Groundwater Flow under Irrigation Canals Lied on Inclined Cut-off Walls with Different Angles

One of the main issues threatening hydraulic structures is the uplift pressure caused by the water flow in the porous media under the structures. Cut-off walls installed underneath a hydraulic structure can reduce the uplift pressure, by changing the water flow velocity, and as a result, the possibility of cracking and fracturing in the body of the structure. In this study, the effect of inclined cut-off walls with different angles of inclination (to the horizontal axis) underneath an irrigation canal (with laboratory dimensions) on the water flow velocity in the porous medium was investigated. The changes in the velocity due to the inclination were obtained using the Hydrus-2D numerical model. The velocity under the canal with no cut-off walls showed slight fluctuations, but increased owing to all the angles of inclination, reaching its maximum at the location of the cut-off walls. The most effective cut-off walls in increasing the velocity were the closest ones to the horizontal axis, i.e., those with angles of 15°, 30° and 165°, while the less effective angles were 90° and 120°, which were closer to the vertical line. The velocity just below the canal bottom increased with an increase in the angle, so that it changed by 18.05% and 209.45% due to the angles 15° and 165°, respectively. In fact, the cut-off walls performed better as they inclined from the earth’s surface to the canal bottom. In general, the angle of inclination should be selected based on the groundwater level, vulnerability of the walls and bottom of the canal, and economic considerations.