Cyclic CPT Measurements of Disturbed Soil State

Disturbed soil states in geotechnical problems occurs together with large uncertainties. During earthquake, disturbed sand can become either more or less resistant to liquefaction. Due to the cyclic loading, offshore wind turbine foundations can episodically loose or recover the stiffness. In both cases, the initial in-situ soil state is lost, as disturbed soil state evolves during cyclic loading. Thus, it is important to develop a testing procedure that combines observations of both the initial condition and the long-term disturbed soil state.
This paper presents the results of cone penetration tests (CPT-s). A conventional use of CPT leads to undisturbed soil results. However, the paper describe a non-conventional use of this method, where CPT is performed multiple times in the same location. The first penetration measures the undisturbed sand strength and stiffness, whereas the second and later penetrations observe evolving disturbed state of sand. The ‘cyclic CPT’ curve of cone resistance qc converges while repeating the test, resulting in a final disturbed soil profile for initial sand state.