مژده محمدیون

Seepage is one of the main reasons of slopes destructions. In slopes, due to fluctuations of groundwater depth or water level in an earth dam, a channel or river, gradient of seepage exceeds its critical value and the boiling phenomenon happens. In this study, the performance of geogrid plates in controlling the boiling of slope due to rising of groundwater level or drawdown of channel water surface was investigated using an experimental model. Geogrid plates with three lengths of 10, 15 and 20 cm and spacings of 1, 2, 3 and 4 cm were placed in the slope. The experiments were carried out at different depths of groundwater and channel water. Results showed that in the best model of geogrid (plates with 20 cm length and spacing of 1 cm) gradient of boiling increased 71.5 and 236 percent due to ascending of groundwater and descending of channel water conditions, respectively as compared to the control model. By increasing the length of plates or reducing the spacing between the plates, gradient of boiling increased. In all plates with different spacings, the number of non-occurrence of boiling in the descending condition of the channel water was less than that in the ascending condition of the groundwater. This is due to the simultaneous effects of hydrostatic and pore water pressure of the saturated soil of upper layers. In the ascending condition of the groundwater, boiling occurred mostly in the relative water depths equal to 0.167 and 0.333. In the descending of channel water conditions, critical status happened when the groundwater level was high.

Pressurized flushing is one of the common methods in sediment flushing of dam reservoirs. In this method, sediments settled in the reservoir are released out of the dam together with water flow using the bottom outlet. For increasing the performance of pressurized flushing, it is attempted to fall down water level to minimum height of operation. Also, in the previous researches, the performance of different hydraulic and structural methods was evaluated in order to increase the pressurized flushing. Researchers have always tried to recognize the process of flushing and effective parameters and therefore, propose efficient procedures to increase the performance of flushing. Aim of this study is to investigate experimentally the effect of the number of rows, height and arrangement of submerged vanes in the enhancement of flushing reservoir.
To carry out the experiments of this research, a physical model including sediment reservoir, settling basins and water supplied tank was used. Submerged vanes were set up in front of bottom outlet with two heights (HV/D>1 HV/D Results showed that with decreasing the raw number of vanes in parallel arrangement, the performance of sediment flushing was increased. On the other hand, one-raw submerged vanes (double vanes) with relative height HV/D=0.5 and 2 have the best flushing performance with 173 and 231 percentages respectively compared with control model. Also, submerged vanes with relative height HV/D=2 have better performance than ones with relative height HV/D=0.5. The radial arrangement of vanes increased effectively the flushing performance. So that the flushing performance of submerged vanes relative height HV/D=0.5 and 2 increased about 11.33 and 4.1 times compared with the control model. In the radial arrangement, the flushing performance of vanes with relative height HV/D= 2 were less than ones with relative height HV/D=0.5 because of focusing the approaching inflow on the back of the side vanes.
Radial arrangement could increase the flushing intensity (especially with increasing the water depth of reservoirs). This condition is a relative advantage for flushing. In the other words, the flushing operation has more efficiency in the full condition of dam reservoirs and it is not necessary to fall down the water level of reservoir.