On the uniaxial compression strength of frozen gravelly soils

Abstract

Frozen gravelly soils are often encountered in both cold regions engineering and urban underground constructions by artificial freezing method. This work takes a gravelly sand in Beijing as the basic material. Gravel grains of 10–20 mm in size are obtained and mixed with sand grains at certain ratios and then saturated frozen samples are prepared. Uniaxial compression test is used to study the uniaxial compression strength (UCS) of the material under 3 temperatures and 3 strain rates. Together with 4 gravel contents, 36 combinations are investigated. Test results show that stress-strain curves generally demonstrate strain-softening manner, with different strain energy dependent upon temperature and strain rate on the one hand, and on gravel content upon the other hand. An inclination of approximately 55° to 58° is found for the failure surface. UCS is obtained from all tests for analysis. It is found that the UCS of frozen gravelly soil increases with the decrease of temperature and the increase of strain rate. Generally accepted empirical relationships for fined-grained frozen soils are still applicable with the correlation coefficient of very close to 1. Gravel content plays another important role in the UCS of frozen gravel soil. UCS is found to decrease significantly with the increase of gravel content at high strain rate. At relatively low strain rates however, influence of gravel content on UCS turns out to be complicated. Mechanism of the mechanical performance of the sand-gravel-ice system is proposed in terms of gravel contents, ice contents as well as strain rate.