Deformation and critical dynamic stress for compacted volcanic ash subjected to monotonic and dynamic loads

Abstract

Volcanic ash is widespread in volcanic areas and is considered as a potential construction material. Therefore, volcanic ash can be used as subgrade material when building highways and railways in volcanic areas. However, there is limited research on the critical dynamic stress as well as deformation characteristics of volcanic ash under dynamic load. The Global Digital System (GDS) monotonic triaxial tests and dynamic triaxial tests are presented in this paper to quantify the critical dynamic stress as well as deformation characteristics of volcanic ash subjected to monotonic and dynamic loads. The critical dynamic stress and deformation of volcanic ash are affected by stress level, water content and dynamic stress amplitude. Under monotonic loads, the strength of volcanic ash decreases with increasing water content and increases with increasing confining pressure. The deformation of volcanic ash exhibits strain softening behavior which is enhanced with increasing water content and weakened with increasing confining pressure. According to the shakedown theory, the patterns of accumulative plastic strain for the volcanic ash under different dynamic stress amplitudes are classified into three categories, named plastic shakedown, plastic creep, and incremental collapse. This study redefines the shakedown limits for volcanic ash based on the shakedown theory. The adoption of new shakedown limits provides more accurate descriptions of deformation characteristics at different stress levels, water contents and dynamic stress amplitudes. Based on the new shakedown limits, this paper presents empirical models for the calculation of critical dynamic stress for volcanic ash shakedown limits using regression analysis. As a contribution to the literature and potential engineering applications, the proposed models may provide theoretical significance for the subgrade state evaluation.