Strain measurements in floating ice platforms and their application to platform design

Abstract

The use of the natural ice cover in the Canadian high arctic for offshore petroleum exploration has made possible the drilling of 10 exploratory wells at very reasonable cost. The natural ice is thickened in the loaded area by flooding and freezing in thin layers and required ice thicknesses are obtained using theory for laterally loaded elastic, homogenous plates on elastic foundations. The suitability of this type of theory, which assumes linear strain distribution through the section and a neutral axis at the middle plane, has been questioned, especially since the ice behaves as a visco–elastic material and creeps or strains with time.Resistance strain gauges made of 3 m long, 0.127 mm diameter Teflon-coated wire have been used the last two winters to measure strains in the ice platforms. They have worked well and during the winter and spring of 1978 strains at five different levels in an ice platform beneath the heavier loads were measured and recorded continuously for 62 days. Strain profiles were linear with the neutral axis 0.4 m above the middle plane of the 7.1 m thick platform. Maximum measured principal strains were 1300 με and maximum extrapolated extreme fibre strains were 2100 με, confirming that the strains are small. Stress and effective elastic modulus values are shown to decrease rapidly in the early stages of loading.