Effects of di-ammonium phosphate on hydraulic, compaction, and shear strength characteristic of sand and clay soils

Abstract

The large amounts of phosphate fertilizers which are used in agriculture activities in Egypt lead to the contamination of large quantities of soil surrounding the agricultural fields. Also, the use of traditional flood irrigation method makes the problem more worse. An extensive laboratory testing program is carried out to determine the Atterberg limits, compaction characteristics, hydraulic conductivity, and shear strength parameters of clean and contaminated soils. Three types of soils are used including coarse sand, fine to medium sand, and silty clay. Batch tests are used to study the short-term effect of di-ammonium phosphate (DAP) contamination on the soil properties. Contaminated specimens are prepared by mixing the dried soil samples with different di-ammonium phosphate concentrations of 5, 10, and 20 %. The results indicate a significant reduction in Atterberg limits and increase in hydraulic conductivity for silty clay soil with the increase of phosphate concentration. The change that is induced by chemical reaction in the micro-structure of the soil is studied by laser scanning microscope before and after soil contamination. For sand soil, γ dmax is significantly increased with the increase of DAP concentrations up to 5 % and slightly increased with concentrations from 5 to 20 % which indicates excess phosphate in the soil. However, the general trend of hydraulic conductivity is towards reduction. In addition, the friction angle of two sand samples decreases about 10 % due to the increase of DAP concentration up to 20 %. For silty clay, the reduction in cohesion is about 20 % and the increase of friction angle is about 10 % with the increase of DAP up to 20 %.