Evaluating the Efficiency of Crushed Gravel Filters around Field Drains

Abstract

Engineers have employed various ways to protect drain openings from the entry of sediment with varying degrees of success. This study aims to compare and evaluate the hydraulic performance and efficiency of using natural graded gravel filter and crushed gravel filter in drainage systems. An aquifer tank (sand tank) 70 cm long, 50 cm wide and 80 cm high, a perforated drain pipe of 50 mm diameter was used in the laboratory work. The laboratory study was performed with two types of soil: loam and loamy sand. These two soils were used with the two types of gravel filters after taking the particle size distribution test for the two soils. For each case, the inflow was applied to the model from the soil surface (to represent irrigation condition) and from the sides of the tank (to represent sub –surface flow condition and effluence of the groundwater). Each case involved ten runs; for each run, discharge, total head loss, and amount of sediment were recorded. It was found that crushed gravel filter would work similarly to natural graded gravel filter after a certain time from the beginning of runs. It was also found that the discharge and sediment when using crushed gravel filter were close to or equal to that with natural graded gravel filter. The hydraulic conductivity and the exit gradient values were calculated in this research. It was found that their values were so different between the two types of filters, but at the end of the laboratory work, the hydraulic conductivity would be approximately the same. The exit gradient of crushed gravel filter was lower than that of natural graded gravel filter due to the large pores between the filter particles. Finally, the results showed that, it is possible to use crushed gravel filter material in drainage systems, which is less costly and easier to place than natural graded gravel filter.