Strength and deformation characteristics and small strain properties of undisturbed gravelly soils

A series of medium-scale and large-scale triaxial and unconfined compression tests was conducted in order to evaluate the strength and deformation characteristics and small strain properties of undisturbed well-graded gravelly soils retrieved from three tunnel excavation sites in Toyama prefecture, Japan. Undisturbed gravelly soils were taken by means of a new sampling method using thick water-soluble polymer solutions. The strength and deformation characteristics were evaluated mainly by performing sustained loading and large amplitude unloading and reloading cycles during otherwise monotonic loading at a constant strain rate in drained triaxial compression tests. During isotropic consolidation and shearing, at several stress states, eleven very small vertical cycles were applied to evaluate the quasi-elastic deformation property at small strain levels around 0.001% by static measurement. Dynamic measurements using a pair of accelerometers attached to the side surface of the specimen and wave sources attached to the top cap were also conducted at the same stress levels as static measurements in a single test. Several effects including grading characteristics and pressure level on the difference between the moduli measured statically and dynamically were discussed. The relationship between the small strain and strength properties of undisturbed gravelly soils was evaluated. The small strain properties of air-dried dense Toyoura sand in large-scale triaxial compression tests were also investigated in this study to compare the results of undisturbed gravelly soils.