جستجوی مقالات مرتبط با کلیدواژه "نزول آب کانال" در نشریات گروه "کشاورزی"

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.

One of the main reasons of destruction of the coastal slopesand riverbanks is failure of side slopes under the rising water table or sliding of the side slopes under the drawdown of channel water. In this research, effect of variations of water table and channel water level (peak and drawdown conditions of flood, respectively) on the piping of coastal slopes was studied and effect of cutoff wall on the phenomenonwas investigated. Experiments were conducted in a seepage tank having a trapezoidal cross-section with the side slope of 1.5% and 0.58 mm mean diameter of the particles. Cutoff wall was fixed in the relative depths Z/d=0.5, 0.67, 0.83 and 1 (Z is the depth of cutoff wall and d is the depth of channel). Results of peak conditions of flood (rising the water table), under controled experiment showed the relative channel water level was equal to y/d=0.7. In the experiment with cutoff wall Z/d=1 and without occurrance of piping, exit flow gradient was decreased approximately 41 present with respect to the control experiment. Piping was occurred only in the relative channel water level equal to y/d=0.167. Results of drawdown conditions of flood showed, piping phenomenon occured in the all channel water level. In the experiments with cutoff wall, in the cases with high water table, despite of existence of cutoff wall, increasing the exit flow gradient caused piping phenomenon in the all of the experiments because of increasing hydraulic head. Other wise, in the experiment with the relative water table equal to h/d=0.933, piping was occurred in the all depths of cutoff.