Deformational characteristics of subgrade soils in Korea

Deformational characteristics of subgrade soils are important parameters in the mechanistic design of flexible pavement. The subgrade soils are mostly non-plastic sandy in Korea, and seven representative subgrade soils were collected for testing from the actual pavement projects. To evaluate the deformational characteristics of subgrade soils, RC/TS, TX, FF-RC, and cyclicMR tests were performed. The effects of various variables on modulus were studied. The modulus of subgrade soil increases with loading frequency. The maximum shear modulus,Gmax, was significantly affected by confining pressure and water content, but normalized modulus (G/Gmax) reduction curves were almost identical and independent of water content and confining pressure below about 41 kPa. Two representative modulus reduction curves for Korean subgrade soils are suggested. The variation in the modulus with number of loading cycles is small and can be ignored in a practical sense. It has been shown that when the effects of those factors are properly taken into account, the modulus values evaluated by various testing methods are comparable to each other fairly well.