Measuring stiffness of soils in situ

Large scale shakers can be employed to measure the shear modulus of soil as a function of shear strain directly in situ. The method involves applying dynamic loads on a surface foundation while measuring the dynamic response of the soil mass beneath the foundation with embedded instrumentation. The interpretation of these tests for determining the shear modulus nonlinearity requires careful handling of the data. The response of the footing can also be used to assess various methods to estimate the properties of a circular foundation. Different methods can be used to estimate both the shear modulus and the level of strain during the test, either directly from the measured wave forms or using inverse analysis. When compared to laboratory results in the literature, estimated in situ shear moduli at the National Geotechnical Experimentation Site at Texas A&M University show larger elastic threshold shear strains. © 2015 Taylor & Francis Group, London