Ice strain dominates the ice thrust and dynamics on reservoir dams and retaining 17 structures. An exclusively designed laser range finder was deployed to measure the surface ice 18 displacements along six directions at a reservoir in northeastern China. The incompletely 19 confined boundary (ice-boundary bonding), ice cracks development, water level fluctuations, 20 parallel crack dynamics, and ice creep allow the surface ice to move rather than keep still in 21 response to thermal

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... pressure, and thus cause the ice strain deviates from thermal 22 strain. Consequently, a residual strain was introduced and calculated from the recorded 23 displacements. Observations showed that the residual strains were anisotropic and showed 24 diurnal patterns following the air/ice temperature. A scale-dependence of crack development was 25 observed and causes potential scale-effects to residual strains. The real ice strain consists of 26 thermal strain and residual strain. The proportion of the latter increased as time went by. A 27 modified constitutive law accommodating the residual strains was developed to evaluate the 28 impacts of the residual strains and to estimate the surface ice stresses. Modeling results 29 underlined the role of the residual strain in determining both the principal stress and the stress 30 perpendicular to and parallel with the dam face. The residual strain is probably the reason why 31 the observed ice stress is always much lower than the single thermal stress. 32