This report describes laboratory and field tests of deformations in fine-grained subgrade soils (clay and silt). Dynamic triaxial tests have been performed on undisturbed samples in the laboratory, together with determination of CBR, California Bearing Ratio (in several cases using undisturbed samples) and complementary geological analyses. During sampling in the field, measurements have been made with static and dynamic cone penetrometer, mini falling weight deflectometer and vane apparatus. Deformations in the triaxial tests have been analysed and equations for permanent deformation and dynamic modulus of elasticity calculated. The mean E moduli from the triaxial tests agree well with the E moduli proposed in the General Technical Construction Specification for Roads, ROAD 94. A comparison between triaxial and falling weight moduli gave mixed results. A relationship between triaxial modulus and CBR value has been obtained for undisturbed samples of varved clay. The influence of density, grain size distribution, water ratio, plasticity index and capillarity on deformation and E modulus has been studied. The results obtained may be applied in a design programme. It is possible to set an upper limit for the permanent deformation of the finished road surface and to use the given equations to obtain the maximum permissible load on the subgrade. The minimum pavement thickness required is then determined to avoid exceeding this load.
Abstract