Dynamic behavior of volcanic ash of Tajogaite (La Palma, Canary Islands, Spain)

The dynamic characterization of soils is essential for the analysis of their dynamic behavior, soil-structure interaction under seismic loading, seismic design of the constructions to be built on them, soil failure and liquefaction analysis under seismic loading, etc. Dynamic laboratory tests are usually performed over reconstituted sandy material, and sometimes over undisturbed sandy specimens. In this paper the performance of a volcanic sandy material in its fresh natural state, without subsequent consolidation and cementation, is studied to determine its strain dependent shear modulus and damping ratio under range of shear strains considering its location in affected seismic areas. In this study, reconstituted samples in their dry state under different initial relative densities and applied vertical pressures are examined by densification tests performed by cyclic direct simple shear test analyzing vertical strains, shear modulus and damping ratios. The highest densification is observed during the application of the first 10 to 100 cycles. In general, the lowest shear modulus values are obtained for low values of applied vertical stress, and a decrease of damping ratio is observed with the increase of the application of cycles. Also, resonant column tests are performed under different effective confining pressures, observing the general trend of degradation of normalized shear modulus and the increase of damping ratio for the increase of shear strains, with the linear initial relation of shear modulus with shear strains in the range of small strains. The comparison of this non-linear dynamic behavior is performed to the usually applied relations for ordinary sandy materials, providing satisfactory adjustment in this case.