| Popis: |
Pumice-rich soils originating from volcanic eruptions are deposited in various parts of the world, such as in the central region of North Island, NZ. The pumice sand components of these natural pumiceous (NP) soils are known to be crushable and lightweight, resulting in a significant difference in their cyclic resistance ratio (CRR) and small-strain shear modulus (Gmax) when compared to hard-grained (quartz) sands. In this paper, the results of a number of cyclic triaxial and bender element tests performed on reconstituted specimens of three types of NP sands having different pumice contents (PC), as well as on quartz-type Toyoura sand specimens, are discussed. Then, the concept of modified cyclic yield strain, εay,m, which relates the CRR of the specimen to its Gmax, is used. The results indicate that εay,m appears to be dependent only on the soil type, and independent of the confining pressure applied and the relative density of the specimen. All NP sand specimens show higher εay,m when compared to Toyoura sand because of their higher CRR and lower Gmax, with values of εay,m increasing as the PC of the specimen increases. Based on the results obtained, an empirical chart is developed to estimate the CRR of NP sands from their shear wave velocity (Vs) values under field conditions. |
