Residual Strain in a Reservoir Ice Cover: Field Investigations, Causes, and Its Role in Estimating Ice Stress

Abstract

Ice strain dominates the ice thrust and dynamics on reservoir dams and retaining structures. An exclusively designed laser range finder was deployed to measure the surface ice displacements along six directions at a reservoir in northeastern China. The incompletely confined boundary (ice-boundary bonding), ice cracks development, water level fluctuations, parallel crack dynamics, and ice creep allow the surface ice to move rather than keep still in response to thermal deformation/pressure, and thus cause the ice strain to deviate from thermal strain. Consequently, a residual strain was introduced and calculated from the recorded displacements. Observations showed that the residual strains were anisotropic and showed diurnal patterns following the air/ice temperature. A scale-dependence of crack development was observed to cause potential scale-effects to residual strains. The real ice strain consists of thermal strain and residual strain. The proportion of the latter increased as time went by. A modified constitutive law accommodating the residual strains was developed to evaluate the impacts of the residual strains and to estimate the surface ice stresses. Modeling results underlined the role of the residual strain in determining both the principal stress and the stress perpendicular to and parallel with the dam face. The residual strain is probably the reason why the observed ice stress is always much lower than the single thermal stress.