Dynamic Testing of Frozen Soils Under Simulated Earthquake Loading Conditions

Engineers concerned with the development of Alaska and other highly seismic areas underlain by permafrost must have knowledge of dynamic properties of frozen soils under earthquake loading conditions. In response to this need, a cyclic triaxial test system and test methods have been developed to evaluate the dynamic Young's modulus and damping ratio of artificially frozen soils over a range of test conditions which simulate earthquake loadings of permafrost deposits.

The test system developed represents a coupling of conventional closed-loop cyclic triaxial equipment to evaluate the dynamic properties of unfrozen soils with conventional temperature control equipment to evaluate static properties of frozen soils. On-line, real-time data processing has been achieved by coupling a minicomputer to the test system. With the test system, the dynamic Young's modulus and damping ratio can be determined over a range of axial strain amplitudes from 3 × 10^-3 to 10^-1 percent, temperatures from -1 to -10°C (30 to 14°F), frequencies from 0.3 to 5.0 Hz, and confining pressures from 0 to 1400 kN/m² (200 psi). An extensive laboratory program was undertaken to establish suitable methods of specimen preparation, specimen installation, and testing for artificially frozen specimens of clay, silt, sand, and ice.

At present there is no standard test procedure to evaluate dynamic properties of frozen soils under simulated earthquake loading conditions. The material presented provides a basis for the development of a standard test procedure.