Improvement of soil quality has always been of interest to civil engineers. Dune Sand from the desert environment is the most important sediment deposits that have great variation in different parts of the world an important loss. Loose granular soils and sediments sand are categorized as poor soils. Due to their weak capacity, high permeability, as well as some issues in the excavation and digging process, they are problematic in construction. Although cement and chemical polymers have a good performance in soil treatment, they have many detrimental impacts on the environment and spread greenhouse gasses into the atmosphere.So that the use of biopolymers as additives for soil stabilization would be a great solution to reduce environmental problems. In this study, the role of different biopolymers in geotechnical activities has been presented. Casein biopolymer as a new material for soil treatment has been introduced and geotechnical parameters of dune sand treated casein has been investigated. The Unconfined Compression, Direct Shear Soil, and California Bearing Ratio (CBR) tests were performed. Also, the microstructural behavior of sand treated casein was studied by Scanning Electron Microscopy (SEM) images. Uniaxial compressive tests were used for studying the effects of biopolymer contents, curing time, curing temperature, and milk fat content in soil improvement. The shear parameters and the casein usage in road construction projects were investigated by direct shear and CBR tests. Casein biopolymer was made in two types: Casein and Sodium Caseinate; the UCS was increased up to 1570.39 kPa and 1709.3 kPa for 5% of Casein and Sodium Caseinate, respectively. Internal friction angle also rose from 36.66 degrees for untreated sand to 45.98 degrees for casein (1%) treated sand and 42.94 degrees for sodium caseinate (1%) treated sand while cohesion was also increased greatly for both biopolymers treated sand. CBR results show that casein and sodium caseinate could be very useful in improvement of subgrade layers of roads. Overall, because casein can be made from spoiled milk and have a great performance in increasing geotechnical parameters, the use of casein would be a new and great opportunity for soil stabilization and resolve the ecological issues of other additives. Keywords Soil improvement, Loose Sand, Casein Biopolymer, Unconfined Compressive Test, Direct Shear Test, California Bearing Ration Test, SEM
