Very coarse-grained alluvia are challenging materials in geotechnical site characterization. The paper presents a method that can be used to find local correlations between the angle of friction and particle shape for very coarse-grained alluvia. The method is based on the results of a number of in situ direct shear tests carried out in horizontal galleries in the Quaternary coarse-grained alluvia of Tehran from which the angle of friction was determined. Following the in situ tests, images of the grains forming the alluvia were taken to determine their sphericity and roundness. The grain shapes were compared, based on a simple chart presented in previous research, and the importance of the sphericity/roundness ratio for the engineering characteristics is identified. A relationship between the angle of friction, sphericity and roundness is proposed for the coarse-grained alluvia of Tehran. The advantages of the proposed correlation are the elimination of the need for difficult sampling for laboratory tests and/or the costs of in situ tests in low-cost projects or during the preliminary site characterization of large projects. Using this approach similar correlations could be proposed to determine the geotechnical properties of other very coarse-grained alluvia.