Effect of Urban Wastewater on Chemical, Physical and Mechanical Properties of Soil(Case Study: Central Area of Mashhad)

Chemical changes in the soil have a significant effect on its physical and mechanical properties and the rate of settlement. In this research, the effect of urban wastewater on chemical properties and soil engineering characteristics such as Atterberg limits, uniaxial compressive strength and consolidation parameters in central areas of Mashhad have been investigated. Based on the results, some chemical parameters such as Ca, Mg, Al and K decreased after the soil samples has been saturated by wastewater. Also, changing the chemical properties of the soil has changed its physical and mechanical parameters. For example, the consolidation parameters of the selected soil indicate that the (Cc) has increased over time with changes in the concentration of input wastewater. Also, the (Cs) has decreased over time and the rate of change in high concentrations is less. In addition, the results show that low concentrations of wastewater in short time have the greatest effect on reducing the uniaxial strength of soil. An examination of the electron microscope images shows that when the soil sample is saturated with wastewater, a layer of salt is accumulated around the soil particles, which expands the size and surface of the particles and also tends its structure towards the grain pattern. Therefore, simultaneously, the two factors of time and the change in concentration of wastewater affect the physical and mechanical parameters of the soil, and the effect of concentration on the time is more indicative.