundation due to erosion, the following aspects should be evaluated; - Breach by instability of downstream slope; For this purpose, the pore pressure rising or dissipation in downstream shell should be evaluated. In this dam, there is a filter and transition zone in downstream of core, the downstream slope is 2H: 1 V, and the fine content of downstream shell is < 8 %. Thus, the probability of breach by instability of downstream slope has been estimated as 0.02. - Breach by sinkhole development; The probability of breach by sinkhole development is estimated as 0.01 since the clay core material is well graded and the plasticity indices are low to medium, therefore, the core material is not susceptible to form a large void in dam and finally form a sinkhole. 1003