Evaluating the Alluvial Fans in the nNortheast of Rivand as Potential Source of Aggregate and Their Relations to Geomorphological Processes

Aggregates are among the most extensive consumable construction materials and comprise the major volume of concrete. Alluvial fan can be considered as one of the most important landforms that can be appropriate for aggregate exploitation. By passing the time and increasing the age of alluvial fans, their surface sediments are more faced with weathering and consequently decreases the quality of aggregates. In this research, based on the physical characteristics and point load index, the quality of aggregates at the surface of the three desolate, old and new alluvial fans at the north east part of Rivand has been evaluated. Separation of alluvial fans were made based on geo-morphological indices including morphology of alluvial fan surface, weathering rate and drainage pattern.For the existence of different litho logy at alluvial fan's surface, 18 types of common rock were selected at the down and up stream of each alluvial fan, and load point test was made on them. Physical characteristics of the rocks including density, porosity, percentage of water absorption at each alluvial fan was made at its down and up stream part. The research results show that the point load index and density decreases from the new alluvial fans to the old and desolate ones. Porosity amount and the moisture content have a direct relation with the alluvial fan's age, in a way that the oldest and desolate alluvial fan has the highest degree of porosity and saturation moisture content.The results showed that at the surface of all alluvial fans, the strength of aggregates is higher in the fan apex than fan toe, which this issue is due to the lower age and consequently lower weathering of the particles at the up stream of fans. In general, the current research shows that the strength changes of aggregates at the fan's surface is due to the fan's age and their weathering amount, so that the aggregates with lower quality in the old and desolate is due to their long term weathering.