The Confined Compressive Strength of Polycrystalline Ice

Triaxial tests were carried out on randomly oriented, laboratory-made, polycrystalline ice, between strain-rates of 10 –7 and 10 –1 s –1 and with confining pressures from 0.1 to 85 MN m –2 , at –11 ± 1°C. Below strain-rates of about 10 –5 s –1 the confining pressure has little effect, but at higher strain-rates the confining pressure prevents cracking which allows the compressive strength to rise to a value greater than the unconfined compressive strength. At 1.4 ×10 –2 s –1 , the unconfined strength of 12 MN m –2 rises to 26 MN m –2 with a confining pressure of 25 MN m –2 , before dropping slowly with greater confining pressures. Above 10 –2 s –1 the unconfined strength decreases rapidly with increasing strain-rate, but the confined strength continues to increase. The dependence of strain rate on the maximum compressive stress is discussed.