Malihe Keykhee, M Heydarpor, Farhad Mosavi,
Volume 13, Issue 49 (10-2009)
Abstract
Ripraps are placed around bridge piers to prevent scour and secure the piers from failure. Proper riprap cover is essential to be economical. The present study examines using of riprap for reduction of local scour in piers group and the results are compared with data from riprap on a single pier. The models consist of two and three circular-shaped piers in line with the flow, with the diameter of 0.02 m and pier spacing of twice and four times the pier diameter. Four uniform riprap sizes with the diameters of 2.86, 3.67, 4.38 and 5.18 mm were used to cover the piers. The results showed that the effect of wake vortices formed at the downstream side of piers group was decreased as compared with single pier. The reinforcing and sheltering effects caused 31% decrease in front pier and 60% increase in back pier, respectively, for the length of cover riprap. The reinforcing and sheltering effects were decreased by increasing pier spacing, but the riprap pattern was not affected. In triple piers group, scour depth in the second pier was less than the first pier and in the third pier was less than the first and second piers. In double and triple piers group, the sheltering effect reduced the scour depth (46% and 54%, respectively) in the back pier with respect to the single pier. Reduction of dimensions in scour hole of back pier in triple piers group was 67% with respect to double piers group, which is the result of sheltering effect of first and second piers. The best shape for the riprap was semi-oval. The riprap length in double and triple piers group was reduced by 31% and 37.5%, respectively, as compared with the single pier.
A. Hosseini, M. Shafai- Bajestan,
Volume 20, Issue 75 (5-2016)
Abstract
Assessing the root system and its tensile strength is necessary for determine the impact of roots in increasing the soil shear strength. The present study aims to investigate effects of slope and flow of riverbank on root system of riparian POPULOYS trees. In a relatively direct interval, 6 riparian POPULOYS trees were chosen on the slope of Simereh riverbank. To assess the root system, the circular profiles trenching method was utilized. The surface around each tree was divided into four quadrants: upper quadrant, lower quadrant, in slope direction and in flow direction. In every quadrant, number and diameter of roots were measured. The obtained results showed that the highest number of roots were in 90-100 cm depth. 59% of Roots, in the slop direction and 53% of roots in flow direction, were located in the top quadrant. Approximately, 97% of roots had up to 20 mm diameter. The greatest difference in the number of roots in upper, lower, in slop direction and in flow direction quadrants, were seen in diameters up to 5 mm. In slope direction, this difference was almost 2.7 times more than the difference seen in flow direction. The average ratio of root cross-section was 0.26%. The obtained results indicate that the root system of riparian POPULOYS trees on the riverbank is asymmetrical.
